JPH05152687A - Semiconductor optical amplifier - Google Patents

Abstract

PURPOSE:To amplify a TE polarized wave only or a TM polarized wave only by a method wherein a bulk active layer having an ordered state in the orientation [-111] or [1-11] is provided on a (001) semiconductor substrate and an optical waveguide is formed in the orientation [-110] or [1-10] on the substrate. CONSTITUTION:An active layer 100 inserted between clad layers 110 and 120 is provided on a (001) semiconductor substrate 150. This layer 100 is constituted into a bulk quantum well structure having an ordered state in the orientation [-111] or [1-11], a distortionless quantum well structure or a quantum well structure subjected to in-surface compressive distortion. The layer 120 is formed into a mesa type form for forming an optical waveguide and the outside of the mesa of the layer 120 is buried in a current blocking layer 130. The optical wavelength is formed in the orientation [-110] or [1-10]. Moreover, dielectric non-reflection films 180 are respectively provided on an edge of incidence and an edge of emittance for inhibiting oscillations to use as an optical amplifier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to TE polarized light or T polarized light.
The present invention relates to a semiconductor optical amplifier having a filter function of selectively amplifying M polarized light.

[0002]

2. Description of the Related Art Currently, semiconductor optical amplifiers are being actively studied as repeaters for optical communication. The advantage is that
It is expected to be used as an optical amplifier for subscribers because it can amplify 1.3 μm band and has low power consumption. Also, the characteristic is 20d as the net gain of the element.
About B is obtained. Further, regarding the semiconductor optical amplifier in the 0.6 μm band, which is the low loss band of the plastic fiber, it has not been reported because the optical communication market in the 0.6 μm band has not been established. As described above, the main applications of semiconductor optical amplifiers are currently limited to the field of optical communication, but as the characteristics of semiconductor optical amplifiers improve in the future, various applications such as optical measurement and SHG light source It is expected that the uses of will be pioneered.

[0003]

However, in the currently realized semiconductor optical amplifiers, no attempt has been made to positively control and utilize the polarization characteristics. For this reason, a filter function of polarization characteristics that would generate a large amount of demand if realized, that is, only TE polarization, or T
The function of amplifying only M polarization has not been realized.

[0004]

The first structure of the present invention is as follows.
On a (001) semiconductor substrate, [-1 1 1] or [1 -1
In a semiconductor optical amplifier including a bulk active layer having an ordered state in the [1] direction, an optical waveguide is [-1 10] or [1
-10] direction. A second structure of the present invention is [-1 11] on a (001) semiconductor substrate.
Alternatively, in a semiconductor optical amplifier including a quantum well structure active layer having an ordered state in the [1 -11] direction, an optical waveguide is formed in the [-1 1 0] or [1 -1 0] direction. To do. The third structure of the present invention is a semiconductor optical amplifier including a quantum well structure active layer having an ordered state in the [-1 11] or [1 -11] direction on a (001) semiconductor substrate, The well layer of the quantum well structure active layer is subjected to in-plane compressive strain, and the optical waveguide is [-1 10] or [1 -1].
[0] direction. In addition, a fourth configuration of the present invention is that [-1 11] on a (001) semiconductor substrate.
Alternatively, in a semiconductor optical amplifier including a bulk active layer having an ordered state in the [1 -11] direction, an optical waveguide is
] Or [-1 -10] direction. The fifth structure of the present invention is a semiconductor optical amplifier including a quantum well structure active layer having an ordered state in the [-1 1 1] or [1 -1 1] direction on a (001) semiconductor substrate. , The well layer of the quantum well structure active layer is subject to in-plane tensile strain, and the optical waveguide is [1 10] or [-1 -1
[0] direction. Finally, in the sixth configuration of the present invention, in the semiconductor optical amplifiers of the first to fifth configurations, the semiconductor substrate plane orientation is (00
1) It is characterized in that it is turned off within 15 degrees from the surface.

[0005]

A schematic view of the semiconductor optical amplifier of the present invention is shown in FIGS. FIG. 1 is a structural diagram for realizing a semiconductor optical amplifier corresponding to claims 1, 2 and 3 having a function of selectively amplifying only TE polarized waves, and FIG. 2 has a function of selectively amplifying only TM polarized waves. FIG. 6 shows a structural diagram for realizing a semiconductor optical amplifier corresponding to claims 4 and 5. Hereinafter, FIGS. 1 and 2 will be described first, and then a mechanism capable of selectively amplifying only a specific polarized wave will be described. First, the structure of the semiconductor optical amplifier shown in FIG. 1 will be described. An active layer 100 sandwiched between clad layers 110 and 120 is provided on a (001) semiconductor substrate 150. The active layer 100 has a bulk or unstrained quantum well structure having an ordered state in the [-1 1 1] or [1 -1 1] direction, or an in-plane structure as described in claims 1, 2 and 3. It is composed of a quantum well structure subjected to compressive strain. The clad layer 120 has a mesa shape for forming an optical waveguide, and the current block layer 130 fills the outside of the mesa. The optical waveguide is formed in the [-1 1 0] or [1 -1 0] direction.
Further, a dielectric non-reflective film 180 is provided on the incident end face and the emitting end face in order to suppress oscillation and use as an optical amplifier.

