JP3879157B2 - Optical filter and optical module using optical filter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an optical element, an optical filter, and an optical amplifier. In particular, the configuration of the optical filter and the optical amplifier is simplified.Wavelength characteristics of transmittanceThe present invention relates to an optical element that facilitates adjustment of the optical filter, and an optical filter and an optical amplifier that are simplified in configuration and easy to adjust by applying the optical element.
[0002]
The optical amplifier includes a front module that monitors the level of the input signal light, an optical amplifier that amplifies the signal light, and a rear module that extracts the signal light from the output light of the optical amplifier. In practical optical amplifiers, none of these parts are indispensable, but in order to maintain a high signal-to-noise ratio in the optical transmission line and to ensure a code error rate in optical digital communication, it is also necessary to In analog communication, in order to reduce noise itself, the role of the post-stage module that extracts the signal light from the output light of the optical amplifying means is large.
[0003]
A band pass type optical filter is used to extract the signal light from the output light of the optical amplifying means in the subsequent module. This optical filter is required to have good wavelength selectivity, a simple configuration for obtaining good wavelength selectivity, and easy adjustment of wavelength selectivity. If the configuration of the optical filter is simplified and the adjustment is facilitated, the configuration of the optical amplifier is also simplified and the adjustment is facilitated, and the cost is reduced.
[0004]
Therefore, the practical use of an optical element capable of realizing such an optical filter and an optical amplifier, and the practical use of an optical filter and an optical amplifier whose configuration is simplified by applying the optical element are awaited. .
[0005]
By the way, as optical amplifiers, there are optical fiber amplifiers that use optical fibers doped with rare earth ions, particularly erbium ions, in the optical amplification stage, and semiconductor optical amplifiers that use the optical amplification effect in compound semiconductors.
[0006]
In any type, the optical amplifier includes a front module for monitoring the level of the input signal light, an optical amplification stage for amplifying the signal light, and a rear module for extracting the signal light from the output light of the optical amplification stage. Composed. Therefore, hereinafter, the technique of the present invention will be described by taking an optical fiber amplifier that has been steadily put into practical use as an example.
[0007]
[Prior art]
FIG. 9 shows a configuration of a forward pumping type optical fiber amplifier.
In FIG. 9, reference numeral 1 denotes a front-stage module for monitoring an optical coupler 11 for branching a part of input signal light and a level of the input signal light by converting the light branched by the optical coupler 11. And an isolator 13 for preventing the reflected light and spontaneously emitted light from the optical amplification stage and beyond from being transmitted to the input side.
[0008]
An optical amplification stage 2 includes an optical amplification fiber 21 to which erbium ions are added, a laser diode 22 that generates excitation light for amplifying signal light using the optical amplification fiber, and the signal light and the excitation light. And an optical coupler 23 for coupling light. Note that, here, it is assumed that the output of the laser diode 22 is coupled to the optical amplification fiber 21 by using a fiber fusion type coupler, but the output of the laser diode 22 is assumed to be the optical amplification. An element such as a wavelength multiplexing element can also be used as means for coupling to the fiber 21.
[0009]
Further, reference numeral 3 denotes a rear module for isolating the reflected light from the output side to the optical amplification stage, and for removing the excitation light and the spontaneous emission light from the output light of the optical amplification stage to extract the signal light. A band-pass optical filter 32, an optical coupler 38 for branching a part of the signal light, and an electric signal for monitoring the level of the signal light output by converting the signal light branched by the optical coupler 38 And a photodiode 34 to be generated.
[0010]
The configuration of the backward pumping optical amplifier is essentially the same, and it is essential to provide an optical filter in the subsequent module. In the former module, instead of the isolator 13, it is possible to use an optical filter that allows signal light to pass while blocking excitation light and spontaneous emission light.
[0011]
  FIG. 10 shows the principle configuration of a conventional optical element constituting the optical filter. In FIG. 10, reference numeral 50b denotes an optical element. The optical element has a light-transmitting substance, most typically a substrate 51 made of glass, and the wavelength of light.Wavelength characteristics of transmittanceAre formed by a filter film 52 having a different thickness and a transmission film 54 that improves the light transmission between the substrate 51 and the air.
