JP4022792B2 - Semiconductor optical amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor optical amplifying device, and more particularly to a gain-clamped semiconductor optical amplifying device having a wide wavelength band characteristic of an allowable incident power adjustment mechanism used in a wavelength division multiplexing (WDM) communication system. .
[0002]
[Prior art]
In recent years, in response to a dramatic increase in communication demand, the introduction of a wavelength division multiplexing communication system in which a plurality of signal lights having different wavelengths are multiplexed and simultaneously transmitted through a single optical fiber has been studied. A wide wavelength band is required for the optical amplifier to be used.
[0003]
As such an optical amplifying device having a wide wavelength band, a semiconductor optical amplifying device is known. Since this semiconductor optical amplifying device is small in size and capable of operating with low power consumption, the optical amplifying device for a wavelength division multiplexing communication system is used. Promising as a device.
[0004]
In general, in an optical amplifying device, carriers are consumed in the process of amplifying signal light, so that the carrier decrease due to stimulated emission becomes significant when the power of the signal light increases, resulting in a phenomenon of gain saturation that lowers the gain. Will occur.
[0005]
In the above-described semiconductor optical amplifying device, since the carrier lifetime is as short as several hundred picoseconds, gain saturation can follow the fluctuations in the power of the signal light due to the modulation, so that gain modulation may occur and the signal light may be distorted. In a situation where a large number of signal lights are simultaneously amplified in the semiconductor optical amplifier, crosstalk may occur due to mutual gain modulation between the signal lights.
[0006]
In order to suppress such gain modulation, it is necessary to add a mechanism in which the carrier density is constant regardless of the power change of the signal light to the semiconductor optical amplifier, and the most powerful method is to use a laser oscillation mechanism. This method is introduced into a semiconductor optical amplifying device and utilizes the phenomenon that the carrier density is locked to the oscillation threshold carrier density.
[0007]
In this case, as long as the power of the signal light is smaller than the power of the laser oscillation light and the laser oscillation is continued, the gain of the semiconductor optical amplifier is clamped to be constant. In this gain clamp type semiconductor optical amplifying device, in order to make a traveling wave type optical amplifying device without resonating with respect to the signal light, the wavelength of the laser oscillation light is set apart from the wavelength of the signal light. It is widely used to use a reflecting mirror having a wavelength selectivity that provides a high reflectance only with respect to a certain wavelength.
[0008]
For example, a diffraction grating is used as an external reflecting mirror having wavelength selectivity (if necessary, see JC Simon et al, Electronics Letters, vol. 30, pp. 49-50, 1994), or fiber. The use of a grating (fiber diffraction grating) has been proposed (see L. Lablonde et al, ECOC '94, processeds, pp. 715-718, 1994, if necessary).
[0009]
Further, as an example of using an internal reflection mirror having wavelength selectivity, a monolithic DFB (distributed feedback) laser is used (if necessary, P. Dousier et al., International Semiconductor Laser Conference, processes, pp. 185-186). 1994) or using a DBR (distributed Bragg reflection) laser (if necessary, see LF Tiemeier et al, IEEE Photonics Technology Letters, pp. 284-286, 1995). .
[0010]
Further, as another method of constructing the gain clamp type semiconductor optical amplifying device, two two-to-two type so that the laser oscillation light and the signal light are spatially separated in a region other than the semiconductor optical amplification medium. A semiconductor optical amplifying medium is provided in both arms of an optical multiplexer / demultiplexer, that is, a Mach-Zehnder interferometer comprising a 2 × 2 type optical multiplexer / demultiplexer, and one of the input ports of the input side optical multiplexer / demultiplexer and its cross position It has also been proposed to configure a laser resonator by arranging a reflecting mirror made of a multilayer dielectric film at the output port of the output side optical multiplexer / demultiplexer in order to form a gain clamp type semiconductor optical amplifier (if necessary, Ch Holtsmann et al, ECOC '96, processeds, pp. 199-202, 1996).
[0011]
[Problems to be solved by the invention]
In the gain clamp type semiconductor optical amplifying device as described above, the resonator loss is an important parameter for determining the gain and the allowable incident power of the signal light. This situation will be described with reference to FIG.
Refer to FIG.
FIG. 18A is a diagram showing the resonator loss dependence of the gain-optical output characteristics in the semiconductor optical amplifier, and the gain is ½ (= 10 log)._Ten(2≈3.01≈3 dB) is also shown.
Amplifier₁Shows a case of a normal semiconductor optical amplifier of the non-gain clamp type. As the optical output P increases, the gain G gradually decreases and the optical output P_s1However, in the gain clamped semiconductor optical amplifier, the gain is clamped to a constant value until the laser oscillation is stopped.
[0012]
Therefore, laser with large resonator loss₂In this case, the gain is large because the oscillation threshold carrier density is large.₂However, since the power of the laser oscillation light with respect to a certain injection current becomes small, the allowable incident power of the signal light becomes low.
On the other hand, laser with small resonator loss_ThreeIn this case, the gain is small because the oscillation threshold carrier density is small._Three(<G₂However, since the power of the laser oscillation light for a certain injection current increases, the allowable incident power of the signal light increases.₂→ Laser_ThreeThe gain is G₂→ G_ThreeThe saturation light output power becomes P_S2→ P_S3Accordingly, the allowable input power of the signal light that can be appropriately amplified can be increased by reducing the resonator loss, and this situation will be described with reference to FIGS. 18B and 18C. I will explain.
[0013]
See FIGS. 18B and 18C.
18B and 18C show the laser₂And laser_ThreeIs a diagram showing the optical output-current characteristics (LI characteristics) of the laser with a relatively large resonator loss₂In the threshold current I_th-2Laser_ThreeThreshold current I_th-3The laser output becomes larger when the same current flows, so that the laser loss is relatively small._ThreeTherefore, the allowable input power of signal light that can be appropriately amplified can be increased.
[0014]
When such an allowable input power is used for various applications (applications) using a gain clamp type semiconductor optical amplifier having a resonator loss dependency, the characteristics of the gain clamp type semiconductor optical amplifier can be changed depending on the application. Although it is necessary to optimize, in order to optimize the characteristics, it is desirable that the above-described resonator loss can be arbitrarily controlled continuously.
[0015]
However, in the conventional monolithic type semiconductor optical amplifying device, the resonator loss is fixed, and therefore there is a problem that the resonator loss cannot be made variable according to the application.
[0016]
On the other hand, in an external resonator type semiconductor optical amplifier, although the resonator loss can be changed by replacing the diffraction grating and the fiber diffraction grating constituting the external resonator, these are continuously changed and optimized. This is difficult, and when modularized, there is a problem that the resonator loss is fixed as in the monolithic type.
[0017]
Accordingly, an object of the present invention is to continuously control the resonator loss of a gain clamp type semiconductor optical amplifier and to optimize the characteristics of the gain clamp type semiconductor optical amplifier according to the application.
[0018]
Another object of the present invention is to provide a gain-clamped semiconductor optical amplifying device having a simple structure and excellent separation characteristics between signal light and laser light and having high saturation light input / output characteristics.
[0019]
[Means for Solving the Problems]
FIG. 1 is an explanatory view of the principle configuration of the present invention. Means for solving the problems in the present invention will be described with reference to FIG.
FIG. 1 is a conceptual configuration diagram of a semiconductor optical amplifier according to the present invention.
See Figure 1
(1) The present invention provides an effective transmission loss amount for a signal light 7 in a gain clamp type semiconductor optical amplifying apparatus 1 constituted by a semiconductor optical amplifier 2 and a laser resonator including the semiconductor optical amplifier 2 therein. Is characterized in that it has a variable optical attenuation mechanism that can control the amount of resonator loss with respect to laser oscillation light while maintaining a constant value.
[0020]
In this way, a variable optical attenuation mechanism, that is, a variable optical attenuation mechanism, in which the amount of resonator loss with respect to the laser oscillation light can be controlled while the effective transmission loss amount with respect to the signal light 7 is kept constant in the laser resonator. By providing the resonator 3, the resonator loss can be arbitrarily controlled continuously, whereby the characteristics of the gain clamp type semiconductor optical amplifier device 1 can be optimized according to the application.
In the present specification, “semiconductor optical amplifier” and “variable optical attenuator” mean a single “semiconductor optical amplifier” and “variable optical attenuator”, and an electrode or the like is provided in a predetermined semiconductor region. It also means a semiconductor optical amplification region or a variable optical attenuation region which is provided and has an optical amplification function or optical attenuation function.
[0021]
(2) Further, according to the present invention, in the above (1), at least one of the laser resonators is constituted by a reflecting mirror 4 having wavelength selectivity, and a variable optical attenuation mechanism is provided in the laser resonator as a variable optical attenuation mechanism. A device 3 is provided.
[0022]
In this way, at least one of the wavelength selective mirrors 4 constitutes a laser resonator to form a feedback mechanism only for the laser oscillation wavelength, thereby suppressing laser oscillation at the wavelength of the signal light 7. can do.
[0023]
(3) Further, the present invention is characterized in that, in the above (2), a portion where the signal light 7 does not pass is provided in the laser resonator, and the variable optical attenuator 3 is disposed in a portion where the signal light 7 does not pass. And
[0024]
In this manner, a portion where the signal light 7 does not pass is provided in the laser resonator, and the variable optical attenuator 3 is disposed in a portion where the signal light 7 does not pass, whereby the signal light 7 is attenuated by the variable optical attenuator 3. Therefore, the degree of freedom of the variable optical attenuator 3 that can be used can be increased.
[0025]
(4) Further, according to the present invention, in the above (3), the laser resonator has an external resonator structure composed of the reflecting mirror 4 having wavelength selectivity and the reflecting mirror 5 having no wavelength selectivity, so that the reflection having wavelength selectivity is achieved. A beam splitter 6 is inserted between the mirror 4 and the semiconductor optical amplifying device 1, and signal light 7 is incident from the direction perpendicular to the laser resonator via the beam splitter 6. A feature is that the signal light 7 does not pass between the beam splitter 6 and the beam splitter 6.
[0026]
By adopting such a configuration, the signal light 7 whose intensity is halved by the beam splitter 6 is incident on the semiconductor optical amplifier 2, so that even when the signal light 7 is large, gain saturation hardly occurs, and the signal light 7 The upper limit of the allowable incident power can be doubled.
[0027]
(5) Further, according to the present invention, in the above (3), the laser resonator has an external resonator structure composed of a reflective mirror 4 having wavelength selectivity and a reflective mirror 5 having no wavelength selectivity, and reflection having wavelength selectivity. A beam splitter 6 is inserted between the mirror 4 and the semiconductor optical amplifier 1, and signal light 7 is emitted from the direction perpendicular to the laser resonator via the beam splitter 6, so that the reflecting mirror 4 having wavelength selectivity is provided. A feature is that the signal light 7 does not pass between the beam splitter 6 and the beam splitter 6.
[0028]
By adopting such a configuration, the signal light 7 is incident on the semiconductor optical amplifier 2 without loss on the entrance side, so that an appropriate amplified signal can be obtained even when the signal light 7 is weak, The lower limit of the incident power can be halved.
