JPH06169132A - Optical semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing an optical semiconductor device which is excellent in manufacturing reproducibility and where a coupling coefficient between a diffraction grating and guided light is distributed in a direction in which light is guided. CONSTITUTION:An optical semiconductor device equipped with a waveguide structure which guides light rays is composed of an active layer 4 possessed of gain medium and an optical guide layer 3 equipped with diffraction gratings 9 and 10 which carry out a distributed feedback.coupling operation of the guided light rays. A coupling coefficient between the diffraction gratings 9 and 10 and the guided light rays is distributed in a direction in which light is guided by changing the diffraction gratings in order, and the coupling coefficient is set larger at the center of the optical semiconductor device than that at the periphery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device such as a wavelength tunable laser and a wavelength tunable filter used for wavelength division multiplexing optical communication, processing, recording and the like, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, an optical device having a wavelength tunable function has become important with the advancement of technology in the fields of optical communication and optical processing. Particularly, in wavelength division multiplexing communication, a wavelength tunable laser on the transmitting side and a wavelength tunable optical filter on the receiving side are required and are being developed.

As a conventional example, a wavelength tunable function can be obtained by forming a diffraction grating with a constant period on the optical guide layer to stabilize the mode and providing a plurality of electrodes or a phase adjustment region without a diffraction grating. Some have. In this case, the refractive index of the medium is changed by nonuniformly injecting the current, and the oscillation wavelength or the filtering wavelength can be changed while keeping the single mode stable.

Among them, a DFB (distributed feedback) type laser as shown in FIG. 12 is proposed, which is excellent in wavelength tunability and frequency modulation characteristics (change characteristics of shift amount of wavelength with respect to modulation frequency) (1988). Year OQE 89-116
p. 61, 1991 Fall Response 10p-ZM-17, Alley, etc.). This is to increase the coupling efficiency by deepening the diffraction grating 141 at the center of the resonator and to provide the λ / 4 phase shift 144 so that the light density becomes high at the center. Then, strong stimulated emission occurs in the central portion, and the carriers are eaten. However, if the current I _{11b in} this region is increased, the carriers are compensated, oscillation becomes possible with a small number of carriers, the refractive index increases, and the oscillation wavelength becomes long. Shift to the wavelength side. This phenomenon is in phase with the direction in which the oscillation wavelength shifts due to the thermal effect due to the increase in the current, and has the advantage that the wavelength tunable range is widened and the frequency modulation characteristic is uniform over the entire area. In FIG. 12, 14
Reference numeral 0 is an n-InP substrate, 142 is an n-InGaAsP optical guide layer, and 143 is a multiple quantum well (MQW) active layer.

[0005]

However, in this structure, there is a limit to the ratio of the depths of the diffraction grating 141 in the central portion and the peripheral portion. This is because the depth of the diffraction grating 141 is limited to about 1000 Å, which is half the pitch at most. Also, there are many parameters that should be optimized only by the depth ratio,
It has a drawback that it is difficult to obtain a constant depth ratio with good reproducibility.

Therefore, an object of the present invention is to provide a diffraction grating for distributed feedback coupling of guided light, which has a wide degree of freedom in the ratio of coupling efficiencies, is easily reproducible in fabrication, and is easy to fabricate as designed. An object of the present invention is to provide a provided optical semiconductor device, a method of using the same, and a method of manufacturing the same.

[0007]

In order to achieve the above object, an optical semiconductor device according to the present invention has a waveguide structure for guiding light, and performs distributed feedback coupling of the guided light with an active layer having a gain medium. In an optical semiconductor device including an optical guide layer having a diffraction grating for performing, the coupling coefficient between the diffraction grating and the guided light is distributed in the waveguide direction, and is made larger in the central portion than in the peripheral portion where the device is input and output. And

