JPH06310751A - Photodetector having diffraction grating and optical communication network using the same - Google Patents

Abstract

(57) [Abstract] [Purpose] A photodetector having a demultiplexing function that utilizes the fact that the emission angle of the diffracted light emitted from the optical waveguide formed with the diffraction grating depends on the wavelength of the light, And an optical communication network using this device. A light quantity control means such as an optical amplifier 20 having one or both of an optical attenuation function and an optical amplification function is guided so that the intensity of incident light on a waveguide 21 in which a diffraction grating 9 is formed is substantially constant. It is provided on the incident side of the waveguide 21. By controlling the light quantity control means, it is possible to suppress the deterioration of the wavelength demultiplexing function due to the change of the equivalent refractive index of the waveguide 21 accompanying the change of the incident light intensity. The incident light always contains continuous light,
The waveguide may oscillate at the Bragg wavelength of the diffraction grating in the state where no light is incident. As the photodetector array 11, one having no wide dynamic range can also be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an emission angle of diffracted light which is emitted from an optical waveguide having a diffraction grating to the outside of the waveguide.
The present invention relates to a photodetector having a demultiplexing function utilizing the dependence on the wavelength of light, and an optical communication network such as wavelength division multiplexing optical communication using the same.

[0002]

2. Description of the Related Art In a photodetector having a diffraction grating already proposed, the diffracted light emitted outside the waveguide is
Part of the light propagating in the optical waveguide is emitted as diffracted light outside the waveguide at a fixed rate determined by the coupling efficiency between the diffraction grating and the waveguide, and this is received by multiple photodetectors. Alternatively, in order to increase the detection sensitivity, an optical amplification unit for amplifying the incident light at a constant magnification is provided at the light incident end.

[0003]

However, in the above proposed example, when the incident light intensity on the waveguide in which the diffraction grating is formed fluctuates, the equivalent refractive index of the waveguide fluctuates accordingly. The emission angle of the diffracted light emitted outside the waveguide changes. Therefore, even if light of the same wavelength is incident, the output angle of the diffracted light changes depending on the intensity,
The wavelength demultiplexing function deteriorates. Further, when the intensity of incident light changes, the intensity of diffracted light also changes accordingly, so that there is a defect that a photodetector that receives diffracted light requires a wide dynamic range.

More specifically, it is as follows.

The light incident on the waveguide having the diffraction grating is diffracted by the diffraction grating and radiated from the upper surface of the waveguide. The inclination angle φ of the diffracted light from the waveguide normal direction satisfies the following relationship with the pitch Λ of the diffraction grating and the wavelength λ of the incident light. sin φ = n _eff −qλ / Λ (1) where q is an integer and n _eff is the equivalent refractive index of the waveguide.

Therefore, as described above, if the wavelength λ of the incident light changes, the inclination angle φ also changes, so that the diffracted light is split and emitted. Therefore, by receiving the demultiplexed light by separate photodetecting elements, it is possible to demultiplex and detect the wavelength-multiplexed signal and the like.

Here, by providing the waveguide with an active layer and means for injecting current into the active layer, it is possible to give the waveguide a gain, amplify the guided light, and greatly improve the minimum receiving sensitivity. it can.

However, if the amplification degree is increased significantly, laser oscillation occurs at the Bragg wavelength λ _B (= 2n _eff Λ / m) of the diffraction grating, and sufficient amplification cannot be obtained.

Further, as described above, when the wavelength multiplicity of the incident light fluctuates, the incident intensity also fluctuates, so that the equivalent refractive index of the waveguide fluctuates, and accordingly, the diffracted light emitted outside the waveguide fluctuates. The radiation angle changes, and the wavelength resolution deteriorates.

Therefore, an object of the present invention is to solve the above-mentioned problems, and the radiation angle of the diffracted light emitted outside the waveguide from the optical waveguide used in optical communication or the like in which the diffraction grating is formed is the wavelength of the light. (EN) Provided are a photo-detecting device having a demultiplexing function and the like, and an optical communication network or wavelength division multiplexing optical communication system using these devices.