[0012]
Here, the filter film is usually formed by laminating a thin film of titanium dioxide and a thin film of silicon dioxide, and varies depending on the wavelength due to combined interference between reflected light and transmitted light between the thin films formed in the multilayer. Presents transmittance.
[0013]
However, in order to sufficiently reduce the transmittance with respect to the light of other wavelengths than the transmittance of the signal light, it is necessary to use a plurality of optical elements having the configuration shown in FIG.
FIG. 8 shows an example of the configuration of a subsequent module of a conventional optical amplifier.
[0014]
  In FIG. 8, 31 is an isolator, 32-2 and 32-3 are optical elements constituting an optical filter, 32-4 and 32-5 are fixing plates for bonding and fixing the optical elements, and 32-6 and 32-7 are A screw for fixing to the bottom surface of the case, which will be described later, while adjusting the angle of the fixing plate, 38 is an optical coupler for branching a part of the output light, 34 is a photodiode for monitoring the level of the output signal light, Is a case of a rear module, 36-1 and 36-2 are an input side connector and an output side connector, and 37-1 and 37-2 are an input side optical fiber and an output side optical fiber, respectively.
  The optical filter 32 has twoOneOptical elements 32-2 and 32-3OneFixed plates 32-4 and 32-5OneOf the screws 32-6 and 32-7.
[0015]
  In other words, the latter module shown in FIG. 8 is an example in which two optical elements shown in FIG.
  When the case 35 is leveled, the input side connector 36-1 and the isolator 31OneThe optical elements 32-2 and 32-3, the optical coupler 38, and the output-side connector 36-2 are arranged at the same level, and the light emitted from the input-side connector 36-1 is the output side of these components. The position is fixed so as to be incident on the connector 36-2.
  A plurality of lines drawn in the case 35 are connected to the input side connector 36-1 and the isolator 31.OneThe boundary of the cutting part performed so that the height of the bottom face of the case 35 may be changed in order to arrange the optical elements 32-2 and 32-3, the optical coupler 38, and the output side connector 36-2 on the horizontal line is shown.
[0016]
  The optical filter 32 in the latter module of FIG.Wavelength characteristics of transmittanceIs adjusted by adjusting the angles of the two fixing plates 32-4 and 32-5 with respect to the optical axis of the signal light while the screws 32-6 and 32-7 are temporarily fixed. This is done by adjusting the angles of the two optical elements 32-2 and 32-3.
[0017]
[Problems to be solved by the invention]
By the way, the dimensions of the substrates constituting the optical elements 32-2 and 32-3 are usually about 2.5 mm in length and width and about 2 mm in thickness. Not directly, but after depositing a filter film and a coupler film on a wafer having a diameter of about 2 to 8 inches, it is cut out (referred to as scribing) to the above dimensions.
[0018]
Accordingly, since the size of the wafer cannot be ignored, the thickness of the film formed between the central portion and the peripheral portion of the wafer will inevitably vary, and the optical elements taken from close positions on the wafer will be affected. Then, the film thickness variation is small, and the film thickness variation is negligible on the same optical element.
[0019]
However, after scribing such a wafer and separating it into optical elements, it is extremely troublesome to manage the optical elements while maintaining the positional relationship on the wafer. For this reason, the optical element selected when assembling the latter module is not necessarily taken from a position near the wafer.
[0020]
Now, the transmittance of light with different wavelengths in the filter film is different because of the combined interference of transmitted light and reflected light in the multilayered titanium dioxide and silicon dioxide thin films, but the distance that light passes through the filter film. Also related.
[0021]
  Therefore, when the thickness of the filter film varies, the wavelength of transmitted light in each optical element varies. And what each isWavelength characteristics of transmittanceThus, two optical elements are selected without knowing whether or not they are fixed to the fixing plate one by one.