More specifically, increasing the coupling coefficient in the central portion is dependent on the wavelength λ of the guided light, the effective refractive index n of the waveguide layer, and the pitch Λ of the diffraction grating in the distributed feedback coupling of the guided light. The order m (= 2nΛ / λ) of the diffraction grating is
Go by lowering it in the center than in the periphery,
The pitch Λ of the diffraction grating determined with respect to the wavelength λ of the guided light (= 2nΛ / m, where n is the effective refractive index of the waveguide layer and m is the order of the diffraction grating) is matched (λ = 2nΛ / m) at the center. Is satisfied) to increase the coupling coefficient and change it in the peripheral portion to lower the coupling coefficient from the matching state, or to make the central diffraction grating closer to the active layer than the peripheral diffraction grating. Or by controlling the shape of the diffraction grating (rectangle, triangular wave, sine wave, etc.) so that the coupling coefficient is larger in the central diffraction grating than in the peripheral diffraction grating. , A rectangular shape at the center and a sine wave at the periphery, or a rectangular shape at the center and a triangular wave at the periphery, and the Fourier series expansion of the shape of the diffraction grating. The second-order component of time is at the center It is done by controlling so that it is larger than the surrounding area.

Further, in the method of manufacturing an optical semiconductor device according to the present invention for achieving the above object, the order of the diffraction grating in the central portion is the first order, the order of the peripheral portion is the second order, and the optical guide layer is formed. The step of forming a diffraction grating includes a first step of forming a secondary diffraction grating, a second step of applying a resist evenly on the diffraction grating, and a resist leaving only a portion for forming a primary diffraction grating. In the third step, and the dry etching is used to etch the resist and the exposed crystal planes.
It is characterized in that it includes a fourth step of producing a first-order diffraction grating having a pitch half that of the next diffraction grating, and that the diffraction grating in the central part has a first order and the peripheral part has a second order. A step of forming a diffraction grating on the light guide layer, a first step of forming a second-order diffraction grating, a second step of applying a resist on the diffraction grating flatly, and a first-order diffraction grating A third step of covering the resist and the exposed crystal plane by dry etching, and a fourth step of producing a first-order diffraction grating with a half pitch of the second-order diffraction grating. The fifth step of removing only the resist in the portion where the first-order diffraction grating is formed by dry etching, and selectively etching only the portion where the first-order diffraction grating is formed to form the active layer only in the portion of the first-order diffraction grating. And a sixth step of approaching And the step of forming a diffraction grating in the light guide layer, the step of covering only one of the diffraction grating in the central portion and the diffraction grating in the peripheral portion with a resist, and the diffraction grating in the central portion and the peripheral portion. And selectively etching only the other part of the grating to bring only the part of the diffraction grating in the central part closer to the active layer.

For example, in the present invention, as shown in FIG.
By controlling the order of the diffraction grating, non-uniform coupling efficiency is obtained in the cavity direction. The degree of collation is m
And the pitch is Λ, the oscillation wavelength is λ, and the effective refractive index of the medium is n, there is a relation of Λ = mλ / 2n. Generally, if the shape and depth are the same, the degree is m
The smaller is, the greater the coupling efficiency. In FIG.
The next diffraction grating 9 and the first-order diffraction grating 10 are formed in the central part and the λ / 4 phase shift 11 is provided so that the coupling efficiency is increased in the central part.

In addition, as shown in FIG. 4, there is also a method of providing a step at the central portion to bring the correlation close to the active layer 4 so as to enhance the coupling efficiency.

If the coupling efficiency is controlled by such a method,
The degree of freedom in the ratio of coupling efficiencies is expanded, and the wavelength variable range can be widened. In addition, reproducibility in production is easily obtained, and a device as designed is easily produced.

[0013]

[Embodiment 1] FIG. 1 is a structural diagram of a wavelength tunable DFB laser and a filter according to a first embodiment of the present invention. This embodiment is applied to the InGaAsP / InP system 1.55 μm band. The diffraction gratings 9 and 10 are provided below the active layer 4, the center portion is a first-order diffraction grating 10 having a λ / 4 phase shift region 11, and the peripheral portion is a second-order diffraction grating 9. The length of each region is 300μ for the primary grating unit 10.
m, the secondary grating portions 9 on both sides are each 200 μm, and the total length is about 7
It is 00 μm.

