JP2000162654A - Polarization-independent optical semiconductor device - Google Patents

Abstract

(57) [Summary] A polarization-independent optical semiconductor device includes: a single pump light and a single signal light;
Only two polarization-independent converted lights are generated. A directional coupler (1), a gain waveguide (2) having two mutually orthogonal linearly polarized lights as effective eigenpropagation modes and not constituting an optical resonator, and an (n + 1/4) wavelength plate for two linearly polarized lights. 3 and the reflecting mirror 4
Pump light 5 composed of continuous wave laser light containing two linearly polarized light components equally divided from one of the input waveguides of the directional coupler 1 while being arranged in series along the optical axis, and A signal light 6 having a wavelength different from that of the pump light 5 is incident from one of the input waveguides of the sexual coupler 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization-independent optical semiconductor device, and more particularly, to a simple polarization-independent wavelength conversion element or a polarization-independent dispersion compensation element used in an optical communication system. The present invention relates to a polarization independent optical semiconductor device having a characteristic optical input / output configuration.

[0002]

2. Description of the Related Art Optical fiber communication has been widely used for trunk line communication since a large amount of information can be transmitted by one optical fiber, but recently, multimedia information has been provided to ordinary households. FTTH (Fiber to
the Home: Pull the optical fiber to the general home,
Attempts to provide large-capacity information such as images) have been proposed and are becoming practical.

Most optical semiconductor devices, such as semiconductor lasers used in optical communication systems currently in practical use, have polarization dependence, whereas optical fibers for transmitting signal light are: Since it is not designed to preserve the polarization information of the propagating light, a specific polarized light cannot be expected after transmission.

In a wavelength division multiplexing communication system which is regarded as a next generation communication means, a wavelength conversion system having a large conversion band is indispensable, but light propagating in an optical fiber has a waveform distorted by chromatic dispersion. Therefore, a system for compensating for this dispersion is indispensable for large-capacity long-distance transmission. Therefore, in a wavelength division multiplex communication system, a wavelength converter and a dispersion compensator that do not depend on the polarization state of input light are required.

That is, since the light propagating through the optical fiber has a different propagation speed depending on the wavelength, the waveform, that is, the light pulse width or the like changes. Change in a direction that offsets the change,
By propagating the optical pulse changed by the wavelength conversion through the optical fiber once again, the optical pulse waveform can be returned to the original state, whereby the wavelength converter functions as a dispersion compensator.

Conventionally, in order to realize such a polarization independent type wavelength conversion, a pump composed of two CW lights (continuous oscillation laser lights) having mutually orthogonal polarization planes and different wavelengths is provided to a semiconductor optical amplifier. It has been proposed to realize polarization independence by introducing light and injecting signal light having a wavelength different from these wavelengths into the semiconductor optical amplifier. This principle will be described with reference to FIG. I do.

FIG. 6A shows two pumps incident on a semiconductor optical amplifier.
Light P₁, P_TwoFIG. 7 is a diagram showing the wavelength and relative intensity of the signal light S.
Yes, for example, pump light P₁The wavelength λ_P1TE (Tra
nsverse Electric) polarized light and pump
Light P_TwoThe wavelength λ _P2TM (Transverse Ma)
g) and the wavelength of the signal light S is λ._SToss
You.

Referring to FIG. 6B, FIG. 6B shows converted light of three phase conjugate waves output when two pump lights P ₁ and P ₂ and a signal light S enter a semiconductor optical amplifier. This shows the relationship between the wavelengths of C ₁ , C ₂ , and C ₃ . The two pump lights P ₁ , P ₂ and the remainder of the signal light S that did not contribute to the generation of the phase conjugate light due to the nonlinear interaction are also output.

In this case, the converted light C due to the nonlinear interaction (four-wave mixing) between the two pump lights P ₁ and P ₂ and the signal light S.
₁ , C ₂ , C ₃ , that is, the emission intensity of the phase conjugate light is the intensity of the signal light S, the intensity of the same polarization component as the signal light S among the pump lights P ₁ and P ₂ , and the intensity of the converted light. It will be determined by the linear gain you feel.

The converted light C ₁ is generated by the interaction between the pump light P ₁ and the signal light S, and its angular frequency ω _C1 (=
2πc / λ _C1 : c is the speed of light) is ω _C1 = 2ω _P1 −ω _S , and the converted light C ₂ is generated by the interaction between the pump light P ₂ and the signal light S, and the angular frequency ω _C2 is ω _C2 = 2ω _P2 −ω _S

On the other hand, the converted light C_ThreeIs two pump lights
P₁, P_TwoAnd the signal light S,
Angular frequency ω_C3Is ω_C3= Ω_P1+ Ω_P2−ω_S And this converted light C_ThreeOnly polarization-independent converted light
The converted light C _ThreeSelectively retrieve only
A polarization independent wavelength conversion mechanism
Yes (if necessary, IEEE Photon. Let
t. , Vol. 10, pp. 352, 1998).