[0022]
  For this reason, when adjusting the transmittance as an optical filter, the fixing plates 32-4 and 32-5 to which the two optical elements are fixed are temporarily fixed to the case 35 by the screws 32-6 and 32-7. Try adjusting the angles of the fixed plates 32-4 and 32-4 with respect to the optical axis separately to obtain the desired transmittance.WavelengthYou have to work to find the angle that will be characteristic. This is the desired transmittanceWavelengthIt is common to encounter that the angle of each optical element must be adjusted many times in order to converge on the characteristics.
[0023]
  As a simpler adjustment method, only one fixed plate with an optical element fixed is temporarily fixed to the subsequent module, and its angle with respect to the optical axis of the signal light is adjusted to adjust the transmittance.WavelengthAfter searching for the best point of the characteristics, the fixing plate to which the remaining optical elements are fixed is also temporarily fixed. Next, only the angle of the fixing plate to which the optical elements are temporarily fixed is adjusted, and the transmittance of the entire optical filter is adjusted.WavelengthThere are also ways to optimize the properties. In this case, it is not necessary to adjust the angle of the two optical elements, and it is not necessary to perform the adjustment several times, but this still requires a two-stage adjustment.
[0024]
As described above, the conventional post-stage module has a difficulty in adjusting the optical filter.
In addition, it is necessary to use a plurality of optical elements, which hinders simplification of the configuration of the optical filter and the optical amplifier.
[0025]
In view of such problems, the present invention simplifies the configuration of an optical filter and an optical amplifier, makes it easy to adjust the transmission characteristics of the optical filter and the optical amplifier, and simplifies the configuration by applying the optical element. It is an object of the present invention to provide an optical filter and an optical amplifier which can be easily adjusted.
[0026]
[Means for Solving the Problems]
  The present invention solves the above problems,An optical module according to the present invention includes a reflecting means for reflecting input light from an input connector, a substrate made of a light-transmitting material having opposing first and second surfaces that are flat and not parallel to each other, and Formed on the second surface of the substrate, the first film formed on the first surface of the substrate, the wavelength characteristic of the transmittance with respect to the incident light is different depending on the incident angle of the incident light, and the film thickness is constant A second film that reflects the light incident on the substrate from the first surface through the first film by the second reflection characteristic and transmits and emits the light by the third transmission characteristic. An optical filter that transmits and reflects the output light of the means and outputs the reflected light to an output connector facing the input connector, and the light input to the optical filter is incident on the substrate through the first film The second reflection characteristic in the second film. An optical filter that is reflected and output through the substrate and the first film, and is transmitted through the second film according to the third transmission characteristic, and an optical diode that monitors the transmitted light of the optical filter And adjusting means for adjusting the incident angle of the optical filter with respect to the output light of the reflecting means, and adjusting the incident angle by the adjusting means adjusts the center wavelength of the transmission band of the optical filter. Be.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
  FIG. 1 is a principle diagram showing the configuration of the optical element of the present invention.
In FIG. 1, reference numeral 50 denotes an optical element, which is composed of a substrate 51 made of a material having good transparency, typically glass, a filter film 52 and an optical coupler film 53.
  Since the substrate 51 is about 2.5 mm in length and width and about 2 mm in thickness, the thickness of the filter film 52 is constant on the surface of the substrate, and its refractive index can also be made constant.
  FIG. 1 shows a case where the thickness of the substrate 51 is constant as the most basic configuration.
[0028]
Then, the signal light is incident from the filter film 52 side of the optical element on the incident angle θ.₁The refractive index of the substance outside the optical element (usually air, which will be described in consideration of only air) is n.₁And the refractive index of the filter film 52 is n₂And the refractive index of the substrate 51 is n_ThreeThen, the angle θ of the light in the filter film with respect to the normal line of the substrate 51₂Is n₁Sin θ₁= N₂Sin θ₂          (1)
The angle obtained by.