[0029]
(6) Further, according to the present invention, in the above (3), the laser resonator has an external resonator structure including a pair of wavelength-selective reflecting mirrors 4 and both the semiconductor optical amplifier 2 and the wavelength-selective reflections. Each of the beam splitters 6 is inserted between the mirror 4 and the signal light 7 is input / exited from the direction perpendicular to the laser resonator via the beam splitter 6. 6 is characterized in that the signal light 7 does not pass through the two regions between the two.
[0030]
By adopting such a configuration, although the loss of the signal light 7 is increased, it is not necessary to use the incident / exit end face of the optical fiber as a part of the reflecting mirror. Return light of the signal light 7 due to reflection can be prevented.
[0031]
(7) Further, according to the present invention, in the above (2), the variable optical attenuator 3 changes the optical attenuation with respect to the laser oscillation wavelength without providing a portion where the signal light 7 does not pass in the laser resonator. However, the variable optical attenuator 3 that does not effectively attenuate the signal light 7 is disposed.
[0032]
Thus, by not providing a portion through which the signal light 7 does not pass in the laser resonator, loss due to the beam splitter 6 is eliminated, so that the signal light 7 can be used efficiently and the number of parts can be reduced. However, since the signal light 7 passes through the variable optical attenuator 3, it is necessary to consider the attenuation characteristics of the variable optical attenuator 3 so that the signal light 7 is not effectively attenuated.
In the present application, “the signal light 7 is not effectively attenuated” means that attenuation is not intended to occur, and even if there is unavoidable attenuation, it is not regarded as attenuated. .
[0033]
(8) Further, according to the present invention, in the above (7), the laser oscillation wavelength is set shorter than the wavelength of the signal light 7 by the reflection mirror 4 having wavelength selectivity, and the laser oscillation is performed as the variable optical attenuator 3. An electroabsorption optical modulator having an absorption edge wavelength on the shorter wavelength side than the wavelength is used.
[0034]
As described above, as the variable optical attenuator 3 that does not effectively attenuate the signal light 7 and selectively attenuates only the laser oscillation light, the electroabsorption having an absorption edge wavelength shorter than the laser oscillation wavelength. A type optical modulator is preferred.
[0035]
(9) Further, the present invention is characterized in that, in the above (8), the semiconductor optical amplifier 2 and the variable optical attenuator 3 composed of an electroabsorption optical modulator are monolithically integrated.
[0036]
Since the electroabsorption optical modulator can be formed with a pin structure using a semiconductor, it is suitable for monolithic integration, and the semiconductor optical amplifier 2 and the variable optical attenuator 3 are aligned by monolithic integration. In addition, since the lens is not necessary, the number of parts can be reduced and the entire apparatus can be downsized.
[0037]
(10) Further, the present invention is characterized in that, in any one of the above (7) to (9), a fiber grating is used as the reflective mirror 4 having wavelength selectivity.
[0038]
As described above, when a portion through which the signal light 7 does not pass is not provided in the laser resonator, a wavelength grating can be obtained by using a fiber grating, that is, a fiber diffraction grating, as the wavelength-selective reflecting mirror 4. The laser resonator structure can be simplified.
[0039]
  (11) Further, in the above (9), the present invention uses a distributed Bragg reflector as the wavelength-selective reflecting mirror 4, and this distributionBraggThe reflector is monolithically integrated with a variable optical attenuator comprising a semiconductor optical amplifier 2 and an electroabsorption optical modulator.
[0040]
As described above, when a distributed Bragg reflector (DBR) is used as the wavelength-selective reflecting mirror 4, the distributed Gragg reflector is replaced with a variable optical attenuator comprising the semiconductor optical amplifier 2 and the electroabsorption optical modulator. By monolithically integrating the device 3, the main components of the device can be formed only by the semiconductor manufacturing process.
[0041]
(12) Further, according to the present invention, in the above (1), the semiconductor optical amplifier 2 is provided on two arms of a Mach-Zehnder interferometer including two 2 × 2 type optical couplers, and a laser resonator is provided on the input side. A variable optical attenuator as a variable optical attenuating mechanism is composed of one of the input ports of the optical multiplexer / demultiplexer and a reflecting mirror arranged at the output port of the optical multiplexer / demultiplexer on the output side in the cross position with respect to the input port. It is provided between the optical combiner / branch and the reflecting mirror in the laser resonator.
[0042]
In this way, by using a Mach-Zehnder interferometer consisting of two 2 × 2 type optical multiplexers / demultiplexers, it is possible to amplify without loss of signal light due to the use of a beam splitter or the like, and the device configuration is simplified. In addition, since the laser oscillation light and the signal light are spatially separated in the region other than the semiconductor optical amplifier, the resonance of the signal light occurs in the laser resonator without providing the laser resonator with wavelength selectivity. There is nothing.
[0043]
(13) Further, in the above (12), the present invention is characterized in that a directional coupler is used as the 2 × 2 type optical multiplexer / demultiplexer.
[0044]
In this way, the Mach-Zehnder interferometer can be made compact by using a directional coupler as the 2 × 2 type optical multiplexer / demultiplexer.
[0045]
(14) Further, the present invention is characterized in that, in the above (12), a multi-mode interferometer is used as the 2 × 2 type optical multiplexer / demultiplexer.
[0046]
In this way, by using a multi-mode coupler as the 2 × 2 type optical multiplexer / demultiplexer, manufacturing tolerance can be improved as compared with the case of using a directional coupler as the 2 × 2 type optical multiplexer / demultiplexer.
[0047]
(15) Further, the present invention is characterized in that, in the above (12) to (14), at least one of the reflecting mirrors is constituted by a reflecting mirror having wavelength selectivity.
[0048]
In this way, by configuring at least one of the reflecting mirrors constituting the laser resonator with a wavelength-selective reflecting mirror, the laser oscillation wavelength is stabilized, and the difference between the wavelength of the signal light and the laser oscillation wavelength is reduced. Amplified signal light that can be maintained stably, thereby preventing non-linear effects due to undesired interaction between the signal light and the laser light, for example, phase conjugate waves due to four-wave mixing, etc. Can only be output from the output port.
[0049]
(16) Further, the present invention is characterized in that, in the above (12) to (15), an electroabsorption optical modulator is used as the variable optical attenuator.
[0050]
As described above, when the Mach-Zehnder interferometer is used, the signal light does not pass through the variable optical attenuator. Therefore, it is not always necessary to use the electroabsorption optical modulator as the variable optical attenuator. An optical modulator may be used. In particular, in the case of monolithic integration, it is preferable to use an electroabsorption optical modulator that can be formed by a pin structure.
[0051]
(17) In the present invention, in the above (12) to (16), the semiconductor optical amplifier, the two 2 × 2 type optical multiplexer / demultiplexers, the variable optical attenuator 3 and the reflecting mirror are monolithically integrated. It is characterized by.
[0052]
In this way, the overall configuration is reduced by monolithically integrating the semiconductor optical amplifier 2, two 2 × 2 type optical couplers, variable optical attenuators, and reflecting mirrors, and the 2 × 2 type optical coupler is integrated. A lens system between the branching device and the variable optical attenuator becomes unnecessary.
[0053]
  (18) Further, according to the present invention, in the gain clamp type semiconductor optical amplifying apparatus 1 constituted by the semiconductor optical amplifier 2 and the laser resonator including the semiconductor optical amplifier 2 inside, the semiconductor optical amplifier 2 is replaced with the Sagnac type light. A laser resonator is configured by arranging a reflecting mirror on the optical waveguide connected to one input / output port of this Sagnac type optical interferometer.And the variable optical attenuator 3 is disposed in the optical waveguide.The optical waveguide connected to the other input / output port is an input / output optical waveguide for the signal light 7.
[0054]
  As described above, when a Sagnac type optical interferometer is used, only one semiconductor optical amplifier 2 is required. Therefore, the gain clamp type semiconductor optical amplifier 1 having a symmetrical structure using a pair of semiconductor optical amplifiers 2 is used. In comparison, since the requirement for the symmetrical operation required for the semiconductor optical amplifier 2 is not required, the possibility of mixing the laser oscillation light and the signal light 7 is further reduced, and a stable optical amplification operation becomes possible.
  Further, by disposing the variable optical attenuator 3 in the optical waveguide constituting the laser resonator, the resonator loss can be controlled continuously and arbitrarily, thereby the gain clamp type semiconductor optical amplifier 1. The characteristics can be optimized according to the application.
[0055]
(19) Further, in the above (18), the present invention is characterized in that a reflecting mirror having wavelength selectivity is used as the reflecting mirror.
[0056]
When a Sagnac type optical interferometer is used, the laser oscillation light and the signal light 7 are spatially separated, so that the resonance of the signal light 7 in the laser resonator can be achieved without providing the laser resonator with wavelength selectivity. However, in order to stabilize the laser oscillation wavelength and stably maintain the difference between the wavelength of the signal light 7 and the laser oscillation wavelength, a reflection mirror having wavelength selectivity should be used as the reflection mirror. As a result, non-linear effects due to undesired interaction between the signal light 7 and the laser light, such as a phase conjugate wave due to four-wave mixing, do not occur, and only the amplified signal light 7 is input / output. Can be output from the other input / output port connected to the optical waveguide.
[0057]
(20) Further, in the above (18) or (19), the present invention is characterized in that in the Sagnac type optical interferometer, the optical waveguide portion and the optical coupler portion other than the semiconductor optical amplifier 2 are constituted by optical fibers. .
[0058]
In this way, by configuring the optical waveguide portion and the optical coupler portion other than the semiconductor optical amplifier 2 in the Sagnac type optical interferometer with optical fibers, a gain clamp type semiconductor optical amplifying device is required without requiring a special fine processing technique. 1 can be configured easily.
[0059]
(21) Further, according to the present invention, in the above (18) or (19), the optical waveguide portion and the optical coupler portion other than the semiconductor optical amplifier 2 in the Sagnac type optical interferometer are configured by a planar dielectric optical circuit. It is characterized by.
[0060]
In this manner, in the Sagnac type optical interferometer, the optical waveguide portion and the optical coupler portion other than the semiconductor optical amplifier 2 are constituted by a planar dielectric optical circuit (PLC), thereby making it possible to obtain a gain clamp type than when an optical fiber is used. The semiconductor optical amplifier 1 can be downsized.
[0061]
(22) Further, in the present invention, in the above (18) or (19), the optical waveguide, the optical coupler portion, the arm, and the semiconductor optical amplifier 2 constituting the Sagnac type optical interferometer are monolithically integrated with a semiconductor. It is characterized by that.
[0062]
Thus, the gain clamp type semiconductor optical amplifier 1 can be made smaller by monolithically integrating the optical waveguide, the optical coupler portion, the arm, and the semiconductor optical amplifier 2 constituting the Sagnac type optical interferometer with a semiconductor. In addition, since the hybrid mounting of the semiconductor optical amplifier 2 is not necessary, problems associated with accuracy such as optical axis alignment between the semiconductor optical amplifier 2 and the arm are solved.
[0063]
(23) Further, in the above (22), the present invention is characterized in that the optical waveguide, the optical coupler portion, and the arm constituting the Sagnac type optical interferometer are also used as the semiconductor optical amplification region.
[0064]
As described above, the optical waveguide, the optical coupler portion, and the arm constituting the Sagnac type optical interferometer are also used as the semiconductor optical amplification region, so that the laser oscillation light and the signal light 7 in the optical waveguide, the optical coupler portion, and the arm 7 are obtained. Can be prevented, and the manufacturing process is greatly simplified.