[0011]

According to the photodetector having the diffraction grating of the present invention, the optical attenuation and optical amplification functions are performed so that the incident light intensity on the waveguide in which the diffraction grating is formed becomes substantially constant. A light amount control means having either or both functions is provided on the incident side of the waveguide. By controlling this light quantity control means, it is possible to suppress the deterioration of the wavelength demultiplexing function due to the change of the equivalent refractive index of the waveguide due to the change of the incident light intensity, and as a photodetector for receiving the diffracted light, a wide dynamic range. Those without a range can also be used.

Further, as the signal for controlling the light quantity control means, the output of the p-i-n structure PD monolithically formed on the side opposite to the incident end or the output of the photodetector for receiving the diffracted light is used. By doing so, the configuration can be simplified.

That is, in the photodetector having the diffraction grating according to the present invention, a plurality of photodetectors are arranged in order to detect the diffracted light emitted from the waveguide from the optical waveguide having the diffraction grating formed therein. The photodetector having a wave function is characterized by including control means for making the light quantity of the diffracted light emitted to the outside of the waveguide substantially constant even if the incident light quantity changes. Specifically, this control means is, for example, an optical amplification section provided on the incident side of the optical waveguide. By changing the injection current into the optical amplification section, the amount of diffracted light emitted outside the waveguide is made incident. Even if the amount of light changes, it is almost constant.

Further, according to the photodetector having the diffraction grating of the present invention, the incident light to the waveguide always includes continuous light, or the optical waveguide having a gain has a Bragg wavelength when no light is incident. By maintaining the gain of the laser oscillation state, it became possible to suppress the fluctuations of the light intensity and the number of injected carriers in the waveguide even if the wavelength multiplicity of the incident light increased or decreased.

Therefore, the variation of the equivalent refractive index of the waveguide is suppressed, and the radiation angle of the diffracted light radiated outside the waveguide does not vary, so that the wavelength resolution can be prevented from lowering even if the wavelength multiplicity increases or decreases. You can

Further, according to the photodetector having the diffraction grating of the present invention, the Bragg wavelength λ _B (= 2n) of the diffraction grating.
_(eff Λ / m) is set to a wavelength range where the gain of the waveguide exists, that is, a wavelength range where the gain is low or a wavelength range where there is no gain, thereby suppressing the occurrence of laser oscillation at the Bragg wavelength and amplifying the guided light. The degree can be increased sufficiently.

Further, in the optical communication network according to the present invention, at least one transmission terminal station for transmitting optical signals of different wavelengths and a reception terminal station for receiving optical signals of plural wavelengths are connected by an optical transmission line. In the communication network, at least one receiving terminal station is provided with the above photodetection device.

[0018]

1 is a drawing showing the left half of the device in order to best show the features of the first embodiment of the present invention. An optical waveguide 21 having a diffraction grating 9 formed therein and an optical amplifier 20 are monolithic. Is configured. A plurality of photodetectors 11 are arranged in a line in the extending direction of the waveguide 21 in a direction perpendicular to the upper surface of the optical waveguide 21.

The pitch Λ of the diffraction grating 9 is the wavelength λ of the incident light.
On the other hand, the relationship of Λ˜λ / n _eff (n _eff : effective refractive index of the waveguide) is satisfied, and the waveguide 2 is formed by the diffraction grating 9.
1, the diffracted light 10 emitted in the normal direction and the waveguide 21.
Let φ be the angle formed by the perpendicular line of φ, φ satisfies the following relation with respect to the wavelength λ of light. dφ / dλ = 1 / cosφ [dn _eff / dλ−1 / Λ] (1) Therefore, the diffracted light of the incident light (wavelength λ + Δλ _i ) having different wavelengths has different emission angles (φ + Δφ _i ) and therefore the diffracted light Is received by the plurality of detectors 11. In this way, a plurality of signals sent in respective wavelengths are demultiplexed, converted into electric signals by the respective photodetectors 11, passed through the signal processing / analyzing device 12, and then various information / video equipment. Entered in.