[0029]
  Angle θ found by equation (1)₂When light is incident on the substrate 51, the substrate 51And filter membrane 52 interfaceThe angle θ of the light in the substrate 51 with respect to the established normal_ThreeIs
  n₂Sinθ₂= N_ThreeSinθ_Three      (2)
The angle obtained by.
[0030]
The light in the substrate 51 is incident on the interface between the substrate 51 and the coupler film 53._ThreeIs incident at an angle, part of which is emitted into the air through the coupler film 53, and most of the light is reflected at the interface between the substrate 51 and the coupler film 53.
[0031]
  Accordingly, the reflected light is reflected from the substrate 51.And filter membrane 52 interfaceΘ relative to the normal_ThreeIt propagates through the substrate 51 at an angle to reach the filter film 52.
  The relationship between the refractive index of the filter film 52 and the substrate 51 is as described above.(1)The light is the same as the substrate 51.And filter membrane 52 interfaceThe above θ with respect to the normal₂It propagates through the filter film 52 at an angle of and reaches the interface between the air and the filter film 52.
[0032]
  Since the relationship between the filter film 52 and the refractive index of air is the same as described above, the light isInterface between filter 52 and airThe above θ with respect to the normal₁It is emitted into the air at an angle of.
  That is, the incident light passes through the filter film 52 twice and is emitted into the air, and the incident angle to the filter film 52 is equal to the emission angle from the filter film 52.
[0033]
  Therefore, by using the optical element of FIG. 1, the same transmittance as using two conventional optical elements whose characteristics are exactly the same.WavelengthCharacteristics can be obtained.
  That is, as described above, since the thickness of the filter film 52 on the substrate 51 is constant, the distance that the light actually propagates through the filter film 52 at the first time and the light through the filter film 52 at the first time. The actual propagation distance is equal. Therefore, the transmittance when light passes through the filter film 52 for the first time.WavelengthCharacteristics and transmittance when light passes through the filter film 52 for the second timeWavelengthIt becomes equal to the characteristic.
[0034]
  In other words, in the conventional type optical filter, the transmittance of two optical elementsWavelengthA characteristic corresponding to the case where there is no variation in the characteristic can be obtained.
  In addition, since the wavelength of the light transmitted through the filter film can be made variable according to the distance that the light propagates through the filter film, the wavelength of the transmitted light can be easily adjusted by adjusting the incident angle θ1 of the light. .
[0035]
  Therefore, if the optical element of FIG. 1 is applied to a subsequent module, the transmittance is adjusted by adjusting the angle of the optical element with respect to the optical axis of the signal light.WavelengthWhen adjusting the characteristics, the number of optical elements to be adjusted is one, and the incident angle to the optical element is always equal to the emission angle from the optical element, so that the adjustment becomes extremely easy.
[0036]
Note that the refractive index of air is about 1, and when glass is used for the substrate, the refractive index is about 1.5, and the equivalent refractive index of the filter film is a little more than 2. Incident angle θ₁If you set₂And θ_ThreeTherefore, it is possible to design the size of the optical element by referring to them.
[0037]
FIG. 2 shows the basic configuration of the latter module.
In FIG. 2, 31 is an isolator, 32-1 is an optical element of the present invention, 33 is an optical reflector, and 34 is a photodiode that generates an electrical signal for monitoring the level of output light. In addition, the optical connector and optical fiber which comprise a back | latter stage module are abbreviate | omitting illustration.
[0038]
In the principle configuration of the rear module shown in FIG. 2, the signal light input to the rear module passes through the isolator 31 and then enters the optical reflector 33, is reflected by the optical reflector 33, and enters the optical element 32-1. The
[0039]
The optical element 32-1 has a filter film and a coupler film formed on a substrate.
The signal light reflected by the optical reflector 33 enters the optical element 32-1 from the filter film side. The signal light is refracted and reflected in the optical element 32-1, and most of the signal light is emitted to the filter film side of the optical element 32-1 and becomes output light.