A method of manufacturing this device will be described with reference to FIG. In (a), the n-InP cladding layer 2 is grown on the n-InP substrate 1 by the LPE (liquid phase epitaxy) method.
In (b), a secondary diffraction grating 9 having a λ / 4 shift 11 is manufactured by using a phase shift mask method. At this time, the diffraction grating 9 has a pitch of 480 nm and a depth of 50 nm.
Is. In (c), the resist 20 is applied under the condition that does not reflect the unevenness of the diffraction grating 9, and after baking, only the region where the primary grating 10 is formed is opened with the resist 21 of a different material. The former resist 20 is, for example, AZ
1350J (manufactured by Hoechst) is diluted 10 times with thinner, and the latter resist 21 is, for example, OMR87.
(Manufactured by Tokyo Ohka Co., Ltd.) is used.

Next, in (d), selective etching of the resist 20 and the InP crystal 2 is performed by RIBE (reactive ion beam etching) using Ar + Cl ₂ mixed gas. The selection ratio between the resist 20 and the crystal 2 is approximately 4: 1. In this etching, the resist 20 is thin at the convex portion of the secondary lattice 9 that has already been manufactured, and the crystal 2 is exposed as the etching progresses.
However, since the resist 20 is thick in the concave portion, the crystal 2 is not exposed. Therefore, when controlled by an appropriate etching time, as shown in (d), it is divided into a concave portion where the resist 20 remains and an exposed concave portion for the crystal 2, and a grating having a half pitch and a depth of the first diffraction grating 9, that is, a pitch. The primary grating 10 having a depth of 240 nm and a depth of 25 nm is formed. If the resists 20 and 21 are removed in (e),
Areas of the primary lattice 10 and the secondary lattice 9 are formed.

Subsequently, in (f), an n-InGaAsP optical guide layer (λ = 1.15 μm) 3, an undoped MQW active layer 4, a p-InP cladding layer 5 are formed by MOCVD (metal organic chemical vapor deposition). The p-InGaAsP cap layer 6 is grown. The active layer 4 is a well layer InGaAs
The P-type barrier layer InGaAsP (λ = 1.3 μm) has three wells, and the MQW has an SCH structure sandwiched between InGaAsP (λ = 1.3 μm). After that, high-resistance InP12 is embedded and grown, the electrodes 7 and 8 are processed, and a non-reflective coating is applied to one end surface, whereby the device shown in FIG. 1 can be manufactured.

Next, the operation of this apparatus will be described. Three
When a current is evenly injected into all of the two electrodes 7, the coupling efficiency at the central portion is high, so that the light density at the central portion is large as shown in FIG. 9A, and the refractive index increases accordingly.
In such a state, the oscillation threshold rises because the refractive index distribution is generated, and the carrier density increases in the entire device, so that the oscillation wavelength is on the short wavelength side due to the plasma effect.

On the contrary, if the current I _{1b in the} central portion is increased while keeping the power constant and I _1a and I _1c are reduced accordingly, the light density becomes high in the central portion as shown in FIG. 9A. In order to compensate for the decrease in the carrier density, a uniform carrier distribution, that is, a uniform refractive index distribution is realized as shown in (b). As a result, the oscillation threshold is lowered, the carrier density of the entire device is reduced, and the oscillation wavelength is on the long wavelength side.

At this time, the greater the nonuniformity, the wider the wavelength tunable range, but with this device, a coupling efficiency ratio of 1: 3 is obtained, and continuous tunability of about 3 nm is possible.

When frequency modulation is performed by the central current I _1b , the wavelength shift direction due to heat and the wavelength shift direction due to the effect of carriers are in phase, so the wavelength shift amount is substantially flat up to a modulation frequency of about 10 GHz. Good modulation characteristics were obtained.

Further, by controlling the bias current in the vicinity of the oscillation threshold of the laser, when light is incident from the outside, it operates as an optical filter that selectively amplifies only a certain specific wavelength and emits it from the opposite side. as mentioned above,
If the current is injected nonuniformly, it operates as a wavelength tunable filter and is used as the receiving side of wavelength division multiplexing optical communication. The pass band at this time is about 0.05 nm, and the variable width is about 3 n.
m is obtained.

The device of this embodiment has been described above. However, by changing the depth of the diffraction grating and the distance from the active layer of the diffraction grating as described in the second embodiment, the coupling efficiency in the direction of the resonator can be improved. Various characteristics can be obtained depending on the degree of modulation. Further, as shown in FIG. 3, a diffraction grating without a λ / 4 shift may be used.