[0067]
DETAILED DESCRIPTION OF THE INVENTION
Here, the first to sixth embodiments of the present invention will be described with reference to FIGS. 2 to 7. First, the first embodiment of the present invention will be described with reference to FIG. .
See Figure 2
FIG. 2 is a conceptual configuration diagram of the gain-clamped semiconductor optical amplifier according to the first embodiment of the present invention. The optical fiber 12 and the optical fiber 12 for inputting the optical input 11 as signal light are shown in FIG. A lens 13 that converts the light input 11 into a parallel light beam; a beam splitter 14 that transmits half of the converted light input 11 and reflects the remaining half; a lens 15 that focuses the reflected light input 11; A semiconductor optical amplifier 16 for amplifying the focused optical input 11; a pair of lenses 17 and 18 for converging and guiding the optical input 11 amplified by the semiconductor optical amplifier 16 and spread and emitted to the optical fiber 19, and The optical fiber 19 constitutes an optical amplification system for signal light, and the amplified signal light is emitted from the optical fiber 19 as an optical output 20.
[0068]
The gain-clamped semiconductor optical amplifying device includes a variable optical attenuator 21 and a diffraction grating 22. The gain-clamped semiconductor optical amplifying device has a cleaved end face formed by cleaving the incident side of the diffraction grating 22 and the optical fiber 19. A laser resonator having wavelength selectivity is configured, and a variable optical attenuator 21 is disposed in a portion where the signal light between the beam splitter 14 and the diffraction grating 22 does not pass to control the resonator loss of the laser resonator. .
[0069]
In this case, the “part where the signal light does not pass” means a region where the optical input 11 that is effectively used as the signal light does not pass. The optical input 11 is reflected by the cleavage end face of the optical fiber 19. Although passing through the variable optical attenuator 21 and reaching the diffraction grating 22, the diffraction grating 22 has wavelength selectivity, so that the reflected light input 11 does not travel again to the semiconductor optical amplifier side as signal light. Therefore, such a region where the optical input 11 that is effectively used as signal light does not pass is defined as “a portion where the signal light does not pass”.
[0070]
In this case, the semiconductor optical amplifier 16 uses a non-reflective coating (AR coating) made of a multilayer dielectric film so that no reflection occurs at the input / output end face, and is perpendicular to the optical axis of the active layer. It is desirable that the cross-sectional shape is a square or a gain MQW (multiple quantum well) structure having a tensile strain is used so that polarization does not depend on the gain.
[0071]
Further, this semiconductor optical amplifier 16 has an oscillation wavelength of 1.5 μm band (1.5 to 1. .5) by considering the material and structure of the active layer from the viewpoint of attenuation characteristics in an optical fiber used for long-distance optical communication. 6 μm), and the inclination of the diffraction grating 22 with respect to the optical axis is controlled so as to form a laser resonator only for a set oscillation wavelength of 1.5 μm band.
[0072]
As the variable optical attenuator 21, various commercially available variable optical attenuators are used. Since the optical input 11 that is effectively used as signal light does not pass through the variable optical attenuator 21, the variable optical attenuator 21 is used. As the attenuation characteristic, a variable optical attenuator having any configuration may be used as long as it can attenuate light having a laser oscillation wavelength, for example, a wavelength of 1.51 μm, and the attenuation amount is arbitrarily controlled. To do.
[0073]
In the first embodiment, the signal light is attenuated by ½ by the beam splitter 14 before being amplified by the semiconductor amplifier 16 and is incident on the semiconductor amplifier 16, so that the system as viewed from the optical fiber 12 is effective. The saturation input power is increased, and the upper limit of the allowable incident power of the optical input 11 as the signal light at the stage of entering the optical fiber 12 can be doubled.
Therefore, this configuration is suitable when the power of the signal light is large.
[0074]
Further, since the external resonator constituted by the diffraction grating 22 and the cleaved end face of the optical fiber 19 has a wavelength dependency depending on the tilt angle of the diffraction grating 22, the material and structure of the active layer of the semiconductor optical amplifier 16 are used. Since it acts as a laser resonator only for the wavelength specified by, and does not cause laser oscillation at the wavelength of the signal light, it is possible to lock the carrier density to the oscillation threshold carrier density determined by the resonator loss. So that the gain can be clamped to a predetermined value.
[0075]
Further, in the first embodiment, since the variable optical attenuator 21 is provided in the external resonator, the resonator loss is continuously controlled to an arbitrary value by the attenuation amount of the variable optical attenuator 21. Thereby, the characteristics of the semiconductor optical amplifier can be set to optimum values according to various applications.
[0076]
Next, a second embodiment of the present invention will be described with reference to FIG. 3. In the second embodiment, the input side and the output side of the first embodiment are reversed. The other configurations are the same as those in the first embodiment.
See Figure 3
FIG. 3 is a conceptual configuration diagram of a gain-clamped semiconductor optical amplifier device according to the second embodiment of the present invention, in which an optical input 11 that is signal light parallel to the optical axis of the semiconductor optical amplifier 16 is incident. Optical fiber 19, a pair of lenses 18 and 17 for converging the optical input 11 from the optical fiber 19, a semiconductor optical amplifier 16 for amplifying the converged optical input 11, and amplifying and spreading out in the semiconductor optical amplifier 16. A lens 15 that converts the converted light input 11 into a parallel light beam, a beam splitter 14 that transmits half of the converted light input 11 and reflects the remaining half in the vertical direction, and a reflected light input 11 The lens 13 that converges and guides to the optical fiber 12 and the optical fiber 12 constitute an amplification system for signal light, and the amplified signal light is emitted from the optical fiber 12 as an optical output 20.
[0077]
This gain clamp type semiconductor optical amplifying device also includes a variable optical attenuator 21 and a diffraction grating 22, and is connected to the semiconductor optical amplifier 16 by a cleavage end face formed by cleaving the emission side of the diffraction grating 22 and the optical fiber 19. A laser resonator having wavelength selectivity is configured, and a variable optical attenuator 21 is disposed in a portion where the signal light between the beam splitter 14 and the diffraction grating 22 does not pass to control the resonator loss of the laser resonator. .
[0078]
In this case, a half of the amplified light input 11 also passes through the region between the beam splitter 14 and the diffraction grating 22. However, since the diffraction grating 22 has wavelength selectivity, this amplified 1 Since the / 2 optical input 11 is reflected and is not effectively used again as signal light, in this second embodiment as well, the region between the beam splitter 14 and the diffraction grating 22 is referred to as “signal light. It is defined as “the part that does not pass”.
[0079]
In the second embodiment, since the signal light is amplified by the semiconductor amplifier 16 and then attenuated to 1/2 by the beam splitter 14, the allowable incident power of the optical input 11 cannot be increased. Since the signal is amplified before being attenuated to 2, it can be appropriately amplified even when the optical input 11 as signal light is weak.
[0080]
Also in the second embodiment, since the variable optical attenuator 21 is provided in the external resonator, the resonator loss is continuously controlled to an arbitrary value by the attenuation amount of the variable optical attenuator 21. The characteristics of the semiconductor optical amplifying device can be set to optimum values according to various applications.
[0081]
Also in this case, since the variable optical attenuator 21 is disposed in a portion where the signal light between the beam splitter 14 and the diffraction grating 22 does not pass, the degree of freedom of attenuation characteristics of the variable optical attenuator 21 that can be used. Can be increased.
[0082]
Next, a third embodiment of the present invention will be described with reference to FIG. 4. In the third embodiment, the light input 11 is incident through the beam splitter 14 and the light output 20 is input. Is taken out via the beam splitter 23, and the other configuration is exactly the same as in the first embodiment.
See Figure 4
FIG. 4 is a conceptual configuration diagram of a gain-clamped semiconductor optical amplifier device according to a third embodiment of the present invention. The optical fiber 12 and the optical fiber 12 for inputting an optical input 11 as signal light are shown in FIG. A lens 13 that converts the light input 11 into a parallel light beam; a beam splitter 14 that transmits half of the converted light input 11 and reflects the remaining half; a lens 15 that focuses the reflected light input 11; A semiconductor optical amplifier 16 that amplifies the focused optical input 11, a lens 17 that converts the optical input 11 that has been amplified and emitted from the semiconductor optical amplifier 16 into a parallel beam, and 1 / of the converted optical input 11. 2, the remaining half of the beam splitter 23, a pair of lenses 24 that focuses the reflected light input 11 and guides it to the optical fiber 19, and the optical fiber 19 increases the signal light. System is configured, the signal light amplified is emitted as the light output 20 from the optical fiber 19.
[0083]
In the third embodiment, a pair of diffraction gratings 22 and 25 and a variable optical attenuator 21 are provided, and the pair of diffraction gratings 22 and 25 constitute an external resonator having wavelength selectivity. The variable optical attenuator 21 is disposed in the portion where the signal light between the beam splitter 23 and the diffraction grating 22 does not pass, and the resonator loss of the laser resonator can be controlled arbitrarily and continuously according to the application.
[0084]
Further, half of the signal light before and after amplification is lost in the beam splitters 14 and 23, and thus the loss increases. However, since the optical fiber 12 or the optical fiber 19 is not used as a component of the external resonator, the input / output It is not necessary to make the input end surface or the output end surface of the optical fiber 12 and the optical fiber 19 that are ends into a cleaved end surface, and therefore, a non-reflecting surface or a low-reflecting surface can be provided, so that reflection loss at the input / output ends is reduced. .
[0085]
Also in the third embodiment, since the variable optical attenuator 21 is disposed in a portion where the signal light between the beam splitter 23 and the diffraction grating 22 does not pass, the variable optical attenuator 21 that can be used is used. The degree of freedom of the damping characteristic can be increased.
The variable optical attenuator 21 may be disposed in a portion where the signal light between the opposite beam splitter 14 and the diffraction grating 25 does not pass.
[0086]
Next, a fourth embodiment of the present invention will be described with reference to FIG. 5. In this fourth embodiment, signal light is input and output without using a beam splitter. In the laser resonator, there is no portion where the signal light does not pass.
See Figure 5
FIG. 5 is a conceptual configuration diagram of a gain-clamped semiconductor optical amplifier according to a fourth embodiment of the present invention, in which an optical input 11 that is signal light is incident and an external resonator is provided on the output end side. A fiber grating provided with a diffraction grating for constituting, that is, a fiber diffraction grating 26, a pair of lenses 13 and 15 for focusing the light input 11 from the fiber diffraction grating 26, and transmitting the focused light input 11 without attenuation. In addition, a variable optical attenuator 21 for arbitrarily attenuating laser oscillation light, a pair of lenses 18 and 17 for converging the light input 11 transmitted through the variable optical attenuator 21, and a semiconductor light for amplifying the converged light input 11 The optical input 11 that has been amplified by the amplifier 16 and the semiconductor optical amplifier 16 and spread and emitted is focused and guided to a fiber diffraction grating 29 provided with a diffraction grating for forming an external resonator on the incident end side. A pair of lenses 27, 28 and, is constituted by the fiber grating 29, the signal light amplified is emitted from the fiber grating 29 as an optical output 20.