The far field pattern (FFP) of the diffracted light 10 is very narrow in the direction along the waveguide 21,
For example, the spread angle (θ _P ) is about 0.2 °,
The divergence angle (θ _t ) is wide in the direction traversing the waveguide 21.
Is about 15 °. Therefore, the wavelength of the incident light is 0.5n
If it changes by about m, the emission angle, that is, the inclination angle φ changes by about 0.2 °, so that it changes by about the beam diameter of the diffracted light 10 in the direction along the waveguide 21. Therefore, if the size of the light-receiving surface of each element in the direction along the waveguide 21 of the photodetector array 11 is set to be the beam diameter (θ _P ) of the first-order diffracted light,
A wavelength change of about nm can be detected. Since the wavelength resolution is limited by the spread angle (θ _P ) of the diffracted light 10 diffracted upward in the direction along the waveguide 21, the coupling efficiency between the diffraction grating 9 and the optical waveguide of the waveguide 21 with the diffraction grating is reduced. In addition, by making the optical waveguide 21 with the diffraction grating long, it is possible to narrow θ _P and improve the wavelength resolution.

On the other hand, the optical waveguide 2 on which the diffraction grating 9 is formed
In order to always keep the intensity of the incident light on the beam No. 1 constant, the injection current to the optical amplifier 20 is controlled according to the intensity of the diffracted light 10. As a feedback signal for the injection current control device 13 that controls the injection current to the optical amplifier 20,
A control signal corresponding to the sum of the outputs of the plurality of photodetectors 11 is input from the signal processing / analyzing device 12.

In FIG. 1, the optical amplifier 20 includes an InP substrate 2, an InGaAsP optical guide layer 3, and an InGaAsP.
(Energy gap, Eg to 0.8 eV) active layer 4,
It is composed of an InP upper light confinement layer 5, an InGaAs contact layer 7, an InP high resistance buried layer 6, and metal electrodes 1 and 8 of p and n. On the other hand, the waveguide 2 with the diffraction grating
1 comprises an InP substrate 2, which is the same as the optical amplifier 20, a diffraction grating 9 having a pitch Λ, an InGaAsP (Eg to 0.95 eV) optical guide layer 3, and an InP upper optical confinement layer 5. Although not shown in FIG. 1, a dielectric antireflection film is formed on the incident end face and the opposite end face to prevent reflection of light.

In the figure, when light is incident on the optical amplifier 20, the incident light is amplified with an amplification factor according to the injection current of the optical amplifier 20, and the diffraction grating 9 of the waveguide with diffraction grating 21 causes the upper surface of the waveguide. Diffracted light 10 is emitted from the. If the incident light includes a plurality of wavelengths, the emission angle of the diffracted light 10 is
The wavelength changes according to equation (1), and diffracted light corresponding to the wavelength is emitted. By receiving the respective diffracted lights 10 by different photodetectors 11, the wavelength-multiplexed signals can be demultiplexed into respective wavelengths and received.

On the other hand, when the time average intensity of the incident light changes with time, if the injection current of the optical amplifier 20 is kept constant, the optical waveguide 21 in which the diffraction grating 9 is formed responds to the change of the incident light intensity. Of the diffracted light 10 at each wavelength with the change in the equivalent refractive index of the waveguide 21 even though the intensity of the incident light fluctuates and the wavelength of the incident light is the same.
Fluctuates. Therefore, the controller 13 controls the injection current of the optical amplifier 20 by using the intensity of the diffracted light 10 received by the plurality of photodetectors 11 as a feedback signal, and the diffracted light 1
The intensity fluctuation of 0 is reduced. As a result, the fluctuation of the incident light intensity on the optical waveguide 21 in which the diffraction grating 9 is formed is also reduced, so that the reduction of the demultiplexing function due to the fluctuation of the incident light intensity can be significantly suppressed.

FIG. 2 is a schematic diagram showing one form of a wavelength division multiplexing optical communication network using the photodetector of the present invention shown in FIG.

