JPH06130438A - Photodetection device having diffraction grating and optical communication network - Google Patents

Abstract

(57) [Abstract] [Purpose] A photodetector having a wavelength tracking function, a demultiplexing function, and the like used in optical communication and the like. A photodetector including a semiconductor optical waveguide including an active layer 4 on which light is incident, a diffraction grating formed on the waveguide, and a plurality of portions for detecting diffracted light 11 emitted to the outside of the waveguide. And a container 12. A polarizing plate 10 that selectively transmits only a specific polarized component of the diffracted light 11 is disposed between the waveguide and the photodetector 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetector having a wavelength tracking function used in optical communication and the like, in which the emission angle of the diffracted light emitted from the optical waveguide in which the diffraction grating is formed to the outside of the waveguide is optical. The present invention relates to a photodetector having a demultiplexing function that utilizes wavelength dependence of wavelengths, a wavelength multiplexing transmitter / receiver used in the field of optical communications, and an optical communication network or wavelength multiplexing optical communication system using these devices. .

[0002]

2. Description of the Related Art Conventionally, a photodetector having a diffraction grating is
When the light propagating through the optical waveguide includes both TE and TM polarization components, since the equivalent refractive index of the waveguide is different for each polarization component, two radiation angles corresponding to the respective polarization components are different. Diffracted light is emitted toward the photodetector.

[0003]

SUMMARY OF THE INVENTION In the above conventional example,
If the incident light is only horizontally polarized light or only vertically polarized light, there is only one diffracted light that is emitted outside the waveguide, so no obstacle occurs. However, when the incident light enters the waveguide of the photodetector from the optical fiber, the incident light is
Since both vertical polarization components are included, two diffracted lights with slightly different exit angles are generated for the respective polarization components, and the demultiplexing function is significantly deteriorated.

Further, since the polarization state of the light incident from the single mode fiber to the waveguide in which the diffraction grating is formed fluctuates, in order to always allow only a single polarization to enter the waveguide, the polarization Control was essential.

However, this polarization control is complicated, and the polarization states of optical signals sent from different points are different, as in a wavelength-multiplexed local area network. It was almost impossible to receive at the same time.

An object of the present invention is to solve the above problems by using a photodetector having a wavelength tracking function used in optical communication and the like, and diffracted light emitted from the optical waveguide having a diffraction grating to the outside of the waveguide. (EN) Provided are a photodetector device having a demultiplexing function that utilizes the fact that the radiation angle of the device depends on the wavelength of light, and an optical communication network or wavelength division multiplexing optical communication system using these devices.

[0007]

According to the first aspect of the present invention, by arranging a polarizing plate between an optical waveguide having a diffraction grating and a photodetector having a plurality of photodetectors, incident light can be obtained. Even when two diffracted lights are generated due to the inclusion of both horizontal and vertical polarization components, the polarizing plate selectively transmits either one of the diffracted lights, so that only one light is incident on the photodetector. . Therefore, even when the incident light includes both horizontal and vertical polarization components, it is possible to realize a photodetector in which the demultiplexing function is not deteriorated.

According to a second aspect of the present invention, a photodetector having a plurality of photodetectors is provided with a photodetector array for receiving only TE polarized light and a TM polarized diffracted light. With the configuration of the photodetector array that receives only the light, it is possible to receive the signal light independent of the polarization state. In addition, it becomes possible to receive simultaneously multiple signals with different polarization states such as wavelength-division-multiplexed local area network.

In the case of the first embodiment of the present invention, when either one of the two diffracted lights is removed by the polarizing plate, the received signal intensity largely changes depending on the polarization state, and the polarization of the signal is changed. If the polarization is opposite to the received polarization, a situation in which the polarization cannot be received occurs. However, in the second embodiment of the present invention, it is possible to always receive a signal at a constant level without depending on the polarization state.

Further, in an optical communication network in which at least one transmitting terminal station for transmitting optical signals of different wavelengths and a receiving terminal station for receiving optical signals of plural wavelengths are connected by an optical transmission line, at least one transmitting terminal station is connected. The receiving terminal station is provided with the above-mentioned photodetector.

Further, in the optical communication network, a wavelength tunable DBR-LD (distributed reflection type semiconductor laser) is used as a wavelength multiplex light source, and the wavelength spacing of wavelength multiplexing is the longitudinal mode spacing of the wavelength tunable DBR-LD or its It is characterized by using an integral multiple.