[0040]
Therefore, the excitation light component contained in the light incident on the optical filter and the spontaneous emission light generated in the optical amplification section are attenuated and emitted from the optical filter, and the signal-to-noise ratio in the output light is improved.
[0041]
On the other hand, a part of the signal light is branched by the coupler film of the optical element 32-1, is emitted from the optical element 32-1, enters the optical diode 34, and the optical diode 34 monitors the level of the signal light. Is converted into an electrical signal.
[0042]
Therefore, in the conventional rear module, four optical components are required on the optical axis of the signal light, whereas in the rear module of the present invention, three optical components are arranged on the optical axis of the signal light. It is sufficient to simplify the configuration of the subsequent module.
[0043]
As will be described later, as the necessity of increasing the number of times signal light passes through the filter film increases, the simplification effect increases.
[0044]
DETAILED DESCRIPTION OF THE INVENTION
  FIG. 3 is an actual measurement example of the characteristics of the optical filter of the present invention.
  FIG. 3 shows the total transmittance when the signal light is passed through the filter film of the optical element twice in the optical filter constituted by using one optical element of the present invention.WavelengthThe characteristic is the unit transmittance when the signal light passes through the filter film of the optical element once.WavelengthIt is displayed together with the characteristics. Transmittance is expressed in decibels, so total transmittanceWavelengthIt can be seen that the characteristic is twice the transmittance of the unit.
[0045]
In FIG. 3, the transmittance with respect to the passing wavelength is displayed as 0 dB, but this is because the transmittance is displayed with reference to the transmittance at the wavelength with the highest transmittance. Loss and the branching loss in the coupler film are added. This loss is usually realized at about 1 dB or less.
[0046]
By the way, in the principle configuration shown in FIG. 1 or FIG. 2, the configuration in which the signal light passes through the filter film twice in the optical element of the present invention has been described as an example, but the number of times the signal light passes through the filter film is described. It is not limited to twice.
[0047]
That is, for example, in the configuration of FIG. 2, if a reflection film is formed in the vicinity of the point where the signal light is emitted from the optical element 32-1 into the air, the signal light is reflected and again the filter film 52 and the substrate 51. It passes through the coupler film 53 and is reflected by the coupler film 53 again, passes through the substrate 51 and the filter film 52, and reaches the interface between the filter film and air. In this respect, if the reflecting film is not formed, the signal light passes through the filter film a total of four times and is emitted from the optical element. By doing so, the transmittance characteristics of the optical filter can be made steeper without changing the simplicity of the configuration of the subsequent module and the ease of adjustment of the optical filter.
[0048]
Even if the reflection film for increasing the number of times signal light passes through the filter film is formed at the interface between the filter film and air (on the filter film), it is formed at the interface between the filter film and the substrate (under the filter film). Alternatively, the filter film and the reflection film may be selectively formed depending on the region on the substrate without forming the filter film and the reflection film in an overlapping manner.
[0049]
In the optical element shown in FIGS. 1 and 2, an example is shown in which a coupler film is formed on the surface facing the surface on which the filter film is formed, but it is formed on the surface facing the surface on which the filter film is formed. The film is not limited to a coupler film. The reason for forming the coupler film here is for the purpose of extracting a part of the signal light as monitor light through the coupler film, but when it is not necessary to extract the monitor light, it faces the surface on which the filter film is formed. A total reflection film may be formed on the surface. In any case, a film having reflection characteristics may be formed on the surface facing the surface on which the filter film is formed. In the latter case, no loss occurs when reflection loss occurs, so the absolute loss with respect to the pass wavelength of the optical filter is small.
[0050]
FIG. 4 shows a configuration of a rear module to which the optical filter of the present invention is applied.
In FIG. 4, 31 is an isolator, 32-1 is an optical element of the present invention, 32-4 is a fixing plate for fixing the optical element, 32-6 is a screw for fixing the fixing plate to a case described later, and 33 is a light. Reflector 34 is a photodiode for generating an electric signal for monitoring the level of signal light, 35 is a case, 36-1 and 36-2 are an input side connector and an output side connector, and 37-1 and 37-, respectively. Reference numeral 2 denotes an input side optical fiber and an output side optical fiber.