In the figure, each transmitting terminal station 201, 20
1, ..., 20N is a wavelength tunable DB for the electrical / optical conversion unit.
Transmitting at an arbitrary wavelength λ _i (1 ≦ i ≦ n) from the wavelength (λ ₁ , ..., λ _n ) that has an R-LD and can control the injection current to the DBR region and oscillate. To start. At this time, if there are a plurality of transmitting end stations that desire to transmit at the same time, the wavelengths λ _j , λ _k , ...
-Transmit with (1 ≤ j, k, ... ≤ n, i ≠ j ≠ k ...).

All transmitting terminal stations 201, 201, ..., 20
The optical signal sent from N is sequentially or collectively multiplexed by the branching / combining device 301 and sent to the receiving side by the optical transmission line 400. On the other hand, each receiving terminal 501, 5
The photoelectric conversion units 01, ..., 50M are composed of the photodetector having the demultiplexing function shown in FIG. Optical transmission line 4
The wavelength-division-multiplexed signal sent by 00 is branched by the branching / combining unit 302, and then received by each receiving terminal station 50.
, 501, ..., 50M.

The input wavelength-multiplexed signal is demultiplexed into each wavelength by a photodetector having a demultiplexing function, and then a signal of a desired wavelength is selected and taken into the receiving terminal station. At this time, a plurality of signals having different wavelengths, or if necessary, all signals can be simultaneously captured.

FIG. 3 is a drawing best showing the features of the second embodiment of the photodetecting device of the present invention, in which the photodetecting element array is located at a position where the diffracted light emitted from the semiconductor optical waveguide having the diffraction grating can be received. Are arranged.

The semiconductor optical waveguide having the diffraction grating is Ga
Ga is formed on the As substrate 33 by metalorganic vapor phase epitaxy or the like.
As buffer layer (not shown), AlGaAs lower optical confinement layer 34, GaAs / AlGaAs multiple quantum well active layer 3
6. After laminating the AlGaAs optical waveguide layer 37, after forming the diffraction grating 38 by the interference exposure method or the like, further forming AlG
The aAs upper light confinement layer 39 and the AlGaAs contact layer 40 are formed by stacking.

After that, Al for confining light in the lateral direction is used.
A GaAsBH buried layer 35 is formed, and further metal electrodes 31 and 41 for current injection are formed.
A window 42 through which the diffracted light 43 is emitted is formed in the window.

The Bragg wavelength λ _B of the pitch Λ of the diffraction grating 38 is set to a wavelength range in which the gain of the GaAs / AlGaAs multiple quantum well active layer 36 is low. Specifically, the GaAs / AlGaAs multiple quantum well active layer 3
6 is GaAs (well, thickness: 6 nm) / Al _0.2 G
a _0.8 As (thickness: 10 nm), which is composed of 5 wells, and the gain band expands with an increase in injection current, but peaks at 845 nm and reaches 825 nm to 875 n.
It is about m. Therefore, the pitch Λ of the diffraction grating 38
May be set so that the Bragg wavelength λ _B is outside this gain band.

The equivalent refractive index n _eff of the waveguide is approximately 3.
41, the pitch Λ of the diffraction grating with the Bragg wavelength λ _B outside the gain band is Λ (<λ _B = 825 nm) Λ (> λ _B = 875 nm) m = 1 <121 0.0 nm> 128.3 nm = 2 <241.9> 256.6 = 3 <362.9> 384.9. Therefore, the settable grating pitch Λ
Is Limited to

In this embodiment, the diffraction grating pitch Λ is set to 23.
It was formed with a thickness of 5 nm. At this time, the radiation angle φ (angle formed with the waveguide normal direction) when the guided light of the wavelength λ is radiated to the outside of the waveguide by the diffraction grating 38 is determined by the equation (1) (q = 1). Therefore, a plurality of photodetector element rows 44 having light receiving surfaces (propagating directions of guided light) corresponding to the spread angle of the diffracted light 43 are arranged at this position.