[First Embodiment] FIG. 1 is a view best showing the features of the present embodiment. An optical waveguide with a diffraction grating is composed of an optical amplifying section and a diffracted light emitting section. A plurality of photodetector sections 12 are arranged in a line in the direction perpendicular to the waveguide of the diffracted light emitting section, facing the waveguide, and a polarizing plate 10 is arranged between the two.

The optical waveguide with a diffraction grating has a rib waveguide structure, and the optical amplification section includes an n-GaAs buffer layer 2 on an n-GaAs substrate (not shown) and n-Al _x Ga _1-x. As 1st optical confinement layer 3, 10 GaAs layers and Al _y Ga _1-y A
an active layer 4 having a multi-quantum well structure including 11 s (0 <y ≦ x) layers, a p-Al _x Ga _1-x As second optical confinement layer 5,
Si ₃ N ₄ electrical insulating layer 6, p-GaAs contact layer 8,
And n and p metal electrodes 1 and 7.

A diffraction grating is formed in the rib waveguide 9 of the diffracted light emitting portion (not shown), and the pitch Λ of the diffraction grating is Λ = λ / n _eff (n _eff : Equivalent refractive index of waveguide) is satisfied.

Although not shown in the drawing, a reflection-free coating is applied to the external light incident end surface of the optical amplification section to suppress the laser oscillation in the optical amplification section and increase the saturation injection current density. I have to.

With the optical amplifier section kept in forward bias,
When external light is incident on the rib waveguide 9, the incident light is amplified by the optical amplification section and is emitted from the diffracted light emission section in a direction substantially perpendicular to the waveguide. At this time, the incident light is only the horizontal polarization component,
Alternatively, a single first-order diffracted light can be obtained if it is composed of only vertically polarized components.

Angle formed by diffracted light with respect to the vertical line of the waveguide (emission angle)
θ is −0.3 to 0.4 deg / n with respect to the wavelength of incident light.
It changes for every m. Since the divergence angle of the diffracted light is very narrow in the extending direction (θ _P ) of the waveguide and is 0.2 ° or less,
The length in the waveguide extending direction of the light receiving surface of each detector of the detector 12 including the row of photo detectors is defined as the spread angle (θ) of the diffracted light.
By setting it to about _P ), wavelength resolution of 0.5 nm or less is possible.

However, when the incident light includes both horizontal and vertical polarization components, since the propagation constant of the waveguide varies depending on the polarization, the two output angles slightly differ depending on the respective polarization components. Diffracted light is generated. However, the polarization plate 10 selectively transmits only one polarization component, so that only one polarization component 11 is incident on the photodetector array 12. Therefore, even if the incident light includes both horizontal and vertical polarization components, the demultiplexing function does not deteriorate.

[0018]

[Second Embodiment] A second embodiment of the present invention will be described with reference to FIG.
FIG. 2 is a configuration diagram of a second embodiment of a photodetecting device having an optical waveguide with a diffraction grating and a photodetecting element array 32 according to the present invention. In the figure, on an n-GaAs substrate 22, _{sequentially, n-Al x Ga 1-} x As light confinement layer 23, Al _y G
a _1-y As optical waveguide layer 24 (0 ≦ y <x <1), p-Al _x
Ga _1-x As optical confinement layer 25, p-Al _z Ga _1-z As
A contact layer 28 (0 <z <1) is formed. Lateral confinement is due to the high resistance Al on both sides of the striped waveguide.
_x Ga _1-x As embedded layer 35.

An upper p-type electrode 27 having a diffracted light emitting window 36 is formed on the contact layer 28, and n−
An n-type electrode 21 is formed on the back surface of the GaAs substrate 22. A diffraction grating (not shown) is formed inside the Al _y Ga _1-y As optical waveguide layer 24 or at a position within the wavelength range of light from the waveguide layer 24. Further, three elements P are provided directly above the diffracted light emitting window 36 of the optical waveguide with the diffraction grating.
A photodetector array 32 composed of D is arranged. Also,
A polarizing plate 38 is also arranged directly above the diffracted light emitting window 36. The function of this is as described in the first embodiment.

In the above structure, when light is input to the waveguide, the diffracted light is emitted to the upper surface of the waveguide by the diffraction grating formed in the optical waveguide layer 24 or in the vicinity of the waveguide including the optical waveguide layer 24.