[0087]
The external resonator in this case is configured between a pair of fiber diffraction gratings 26 and 29 which are provided with a refractive index distribution on the incident end face side or the outgoing end face side to form a diffraction grating, and uses a normal diffraction grating. However, since the wavelength dependence of the external resonator is determined by the period of the diffraction grating provided in the fiber diffraction gratings 26 and 29, it is fixed unless the fiber diffraction gratings 26 and 29 are replaced. Will be.
However, there is usually no problem because the laser oscillation wavelength of the semiconductor optical amplifier 16 is determined at the time of element design.
Note that one of the fiber diffraction gratings 26 and 29 may be replaced with a normal optical fiber whose end face is cleaved, and a combination of a fiber diffraction grating and a normal optical fiber may be used.
[0088]
In this case, since the variable optical attenuator 21 is provided in the portion through which the signal light passes, the attenuation characteristic of the variable optical attenuator 21 is accurately set so that the signal light is not attenuated in the variable optical attenuator 21. There is a need to.
For example, a pin structure electroabsorption optical modulator is used as such a variable optical attenuator 21, the absorption edge wavelength of the electroabsorption optical modulator is shorter than the laser oscillation wavelength, and an electric field is applied. In this case, it is necessary to accurately set the absorption edge wavelength to move to the long wavelength side so that the laser oscillation light is absorbed, and the wavelength of the signal light is not absorbed even by the application of an electric field. It is necessary to set the longer wavelength side.
[0089]
The configuration of the semiconductor optical amplifier 16 used in the fourth embodiment is exactly the same as that in the first embodiment, and is formed of a multilayer dielectric film so that no reflection occurs at the end face. Polarized to gain by using a non-reflective coating and making the cross section perpendicular to the optical axis of the active layer square or using a strained MQW (multiple quantum well) structure with tensile strain It is desirable to configure so that no dependency occurs. Furthermore, from the viewpoint of attenuation characteristics in an optical fiber used for long-distance optical communication, a gain wavelength of 1.5 μm band is considered by considering the material and structure of the active layer. It is desirable to set so that
[0090]
As described above, since the beam splitter is not used in the fourth embodiment, the light loss due to the beam splitter, that is, the transmitted light loss can be eliminated, and the ordinary diffraction grating is not used. The entire configuration of the apparatus is simplified and miniaturized, and the incident / exit end faces of the fiber diffraction gratings 26 and 29 do not constitute an external resonator, and therefore do not need to be cleaved end faces. It is possible to prevent signal signal reflection loss and undesired return light by providing a function and making the incident / exit end face non-reflective or low-reflective.
[0091]
Next, a fifth embodiment of the present invention will be described with reference to FIG. 6. In the fifth embodiment, a semiconductor optical amplifier and a variable optical attenuator are monolithically integrated. Other configurations are the same as those in the fourth embodiment.
See FIG.
FIG. 6 is a conceptual configuration diagram of a gain-clamped semiconductor optical amplifier device according to a fifth embodiment of the present invention, in which an optical input 11 that is signal light is incident and an external resonator is provided on the output end side. A fiber diffraction grating 26 provided with a diffraction grating for constituting, a pair of lenses 13 and 15 for converging the light input 11 from the fiber diffraction grating 26, the focused light input 11 transmitted without being attenuated, and a laser A variable optical attenuator that arbitrarily attenuates oscillation light, that is, a variable optical attenuation region 33, and a semiconductor optical amplifier that amplifies the optical input 11, that is, a semiconductor optical amplification region 32, are monolithically integrated on the semiconductor substrate 31. A monolithic optical semiconductor device 30 and a fiber optic provided with a diffraction grating for converging the light input 11 amplified and emitted from the semiconductor optical amplification region 32 to form an external resonator on the incident end side. A pair of lenses 17 and 18 leading to lattice 29 and, is constituted by the fiber grating 29, the signal light amplified is emitted from the fiber grating 29 as an optical output 20.
In this case as well, one of the fiber diffraction gratings 26 and 29 may be replaced with a normal optical fiber whose end face is cleaved, and a combination of a fiber diffraction grating and a normal optical fiber may be used.
[0092]
In this case, the monolithic optical semiconductor device 30 includes, for example, an InGaAsP / InP double heterojunction structure formed on a semiconductor substrate 31 made of n-type InP by a normal epitaxial growth method, and one region serves as a semiconductor optical amplification region 32. The other region is a variable light attenuation region 33 made of an electroabsorption optical modulator having a pin structure.
[0093]
For example, the period of the optical fiber diffraction gratings 26 and 29 is set so that the laser oscillation wavelength in the semiconductor optical amplifying region 32 is, for example, 1.51 μm, and the gain of the active layer is eliminated in order to eliminate the polarization dependence of the gain. The cross-sectional shape perpendicular to the optical axis is a square or a strained MQW (multiple quantum well) structure having a tensile strain.
[0094]
On the other hand, in order to prevent the attenuation of the signal light in the variable light attenuation region 33 and the attenuation of the laser oscillation light when no electric field is applied, for example, the composition of the InGaAsP light absorption layer is 1.48 μm. As described above, the variable optical attenuation region 33 may be formed by regrowth in a portion from which a part of the semiconductor optical amplification region 32 is removed, so that the attenuation characteristic of the variable optical attenuation region can be accurately determined at the element design stage. .
Also in this case, a non-reflective coating made of a multilayer dielectric film is applied so that reflection does not occur on the incident / exit end face of the monolithic optical semiconductor device 30.
[0095]
As described above, since the beam splitter is not used in the fifth embodiment, the optical loss due to the beam splitter can be eliminated, and the semiconductor optical amplifier and the variable optical attenuator are monolithically integrated. Therefore, the variable optical attenuator can be reduced in size, and further, since a pair of lenses provided between the semiconductor optical amplifier and the variable optical attenuator is not required, the overall configuration of the apparatus can be simplified and reduced in size. it can.
[0096]
Also in this case, since the incident / exit end faces of the fiber diffraction gratings 26 and 29 do not constitute an external resonator, they do not need to be cleaved end faces. Therefore, by making the incident / exit end faces non-reflective or low-reflective. It is possible to prevent reflection loss of signal light and unwanted return light.
[0097]
Next, a sixth embodiment of the present invention will be described with reference to FIG. 7. In this sixth embodiment, a reflection that constitutes a laser resonator with respect to a semiconductor optical amplifier and a variable optical attenuator. The mirror is monolithically integrated as a DBR (distributed Bragg reflector) region.
See FIG.
FIG. 7 is a conceptual configuration diagram of a gain-clamped semiconductor optical amplifier device according to a sixth embodiment of the present invention, and an optical fiber 12 that receives an optical input 11 that is signal light, and an optical input from the optical fiber 12. A pair of lenses 13 and 15 for focusing 11, a variable light attenuation region 33 for transmitting the focused light input 11 without being attenuated, and arbitrarily attenuating laser oscillation light, and semiconductor light for amplifying the light input 11 A monolithic optical semiconductor device 34 in which amplifying region 32 is integrated monolithically on semiconductor substrate 35 and a pair of DBR regions 36 and 37 for forming a laser resonator are integrated on the input / output end face side, semiconductor light An optical fiber provided with a diffraction grating for converging the light input 11 amplified in the amplification region 32 and emitted from the DBR region 37 to form an external resonator on the incident end side A pair of lenses 17 and 18 leading to 9 and is constituted by an optical fiber 19, the signal light amplified is emitted as the light output 20 from the optical fiber 19.
[0098]
In this case, the monolithic optical semiconductor device 34 has, for example, an InGaAsP / InP double heterojunction structure formed on a semiconductor substrate 31 made of n-type InP by a normal epitaxial growth method, and one region is used as a semiconductor optical amplification region 32. The other region is a variable optical attenuation region 33 made of an electro-absorption optical modulator having a pin structure, and is provided with periodic irregularities on both side surfaces to form diffraction gratings to form DBR regions 36 and 37. .
[0099]
The laser oscillation wavelength in the semiconductor optical amplification region 32 is set to be, for example, 1.51 μm, and the period of the diffraction gratings of the DBR regions 36 and 37 is set. The cross-sectional shape perpendicular to the optical axis is square or has a strained MQW (multiple quantum well) structure with tensile strain, prevents attenuation of signal light in the variable optical attenuation region 33, and applies an electric field. In order to prevent the attenuation of the laser oscillation light in the case where it is not performed, it is desirable to set the composition of the InGaAsP light absorption layer constituting the variable light attenuation region 33 to be 1.48 μm.
[0100]
On the other hand, the composition of the optical waveguide core layer of the DBR regions 36 and 37 is set to a wavelength shorter than the laser oscillation wavelength, for example, 1.30 μm so that the DBR regions 36 and 37 do not absorb laser oscillation light. Thus, periodic irregularities may be formed in the vicinity of the optical waveguide core layer.
[0101]
Thus, since the beam splitter is not used in the sixth embodiment, the optical loss due to the beam splitter can be eliminated, and the semiconductor optical amplifier 16, the variable optical attenuator 21, and the DBR region 36, 37 is monolithically integrated, the overall configuration of the device including the laser resonator structure can be simplified and reduced in size.
[0102]
In this case, since the laser resonator is composed of a pair of DBR regions 36 and 37, it is not necessary to form an external resonator using a fiber diffraction grating or the like. Ordinary optical fibers 12 and 19 may be used, and reflection and loss of signal light and undesired return light can be prevented by making the input and output end faces of the optical fibers 12 and 19 non-reflective or low reflective. .
[0103]
Next, with reference to FIG. 8 to FIG. 12, gain clamp type semiconductor optical amplifiers using Mach-Zehnder interferometers according to seventh to eleventh embodiments of the present invention will be described.
See FIG.
FIG. 8 is a conceptual configuration diagram of a gain-clamped semiconductor optical amplifier device according to a seventh embodiment of the present invention. A Mach-Zehnder interferometer 40 serving as a basic component of the gain-clamped semiconductor optical amplifier device is A pair of arms between the two directional couplers 46 and 47, using the two directional couplers 46 and 47 formed on the semiconductor substrate 45 as two 2 × 2 (2 to 2) type optical couplers. Both are provided with semiconductor optical amplifiers 48 and 49, and light input as signal light input to one input port of the preceding directional coupler 46 from the focusing optical fiber 42 provided with a lens at the tip. 41 is branched in half at the coupling portion of the directional coupler 46 and amplified by the semiconductor optical amplifiers 48 and 49, and then coupled at the coupling portion of the directional coupler 47 in the subsequent stage. Input It is output as the light output 44 from the output port of the over preparative and cross (Cross) position via a focusing optical fiber 43.
[0104]
On the other hand, the laser resonator was provided on the outer end face of the highly reflective film 50 made of a multilayer dielectric film provided on the cleaved end face of the other output port of the directional coupler 47 in the subsequent stage and the variable optical attenuator 52. The variable optical attenuator 52 is inserted into the laser resonator via the lens pair 51, and the variable optical attenuator 52 can continuously and continuously reduce the resonator loss. Can be controlled.
[0105]
In this case, the Mach-Zehnder interferometer 40 includes, for example, an InGaAsP / InP double heterojunction structure in which an active layer has a strained MQW structure having a wavelength composition of 1.55 μm on a semiconductor substrate 45 made of n-type InP. After forming the laminated structure for forming the semiconductor optical amplifiers 48 and 49 and removing the region other than the region for forming the semiconductor optical amplifiers 48 and 49, the optical component whose wavelength composition becomes 1.30 μm, for example, in the removal portion A semiconductor optical amplifier sandwiched between two 2 × 2 type directional couplers 46 and 47 by laminating a double heterojunction structure having a wave core layer and performing mesa etching into a shape as shown in the figure 48 and 49 are formed.