[0023]

[Embodiment 2] FIG. 4 is a sectional view of a wavelength tunable DFB laser according to a second embodiment of the present invention in the cavity direction.

In this device, although the orders of the diffraction gratings 28 and 29 are constant, there is a region near the active layer 4 where the coupling efficiency is high in the central portion. In this embodiment, the diffraction gratings 28 and 29
Is a primary grating with a λ / 4 shift with a pitch of 240 nm,
The step difference between the central portion and the peripheral portion is 0.1 μm.

An outline of the manufacturing process is shown in FIG. A resist (for example, OMR87) 41 having a desired length (300 μm) is covered as a step portion, and wet etching is performed by a surface orientation-independent etchant by 0.1 μm. As the etchant, sulfuric acid: hydrogen peroxide solution: water = 1: 1: 40 controlled at 0 ° C. was used. Alternatively, dry etching may be performed by RIBE. After that, the same steps as in Example 1 are performed.

This device does not produce a large difference in coupling ratio as in Example 1, but is easy to manufacture. In the device of this example, a wavelength tunable width of about 1.5 nm was obtained based on the same operating principle as that of the example 1.

[0027]

[Third Embodiment] In the above description, the InP-based material and the structure in which the diffraction grating is provided below the active layer 4 have been described.
An As-based material or another material may be used, or the diffraction grating may be provided on the active layer.

FIG. 6 shows a diffraction grating 9 made of a GaAs material.
10 is provided on the active layer 32, and the first and second embodiments are provided.
Taking into consideration the above concept, an example is shown in which a step is provided in the portion of the primary lattice 10 so as to be close to the active layer 32, and the difference in coupling rate is further increased. The length of the central portion is 300 μm, and the length of the peripheral portions is 200 μm.

An outline of the manufacturing process of this embodiment will be described with reference to FIG. In (a), n-GaAs substrate 30
On top, an n-GaAs buffer layer (not shown), thickness 1.5
μm n-Al _0.45 Ga _0.55 As cladding layer 31, active layer 32, 40 nm thick p-Al _0.4 Ga _0.6 As carrier confinement layer 33, 0.25 μm thick p-Al _0.15 G
a _0.85 As optical guide layer 34 is laminated by a molecular beam epitaxial method.

The structure of the active layer 32 is GaAs (thickness: 6 n).
m) quantum well layer and Al _0.2 Ga _0.8 As that separates it
It is a stack of three barrier layers (thickness 10 nm). On the outside, there is a GRIN-SCH layer having a thickness of 50 nm and gradually changing Al composition.

The second-order diffraction grating 9 having a pitch of 244 nm and a depth of 100 nm is formed on the light guide layer 34, and the first-order diffraction grating 10 is formed in a desired region at the center in the same steps as in Example 1 (FIG. 7). (B), (c)). Subsequently, in (d), the resist is removed by RIE (reactive ion etching) in oxygen gas. At this time, the resist (AZ135) slightly left on the diffraction grating 10
0J) 20 only, other resist (OMR87) 2
1 controls so that it may remain slightly. In (e),
Sulfuric acid: hydrogen peroxide: water = 1: 1: 40 at 0 ° C., only the region of the primary diffraction grating 10 is etched by 0.1 μm to form a step. In (f), p-Al _0.45 Ga _{0.55 with} a thickness of 1.5 μm was formed by LPE (liquid phase epitaxy)
An As clad layer 35 and a p-GaAs cap layer 36 having a thickness of 0.5 μm are grown. After that, high resistance Al _0.45 Ga
Electrode 37, 38 embedded with _0.55 As12 (see FIG. 1)
The device shown in FIG. 6 is manufactured by applying a process and an antireflection coating.

The principle of operation is the same as that described so far, but since the distance to the active layer and the diffraction grating order are both changed, a difference in coupling efficiency can be further provided as compared with the first embodiment. As a result, the variable wavelength range is expanded to about 4 nm.