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

In this embodiment, the equivalent refractive index of the waveguide is 3.
Since it is 4 to 3.5, a diffraction grating of about 0.24 μm is formed for incident light in the 0.8 μm band (q = 1).

At this time, the change in the tilt angle θ with respect to the change in the wavelength of the incident light was dθ / dλ to −0.3 to −0.4 deg / nm.

Far-field pattern of diffracted light (FF
P) is very narrow in the direction along the waveguide, its divergence angle (θ _P ) is 0.2 ° or less, and it is wide in the direction crossing the waveguide, and its divergence angle (θ _t ) is about 15 °. . Therefore, if the wavelength of the incident light changes by about 0.5 nm, the emission angle, that is, the tilt angle θ changes by about 0.2 °, so that the beam diameter of the diffracted light changes in the direction along the waveguide. Therefore, each element P in the direction along the waveguide of the photodetection element array 32 is
If the size of the light-receiving surfaces D1, 2, 3 is set to the beam diameter (θ _P ) of the first-order diffracted light, a wavelength change of about 0.5 nm can be detected. The wavelength resolution is limited by the spread angle (θ _P ) of the diffracted light that is diffracted upward in the direction along the waveguide, so that the absorption loss of the waveguide with a diffraction grating can be reduced,
By reducing the coupling efficiency between the diffraction grating and the optical waveguide, the region where the diffracted light of the optical waveguide with the diffraction grating is emitted is lengthened, thereby making θ _P narrower and the wavelength resolution ˜0.
It is possible to raise it to about 1 mm.

FIG. 3 is a simple block diagram of the photodetector of FIG. 2 having a wavelength tracking function. In FIG. 3, first, as an initial setting before the start of reception, the strongest region of the intensity distribution of the diffracted light of the light incident on the optical waveguide is the photodetector array 3.
The injection current control circuit 45 controls the injection current of the optical waveguide so that the Bragg wavelength of the diffraction grating is changed so that the light is incident on the element PD2 at the center of 2. At this time, another detection element PD
1, the amount of light incident on the PD 3 is set so that both are equal or zero. Reception is started in this state.

When the wavelength of the incident light changes to the longer side during reception, the incident light amount of the detecting element PD2 decreases and the incident light amount of the detecting element PD1 increases and the incident light amount of the detecting element PD3 decreases or remains zero. Is. In the comparison circuit 46, P
D1 (amount of incident light on detection element PD1) -PD3, and PD
By calculating 2-PD1 (or PD3), the amount and direction of change in the wavelength of this incident light can be known. Therefore, the comparison circuit 46 controls the injection current control circuit 45 to reduce the injection current to the optical waveguide and shift the Bragg wavelength of the diffraction grating to the long wavelength side. With this, the incident light amounts of the detection elements PD1 and PD3 are made equal or zero, so that the strongest incident region of the diffracted light becomes the detection element PD2 at the center. On the other hand, when the wavelength of the incident light changes to the shorter side and the amount of the incident light changes, the injection current to the optical waveguide is increased in the same manner to shift the Bragg wavelength of the diffraction grating to the short wave side, Similarly, the outgoing angle of the diffracted light is controlled. In this way, even if the wavelength of the incident light changes, the diffracted light from the optical waveguide can always enter the detection element PD2 at the center of the photodetection element array 32, and the wavelength tracking of the incident light becomes possible.
At this time, the relationship between the injection current and the Bragg wavelength of the diffraction grating is measured in advance and stored in the injection current control circuit 45.

As described above, the far-field pattern (FFP) of the diffracted light emitted from the optical waveguide is very narrow in the direction along the waveguide and its spread angle (θ _P ) is 0.2 ° or less. It is wide in the direction crossing the waveguide, and its spread angle (θ _t ) is about 15 °. Since the divergence angle in the direction crossing the waveguide is large as described above, the amount of light incident on the photodetector array 32 becomes about several percent of the total emitted light amount.

Therefore, a cylindrical lens 37 is arranged between the optical waveguide and the photodetector array 32 to collect the diffracted light in the direction traversing the waveguide, whereby the detector array 3 is formed.
The amount of light entering the optical waveguide 2 is increased so that wavelength tracking can be effectively performed even if the light entering the optical waveguide is weak.