[0106]
In the seventh embodiment, since the laser oscillation light and the signal light are spatially separated in the region other than the amplification region, it is not necessary to give the laser resonator wavelength dependency, and a normal cleavage plane is used. The reflector can be made up of a high-reflectivity multilayer dielectric film or the like provided on itself or the cleavage plane, simplifying the resonator structure, and the oscillation threshold value where the carrier density is determined by the resonator loss It can be locked to the carrier density so that the gain can be clamped to a predetermined value.
[0107]
Further, since the variable optical attenuator 52 is provided in a portion through which signal light does not pass, the variable optical attenuator 52 can be used because it is sufficient to consider only the attenuation characteristic with respect to the laser oscillation light. The degree of freedom of 52 becomes large, and various commercially available optical attenuators can be used.
[0108]
In the seventh embodiment, since the beam splitter is not used, the optical loss due to the beam splitter can be eliminated and the configuration of the entire apparatus is simplified.
Although the converging optical fibers 42 and 43 are used as optical fibers for input and output, the converging optical fibers are not limited to the converging optical fiber, and a pair of lenses and a normal lens are used as in the sixth embodiment. A combination with other optical fibers may also be used.
[0109]
Next, an eighth embodiment of the present invention will be described with reference to FIG. 9. In the eighth embodiment, a 3 dB multimode interferometer is used as a 2 × 2 type optical multiplexer / demultiplexer. The other configuration is exactly the same as that of the seventh embodiment.
See FIG.
FIG. 9 is a conceptual configuration diagram of a gain-clamped semiconductor optical amplifier device according to an eighth embodiment of the present invention. A Mach-Zehnder interferometer 60 serving as a basic component of the gain-clamped semiconductor optical amplifier device is Two 3 dB multimode interferometers 66 and 67 formed on the semiconductor substrate 65 are used as two 2 × 2 type optical multiplexer / demultiplexers, and both of the pair of arms between the two multimode interferometers 66 and 67 are used. Semiconductor optical amplifiers 68 and 69 are provided, and an optical input 61 as signal light input to one input port of a multi-mode interferometer 66 in the previous stage from a focusing optical fiber 62 provided with a lens at the tip, After being branched in half at the interference section of the multimode interferometer 66 and amplified by the semiconductor optical amplifiers 68 and 69, the multimode interferometer 66 is connected at the interference section of the subsequent multimode interferometer 67. Is, from the output port of the input port and the cross position where the signal light is input through a focused optical fiber 63 is outputted as an optical output 64.
[0110]
The laser resonator in this case is also provided on the outer end face of the highly reflective film 70 made of a multilayer dielectric film provided on the cleaved end face of the other output port of the subsequent multimode interferometer 67 and the variable optical attenuator 72. In this laser resonator, a variable optical attenuator 72 is inserted through a lens pair 71, and the resonator loss can be made arbitrarily continuous by the variable optical attenuator 72. Can be controlled.
[0111]
In this case, the Mach-Zehnder interferometer 60 is formed by laminating, for example, an InGaAsP / InP double heterojunction structure in which an active layer has a strained MQW structure having a wavelength composition of 1.55 μm on a semiconductor substrate 65 made of n-type InP. After forming the laminated structure for forming the semiconductor optical amplifiers 68 and 69 and removing the region other than the region for forming the semiconductor optical amplifiers 68 and 69, the optical component having a wavelength composition of 1.30 μm, for example, in the removed portion. A semiconductor optical amplifier sandwiched between two 2 × 2 type multimode interferometers 66 and 67 by laminating a double heterojunction structure having a wave core layer and performing mesa etching into a shape as shown in the figure 68 and 69 are formed.
[0112]
In the eighth embodiment, since 3 dB multimode interferometers 66 and 68 are used as the 2 × 2 type optical multiplexer / demultiplexer, the 2 × 2 type optical multiplexer / demultiplexer is used as in the seventh embodiment. The manufacturing tolerance of the 2 × 2 type optical multiplexer / demultiplexer can be increased, that is, the tolerance of dimensional accuracy can be increased, compared with the case where the directional couplers 46 and 47 are used as a coupler, thereby increasing the yield of the semiconductor optical amplifier. Can be manufactured.
[0113]
Also in the eighth embodiment, since the laser oscillation light and the signal light are spatially separated in the region other than the amplification region, it is not necessary to give the laser resonator wavelength dependency. Since the reflecting mirror can be composed of the cleavage plane itself or a high-reflectivity multilayer dielectric film provided on the cleavage plane, the resonator structure is simplified, and the beam splitter is not used. Since the resulting optical loss can be eliminated, the configuration of the entire apparatus can be further simplified.
In this case as well, the converging optical fibers 42 and 43 are used as optical fibers for input and output. However, the converging optical fibers are not limited to the converging optical fibers, and a pair of optical fibers are used as in the sixth embodiment. A combination of this lens and a normal optical fiber may be used.
[0114]
Further, since the variable optical attenuator 72 is provided in a portion through which the signal light does not pass, the variable optical attenuator 72 can be used because it is sufficient to consider only the attenuation characteristic with respect to the laser oscillation light. Various commercially available optical attenuators that increase the degree of freedom of 72 can be used.
[0115]
Next, a ninth embodiment of the present invention will be described with reference to FIG. 10. In this ninth embodiment, the fiber resonator is used to give wavelength selectivity to the laser resonator. Other configurations are the same as those in the eighth embodiment.
See FIG.
FIG. 10 is a conceptual configuration diagram of a gain-clamped semiconductor optical amplifier device according to a ninth embodiment of the present invention. A Mach-Zehnder interferometer 60 serving as a basic component of the gain-clamped semiconductor optical amplifier device is In exactly the same manner as in the eighth embodiment, two 3 dB multimode interferometers 66 and 67 formed on the semiconductor substrate 65 are used as two 2 × 2 type optical multiplexer / demultiplexers. Semiconductor optical amplifiers 68 and 69 are provided on both of a pair of arms between the optical devices 66 and 67, and one input port of the multi-mode interferometer 66 in the preceding stage from the focusing optical fiber 62 provided with a lens at the tip. The optical input 61 as the signal light input to the multimode interferometer 66 is branched in half at the interfering portion of the multimode interferometer 66 and amplified by the semiconductor optical amplifiers 68 and 69, and then the subsequent stage of the optical input 61. Are combined at the interference portion of Chimodo interferometer 67, the signal light is outputted as an optical output 64 via a focusing optical fiber 63 from the output port of the input port and the cross position input.
[0116]
On the other hand, the laser resonator in this case is disposed outside the variable optical attenuator 72 and the highly reflective film 70 made of a multilayer dielectric film provided on the end face of the other output port of the multimode interferometer 67 in the subsequent stage. In this resonator, a variable optical attenuator 72 is inserted through a lens pair 71, and the resonator loss can be controlled arbitrarily and continuously by the variable optical attenuator 72. Can do.
[0117]
In the ninth embodiment, since the laser resonator has wavelength selectivity by the fiber diffraction grating 74, the laser oscillation wavelength is stabilized, and an undesirable nonlinear interaction with the signal light occurs. And stable signal light amplification is possible. For example, when the laser oscillation wavelength is unstable, if the laser oscillation wavelength shifts to a longer wavelength side than the intended wavelength, the wavelength difference λ from the signal light₁−λ₂Since the phase conjugate wave is generated by the four-light mixing and is output from the output port as the optical output 64 together with the signal light, the phase conjugate wave is separated and removed for stable optical communication. Although it is necessary to provide a filter or the like, such a problem does not occur in the ninth embodiment.
[0118]
Also in the ninth embodiment, since the 3 dB multimode interferometers 66 and 67 are used as the 2 × 2 type optical multiplexer / demultiplexer, the 2 × 2 type is used as in the seventh embodiment. The manufacturing tolerance of the 2 × 2 type optical multiplexer / demultiplexer can be increased as compared with the case where the directional couplers 46 and 47 are used as the optical multiplexer / demultiplexer, whereby the semiconductor optical amplifier can be manufactured with a high yield.
Other operational effects, characteristics, etc. are the same as those in the eighth embodiment.
[0119]
Next, a tenth embodiment of the present invention will be described with reference to FIG. 11. In this tenth embodiment, a laser resonator has wavelength selectivity using a pair of fiber diffraction gratings. The variable optical attenuator is monolithically integrated into the Mach-Zehnder interferometer 60 as an electroabsorption optical modulator, and the other configuration is exactly the same as in the ninth embodiment.
See FIG.
FIG. 11 is a conceptual configuration diagram of a gain-clamped semiconductor optical amplifier device according to a tenth embodiment of the present invention. A Mach-Zehnder interferometer 60 serving as a basic component of the gain-clamped semiconductor optical amplifier device is Similar to the eighth embodiment, two 3 dB multimode interferometers 66 and 67 formed on the semiconductor substrate 65 are used as two 2 × 2 type optical multiplexer / demultiplexers. Semiconductor optical amplifiers 68 and 69 are provided on both of the pair of arms between 66 and 67, and from the converging optical fiber 62 provided with a lens at the tip to one input port of the multi-mode interferometer 66 in the preceding stage. The optical input 61 as the input signal light is branched in half at the interference section of the multimode interferometer 66 and amplified by the semiconductor optical amplifiers 68 and 69, and then the subsequent stage of the multi-mode interferometer 66 is amplified. Are combined at interferometer mode interferometer 67, the signal light is outputted as an optical output 64 via a focusing optical fiber 63 from the output port of the input port and the cross position input.
[0120]
On the other hand, the laser resonator in this case includes an optical fiber diffraction grating 76 provided on the end face side of the other output port of the subsequent multimode interferometer 67 and an end face of the other input port of the preceding multimode interferometer 66. In the tenth embodiment, the variable optical attenuator is used as the electroabsorption optical modulator 75, and the other multimode interferometer 66 in the previous stage is used. Are monolithically integrated on the input port side.
[0121]
In this case, the Mach-Zehnder interferometer 60 is formed by laminating, for example, an InGaAsP / InP double heterojunction structure in which an active layer has a strained MQW structure having a wavelength composition of 1.55 μm on a semiconductor substrate 65 made of n-type InP. After forming the laminated structure for forming the semiconductor optical amplifiers 68 and 69 and removing the region other than the region for forming the semiconductor optical amplifiers 68 and 69, the optical component having a wavelength composition of 1.30 μm, for example, in the removed portion. After laminating a double heterojunction structure having a wave core layer, and then removing a part of the laminated structure in the vicinity of the region where the multi-mode interferometer 66 of the previous stage is formed, the wavelength composition is 1.48 μm as an absorption layer By laminating a pin structure for forming an electroabsorption optical modulator composed of an InGaAsP layer, and mesa etching into a shape as shown in the figure, Two 2 × 2 type multi-mode interferometers 66 and 67, semiconductor optical amplifiers 68 and 69 sandwiched therebetween, and an electroabsorption optical modulator 75 are formed, and the electroabsorption optical modulator 75 is formed. Thus, the resonator loss can be controlled arbitrarily and continuously.