Next, the semiconductor optical amplifier shown in FIG. 2 will be described. Similar to FIG. 1, an active layer 100 sandwiched between clad layers 110 and 120 is provided on a (001) semiconductor substrate 150. As described in claims 4 and 5, the active layer 100 is composed of a bulk having an ordered state in the [-1 11] or [1 -11] direction, or a quantum well structure subjected to in-plane tensile strain. ing. The clad layer 120 has a mesa shape for forming an optical waveguide, and the current block layer 130 fills the outside of the mesa. The optical waveguide is formed in the [1 1 0] or [-1 -1 0] direction. Furthermore, in order to suppress oscillation and use as an optical amplifier, the dielectric non-reflective film 1 is formed on the incident end face and the emitting end face.
Equipped with 80.

Next, the mechanism of why the semiconductor optical amplifier having the structure shown in FIGS. 1 and 2 can selectively amplify only a specific polarized wave will be described. It is generally known that, in the case of a semiconductor having no anisotropy such as a bulk crystal, the gains of TM polarized wave and TE polarized wave are equal and the TM / TE ratio is 1. This is because the dipole vector formed in the semiconductor is isotropic, so that it is uniformly coupled to both the TM polarized electric vector and the TE polarized electric vector.

However, it is known that a natural superlattice having an ordered state in the [-1 11] or [1-1 1] direction is formed in the AlGaInP semiconductor.
For example, Gomei et al. Reported in Applied Physics Letters (A. Gomyo et al., Appl. Phys.
Lett., Vol.50, pp.673 1987). When a natural superlattice is formed, the dipole vector has anisotropy in the [1 1 0] direction because it has an ordered state in the [-1 1 1] or [1 -1 1] direction. As a result, the coupling with the electric vector of the [1 1 0] component becomes large. Therefore, when the optical waveguide is formed in the [-1 1 0] or [1 -1 0] direction (corresponding to claim 1), the gain of the TE mode having the electric vector in the [1 1 0] direction becomes strong and TM / TE <1, whereas
When an optical waveguide is formed in the [1 1 0] or [-1 -1 0] direction (corresponding to claim 3), the gain of the TE mode having an electric vector in the direction orthogonal to [1 10] becomes weak and TM
/ TE> 1. The above is the explanation that the semiconductor optical amplifier having the structure of FIGS. 1 and 2 can selectively amplify only a specific polarized wave. The above idea is based on the fact that Mascarenhas et al. (A. Mascarenhas et al.,
Phys. Rev. Lett., Vol.63, No.19, pp.2108 1989.), supported by photoluminescence experiments or our measurement results of TM / TE ratio with different optical waveguide directions. ing.

Further, it is generally known that the polarization plane dependence of gain appears by introducing a quantum well structure (no strain), and has an ordered state in the [-1 1 1] or [1 -1 1] direction. TE by incorporating a quantum well structure in the active layer
It is possible to further enhance the mode selectivity. (Corresponding to claim 2)

Regarding the introduction of strain, which has been actively researched recently, it is known that the TE mode is strengthened by applying in-plane compressive strain to the quantum well structure and the TM mode is strengthened by applying in-plane tensile strain. Has been. Therefore, by adding a quantum well structure with in-plane compressive strain to an active layer that also has an ordered state in the [-1 1 1] or [1 -1 1] direction, semiconductor light with higher TE mode selectivity can be obtained. By adding a quantum well structure with in-plane tensile strain to an active layer in which the amplifier (corresponding to claim 3) has an ordered state in the [-1 1 1] or [1 -11 1] direction, A semiconductor optical amplifier with high TM mode selectivity (corresponding to claim 5) can be realized.

[0011] Finally, the above explanation is for the case of the (001) semiconductor substrate, but in the [-1 1 1] direction or [1 -1] direction.
An ordered state in the 1] direction is also formed in a crystal in which the substrate is off from the (001) surface by a few ten degrees. Therefore, (00
1) A semiconductor optical amplifier having a similar polarization characteristic selecting function can be realized with respect to the semiconductor optical amplifiers of FIGS. 1 and 2 formed on a semiconductor substrate having an off angle within 15 degrees off the plane. The above is the operation of the present invention.

[0012]