[0029]

[Third Embodiment] FIG. 4 is a view best showing the features of this embodiment, in which an optical waveguide in which a diffraction grating is formed and an optical amplifier are monolithically constructed. A photodetector array 64 that receives only TE polarized light and a photodetector array 65 that receives only TM polarized diffraction light are arranged in the extending direction of the waveguide in a direction perpendicular to the upper surface of the optical waveguide. ing.

In FIG. 4, which shows only the left half of the device, the optical amplifying section includes an InP substrate 52, an InGaAsP optical guide layer 53 having a band gap energy of 0.95 eV, an InGaAsP active layer 54 having a band gap energy of 0.8 eV, It is composed of an InP upper optical confinement layer 55, an InGaAs contact layer 57, an InP high resistance buried layer 56, and ohmic electrodes 51 and 58 of p and n.
On the other hand, the waveguide in which the diffraction grating 59 is formed is the same InP substrate 52, the diffraction grating 59 having the pitch Λ, the In
GaAsP optical guide layer 53, InP upper optical confinement layer 55
It is composed of. Reference numeral 63 is an injection current control device for the optical amplification section. Although not shown in the figure, a dielectric antireflection film is formed on the incident end face and the opposite end face to prevent reflection of light. Further, the pitch Λ of the diffraction grating 59 is Λ to λ / n _eff (n _eff : for the wavelength λ of the signal light).
The equivalent refractive index of the waveguide) is satisfied.

In the drawing, after the incident light is amplified by the optical amplification section, the diffraction grating 59 of the waveguide in which the diffraction grating is formed emits the diffracted light from the upper surface of the waveguide. At this time, if the incident light has both TE and TM polarization components, two diffracted lights 67 and 68 corresponding to the respective polarization components and having different emission angles φ ₁ and φ ₂ are generated. Since the two diffracted lights have a large divergence angle in the direction crossing the waveguide, the photodetector array 6
The incident light intensity is approximately equal to 4, 65, but the photodetector array 6
In FIG. 4, only TE-polarized diffracted light is received, and in the photodetector array 65, only TM-polarized diffracted light is received. It became possible to receive signals with almost constant intensity without depending on the wave condition.

When a plurality of signals are wavelength-multiplexed, the TE polarization component and TM of the same signal are initially set.
By specifying the photodetector or photodetector that is receiving the polarization component and setting it to add the signals, multiple signals with different polarization states can be received simultaneously and with almost constant signal strength. It became possible to do.

[0033]

[Fourth Embodiment] FIG. 5 is a cutaway perspective view of a two-electrode variable wavelength DBR-LD which constitutes an electrical / optical conversion unit of an individual transmitting terminal in an optical communication network of the present invention, and shows a reflection characteristic in a DBR region. Is formed to be narrower than the longitudinal mode interval of DBR-LD. In FIG. 5, in the active region and the DBR region, n-Al is formed on the n-GaAs substrate 72.
_x Ga _1-x As optical confinement layer 73, Al _y Ga _1-y As optical waveguide layer 74, Al _n Ga _1-n As (0 ≦ n <y <x <1) active layer 741, high resistance Al _y Ga _1-y As embedded layer 75,
_{p-Al x Ga 1-x} As light confinement layer 76, p-Al _z G
An a _{1 -z} As (0 <z <1) contact layer 77 is formed, and an n-type electrode 71 is formed on the opposite side of the n-type substrate 72. A diffraction grating 80 is provided in the optical waveguide portion of the DBR region.
And the p-type electrode 81 is formed on the contact layer 77. An upper p-type electrode 78 is formed in the active region. A groove 79 is formed between the active region and the DBR region at least through the electrode and the contact layer 77.

When a current above the threshold value is injected into the active region of the DBR-LD, oscillation starts at a wavelength at which the reflection characteristics of the DBR and the longitudinal mode substantially match. When carriers are injected into the DBR region in this state, the effective refractive index changes due to the plasma effect, and the central wavelength of the reflection characteristics shifts to the short wavelength side, so the reflectance of the DBR at the oscillation wavelength decreases,
Light output is reduced. Furthermore, if carriers are injected, DB
Since the reflectance of R is further reduced, almost no optical output is obtained, and the center wavelength of the reflection characteristic approaches the wavelength of the adjacent longitudinal mode on the short wavelength side. When carriers are further injected, the reflectance of the DBR at the wavelength of the adjacent longitudinal mode increases, and oscillation is started at this wavelength, so the oscillation wavelength shifts to the short wavelength side by one longitudinal mode.