[0122]
In this way, the variable optical attenuator can be miniaturized by using the electroabsorption optical modulator 75 integrated as the variable optical attenuator. Further, the multimode interference between the electroabsorption optical modulator 75 and the preceding stage can be reduced. Since the lens pair 71 between the optical device 66 and the device 66 is not necessary, the semiconductor optical amplifier can be further downsized.
[0123]
In the tenth embodiment, since the laser resonator is composed of a pair of fiber diffraction gratings 74 and 76, the laser oscillation wavelength is more stable, and undesirable nonlinear interaction with the signal light occurs. It is possible to amplify the signal light stably without any occurrence, and other operational effects, characteristics, etc. are the same as in the eighth embodiment.
[0124]
In the tenth embodiment, the electroabsorption optical modulator 75 that can be easily integrated is used as the variable optical attenuator. In this case, the Mach-Zehnder interferometer 60 is used. Since light and laser oscillation light are spatially separated in regions other than the amplification region, and therefore, no special light absorption characteristics are required for the electroabsorption optical modulator 75, a variable optical attenuator having another configuration, for example, A current injection type semiconductor light absorption element or the like may be used.
[0125]
Next, an eleventh embodiment of the present invention will be described with reference to FIG. 12. In the eleventh embodiment, a DBR region serving as a reflector having wavelength selectivity is used as a laser resonator. The mode interference unit is monolithically integrated on the input / output port side, and the other configurations are the same as those in the tenth embodiment.
See FIG.
FIG. 12 is a conceptual configuration diagram of a gain-clamped semiconductor optical amplifier according to an eleventh embodiment of the present invention. A Mach-Zehnder interferometer 60 serving as a basic component of the gain-clamped semiconductor optical amplifier is Similar to the eighth embodiment, two 3 dB multimode interferometers 66 and 67 formed on the semiconductor substrate 65 are used as two 2 × 2 type optical multiplexer / demultiplexers. Semiconductor optical amplifiers 68 and 69 are provided on both of the pair of arms between 66 and 67, and from the converging optical fiber 62 provided with a lens at the tip to one input port of the multi-mode interferometer 66 in the preceding stage. The optical input 61 as the input signal light is branched in half at the interference section of the multimode interferometer 66 and amplified by the semiconductor optical amplifiers 68 and 69, and then the subsequent stage of the multi-mode interferometer 66 is amplified. Are combined at the interference of the modes interferometer 67, the signal light is outputted as an optical output 64 via a focusing optical fiber 63 from the output port of the input port and the cross position input.
[0126]
On the other hand, the laser resonator in this case includes a DBR region 77 provided on the other output port side of the subsequent multimode interferometer 67 and a DBR provided on the other input port side of the preceding multimode interferometer 66. In the eleventh embodiment, as the variable optical attenuator 79, an electroabsorption optical modulator is monolithically integrated on the other input port side of the preceding multimode interferometer 66. Is provided.
[0127]
In this case, the Mach-Zehnder interferometer 60 is also formed by laminating an InGaAsP / InP double heterojunction structure having an active layer having a strained MQW structure with a wavelength composition of 1.55 μm on a semiconductor substrate 65 made of n-type InP. After forming a laminated structure for forming the semiconductor optical amplifiers 68 and 69 and removing the region other than the region for forming the semiconductor optical amplifiers 68 and 69, the wavelength composition in the removal portion is shorter than the laser oscillation wavelength. For example, after laminating a double heterojunction structure having an optical waveguide core layer of 1.30 μm, and then removing a part of the laminated structure in the vicinity of the region where the multi-mode interferometer 66 of the previous stage is formed, as an absorption layer A pin structure for forming an electro-absorption optical modulator composed of an InGaAsP layer having a wavelength composition of 1.48 μm is laminated, and a mesa layer is formed into the shape shown in the figure. The two 2 × 2 type multi-mode interferometers 66 and 67, the semiconductor optical amplifiers 68 and 69, the variable optical attenuator 79, and the DBR regions 77 and 78 sandwiched between them are formed by the In addition, the resonator loss can be arbitrarily controlled continuously by the variable optical attenuator 79.
The DBR regions 77 and 78 form a diffraction grating by forming periodic irregularities in the vicinity of the optical waveguide core layer after the optical waveguide core layer is grown or before the optical waveguide core layer is grown. Then, a predetermined layer structure is formed by laminating.
[0128]
Since the laser resonator is formed as an internal resonator using the DBR regions 77 and 78 in this way, the device configuration is simplified, so that the assembly of the device is facilitated, and the variable optical attenuator 79 is also provided. Since it is integrated, the variable optical attenuator 79 can also be reduced in size, whereby the semiconductor optical amplifier can be further reduced in size.
[0129]
In the eleventh embodiment, since the laser resonator is composed of a pair of DBR regions 77 and 78, the wavelength selectivity of the laser resonator is set at the element design stage and the manufacturing stage. The attention about wavelength selectivity when using an external resonator is alleviated, and other functions, effects, characteristics, etc. are the same as those in the tenth embodiment.
[0130]
In the eleventh embodiment, an electroabsorption optical modulator that can be easily integrated is used as the variable optical attenuator 79. Also in this case, the variable optical attenuator 79 has special light absorption characteristics. Therefore, a variable optical attenuator having another configuration, such as a current injection type semiconductor light absorption element, may be used.
[0131]
Next, with reference to FIGS. 13 to 17, a gain clamp type semiconductor optical amplifying device using the Sagnac type interferometer of the twelfth to sixteenth embodiments of the present invention will be described.
See FIG.
FIG. 13 is a conceptual configuration diagram of a gain clamped semiconductor optical amplifier according to a twelfth embodiment of the present invention. A Sagnac interferometer 80 constituting the gain clamped semiconductor optical amplifier is an optical fiber. The input / output side optical waveguide 82 for the configured signal light, the directional coupler 83 also configured with an optical fiber, the arms 84 and 86, the semiconductor optical amplifier 85 disposed between the arms 84 and 86, and also with the optical fiber. A laser-side optical waveguide 88 that constitutes a laser resonator and a highly reflective film 89 made of a multilayer dielectric film are included.
[0132]
In this case, the laser resonator includes a highly reflective film 89, a laser-side optical waveguide 88, a directional coupler, arms 84 and 85, and a semiconductor optical amplifier 85, and the laser oscillation light generated by the semiconductor optical amplifier 85 is Then, the light is reflected by the highly reflective film 89 and again travels toward the arm side. At that time, the directional coupler 83 constituting the optical coupler is divided into two parts, a clockwise laser oscillation light and a counterclockwise laser oscillation light. However, the phase of the counterclockwise laser oscillation light propagating to the cross side in the directional coupler 83 is shifted by π / 2, while the clockwise laser oscillation light is also crossed from the arm 84 in the directional coupling 83. When returning to the laser-side optical waveguide 88 on the side, the phase is shifted by π / 2. Therefore, in the laser-side optical waveguide 88, the counterclockwise laser oscillation light and the clockwise laser oscillation light have the same level. It becomes a phase and does not disappear due to interference.
[0133]
On the other hand, although there is no change in the phase of the component of the clockwise laser oscillation light from the arm 84 to the input / output side optical waveguide 82 via the directional coupler 83, the arm 86 of the counterclockwise laser oscillation light is not changed. Since the component heading toward the input / output side optical waveguide 82 on the cross side through the directional coupler 83 crosses the directional coupler 83 twice, its phase is shifted by (π / 2) × 2 = π. In the input / output side optical waveguide 82, the clockwise laser oscillation light and the counterclockwise laser oscillation light have opposite phases and disappear due to interference, so that the laser oscillation light is output from the input / output side optical waveguide 82. Absent.
[0134]
The same applies to the signal light. The optical input 81 input to the input / output side optical waveguide 82 is amplified by the semiconductor optical amplifier 85, propagates through the annular arms 84 and 86, and is then input / output side optical again. The amplified optical output 87 is output from the waveguide 82 and does not propagate through the laser-side optical waveguide 88.
[0135]
Therefore, in this Sagnac type optical interferometer 80, the laser oscillation light and the signal light are completely spatially separated, so that it is not necessary to make the laser resonator wavelength dependent, and normal light Since the reflecting mirror can be constituted by the cleavage plane of the fiber itself or a multilayer dielectric film having a high reflectivity provided on the cleavage plane, the resonator structure is simplified.
[0136]
In the twelfth embodiment, since the Sagnac type optical interferometer 80 is used, only one semiconductor optical amplifier 85 is required, and the seventh to eleventh embodiments using a pair of semiconductor optical amplifiers are used. Compared with the configuration, the requirement on the symmetric operation required for the semiconductor optical amplifier 85 can be eliminated, and therefore the laser oscillation light and the signal light can be spatially separated more stably.
[0137]
Further, in the twelfth embodiment, since the portion other than the optical amplifier 85 of the Sagnac type optical interferometer 80 is configured using an optical fiber, stable operation is not required without requiring a special fine processing technique. Thus, a gain clamp type semiconductor optical amplifying device capable of achieving the above can be configured.
[0138]
Next, a thirteenth embodiment of the present invention will be described with reference to FIG. 14. In the thirteenth embodiment, a laser is used instead of the high reflection film 89 in the twelfth embodiment. A diffraction grating 90 is provided at the end of the side optical waveguide 88, that is, the laser side optical waveguide 88 is configured by a fiber diffraction grating, and other configurations are completely the same as those of the twelfth embodiment. Since it is similar, the description will be simplified.
See FIG.
FIG. 14 is a conceptual configuration diagram of a gain clamped semiconductor optical amplifier according to a thirteenth embodiment of the present invention. A Sagnac interferometer 80 constituting the gain clamped semiconductor optical amplifier is an optical fiber. The input / output side optical waveguide 82 for the configured signal light, the directional coupler 83 also configured with an optical fiber, the arms 84 and 86, the semiconductor optical amplifier 85 disposed between the arms 84 and 86, and also with the optical fiber. The laser-side optical waveguide 88 that constitutes the laser resonator and the diffraction grating 90 formed at one end of the laser-side optical waveguide 88 are configured.
[0139]
The operating principle and main features in this case are the same as in the twelfth embodiment, but in the thirteenth embodiment, a diffraction grating 90 is formed at one end of the laser-side optical waveguide 88. Therefore, the oscillation wavelength of the laser oscillation light is stabilized, and the difference between the wavelength of the signal light and the wavelength of the laser oscillation light can be stably maintained. Generation of a nonlinear effect or the like due to an undesired interaction between light and laser oscillation light can be prevented.
[0140]
Next, a fourteenth embodiment of the present invention will be described with reference to FIG. 15. In this fourteenth embodiment, a planar optical circuit (PLC) using a dielectric as a part other than the semiconductor optical amplifier. ).
See FIG.
FIG. 15 is a conceptual configuration diagram of a gain-clamped semiconductor optical amplifier according to a fourteenth embodiment of the present invention. A Sagnac interferometer 100 constituting the gain-clamped semiconductor optical amplifier is a quartz substrate or the like. The optical input / output side optical waveguide 103 for the signal light provided on the PLC substrate 102, the directional coupler 104, the arms 105 and 107, the semiconductor optical amplifier 106 provided in the middle of the arms 105 and 107, and the laser resonator. And a diffraction grating 110 formed at one end of the laser-side optical waveguide 109.