[0051]
When the case 35 is horizontal, the input-side connector 36-1, the isolator 31, the optical element 32-1, the optical reflector 33, and the output-side connector 36-2 are arranged at the same level and their components. Is fixed while maintaining a positional relationship such that light emitted from the input-side connector 36-1 is incident on the output-side connector 36-2. A plurality of lines drawn in the case 35 are arranged in order to arrange the input side connector 36-1, the isolator 31, the optical element 32-1, the optical reflector 33, and the output side connector 36-2 at the same level. The boundary of the cutting part performed so that the height of the bottom face of 35 may be changed is shown.
[0052]
Therefore, in the configuration of the rear module shown in FIG. 4, the signal light input to the rear module is incident on the optical reflector 33 after passing through the isolator 31, reflected by the optical reflector 33, and incident on the optical element 32-1. The
[0053]
The signal light is incident on the optical element 32-1 from the filter film side, and the signal light is refracted and reflected in the optical element 32-1, and most of the signal light is on the filter film side of the optical element 32-1. To output light.
[0054]
Therefore, the excitation light component contained in the light incident on the optical filter and the spontaneous emission light generated in the optical amplification section are attenuated and emitted from the optical filter, and the signal-to-noise ratio in the output light is improved.
[0055]
On the other hand, a part of the signal light passes through the coupler film of the optical element 32-1, is emitted from the optical element 32-1, and enters the photodiode 34, and the level of the signal light is monitored by the photodiode 34. It is converted into an electrical signal.
[0056]
  Light incident on the photodiode passes through the filter film once. Therefore, even in the light incident on the photodiode, the excitation light component and the spontaneous emission light are transmitted in the unit of FIG.WavelengthSince the attenuation is equal to the characteristic, the signal-to-noise ratio is improved also in the electric signal for monitoring the signal light.
[0057]
In the latter module shown in FIG. 4, the transmittance characteristic of the optical filter is adjusted in a state where the fixing plate 32-4 to which the optical element 32-1 is fixed is temporarily fixed by a screw 32-6. It is only necessary to adjust the angle between -4 and the optical axis of the signal light.
[0058]
  Since the thickness of the filter film on the optical element 32-1 is constant and the distance that the signal light actually propagates through the filter film is the same every time it passes, the fixed plate 32-4 is light of the signal light. Transmittance as an optical filter no matter what the angle with the axis isWavelengthCharacteristic is transmittance when passing once through filter membraneWavelengthThe characteristic is added (when the transmittance is expressed in decibels). Therefore, it is very easy to adjust the characteristics of the optical filter to the desired characteristics.
[0059]
The bonus advantage of the configuration of FIG. 4 is that the length from the input side to the output side of the rear module can be shortened because the optical path of the signal light is bent by the optical reflector 33. By appropriately selecting the angle of the optical path bending by the optical reflector, it is not necessary to increase the width of the rear module so that the rear module can be reduced in size.
[0060]
Incidentally, the latter module of FIG. 4 includes only a photodiode for monitoring the level of output light. However, if a photodiode is provided on the reverse extension of the output light emitted from the optical element 32-1. It is also possible to monitor the reflected light when the output side optical fiber is disconnected or the output side connector is disconnected.
[0061]
  FIG. 5 shows a change in the center wavelength of the pass band due to a change in the incident angle of light to the optical element, that is, a shift in the pass band due to a change in the incident angle of light to the optical element.
  The reason why the pass band is shifted due to the variation of the incident angle of light is that the distance that the light actually propagates through the filter film varies due to the variation of the incident angle. Actually, the fluctuation of the pass band is the transmittance in the optical filter using a plurality of optical elements shown in FIG.WavelengthIt was difficult to adjust the characteristics.