Therefore, the two-electrode variable wavelength DBR-LD
It is possible to discretely change the oscillation wavelength at almost the longitudinal mode interval of the DBR-LD by controlling the injection current into the DBR region.

On the other hand, as a photodetector having a demultiplexing function, which constitutes an optical / electrical conversion section of each receiving terminal station, the optical detection apparatus shown in FIGS.
Use the one described in. Next, the operation of this embodiment will be described. Spread angle of synchrotron radiation in the waveguide extension direction (θ
_P ) is very narrow, less than 0.2 °. On the other hand, the wavelength dependence of the emission angle θ of the emitted light in the waveguide extension direction is up to −0.4d.
Since it is EG / nm, a wavelength resolution of about 0.5 nm can be obtained by setting the length of the light receiving surface of each detector in the waveguide extension direction to about the divergence angle (θ _P ) of the emitted light. . Therefore, the effective resonator length L of the DBR-LD is
By adjusting the _eff (the sum of the active region length L _act and the effective DBR length L _DBR ) to set the longitudinal mode interval to the same level as the wavelength resolution of this photodetector, wavelength-multiplexed signals are transmitted from the transmission side. Demultiplexes all incoming signals into individual wavelengths,
Moreover, it is possible to simultaneously receive signals of all wavelengths if necessary.

In the optical communication network of the present invention,
Since the oscillation wavelength of each transmitting terminal station is selected from the discrete oscillation wavelengths of the longitudinal mode intervals, it is not necessary to strictly stabilize it, and control becomes much easier.

FIG. 6 is a schematic diagram showing one form of a wavelength division multiplexing optical communication network using the transmitting / receiving device of the present invention shown in FIG. 5 and FIG. 1 or 4.

In the figure, each transmitting terminal has the wavelength variable DBR-LD of FIG.
Wavelength (λ ₁ ·
· From lambda _n), it starts transmission at any wavelength _{λ n (1 ≦ i ≦ n} ). At this time, if there are a plurality of transmitting terminal stations desiring to transmit at the same time, wavelengths λ _j , λ _k ... (1 ≦ j, k, ... ≦ n, i) that are not used by the respective transmitting terminal stations. ≠ j ≠ k
...) can be transmitted.

All transmitting terminal stations 201, 202, ..., 20
The optical signals sent from N are 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
The optical / electrical converters 502, ..., 50M are configured by photodetectors having a demultiplexing function. Optical transmission line 400
The wavelength-multiplexed signal sent by the branching / combining device 302 is branched by the branching / combining device 302, and then received by each of the receiving terminal stations 501, 5
02, ..., 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.

[0042]

As described above, according to the photodetector of the first embodiment of the present invention, the optical waveguide having the diffraction grating and the diffracted light emitted from the optical waveguide to the outside of the waveguide are detected. By disposing polarizing means such as a polarizing plate that selectively transmits only a specific polarized component between the light detecting means of
It is possible to realize a photodetector having a good demultiplexing function even when the incident light on the optical waveguide contains both horizontal and vertical polarization components.

Further, according to the photodetector of the second aspect of the present invention, as described above, it is composed of the optical waveguide in which the diffraction grating is formed and the photodetector having a plurality of photodetectors. In a photodetector having a demultiplexing function and the like, by configuring the plurality of photodetectors with a detector that detects TE polarization and a detector that detects TM polarization, the polarization state of incident signal light is changed. It became possible to receive signals of constant intensity without depending on them.
In addition, it became possible to receive multiple signals with different polarization states at the same time with constant intensity without depending on each polarization state.

Further, when the photodetector of the present invention is used as an optical / electrical conversion unit of a receiving terminal station of a wavelength division multiplexing optical communication network, after wavelength division multiplexed signals are demultiplexed into respective wavelengths, a plurality of signals or It is possible to receive all signals simultaneously if desired.

Further, as described above, in the wavelength division multiplexing optical communication network, the wavelength tunable DBR-LD is used as the light source of the transmitting terminal, and the wavelength division of the wavelength division multiplexing is set to the longitudinal mode interval of the wavelength tunable DBR-LD. Alternatively, by using a photodetector having a demultiplexing function as a detector of the receiving end station, the wavelength multiplicity can be increased and the configuration of the transmitting end station can be simplified.