[0141]
In this case, the Sagnac interferometer 100 is formed by using a CVD method on a PLC substrate 102 such as a quartz substrate.₂Lower clad layer made of film and GeO₂SiO with high refractive index by doping₂After depositing the core layer made of a film, reactive ion etching forms an “Ω” -shaped pattern that constitutes the input / output side optical waveguide 103, the directional coupler 104, the arms 105 and 107, and the laser side optical waveguide 109. Etch the core layer.
[0142]
Then, again, SiO is formed by CVD.₂After depositing the upper clad layer made of a film, the diffraction grating 110 is formed on one end of the laser-side optical waveguide 109 using the interference exposure method, and then the central portion of the annular optical waveguide constituting the arms 105 and 107 is formed. A recess reaching the PLC substrate 102 for hybrid mounting of the semiconductor optical amplifier 106 is formed. Finally, the semiconductor optical amplifier 106 is hybrid mounted in this recess with the optical axis aligned with the arms 105 and 107.
As the semiconductor optical amplifier 106 in this case, for example, an InGaAsP / InP-based semiconductor optical amplifier whose active layer has a strained MQW structure with a wavelength composition of 1.55 μm may be used.
[0143]
In the fourteenth embodiment, the parts other than the semiconductor optical amplifier of the Sagnac type interferometer 100 are formed by a planar optical circuit (PLC) using a dielectric, so the twelfth and Compared to the thirteenth embodiment, the apparatus configuration can be greatly simplified and downsized.
The operating principle and main features are the same as in the thirteenth embodiment. The optical input 101 is amplified by the semiconductor optical amplifier 106 and then output from the input / output side optical waveguide 103 as the optical output 108. The
[0144]
In the fourteenth embodiment, the material configuration and manufacturing method of the PLC are not limited to the above-described material configuration and manufacturing method. For example, the film formation method of the cladding layer and the core layer is a normal one. The method is not limited to the atmospheric pressure CVD method, and a plasma CVD method or a low pressure CVD method may be used, and further, a flame deposition method may be used.
[0145]
In order to form the core layer, SiO₂The dopant doped into GeO is GeO₂Is not limited to TiO₂Or P₂O_FiveEtc., and the core layer may be made of SiO._xN_yH_zOther material systems such as the above may be used.
[0146]
Next, a fifteenth embodiment of the present invention will be described with reference to FIG. 16. In the fifteenth embodiment, the entire Sagnac type optical interferometer is constructed monolithically using a semiconductor. is there.
See FIG.
FIG. 16 is a conceptual configuration diagram of a gain clamped semiconductor optical amplifier according to a fifteenth embodiment of the present invention. A Sagnac interferometer 120 constituting the gain clamped semiconductor optical amplifier is a semiconductor substrate 122. The input / output side optical waveguide 123 for the signal light, the directional coupler 124, the arms 125 and 127, the semiconductor optical amplifier 126 provided between the arms 125 and 127, and the laser side optical waveguide constituting the laser resonator. 129 and a diffraction grating 130 formed at one end of the laser-side optical waveguide 129.
[0147]
In this case, the Sagnac interferometer 120 has, for example, an InGaAsP / InP double heterojunction structure in which an active layer has a strained MQW structure having a wavelength composition of 1.55 μm on a semiconductor substrate 122 made of n-type InP. After forming a laminated structure for forming the semiconductor optical amplifier 126 and removing the region other than the region for configuring the semiconductor optical amplifier 126, the removal portion has a wavelength composition shorter than the laser oscillation wavelength, for example, A double heterojunction structure having an optical waveguide core layer with a thickness of 1.30 μm is stacked, and then mesa-etched into an “Ω” shape to thereby form an input / output side optical waveguide 123, a directional coupler 124, arms 125, 127, And the laser side optical waveguide 129 is formed.
Note that the diffraction grating 130, that is, the DBR region is diffracted by forming periodic irregularities in the vicinity of the optical waveguide core layer after the optical waveguide core layer is grown or before the optical waveguide core layer is grown. A lattice is formed, and then the aforementioned predetermined layer structure is laminated.
[0148]
Thus, in the fifteenth embodiment of the present invention, the entire configuration of the Sagnac interferometer 120 is monolithically formed using a semiconductor, so that the entire configuration can be further reduced in size, Since hybrid mounting as in the fourteenth embodiment is not required, optical axis alignment at the time of mounting becomes unnecessary, and deterioration of optical characteristics depending on the accuracy of optical axis alignment does not occur. .
The operating principle and main features are the same as those in the fourteenth embodiment. The optical input 121 is amplified by the semiconductor optical amplifier 126 and then output from the input / output side optical waveguide 123 as the optical output 128. The
[0149]
Next, a sixteenth embodiment of the present invention will be described with reference to FIG. 17. In the sixteenth embodiment, variable light is added to the Sagnac type optical interferometer of the fifteenth embodiment. An electroabsorption optical modulator is monolithically incorporated as an attenuator.
See FIG.
FIG. 17 is a conceptual configuration diagram of a gain clamped semiconductor optical amplifier according to a sixteenth embodiment of the present invention. A Sagnac interferometer 120 constituting this gain clamped semiconductor optical amplifier is a semiconductor substrate 122. The input / output side optical waveguide 123 for the signal light, the directional coupler 124, the arms 125 and 127, the semiconductor optical amplifier 126 provided between the arms 125 and 127, and the laser side optical waveguide constituting the laser resonator. 129, an electroabsorption optical modulator 131 provided in the middle part of the laser side optical waveguide 129, and a diffraction grating 130 provided at one end of the laser side optical waveguide 129.
[0150]
The Sagnac interferometer 120 in this case also has, for example, an InGaAsP / InP double heterojunction structure in which the active layer has a strained MQW structure with a wavelength composition of 1.55 μm on the semiconductor substrate 122 made of n-type InP. After forming a laminated structure for forming the semiconductor optical amplifier 126 and removing the region other than the region for configuring the semiconductor optical amplifier 126, the removal portion has a wavelength composition shorter than the laser oscillation wavelength, for example, After laminating a double heterojunction structure having an optical waveguide core layer having a thickness of 1.30 μm, and then removing a part of the laminated structure in the middle of the region constituting the laser side optical waveguide 129, the wavelength composition as an absorption layer A pin structure for forming an electroabsorption optical modulator 131 composed of an InGaAsP layer having a thickness of 1.48 μm is laminated, and then a mesa is formed in an “Ω” shape. Output-side optical waveguide 123 by etching, a directional coupler 124, the arms 125 and 127, laser optical wave guide 129, and is obtained by forming an electric field absorption optical modulator 131.
Note that the diffraction grating 130, that is, the DBR region is diffracted by forming periodic irregularities in the vicinity of the optical waveguide core layer after the optical waveguide core layer is grown or before the optical waveguide core layer is grown. A lattice is formed, and then the aforementioned predetermined layer structure is laminated.
[0151]
Thus, in the sixteenth embodiment of the present invention, when the entire configuration of the Sagnac interferometer 120 is monolithically formed using a semiconductor, the electroabsorption optical modulator 131 serving as a variable optical attenuator is also provided. Since it is monolithically incorporated, the resonator loss can be continuously controlled to an arbitrary value by the attenuation amount of the electroabsorption optical modulator 131, as in the first to eleventh embodiments. The characteristics of the semiconductor optical amplifier can be set to optimum values according to various applications.
The operating principle and main features are the same as in the fifteenth embodiment, and the optical input 121 is output from the input / output side optical waveguide 123 as the optical output 128 after being amplified by the semiconductor optical amplifier 126. The
[0152]
In the sixteenth embodiment, the electroabsorption optical modulator 131 that can be easily integrated is used as the variable optical attenuator. In this case, the variable optical attenuator has special light absorption characteristics. Since this is not required, a variable optical attenuator having another configuration, for example, a current injection type semiconductor light absorption element or the like may be used.
[0153]
As mentioned above, although each embodiment of the present invention has been described, the present invention is not limited to the configuration described in each embodiment, and various modifications are possible.
For example, the active layer of the semiconductor optical amplifier has a 1.55 μm wavelength composition so that the attenuation in the optical long-distance communication fiber is small, but other compositions such as a 1.3 μm wavelength composition may be used. Is for attenuation characteristics such as the absorption edge wavelength in a variable optical attenuator according to the wavelength composition of the active layer, or for optical waveguide constituting a 2 × 2 type optical multiplexer / demultiplexer, Sagnac type optical interferometer, DBR region, etc. What is necessary is just to change the composition of a core layer.
[0154]
Furthermore, the present invention is not limited to the InGaAsP / InP system when the semiconductor optical amplifier, the variable optical attenuator, the optical waveguide, or the optical coupler is configured by a semiconductor, but a GaAs / AlGaAs system or the like. It may be formed using other compound semiconductors.
[0155]
In addition, the above-described ninth to eleventh embodiments are changed from the eighth embodiment, that is, a reflector having wavelength selectivity such as a fiber diffraction grating is used, and a variable optical attenuator is monolithically integrated. The points to be integrated and the DBR region to be monolithically integrated are applicable to the seventh embodiment as they are.
[0156]
In the seventh to eleventh embodiments, the variable optical attenuator is provided on the input port side of the 2 × 2 type optical multiplexer / demultiplexer on the input side, but the 2 × 2 type optical multiplexer / demultiplexer on the output side is provided. A variable optical attenuator may be provided on the output port side.
[0157]
In the description of the seventh to eleventh embodiments, the wavelength composition of the optical waveguide core layer of the DBR region or 2 × 2 type optical multiplexer / demultiplexer is used in order to prevent undesired absorption of laser oscillation light. Is set to a wavelength shorter than the wavelength composition of the active layer of the semiconductor optical amplifier, but may have the same structure as the semiconductor optical amplifier. In this case, the DBR region or 2 is set so as to cancel the absorption loss. A × 2 type optical multiplexer / demultiplexer may be forward-biased.
[0158]
In the description of the twelfth to fourteenth embodiments, it is assumed that the gain-clamped semiconductor optical amplifier device using a Sagnac optical interferometer is a novel one. However, as in the sixteenth embodiment, a variable optical attenuator may be provided in the middle of the laser side optical waveguide, so that the resonator loss can be set to an arbitrary value. By continuously controlling, the characteristics of the semiconductor optical amplifier can be set to an optimum value according to various applications.
[0159]
As the variable optical attenuator, various commercially available variable optical attenuators are used. Since the optical input that is effectively used as signal light does not pass through the variable optical attenuator, the attenuation characteristic of the variable optical attenuator Any type of variable optical attenuator may be used as long as it can attenuate light with a laser oscillation wavelength, for example, 1.51 μm, and such a variable optical attenuator is hybrid-mounted. By doing so, the amount of attenuation can be controlled arbitrarily.
[0160]
In the description of the fifteenth and sixteenth embodiments described above, in order to prevent undesired absorption of laser oscillation light, an input / output side optical waveguide, a directional coupler, an arm, a laser side optical waveguide, and The wavelength composition of the optical waveguide core layer in the DBR region is set to be shorter than the wavelength composition of the active layer of the semiconductor optical amplifier. However, the same structure as the semiconductor optical amplifier may be used, and the entire configuration is the same. By doing so, the manufacturing process can be greatly simplified.