Incident light passes through the dielectric antireflection film 32 (not shown, but the antireflection film is present on the opposite end face) formed on the end face of the waveguide and is coupled to the optical waveguide layer 37. . At this time, if a forward bias is applied between the electrodes 31 and 41 and a current is injected into the active layer 36, the loss of the optical waveguide is reduced. When the injection current is further increased, a gain band is formed. If the wavelength of the guided light is within this wavelength band,
Since the guided light is amplified, the intensity of the diffracted light 43 demultiplexed by the diffraction grating 38 and radiated to the outside of the waveguide is also increased, and is incident on the plurality of photodetector element rows 44.

On the other hand, the Bragg wavelength λ of the diffraction grating 38
As described above, _B is set outside this gain band, so that oscillation in the DFB mode is suppressed.
Therefore, a large amplification degree can be obtained, and the minimum incident light intensity that can be received by the plurality of photodetector elements 44 can be significantly reduced.

In this embodiment, the guided light composed of a plurality of wavelength-multiplexed signal lights is set within the gain band of the waveguide, but all the wavelengths of the signal lights are within the gain band. Signal light that does not need to be amplified may be present on the long wavelength side of the gain band.

The photodetector of this embodiment can also be used in the wavelength division multiplexing optical communication network shown in FIG.

FIG. 4 shows a third embodiment of the photo-detecting device of the present invention, which has a large amplification factor, is easy to manufacture, and spreads the diffracted light radiated outside the waveguide in the waveguide direction. Angle θ
_{L is} also narrowed, and is composed of three optical amplification units 65 and three diffracted light emission units 66.

The optical waveguide has a rib waveguide structure,
The optical amplifying unit 65 includes the n-GaAs substrate 53 and the n-Ga.
As buffer layer (not shown), n-Al _x Ga _1-x As 1st
Light confinement layer _{54, GaAs / Al y Ga 1} -y As (0 <y
<X) Active layer 56 having a multiple quantum well structure, p-Al _x Ga
_1-x As second optical confinement layer 59, electrical insulation layer 62, p-G
aAs contact layer 60 and n, p metal electrode 5
It is composed of 1, 61.

In the rib waveguide 63 of the diffracted light emitting portion 66,
A diffraction grating is formed (not shown), and the Bragg wavelength λ _{B of the} diffraction grating pitch Λ is set outside the gain band of the optical amplifier 65. The external light incident end face and the opposite end face are coated with a non-reflective coating,
It suppresses the increase of incidence efficiency and generation of Fabry-Perot mode due to the space between the end faces.

In FIG. 4, the length of the optical amplification section 65 is ˜1.
The length of the diffracted light emitting portion 66 is 50 nm, and the length of the diffracted light emitting portion 66 is 400 nm. By controlling the injection current to each optical amplification portion 65 to match the phase of the guided light, it is as if the length is 2 to 3 times. Since it has the same function as one diffracted light emitting portion, the spread angle θ _L of the diffracted light in the waveguide direction can be reduced to a fraction, and the wavelength resolution can be improved.

Since this embodiment is made of AlGaAs, the diffracted light emitting portion 66 also has an active layer 56. In order to reduce absorption loss in this portion, a multiple quantum well structure is used as the active layer. However, in the case of the InP system, the active layer can be stacked on the diffraction grating and the active layer of the diffracted light emitting portion can be easily removed, so that the degree of freedom in designing the gain band is increased. The operation of this embodiment is substantially the same as that of the second embodiment. Further, the photodetector of this embodiment can be used in the wavelength division multiplexing optical communication network shown in FIG.

FIG. 5 is a drawing best showing the features of the fourth embodiment of the photodetector of the present invention. The optical waveguide having a diffraction grating is composed of an optical amplifying section 88 and a diffracted light emitting section 89. There is.

In the direction perpendicular to the waveguide of the diffracted light emitting portion 89,
A plurality of photodetector elements 84 are arranged in a line in opposition to the waveguide.