Further, since the wavelength tunable DBR-LD only needs to oscillate at the longitudinal mode interval, it has a wide maximum wavelength tunable range and is easy to control as compared with the continuous wavelength tunable case.
The wavelength multiplicity can be further increased.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of a photodetector having a diffraction grating embodying the present invention.

FIG. 2 is a schematic configuration diagram of a second embodiment of a photodetecting device in which a condensing cylindrical lens is arranged between an optical waveguide and a photodetecting means.

FIG. 3 is a block diagram of a configuration for providing a wavelength tracking function in the second embodiment.

FIG. 4 is a photodetector having a demultiplexing function and the like, which is configured by an optical waveguide having a diffraction grating formed according to the present invention, a detector array for detecting TE polarization and a detector array for detecting TM polarization. The schematic block diagram of 3rd Example of this.

FIG. 5 is a schematic diagram of the structure of a wavelength tunable DBR-LD that constitutes the electrical / optical conversion unit of the transmission terminal station of the present invention.

FIG. 6 is a schematic diagram of a wavelength division multiplexing optical communication network embodying the present invention.

[Explanation of symbols]

1, 7, 21, 27, 51 ,. 58, 71, 78, 81
Metal electrode 2, 22, 52, 72 GaAs substrate and buffer layer 3, 5, 23, 25, 55, 73, 76 AlGaAs
Light confinement layer 4, 24, 54, 74, 741 Active layer 6 Electrical insulating layer 8, 28 GaAs contact layer 9 Rib waveguide having diffraction grating 10, 38 Polarizing plate 11 Diffracted light emitted outside waveguide 12, 32 Photodetector consisting of multiple parts 35, 56, 75 High resistance buried layer 36 Diffracted light emitting window 37 Cylindrical lens 41 Optical waveguide with diffraction grating 45, 63 Injection current control circuit 46 Comparison circuit 53 Optical guide layer 59, 80 Diffraction Grating 64 Photodetector array for detecting TE polarized light 65 TM Photodetector array for detecting polarized light 67, 68 Diffracted light with different polarization state 77 AlGaAs contact layer 79 Electric separation groove 201-20N Transmitting terminal station 301, 302 Branching / combining device 400 Optical transmission line 501 to 50NM Receiving terminal station

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[Procedure amendment]

[Submission date] December 16, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

Further, in the optical communication network, a wavelength tunable DBR-LD (distributed reflection type semiconductor laser) is used as a wavelength multiplexing light source, and the wavelength multiplexing wavelength interval is the longitudinal mode interval of the wavelength tunable DBR-LD or its It is characterized by using an integral multiple.

First Embodiment FIG. 1 is a drawing of a photo-detecting device having a demultiplexing function that best represents the features of the present embodiment. An optical waveguide with a diffraction grating is composed of an optical amplification section and a diffracted light emission section. ing. A plurality of photodetector sections 12 are arranged in a line in the direction perpendicular to the waveguide of the diffracted light emitting section, facing the waveguide, and a polarizing plate 10 is arranged between the two.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

A diffraction grating is formed in the rib waveguide 9 of the diffracted light emitting portion ( not shown ), and the diffraction grating pitch Λ
Is approximately λ˜λ / n _eff (n
_eff : Equivalent refractive index of the waveguide) is satisfied.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

When external light composed of one or more signal lights each having a different wavelength is incident on the rib waveguide 9 while the optical amplifier is held in the forward bias, the incident light is amplified by the optical amplifier and diffracted. The light is demultiplexed into each wavelength in the direction substantially perpendicular to the waveguide and emitted from the light emitting portion .

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

The perpendicular and the angle of the diffracted light waveguide (emission angle) theta is -0.3 the wavelength of the incident light - 0.4De
It changes for every g / nm. Since the divergence angle of the diffracted light is extremely narrow in the waveguide extension direction (θ _P ) and is about 0.2 °, the waveguide extension of the light-receiving surface of each of the detectors of the detector 12 including the photodetector array. By setting the length in the direction to about the spread angle (θ _P ) of the diffracted light, wavelength resolution of about 0.5 nm is possible.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