In that case, it is necessary to forward bias each region so as to cancel the absorption loss.
[0161]
In the description of the thirteenth to sixteenth embodiments, the laser side optical waveguide is provided with a diffraction grating to provide wavelength selectivity. However, as in the twelfth embodiment, a laser is used. A highly reflective film may be provided only on the end face of the side optical waveguide, or a dielectric or semiconductor cleaved surface may be used.
[0162]
【The invention's effect】
According to the present invention, it is possible to continuously adjust the gain and the allowable incident power of signal light, and to realize a gain clamp type semiconductor optical amplifier capable of optimizing the characteristics for each application requirement by one structure. Therefore, it greatly contributes to the practical application of the wavelength division multiplexing optical communication system.
[0163]
In addition, by constructing a gain-clamped semiconductor optical amplifier using a Sagnac optical interferometer, the symmetrical operation characteristics of the semiconductor optical amplifier are no longer required, so that the laser oscillation light and the signal light are reliably separated spatially. In addition, since the overall configuration of the apparatus can be further reduced in size, this point greatly contributes to the practical use of the wavelength division multiplexing optical communication system.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a basic configuration of the present invention.
FIG. 2 is a conceptual configuration diagram of the first embodiment of the present invention.
FIG. 3 is a conceptual configuration diagram of a second embodiment of the present invention.
FIG. 4 is a conceptual configuration diagram of a third embodiment of the present invention.
FIG. 5 is a conceptual configuration diagram of a fourth embodiment of the present invention.
FIG. 6 is a conceptual configuration diagram of a fifth embodiment of the present invention.
FIG. 7 is a conceptual configuration diagram of a sixth embodiment of the present invention.
FIG. 8 is a conceptual configuration diagram of a seventh embodiment of the present invention.
FIG. 9 is a conceptual configuration diagram of an eighth embodiment of the present invention.
FIG. 10 is a conceptual configuration diagram of a ninth embodiment of the present invention.
FIG. 11 is a conceptual configuration diagram of a tenth embodiment of the present invention.
FIG. 12 is a conceptual configuration diagram of an eleventh embodiment of the present invention.
FIG. 13 is a conceptual configuration diagram of a twelfth embodiment of the present invention.
FIG. 14 is a conceptual configuration diagram of a thirteenth embodiment of the present invention.
FIG. 15 is a conceptual configuration diagram of a fourteenth embodiment of the present invention.
FIG. 16 is a conceptual configuration diagram of a fifteenth embodiment of the present invention.
FIG. 17 is a conceptual configuration diagram of a sixteenth embodiment of the present invention.
FIG. 18 is an explanatory diagram of resonator loss dependence of gain-optical output characteristics of a semiconductor optical amplifier device;
[Explanation of symbols]
1 Semiconductor optical amplifier
2 Semiconductor optical amplifier
3 Variable optical attenuator
4 Wavelength selective reflector
5 Reflector without wavelength selectivity
6 Beam splitter
7 signal light
11 Light input
12 optical fiber
13 Lens
14 Beam splitter
15 lenses
16 Semiconductor optical amplifier
17 Lens
18 lenses
19 Optical fiber
20 Light output
21 Variable optical attenuator
22 Diffraction grating
23 Beam splitter
24 lenses
25 Diffraction grating
26 Fiber diffraction grating
27 lenses
28 lenses
29 Fiber diffraction grating
30 Monolithic optical semiconductor device
31 Semiconductor substrate
32 Semiconductor optical amplification region
33 Variable optical attenuation region
34 Monolithic optical semiconductor device
35 Semiconductor substrate
36 DBR region
37 DBR region
40 Mach-Zehnder interferometer
41 Light input
42 Focusing optical fiber
43 Focused optical fiber
44 Light output
45 Semiconductor substrate
46 Directional coupler
47 Directional coupler
48 Semiconductor optical amplifier
49 Semiconductor optical amplifier
50 highly reflective film
51 lens pair
52 Variable Optical Attenuator
53 High reflective film
60 Mach-Zehnder interferometer
61 Light input
62 Focusing optical fiber
63 Focused optical fiber
64 light output
65 Semiconductor substrate
66 Multimode Interferometer
67 Multimode Interferometer
68 Semiconductor optical amplifier
69 Semiconductor optical amplifier
70 High reflective film
71 Lens pair
72 Variable Optical Attenuator
73 High reflective film
74 Fiber diffraction grating
75 Electroabsorption optical modulator
76 Fiber diffraction grating
77 DBR region
78 DBR region
79 Variable Optical Attenuator
80 Sagnac optical interferometer
81 Light input
82 I / O side optical waveguide
83 Directional coupler
84 arms
85 Semiconductor optical amplifier
86 arm
87 Light output
88 Laser side optical waveguide
89 High reflective film
90 diffraction grating
100 Sagnac optical interferometer
101 Light input
102 PLC board
103 Input / output optical waveguide
104 Directional coupler
105 arms
106 Semiconductor optical amplifier
107 arm
108 Light output
109 Laser-side optical waveguide
110 diffraction grating
120 Sagnac optical interferometer
121 Light input
122 Semiconductor substrate
123 Input / output optical waveguide
124 Directional coupler
125 arms
126 Semiconductor optical amplifier
127 arm
128 optical output
129 Laser-side optical waveguide
130 diffraction grating
131 Electroabsorption optical modulator

Claims (23)

  In a gain clamp type semiconductor optical amplifying device comprising a semiconductor optical amplifier and a laser resonator including the semiconductor optical amplifier, laser oscillation light while maintaining an effective transmission loss amount for signal light at a constant value. A semiconductor optical amplifying device comprising a variable optical attenuating mechanism capable of controlling a resonator loss amount with respect to.   2. The semiconductor according to claim 1, wherein at least one of the laser resonators is constituted by a reflecting mirror having wavelength selectivity, and a variable optical attenuator is provided in the laser resonator as the variable optical attenuation mechanism. Optical amplification device.   3. The semiconductor optical amplifying device according to claim 2, wherein a portion through which the signal light does not pass is provided in the laser resonator, and the variable optical attenuator is disposed at a portion through which the signal light does not pass.   The laser resonator has an external resonator structure composed of a wavelength-selective reflector and a non-wavelength-selective reflector, and a beam splitter is inserted between the wavelength-selective reflector and the semiconductor optical amplifier. In addition, signal light is incident from a direction perpendicular to the laser resonator through the beam splitter, and the signal light is not passed between the wavelength selective reflector and the beam splitter. The semiconductor optical amplifier according to claim 3.   The laser resonator has an external resonator structure composed of a wavelength-selective reflector and a non-wavelength-selective reflector, and a beam splitter is inserted between the wavelength-selective reflector and the semiconductor optical amplifier. In addition, the signal light is emitted from a direction perpendicular to the laser resonator through the beam splitter, and the signal light does not pass between the wavelength selective reflector and the beam splitter. The semiconductor optical amplifier according to claim 3.   The laser resonator has an external resonator structure composed of a pair of wavelength-selective reflectors, and a beam splitter is inserted between the semiconductor optical amplifier and both of the wavelength-selective reflectors, and Signal light is input and output from a direction perpendicular to the laser resonator through a beam splitter, and the signal light does not pass through two regions between the pair of wavelength-selective reflectors and the beam splitter; 4. The semiconductor optical amplifier according to claim 3, wherein   A variable optical attenuator in which the amount of optical attenuation can be changed with respect to the laser oscillation wavelength as the variable attenuator without providing a portion through which the signal light does not pass in the laser resonator, but the signal light is not effectively attenuated. The semiconductor optical amplifier according to claim 2, wherein:   Electroabsorption type light having an absorption edge wavelength shorter than the laser oscillation wavelength as the variable optical attenuator while setting the laser oscillation wavelength shorter than the wavelength of the signal light by the wavelength selective reflector. 8. The semiconductor optical amplifier according to claim 7, wherein a modulator is used.   9. The semiconductor optical amplifier according to claim 8, wherein the semiconductor optical amplifier and the variable optical attenuator comprising the electroabsorption optical modulator are monolithically integrated.   10. The semiconductor optical amplifier according to claim 7, wherein a fiber grating is used as the wavelength-selective reflecting mirror. 11. A distributed Bragg reflector is used as the wavelength selective reflector, and the distributed Bragg reflector is monolithically integrated with a variable optical attenuator composed of the semiconductor optical amplifier and the electroabsorption optical modulator. The semiconductor optical amplifier according to claim 9.   The semiconductor optical amplifier is provided in two arms of a Mach-Zehnder interferometer including two 2 × 2 type optical couplers, and the laser resonator is connected to one of the input ports of the optical coupler on the input side and the input port The variable optical attenuator as the variable optical attenuation mechanism includes the optical coupler and the optical coupler in the laser resonator, and a reflecting mirror disposed at the output port of the optical coupler at the output side in the cross position. 2. The semiconductor optical amplifier according to claim 1, wherein the semiconductor optical amplifier is provided between the reflecting mirror and the reflecting mirror.   13. The semiconductor optical amplifier according to claim 12, wherein a directional coupler is used as the 2 × 2 type optical multiplexer / demultiplexer.   13. The semiconductor optical amplifier according to claim 12, wherein a multimode interferometer is used as the 2 × 2 type optical multiplexer / demultiplexer.   15. The semiconductor optical amplifying device according to claim 12, wherein at least one of the reflecting mirrors is constituted by a reflecting mirror having wavelength selectivity.   16. The semiconductor optical amplifier according to claim 12, wherein an electroabsorption optical modulator is used as the variable optical attenuator.   17. The semiconductor optical amplifier, the two 2 × 2 type optical multiplexer / demultiplexers, the variable optical attenuator, and the reflecting mirror are monolithically integrated. Semiconductor optical amplifier. In a gain clamp type semiconductor optical amplifier comprising a semiconductor optical amplifier and a laser resonator including the semiconductor optical amplifier therein, the semiconductor optical amplifier is provided on an arm of a Sagnac optical interferometer, and the Sagnac optical light is provided. An optical waveguide connected to one input / output port of the interferometer to form a laser resonator by arranging a reflecting mirror and a variable optical attenuator arranged in the optical waveguide and connected to the other input / output port A semiconductor optical amplifying device characterized in that an optical waveguide for input / output with respect to signal light is used.   19. The semiconductor optical amplifier according to claim 18, wherein a reflecting mirror having wavelength selectivity is used as the reflecting mirror.   20. The semiconductor optical amplifying device according to claim 18, wherein the optical waveguide portion and the optical coupler portion other than the semiconductor optical amplifier in the Sagnac type optical interferometer are constituted by optical fibers.   20. The semiconductor optical amplifier according to claim 18, wherein the optical waveguide portion and the optical coupler portion other than the semiconductor optical amplifier in the Sagnac type optical interferometer are constituted by a planar dielectric optical circuit.   20. The semiconductor optical amplifier according to claim 18, wherein the optical waveguide, the optical coupler portion, the arm, and the semiconductor optical amplifier constituting the Sagnac optical interferometer are monolithically integrated with a semiconductor.   23. The semiconductor optical amplification device according to claim 22, wherein the optical waveguide, the optical coupler portion, and the arm constituting the Sagnac type optical interferometer are also used as a semiconductor optical amplification region.

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