The optical waveguide having a diffraction grating is formed in a rib structure for confining light in the lateral direction.
Reference numeral 8 denotes an n-GaAs substrate 73, an n-GaAs buffer layer (not shown), and an n-Al _0.5 Ga _0.5 As optical confinement layer 7.
4, an active layer 76 having a multiple quantum well structure with an undoped GaAs / Al _0.3 Ga _0.7 As structure and 20 wells, a p-Al _0.5 Ga _0.5 As optical confinement layer 79, an electrical insulating layer 85, p -A GaAs contact layer 80 and n, p metal electrodes 71, 81. A diffraction grating is formed on the rib waveguide 86 of the diffracted light emitting portion 89 (not shown), and the pitch Λ of the diffraction grating has a wavelength λ _{i of} incident light (i = 0, 1, 2, ... ., K) approximately Λ
˜λ _i / n _eff (n _eff : effective refractive index of waveguide) is satisfied. Further, although the active layer 76 extending from the optical amplification section 88 is used as it is as the waveguide layer, since it is composed of multiple quantum wells, the optical amplification section 88 converts light into a wavelength band having a gain. On the other hand, it is a low-loss waveguide.
Although not shown in the figure, a non-reflective coating is applied to the external light incident end surface of the optical amplification section 88, which makes it possible to suppress laser oscillation and increase the saturation injection current density.

On the other hand, the external incident light is continuous light λ ₀ having a relatively large amount of light and signal light λ _j (j = 1, j = 1,
2, ..., K).

When the external incident light enters the rib waveguide while the optical amplifier 88 is in the forward bias state, the light is amplified and radiated from the diffracted light emitter 89 in the direction substantially normal to the waveguide. The inclination angle φ of this diffracted light from the waveguide normal direction is given by the formula (1)
Since the relationship of is satisfied, the tilt angle φ _i is changed according to the wavelength λ _{i of the} incident light, and the demultiplexed light is emitted. In the formula (1), the equivalent refractive index n _eff of the waveguide has an incident light intensity dependency, and when the incident light intensity to the optical amplification section 88 is about 0.01 mW, the light intensity doubles. The inclination angle φ changed by about −0.1 deg.

Therefore, if the external incident light is composed of a wavelength-division-multiplexed signal whose multiplicity changes, the light intensity changes according to the multiplicity, and the tilt angle also changes and the wavelength resolution deteriorates. In this embodiment, since the external incident light always includes the continuous light λ ₀ having a relatively large amount of light, even if the multiplicity of the signal light changes, the change of the total incident light amount can be suppressed low.

Further, when the signal light is amplified in the optical amplifying section 88, the gain is distributed to the signal light and the amplification degree of the continuous light λ ₀ is lowered, so that the intensity of the guided light to the diffracted light emitting section 89 is reduced. Fluctuations are further reduced. The plurality of photodetector elements 84 include
The diffracted light 87 of continuous light, the intensity of which varies depending on the degree of multiplexing of the signal light, and the diffracted light 83 of signal light wavelength-division multiplexed (see FIG.
In the above, only one signal light is shown).

Therefore, since the fluctuation of the light intensity in the waveguide due to the fluctuation of the multiplicity is reduced, the fluctuation of the radiation angle is suppressed, and the demultiplexing / detection with a small deterioration of the wavelength resolution becomes possible. In the wavelength division multiplexing optical communication network shown in FIG.
The photodetector of this embodiment can also be used.

FIG. 6 shows a fifth embodiment of the photodetector, in which the semiconductor waveguide having a diffraction grating has a BH buried waveguide structure and waits for gain by forward bias.

The semiconductor waveguide is formed on the GaAs substrate 93,
After stacking a GaAs buffer layer (not shown), an AlGaAs lower optical confinement layer 94, a GaAs / AlGaAs multiple quantum well active layer 96, and an AlGaAs optical waveguide layer 97, a diffraction grating 98 is formed by interference exposure and etching.
Further, an AlGaAs upper optical confinement layer 99 and an AlGaAs contact layer 100 are laminated. After that, a stripe is formed and optical confinement in the lateral direction is performed by the AlGaAsBH buried layer 95. Furthermore, a metal electrode 9 for current injection
1, 110 and a window 120 for diffracted light emission are formed. Further, the antireflection film 92 is formed on the incident surface and the end surfaces on the side opposite to the incident side.