[0062]
  However, in the optical filter using the optical element of the present invention, the transmittance of the optical filter is positively used by using the phenomenon that the pass band is shifted due to the change in the incident angle of light.WavelengthThe figure of the characteristic can be decided freely. A configuration for this is shown in FIG.
[0063]
  FIG. 6 shows an optical element using a substrate whose thickness varies in the configuration of FIG.
  In this case, the substrate(51a)And filter membrane(52)Coupler film against normal line at the interface(53)Incident toLightHorns and, Against the above normalCoupler film(53)Reflection fromLightBecause the angle is different, the output angle φ from the filter film to the substrate_ThreeAnd the incident angle φ from the substrate to the filter membrane_FiveAre at different angles.
[0064]
Therefore, the emission angle φ from the air to the filter membrane₂And the incident angle φ from the filter membrane to the air₆Are different from each other, and the distance that the light incident on the filter film from the air propagates through the filter film is different from the distance that the light emitted from the filter film to the air propagates through the filter film.
[0065]
  That is, depending on the configuration of FIG.WavelengthIt is possible to obtain an optical filter in which optical filters having characteristics are cascade-connected in two stages. Therefore, its transmittanceWavelengthThe characteristics are different from those obtained by the configuration of FIG.
[0066]
  The phenomenon shown in FIG. 5 can be arbitrarily utilized by changing the incident angle to the optical element shown in FIG.WavelengthThe characteristics can be determined freely.
[0067]
  FIG. 7 shows the transmittance of the optical filter to which the configuration of FIG. 6 is applied.WavelengthIt is an example of a characteristic.
  In FIG. 7, the characteristic indicated by the broken line is the characteristic on the incident side in FIG. 6, the characteristic indicated by the alternate long and short dash line is the characteristic on the outgoing side in FIG. 6, and the characteristic indicated by the solid line is the total characteristic.
[0068]
As is apparent from the overall characteristics of FIG. 7, the pass wavelength range is narrower than the characteristics of FIG. 3, and the transmittance in the attenuation wavelength range is substantially the same as the characteristics of FIG. This characteristic is determined according to the angle between the surface on which the filter film is formed and the surface on which the coupler film is formed and the specific angle of incidence of light on the filter film, so the surface on which the filter film is formed and the coupler film are formed. Arbitrary filter characteristics can be obtained by making the angle of the surface to be incident and the angle of incidence of light on the filter film different.
[0069]
Moreover, a configuration in which a reflection film is formed on the filter film side to increase the number of times light passes through the filter film and a structure in which a coupler film is used as the reflection film can be applied, as in the case of the configuration in FIG.
[0070]
The configuration of the optical filter and the optical amplifier can be simplified, and the adjustment as the optical filter and the optical amplifier can be facilitated, which is exactly the same as the configuration of FIG.
[0071]
The same effect can be realized even when the thickness of the filter film is changed on the substrate surface while the thickness of the substrate is constant. However, in order to do this, a technique such as forming a potential distribution in the vapor deposition chamber or on the surface of the substrate is required, which causes some difficulty in manufacturing the optical element. On the other hand, changing the substrate thickness on the substrate surface can be realized by polishing a substrate having a constant thickness, so it is easier to form the filter film and the coupler film by changing the substrate thickness. is there.
[0072]
In the above description, the technique of the present invention has been described consistently using an optical fiber amplifier as an example.
However, as optical amplifiers, semiconductor optical amplifiers are being developed and will eventually be put into practical use. Even in the semiconductor optical amplifier, the noise component generated during amplification should be removed to ensure a high signal-to-noise ratio of the output light, as in the case of the optical fiber amplifier. Therefore, it is exactly the same that the optical element of the present invention and the optical filter to which the optical element is applied have the same effect in the semiconductor optical amplifier.
[0073]
Furthermore, since the configuration of the optical fiber amplifier shown in FIG. 9 has been described as a main example, it has mainly been assumed that an optical filter to which the optical element of the present invention is applied is provided in a subsequent module of the optical fiber amplifier. As described at the end of the description of the prior art, since an optical filter may be provided instead of the isolator 13 in the former module of FIG. 9, an optical filter to which the optical element of the present invention is applied can be provided. Is not limited to the latter module.