Further, in the GaAs system, the influence of the wavelength shift due to heat is larger than that in the InP system, so that the present device, which is in phase with the wavelength shift due to the carrier, has a dramatically tunable range as compared with the conventional DFB type device. spread.

[0034]

[Fourth Embodiment] FIG. 8 shows a sectional view of a wavelength tunable DFB laser according to a fourth embodiment of the present invention in the direction of the cavity. In this device, the layer structure is the same as that of the third embodiment, although it is of GaAs type.
Only the part 10a of the primary lattices 10a and 10b is provided with the active layer 32.
The electrode 37 has a five-electrode structure accordingly, and finer control is possible. The lengths of the peripheral portions are all 200 μm, and the primary grating portions 10a and 1 in the central portion are
0b is 300 μm, but it is divided into three parts of 100 μm,
Only 100 μm of the center 10a is closer to the active layer 32 by 0.1 μm.

In this structure, the light density is concentrated only in the central portion, and a wide wavelength variable width can be obtained without losing the single mode property. This device may be made of InP-based material or another material, and the diffraction grating may be provided under the active layer 32.

[0036]

[Embodiment 5] FIG. 10 shows an example of the configuration of an optical-electrical converter (node) 56 connected to each terminal when the apparatus according to the present invention is applied to an optical transmission system, and FIG.
An example of the configuration of an optical transmission system using is shown.

An optical signal is taken into the node 56 through the optical fiber 50 connected to the outside as a medium, and a part of the optical signal enters the wavelength tunable filter 52 according to the present invention by the branching unit 51. The wavelength tunable filter 52 transmits and amplifies only an optical signal having a desired wavelength, and the photodetector 53 directly detects and converts it into an electric signal. On the other hand, when the optical signal is transmitted from the node 56, the light from the wavelength tunable laser 54 according to the present invention is modulated by the optical modulator 55 and is incident on the optical transmission line 50 via the branching unit 51. At this node 56,
The transmission line, the branching portion 51, the wavelength tunable filter 52, the wavelength tunable laser 54, the optical modulator 55, and the light receiver 53 can all be semiconductor integrated types, and can be made extremely compact. In addition, there are two tunable filters and tunable lasers.
It is possible to extend the wavelength variable range by providing a plurality of two or more.

As the network of the optical transmission system, the one shown in FIG. 11 is a bus type, and it is possible to install a number of networked terminals by connecting nodes in the A or B direction. However, in order to connect a large number of nodes, an optical amplifier should be used to compensate for the attenuation of light.
It is necessary to place them in series on 0. Also, by connecting two nodes 56 to each terminal and using two transmission lines, DQ
DB (Distributed Queued Dua)
It is possible to perform bidirectional transmission according to the l Bus) method.

In such an optical network system, by using the device according to the present invention, for example, a wavelength division multiplexing optical transmission network having a wavelength interval of 0.05 nm and a wavelength variable width of 3 nm, that is, a multiplicity of 60 can be constructed. Further, the network system may be a loop type in which A and B in FIG. 11 are connected, a star type, or a combination thereof.

[0040]

Other Embodiments Increasing the coupling coefficient in the central portion is determined with respect to the wavelength λ of guided light (= 2nΛ / m, where n is the effective refractive index of the waveguide layer and m is the order of the diffraction grating). The pitch Λ of the diffraction grating may be matched by increasing the coupling coefficient in the central portion and changing the pitch in the peripheral portion so as to be separated from the matching state and lowering the coupling coefficient.

Alternatively, the shape (rectangle, triangular wave, sine wave, etc.) of the diffraction grating may be controlled so that the coupling coefficient in the central diffraction grating is larger than that in the peripheral diffraction grating. For example, the shape of the diffraction grating may be rectangular at the center and a sine wave at the periphery, or the shape of the diffraction grating may be rectangular at the center and triangular at the periphery. The diffraction grating shape may be controlled by appropriately controlling the selection ratio during etching.

To put this more generally, increasing the coupling coefficient in the central part is such that the second-order component in the Fourier series expansion of the shape of the diffraction grating is larger in the central part than in the peripheral part. Do by controlling.