The pitch Λ of the diffraction grating 98 is set such that the Bragg wavelength λ _B is within the gain band of the multiple quantum well active layer 96 in the wavelength range of low gain on the short wavelength side.
The first-order diffracted light is radiated in the waveguide normal direction. The detection element 140 is arranged here.

With the bias between the electrodes 91 and 110 in the forward direction and no external light incident, the semiconductor waveguide is
The laser oscillation state is maintained at the Bragg wavelength, and the diffracted light 201 is emitted in the waveguide normal direction.

External signal light λ _j (j = 1, 2, ...
., K) is incident, the signal light is amplified and
Since the gain is distributed to the signal light, the light intensity of the Bragg wavelength on the short wavelength side becomes weak. Therefore, the change in the intensity of all the guided light becomes small, and accordingly, the variation of the radiation angle of the diffracted light 130 can be suppressed. The same applies to the case where the multiplicity of the signal light changes, the intensity fluctuation of the guided light is small, and the deterioration of the wavelength resolution can be suppressed.

The photodetector of this embodiment can also be used in the wavelength division multiplexing optical communication network shown in FIG.

[0058]

As described above, according to the photodetector of the present invention, the intensity of light incident on the waveguide having the diffraction grating formed in the preceding stage of the optical waveguide having the diffraction grating is substantially constant. In addition, since the light amount control means having one or both of the light attenuation function and the light amplification function is provided, it is possible to significantly suppress the reduction of the demultiplexing function and the like due to the variation of the incident light intensity to the device. Therefore, it is possible to realize a photodetector having a good demultiplexing function even when the incident light intensity changes with time.

Further, when the photodetector of the present invention is used as an optical / electrical conversion unit of a receiving end station of a wavelength division multiplexing optical communication network, after constantly demultiplexing a wavelength-multiplexed signal into respective wavelengths, It becomes possible to receive a plurality of signals or, if necessary, all signals simultaneously at the same time.

Further, as described above, the optical waveguide having the diffraction grating has a gain, and the Bragg wavelength of the diffraction grating is set to a wavelength range where the gain is absent or low. As a result, the amplification factor can be set to a large value, so that demultiplexing can be performed even with a small amount of incident light.

Further, as described above, in the photodetector having the demultiplexing function composed of the semiconductor optical waveguide in which the diffraction grating is formed and the plurality of photodetectors, the external incident light always has a relatively large light quantity. Even if the wavelength multiplicity of the signal light fluctuates by including a large amount of continuous light, or by holding the semiconductor optical waveguide in the laser oscillation state at the Bragg wavelength with no light incident, the wavelength resolution, etc. will deteriorate. Can be suppressed.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a cross section of a diffracted light emitting portion in which an optical amplifier according to a first embodiment of the present invention and a waveguide with a diffraction grating are formed on the same substrate, and a configuration for control. .

FIG. 2 is a schematic diagram of a wavelength division multiplexing optical communication network embodying the present invention.

FIG. 3 is a partially cutaway schematic perspective view of a second embodiment of the photodetector according to the present invention.

FIG. 4 is a schematic perspective view of a third embodiment of the photodetector device embodying the present invention.

FIG. 5 is a schematic perspective view of a fourth embodiment of the photodetector device embodying the present invention.

FIG. 6 is a partially cutaway schematic perspective view of a fifth embodiment of the photodetector according to the present invention.