[0074]
【The invention's effect】
  As described above in detail, the present invention simplifies the configuration of the optical filter and the optical amplifier,Wavelength characteristics of transmittanceAn optical element that facilitates the adjustment of the optical filter, and an optical filter and an optical amplifier that are simplified in configuration and easy to adjust by applying the optical element. In particular, the ease of adjustment as an optical filter and optical amplifier greatly contributes to cost reduction of the optical filter and optical amplifier.
[0075]
  Further, according to the present invention, the characteristics as an optical filter can be arbitrarily determined.
  Moreover, the transmittanceWavelengthIt is also possible to easily realize an optical filter whose characteristics are steep in the attenuation wavelength region. In this case, the effect of simplifying the configuration of the optical filter and the optical amplifier is increased.
[0076]
Moreover, the technique of the present invention can be applied not only to an optical fiber amplifier but also to an optical semiconductor amplifier.
Therefore, the present invention can contribute to the improvement of characteristics of a wide range of optical amplifiers, the ease of adjustment, and the simplification of the configuration.
[Brief description of the drawings]
FIG. 1 is a principle diagram showing a configuration of an optical element of the present invention.
FIG. 2 shows the principle configuration of a rear module.
FIG. 3 is an actual measurement example of characteristics of the optical filter of the present invention.
FIG. 4 shows a configuration of a subsequent module to which the optical filter of the present invention is applied.
FIG. 5 shows a shift in the pass band due to a change in the incident angle of light to the optical element.
6 is an optical element using a substrate whose thickness varies in the configuration of FIG.
7 is a transmittance of an optical filter to which the configuration of FIG. 6 is applied.WavelengthExamples of characteristics.
FIG. 8 shows a configuration example of a subsequent module of a conventional optical amplifier.
FIG. 9 shows a configuration of a forward pumping type optical fiber amplifier.
FIG. 10 shows a principle configuration of a conventional optical element constituting an optical filter.
[Explanation of symbols]
  1 First module
  2 Optical amplification stage
  3 Later module
  11 Optical coupler
  12 Photodiode
  13 Isolator
  21 Optical amplification fiber
  22 Excitation laser diode
  23 Optical coupler
  31 Isolator
  32 Optical filter
  32-1 Optical Element of the Present Invention
  32-2 and 32-3 Conventional optical elements
  32-4, 32-5 fixed plate
  32-6, 32-7 screw
  34 Photodiode
  35 cases
  36-1 Input side connector
  36-2 Output side connector
  37-1 Optical fiber on the input side
  37-2 Optical fiber on the output side
  38 Optical coupler
  50 Optical elements
  50a Optical element
  50b Optical element
  51 substrates
  52 Filter membrane
  53 Coupler membrane
  54 Permeation membrane

Claims (1)

Reflecting means for reflecting input light from the input connector;
A substrate made of a light-transmitting material having first and second surfaces that are opposed to each other and not parallel to each other, and a wavelength characteristic of transmittance with respect to incident light formed on the first surface of the substrate is Unlike the incident angle of the incident light, and is incident on the first film and, said substrate from said first surface through a second formed on the surface first layer of the substrate is a film thickness constant light Is reflected by the second reflection characteristic and transmitted and emitted by the third transmission characteristic, and transmits and reflects the output light of the reflecting means, and the reflected light faces the input connector. An optical filter that outputs to an output connector, and the light input to the optical filter is incident on the substrate through the first film, and is reflected by the second reflection characteristic on the second film. And output through the first film, and to the second film. An optical filter to be transmitted and outputs the transmission characteristics of the third Te,
A photodiode for monitoring the transmitted light of the optical filter;
Adjusting means for adjusting the incident angle of the optical filter with respect to the output light of the reflecting means,
An optical module characterized in that the center wavelength of the transmission band of the optical filter is adjusted by adjusting the incident angle by the adjusting means .

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