[0043]

As described above, according to the optical semiconductor device of the present invention, since it has the above-mentioned structure, the wavelength tunable width is wide in a single mode, the frequency modulation characteristic is excellent, and the degree of design freedom is large and the reproducibility is large. It is possible to provide a tunable laser and a tunable filter having good characteristics. Thereby, it is possible to construct a high-density wavelength division multiplexing optical transmission network.

[Brief description of drawings]

FIG. 1 is a perspective view of a wavelength tunable laser that is a first embodiment according to the present invention.

FIG. 2 is a diagram showing a manufacturing method according to the first embodiment of the present invention.

FIG. 3 is a perspective view of a first embodiment according to the present invention without a λ / 4 shift.

FIG. 4 is a sectional view of a wavelength tunable laser which is a second embodiment according to the present invention.

FIG. 5 is a diagram showing a manufacturing method according to the second embodiment of the present invention.

FIG. 6 is a sectional view of a wavelength tunable laser which is a third embodiment according to the present invention.

FIG. 7 is a diagram showing a manufacturing method according to the third embodiment of the present invention.

FIG. 8 is a sectional view of a wavelength tunable laser which is a fourth embodiment according to the present invention.

FIG. 9 is a diagram illustrating the principle of a wavelength tunable laser according to the present invention.

FIG. 10 is a diagram showing a configuration example of a node using the device according to the present invention.

11 is a diagram showing a configuration example of an optical transmission network using the node of FIG.

FIG. 12 is a sectional view of a conventional example of a wavelength tunable laser.

[Explanation of symbols]

 1 n-InP substrate 2 n-InP clad layer 3 n-InGaAsP guide layer 4 MQW active layer 5 p-InP clad layer 6 p-InGaAsP cap layer 7,37 p electrode 8,38 n electrode 9 second-order diffraction grating 10, 10a, 10b 1st-order diffraction grating 11 λ / 4 shift part 12 High resistance InP burying layer 20 Resist AZ1350J 21, 41 Resist OMR87 28 Diffraction grating close to active layer 29 Diffraction grating 30 far from active layer 30 n-GaAs substrate 31 n-AlGaAs Cladding layer 32 MQW active layer 33 p-AlGaAs carrier confinement layer 34 p-AlGaAs optical guide layer 35 p-AlGaAs cladding layer 36 p-GaAs cap layer 50 optical fiber 51 branching portion 52 wavelength tunable filter 53 photoreceiver 54 wavelength tunable laser 55 Light modulator 6 node 140 n-InP substrate 141 the diffraction grating 142 n-InGaAsP optical guide layer 143 MQW active layer 144 lambda / 4 shift portion

Claims (17)