EXAMPLES Examples of the semiconductor optical amplifier of the present invention will be shown below by giving concrete numerical examples. First, a semiconductor optical amplifier capable of selectively amplifying the TE polarized light in FIG. 1 will be described.
The semiconductor substrate used is a Si-doped (001) GaAs substrate 150. In addition, vapor phase pyrolysis (hereinafter M
Abbreviated as OVPE method. ) Sequentially with N-type AlGaInP
Cladding layer 110, undoped GaInP and AlGa
Strain-free quantum well structure active layer 10 having a multilayer structure of InP
0, a double heterostructure including a P-type AlGaInP cladding layer 120 is grown. At this time, the quantum well structure active layer is grown under the crystal growth conditions such that the quantum well structure active layer has an ordered state in the [-1 11] direction or the [1 -11] direction. After that, since an optical waveguide is formed by wet etching, P-type Al is used.
The GaInP clad layer 120 is processed into a mesa shape. At this time, the direction of forming the optical waveguide is the [-1 1 0] direction or the [1 -1 0] direction. Then, by the second MOVPE growth, the N-type GaAs current block layer 130 is selectively embedded and grown outside the mesa. And the third MOVP
By E growth, a P-type GaAs contact layer is grown on the front surface. After that, P / N electrodes are formed. Then, it is divided into bars to form an incident end face and an outgoing end face, and a dielectric non-reflective film 180 for suppressing oscillation is formed thereon. The dielectric non-reflective film was made of SiNx in order to keep the reflectance as small as possible, and the reflectance was suppressed to 0.5% or less.
Then, the bar is cut into chips to complete the semiconductor optical amplifier having the structure shown in FIG.

When the amplification characteristics of the semiconductor optical amplifier having the structure shown in FIG. 1 manufactured in this way was measured, the incident light was 0.69 μm.
When m and 5 mW or less, a gain of 9 dB or more was generated for TE polarized light, whereas it was 0.5 for TM polarized light.
It was below dB. From this, it was found that only the TE polarized light can be selectively amplified by the semiconductor optical amplifier having the structure of FIG. 1 of the present invention. In addition, the structure of the active layer is bulk 60n.
When m is set, or when the quantum well structure is subjected to 1.0% in-plane compression strain, the gains for the TE polarized light are 12 dB and 5 dB, respectively. In each case, it was 0.5 dB or less, and it was found that only TE polarized light can be selectively amplified.

Next, a semiconductor optical amplifier having a structure capable of selectively amplifying the TM polarized light of FIG. 2 will be described. The method of manufacturing the semiconductor optical amplifier of FIG. 2 is basically the same as that of the semiconductor optical amplifier of FIG. 2 differs from FIG. 1 in that the direction in which the optical waveguide is formed is [1 10] direction or [-1 -1 0] direction.
That is the direction. Further, in FIG. 2, the active layer has a quantum well structure having a bulk 60 nm or 1.0% in-plane tensile strain. When this element was measured, when the incident light was 0.69 μm and 5 mW or less, gains of 3 dB and 7 dB were obtained for the TM polarized light, while 0.5 dB or less for the TE polarized light. Was suppressed to. From this, the semiconductor optical amplifier of FIG.
It was found that polarized light can be selectively amplified. It should be noted that compared with the gain of TE polarized light in the semiconductor optical amplifier of FIG.
The small gain of TM polarized light in the semiconductor optical amplifier of
It is considered that this is because the reflectances of the entrance end face and the exit end face are not completely zero. The above is the embodiment of the present invention.

[0015]

As described above, according to the present invention,
As in the semiconductor optical amplifier shown in FIG. 1, only the TE mode can be selectively amplified, and as in the semiconductor optical amplifier shown in FIG. 2, only the TM mode can be selectively amplified.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a semiconductor optical amplifier of one embodiment of the present invention that selectively amplifies a TE mode.

FIG. 2 is a schematic diagram of a semiconductor optical amplifier of another embodiment of the present invention that selectively amplifies TM mode.

[Explanation of symbols]

 100 Active layer 110, 120 Clad layer 130 Current blocking layer 140 Cap layer 150 Semiconductor substrate 160, 170 Electrode 180 Dielectric reflection-free film 190 Optical waveguide 200 Incident light 210 Emitted light

Claims (6)

[Claims] 1. [-1 11] on a (001) semiconductor substrate
Alternatively, a semiconductor optical amplifier including a bulk active layer having an ordered state in the [1-1 1] direction and forming an optical waveguide in the [-11 0] or [1 -10] direction. 2. [-1 11] on a (001) semiconductor substrate
Alternatively, the optical waveguide is provided with [-1 1 0] or [1 -1 0] by providing a quantum well structure active layer having an ordered state in the [1-1 1] direction.
A semiconductor optical amplifier characterized by being formed in a direction. 3. [-1 1 1] on a (001) semiconductor substrate
Alternatively, the quantum well structure active layer having an ordered state in the [1-1 1] direction is provided, the well layer of the quantum well structure active layer is subjected to in-plane compressive strain, and the optical waveguide is [-1 10] Alternatively, the semiconductor optical amplifier is formed in the [1 -10] direction. 4. A (001) semiconductor substrate on which [-1 1 1]
Alternatively, a semiconductor optical amplifier comprising a bulk active layer having an ordered state in the [1-1 1] direction and forming an optical waveguide in the [1 1 0] or [-1 -1 0] direction. 5. A [-1 1 1] on a (001) semiconductor substrate.
Alternatively, a quantum well structure active layer having an ordered state in the [1-1 1] direction is provided, the well layer of the quantum well structure active layer is subjected to in-plane tensile strain, and the optical waveguide is [1 1 0] or A semiconductor optical amplifier characterized by being formed in the [-1 -10] direction. 6. The semiconductor according to claim 1, wherein the semiconductor substrate plane orientation is formed on a semiconductor substrate having an off angle within 15 degrees from the (001) plane. Optical amplifier.