The incident light may have only a horizontal polarization component or a vertical polarization component.
A single first-order diffracted light can be obtained if it is composed of only wave components.
To be However, when the incident light contains both horizontal and vertical polarization components, the propagation constant of the waveguide differs depending on the polarization, so two diffracted lights with slightly different exit angles are generated depending on each polarization component. Occurs. However, the polarization plate 10 selectively transmits only one polarization component, so that only one polarization component 11 is incident on the photodetector array 12. Therefore, even if the incident light includes both horizontal and vertical polarization components, the demultiplexing function does not deteriorate.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

[0018]

[Second Embodiment] A second embodiment of the present invention will be described with reference to FIG.
FIG. 2 is a block diagram of a second embodiment of a photodetector having a wavelength tracking function, which is composed of an optical waveguide with a diffraction grating and a photodetector array 32 according to the present invention. In the figure, n-Al _x Ga is deposited on the n-GaAs substrate 22 in order.
_1-x As optical confinement layer 23, Al _y Ga _1-y As optical waveguide layer 24 (0 ≦ y <x <1), p-Al _x Ga _1-x
The As light confinement layer 25 and the p-Al _z Ga _1-z As contact layer 28 (0 <z <1) are formed. Lateral confinement is achieved by high resistance Al _x G on both sides of the striped waveguide.
a _1−x As embedded layer 35.

[Procedure Amendment 8]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Change

[Correction content]

Far-field pattern (F
FP) is very narrow in the direction along the waveguide, its spread angle (θ _P ) is about 0.2 °, and it is wide in the direction crossing the waveguide, and its spread angle (θ _t ) is about 15 °. .
Therefore, if the wavelength of the incident light changes by about 0.5 nm, the emission angle, that is, the tilt angle θ changes by about 0.2 °, so that the beam diameter of the diffracted light changes in the direction along the waveguide.
Therefore, if the size of the light receiving surface of each of the elements PD1, 2, 3 in the direction along the waveguide of the photodetecting element array 32 is set to about the beam diameter (θ _P ) of the first-order diffracted light, a wavelength change of about 0.5 nm will occur. Can be detected. Since the wavelength resolution is limited by the divergence angle (θ _P ) of the diffracted light that is diffracted upwards in the direction along the waveguide, the absorption loss of the waveguide with the diffraction grating can be reduced, or the coupling between the diffraction grating and the optical waveguide can be reduced. By reducing the efficiency, the region for emitting the diffracted light of the optical waveguide with the diffraction grating is lengthened, and thus θ _P is narrowed, and the wavelength resolution is reduced.
It is possible to increase to 0.1 nm .

[Procedure Amendment 9]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

[0029]

[Third Embodiment] FIG. 4 shows the characteristics of the present embodiment best .
It is the figure which improved the polarization dependence of the photon detection device which has a wave function, and the optical waveguide in which the diffraction grating was formed, and the optical amplifier are constituted monolithically. A photodetector array 64 that receives only TE-polarized diffracted light and a photodetector array 6 that receives only TM-polarized diffracted light in a direction perpendicular to the upper surface of the optical waveguide.
5 is arranged in the extending direction of the waveguide.

[Procedure Amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction content]

In the drawings, one or more different wavelengths are used.
After the incident light composed of signal light is amplified by the optical amplifier,
By the diffraction grating 59 of the waveguide having the diffraction grating formed, the light is split into each wavelength and emitted as diffracted light from the upper surface of the waveguide. Now, one of the signal light, TE, as long as the TM both polarization components, corresponding to each of the polarization components, the radiation angle phi _1, phi ₂ different two diffracted light 67 and 68 Occurs.
Since the two diffracted lights have a large divergence angle in the direction crossing the waveguide, they are incident on the photodetector arrays 64 and 65 with almost equal intensity. However, in the photodetector array 64, only TE polarized light is diffracted. Is received and only the TM polarized light is received by the photodetector array 65. Therefore, by adding the received signals, it is possible to obtain an almost constant intensity without depending on the polarization state of the incident light. It became possible to receive the signal.

[Procedure Amendment 11]

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Further, when a plurality of signals having different polarization states are wavelength-multiplexed, as a default setting, a photodetector or an optical detector that receives the TE polarization component and the TM polarization component of each identical signal is used. By specifying the detector and setting it to add the signals, it has become possible to receive a plurality of signals with different polarization states at the same time and with substantially constant signal strength.