[Claims] 1. An optical semiconductor device having a waveguide structure for guiding light, comprising an active layer having a gain medium and an optical guide layer provided with a diffraction grating for performing distributed feedback coupling of the guided light, the optical semiconductor device comprising: A compound semiconductor device, characterized in that the coupling coefficient between a grating and guided light is distributed in the waveguide direction, and is made larger in the central portion than in the peripheral portion for inputting / outputting the device. 2. The compound semiconductor device according to claim 1, wherein the central diffraction grating is provided with a λ / 4 phase shift. 3. Increasing the coupling coefficient in the central portion is determined by the wavelength λ of the guided light, the effective refractive index n of the waveguide layer, and the pitch Λ of the diffraction grating. The compound semiconductor device according to claim 1, wherein the order m (= 2nΛ / λ) is set to be lower in the central portion than in the peripheral portion. 4. The compound semiconductor device according to claim 3, wherein the diffraction grating in the central portion has a first order and the peripheral portion has a second order. 5. Increasing the coupling coefficient in the central portion is determined with respect to the wavelength λ of guided light (= 2nΛ / m, where n is the effective refractive index of the waveguide layer and m is the order of the diffraction grating). The pitch Λ of the diffraction grating is adjusted by increasing the coupling coefficient in the central portion and increasing the coupling coefficient in the peripheral portion, and by changing the pitch Λ away from the matching state to lower the coupling coefficient.
The compound semiconductor device described. 6. The compound according to claim 1, wherein increasing the coupling coefficient in the central portion is performed by bringing the central diffraction grating closer to the active layer than the peripheral diffraction grating. Semiconductor device. 7. The compound semiconductor device according to claim 6, wherein the diffraction grating in the central portion has a first order and the peripheral portion has a second order. 8. The shape of the diffraction grating (rectangular wave, triangular wave, sine wave, etc.) is such that increasing the coupling coefficient in the central portion makes the coupling coefficient larger in the central diffraction grating than in the peripheral diffraction grating. 2. The compound semiconductor device according to claim 1, which is performed by controlling 9. The shape of the diffraction grating is rectangular at the center,
9. The compound semiconductor device according to claim 8, wherein a sine wave is generated in the peripheral portion. 10. The compound semiconductor device according to claim 8, wherein the diffraction grating has a rectangular shape in the central portion and a triangular wave in the peripheral portion. 11. Increasing the coupling coefficient in the central portion is performed by controlling the second-order component in the Fourier series expansion of the shape of the diffraction grating to be larger in the central portion than in the peripheral portion. The compound semiconductor device according to claim 1, which is characterized in that. 12. The compound according to claim 1, wherein the compound is configured so that current can be independently injected into at least three portions along the traveling direction of light, and the compound can function as a distributed feedback laser and a filter. Semiconductor device. 13. An optical semiconductor device having a waveguide structure for guiding light, comprising an active layer having a gain medium and an optical guide layer having a diffraction grating for distributed feedback coupling of the guided light, In the method of manufacturing a compound semiconductor device, wherein the coupling coefficient between the diffraction grating and the guided light is distributed in the waveguide direction and is made larger in the central portion than in the peripheral portion for inputting and outputting the device, the order of the diffraction grating in the central portion Is the first order, the order of the peripheral portion is the second order, and the step of forming the diffraction grating in the light guide layer includes the first step of forming the second order diffraction grating and the second order diffraction grating on the second order diffraction grating. The second step is to apply the resist evenly, the third step is to cover only the part where the first-order diffraction grating is to be covered with another resist, and the resist and the exposed crystal plane are etched by dry etching. Half the pitch of the second-order diffraction grating A method of manufacturing a compound semiconductor device, which comprises a fourth step of manufacturing a first-order diffraction grating. 14. An optical semiconductor device having a waveguide structure for guiding light, comprising an active layer having a gain medium, and an optical guide layer having a diffraction grating for distributed feedback coupling of the guided light, In the method of manufacturing a compound semiconductor device, wherein the coupling coefficient between the diffraction grating and the guided light is distributed in the waveguide direction and is made larger in the central portion than in the peripheral portion for inputting and outputting the device, the order of the diffraction grating in the central portion Is the first order, the order of the peripheral portion is the second order, and the step of forming the diffraction grating in the light guide layer includes the first step of forming the second order diffraction grating and the second order diffraction grating on the second order diffraction grating. The second step of applying the resist evenly, the third step of covering with the resist leaving only the portion where the first-order diffraction grating is formed, and the step of etching the resist and the exposed crystal face by dry etching Of half the pitch of the next grating The fourth step of forming the first-order diffraction grating, the fifth step of removing only the resist in the portion where the first-order diffraction grating is formed by dry etching, and the selective etching of only the portion where the first-order diffraction grating is formed And a sixth step of bringing only the portion of the first-order diffraction grating closer to the active layer. 15. An optical semiconductor device having a waveguide structure for guiding light, comprising an active layer having a gain medium and an optical guide layer having a diffraction grating for performing distributed feedback coupling of the guided light, In the method of manufacturing a compound semiconductor device, wherein the coupling coefficient between the diffraction grating and the guided light is distributed in the waveguide direction and the central part is larger than the peripheral part for inputting and outputting the device, a diffraction grating is provided in the light guide layer. The process of forming, the process of covering only one of the central diffraction grating and the peripheral diffraction grating with a resist, and the selective etching of only the other of the central diffraction grating and the peripheral diffraction grating And a step of bringing only the part of the diffraction grating of the part closer to the active layer. 16. An optical-electrical conversion device comprising the distributed feedback laser and the filter according to claim 12 for the purpose of transmitting and receiving an optical signal. 17. A wavelength division multiplex transmission system comprising the optical-electrical conversion device according to claim 16.