[Explanation of symbols]

1, 8, 31, 41, 51, 61, 71, 81, 91,
110 metal electrode 2, 33, 53, 73, 93 substrate 3, 37, 97 light guide layer 4, 36, 76, 96 active layer 5, 34, 39, 54, 59, 74, 79, 94, 9
9 Light confinement layer 6, 35, 95 High resistance buried layer 7, 40, 60, 80, 100 Contact layer 9, 38, 98 Diffraction grating 10, 43, 83, 87, 130, 201 Radiation outside the waveguide Diffracted light 11, 44, 84, 140 Multiple photodetector arrays for receiving diffracted light 12 Device for processing and analyzing output of photodetector 13 Controlling injection current of optical amplifier according to intensity of diffracted light Device 20, 65, 88 Optical amplifier 21, 66, 89 Waveguide with diffraction grating 62, 85 Insulating layer 63, 86 Rib waveguide 201 to 20N Transmitting terminal station 301, 302 Branching / combining device 400 Optical transmission line 501 to 50M Receiving end Station

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04J 14/02 // H01L 31/10

Claims (13)

[Claims] 1. A photodetector having a demultiplexing function, wherein a plurality of photodetectors are arranged to detect diffracted light emitted outside the waveguide from an optical waveguide on which a diffraction grating is formed,
A photodetector having a diffraction grating, which has a control means such that the amount of diffracted light emitted to the outside of the waveguide is substantially constant even if the amount of incident light changes. 2. The control means is an optical amplification section provided on an incident side of the optical waveguide, and by changing an injection current into the optical amplification section, the quantity of diffracted light emitted outside the waveguide is changed. 2. The photodetector having the diffraction grating according to claim 1, wherein the photodetector has a substantially constant value in accordance with the fluctuation of 3. A semiconductor optical waveguide on which light is incident, a diffraction grating formed on the optical waveguide, and a photodetecting means including a plurality of portions for detecting diffracted light emitted to the outside of the optical waveguide. In the photodetector having, the optical waveguide is formed so as to have a gain with respect to the guided light, and the diffraction grating is set to a wavelength range in which laser oscillation does not occur near its Bragg wavelength. And a photodetector having a diffraction grating. 4. The at least one wave of guided light composed of signal light of one or more waves having different wavelengths,
The photodetector having a diffraction grating according to claim 3, which has a gain. 5. The photodetector having a diffraction grating according to claim 3, wherein a diffraction grating is not formed in a region of the optical waveguide having a gain for the guided light. 6. The photodetector having a diffraction grating according to claim 3, wherein there are a plurality of regions having a gain for the guided light. 7. A semiconductor optical waveguide on which light is incident, a diffraction grating formed on the optical waveguide, and a photodetection unit including a plurality of portions for detecting diffracted light emitted to the outside of the optical waveguide. A photodetector having a diffraction grating, characterized in that the light incident on the semiconductor optical waveguide includes continuous light. 8. The photodetector having a diffraction grating according to claim 7, wherein the wavelength of the continuous light is set to the shortest wavelength or the longest wavelength of usable signal light. 9. A photodetector having a diffraction grating according to claim 7, wherein a part or all of the semiconductor optical waveguide is formed so as to have a gain. 10. A semiconductor optical waveguide on which light is incident, a diffraction grating formed on the optical waveguide, and a photodetecting unit including a plurality of portions for detecting diffracted light emitted to the outside of the optical waveguide. In the photodetector having, the optical waveguide is formed so as to have a gain, and is formed so as to oscillate at the Bragg wavelength of the diffraction grating when no light is incident. Photodetector having. 11. The diffraction grating according to claim 10, wherein the Bragg wavelength is set in a low gain band of an optical amplification section having the optical waveguide formed to have a gain. Light detection device. 12. The Bragg wavelength is set to a short wavelength side of a low gain band of an optical amplification section having the optical waveguide formed so as to have a gain. A photodetector having a diffraction grating. 13. In an optical communication network in which at least one transmitting terminal station for transmitting optical signal lights of different wavelengths and a receiving terminal station for receiving optical signals of a plurality of wavelengths are connected by an optical transmission line, at least one transmitting terminal station is provided. Claims 1, 3 to the receiving terminal station
An optical communication network comprising the photodetector according to item 7 or 10.