[Procedure Amendment 12]

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Further, as described above, in the wavelength division multiplexing optical communication network, the wavelength tunable DBR-LD is used as the light source of the transmitting terminal station, and the wavelength division of the wavelength division multiplexing is set to the longitudinal mode interval of the wavelength tunable DBR-LD. Alternatively, by using a photodetector having a demultiplexing function as a detector of the receiving terminal station, which is an integral multiple thereof, it is possible to increase the wavelength multiplicity and simplify control of the oscillation wavelength .

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[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of a photo-detecting device having a demultiplexing function according to the present invention.

FIG. 2 is a schematic configuration diagram of a second embodiment of a photodetector having a wavelength tracking function in which a condensing cylindrical lens is arranged between an optical waveguide and a photodetector.

FIG. 3 is a block diagram of a configuration for providing a wavelength tracking function in the second embodiment.

FIG. 4 is a demultiplexing function having an improved polarization dependency, which is configured by an optical waveguide having a diffraction grating formed according to the present invention, a detector array for detecting TE polarization and a detector array for detecting TM polarization. FIG. 3 is a schematic configuration diagram of a third embodiment of a photodetector including the above.

FIG. 5 is a schematic diagram of the structure of a wavelength tunable DBR-LD that constitutes the electrical / optical conversion unit of the transmission terminal station of the present invention.

FIG. 6 is a schematic diagram of a wavelength division multiplexing optical communication network embodying the present invention.

[Explanation of Codes] 1,7,21,27,51,58,71,78,81
Metal electrode 2,22,52,72 Substrate and buffer layer 3,5,23,25,55,73,76 Light confinement layer 4,24,54,74,741 Active layer 6 Electrical insulation layer 8,28 GaAs contact Layer 9 Rib waveguide having a diffraction grating 10,38 Polarizing plate 11 Diffracted light emitted outside the waveguide 12,32 Photodetector consisting of multiple parts 35,56,75 High resistance embedded layer 36 Diffracted light emitting window 37 Cylindrical lens 41 Optical waveguide with diffraction grating 45,63 Injection current control circuit 46 Comparison circuit 53,73 Optical guide layer 59,80 Diffraction grating 64 Photodetector array for detecting TE polarized light 65 TM Optical detection for detecting polarized light Array 67, 68 Diffracted light with different polarization states 77 Contact layer 79 Grooves for electrical separation 201 to 20N Transmitting terminal station 301, 302 Branch / merge 40 0 Optical transmission line 501 to 50NM Receiving terminal station

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI Technical display location H01L 31/14 A 7210-4M H01S 3/10 Z 8934-4M 3/18 H04B 10/04 10/06

Claims (7)

[Claims] 1. An optical waveguide into which light is incident, a diffraction grating formed in the waveguide, and a photodetecting means including a plurality of portions for detecting diffracted light emitted to the outside of the waveguide. The photo-detecting device having a diffraction grating, wherein a polarizing means for selectively transmitting only a specific polarization component of the diffracted light is arranged between the waveguide and the photo-detecting means. 2. The photodetector according to claim 1, further comprising a condensing unit arranged between the waveguide and the photodetector for condensing diffracted light in a direction traversing the waveguide. 3. The optical waveguide is composed of a semiconductor,
The photodetector according to claim 1, further comprising at least one optical amplification unit that amplifies the incident light by injecting a current in a part of the waveguide. 4. A photodetector in which a plurality of photodetectors are arranged to detect diffracted light emitted from an optical waveguide formed with a diffraction grating to the outside of the waveguide, wherein the plurality of photodetectors are TE. 1. A photodetector having a diffraction grating, which comprises one or more detectors for detecting polarized waves and one or more detectors for detecting TM polarized waves. 5. The optical waveguide is composed of a semiconductor,
The photodetector according to claim 4, further comprising at least one optical amplification section that amplifies the incident light by injecting a current in a part of the waveguide. 6. A wavelength division multiplexing optical communication network in which at least one transmitting terminal station for transmitting optical signals of different wavelengths and a receiving terminal station for receiving optical signals of a plurality of wavelengths are connected by an optical transmission line. An optical communication network, wherein one receiving terminal station is provided with the photodetector according to claim 1. 7. A wavelength-division-multiplexing optical communication network, wherein the wavelength-division-multiplexing optical communication network uses a longitudinal mode interval of a wavelength tunable DBR-LD or an integral multiple thereof as a wavelength-division multiplexing wavelength.