[0012]

However, conventional polarization-free
In dependent wavelength conversion systems, orthogonal polarizations
Two pump lights P having a wavefront₁, P_TwoAnd the city of signal light S
A system that introduces three lights is required.
, The converted light C having three different wavelengths₁, C _Two, C
_ThreeIs formed, and the converted light C_ThreeOnly have polarization independence
Therefore, this converted light C_ThreeOnly to take out the system
6 light wavelengths will be handled for convenience.
Has a problem that complicated handling is required.

When the wavelengths of the _two pump lights P ₁ and P ₂ are the same, the converted lights C ₁ , C ₂ and C ₃ have ω _C1 =
Since ω _C2 = ω _C3 , the wavelengths become the same. However, in this case, it becomes impossible to separate the converted lights C ₁ and C ₂ having polarization dependence from the converted light C ₃ having no polarization dependency. Problem.

Accordingly, an object of the present invention is to generate only one polarization-independent converted light by using one pump light and one signal light with a simple configuration.

[0015]

FIG. 1 is an explanatory view of the principle configuration of the present invention. Referring to FIG. 1, means for solving the problems in the present invention will be described.

FIG. 1 (1) The present invention relates to a polarization independent optical semiconductor device,
The directional coupler 1, which couples light of different wavelengths, effectively has two mutually orthogonal linearly polarized light as an eigenpropagation mode, and has a gain in at least one of the two linearly polarized light by current injection, and has an optical resonator. Unconfigured gain waveguide 2, (n + ／) for two linear polarizations
A wave plate 3 (where n = 0 or a natural number) and a reflecting mirror 4 are sequentially arranged in series along the optical axis, and two linearly polarized light components from one of the input waveguides of the directional coupler 1 are arranged. And a signal light 6 having a wavelength different from that of the pump light 5 from the other of the input waveguides of the directional coupler 1. .

With such an apparatus configuration, 1
With one pump light 5 and one signal light 6, regardless of the polarization state of the input signal light 6, only one converted light 7 is converted with a constant conversion efficiency independent of the input light polarization regardless of the polarization state of the input signal light 6. Obtainable.

That is, when TE polarized light is incident from the end face of the gain waveguide 2 having two mutually orthogonal linearly polarized lights, ie, TE polarized light and TM polarized light, as effective eigenpropagation modes, the incident light is converted into TE polarized light. The light enters the (n + ／) wave plate 3 while keeping it, and changes its polarization state to circularly polarized light under the action of the (n + ／) wave plate 3. At this time, for example, light emitted from the (n +＋ １) wavelength plate 3 as clockwise circularly polarized light is reflected by the reflecting mirror 4 to become counterclockwise circularly polarized light, and the (n + ／) wavelength plate 3 is moved in the opposite direction. The light is converted into TM polarized light by propagation and enters the gain waveguide 2. Since this TM polarized light is an effective eigenpropagation mode in the gain waveguide 2, it becomes output light from the end face of the gain waveguide 2 while maintaining the polarization state.

The same applies to the case where the TM-polarized light enters from the end face of the gain waveguide 2. Since the TM-polarized light is output this time as TE-polarized light, the light incident on the gain waveguide 2 is independent of the polarization state at the time of incidence. The gain for the TE polarized light and the gain for the TM polarized light in the gain waveguide 2 are felt equally.

Therefore, when the pump light 5 includes the TE polarization component and the TM polarization component equally, the two polarization components have the same gain even when the pump light 5 is emitted back and forth through the gain waveguide 2. As a result, the light is emitted as light containing two polarized components equally. Note that the pump light 5 is 2
In order to include two linearly polarized light components equally, 2
The polarization of the pump light 5 may be adjusted so that the linearly polarized light is inclined by 45 ° with respect to the two linearly polarized lights.

On the other hand, regarding the signal light 6 and the converted light 7,
Although the polarization state at the time of output differs depending on the polarization state of the signal light 6 at the time of incidence, the linear gain perceived as a whole does not depend on the polarization state, so that a conversion efficiency independent of the polarization state of the signal light 6 is obtained, and no polarization is obtained. It becomes a dependent type wavelength converter.

Since the converted light 7 is a so-called phase conjugate wave, the angular frequency ω _c (= 2πc / λ _C ) of the pump light 5 is ω _P , and the angular frequency of the signal light 6 is ω _S Ω _c = 2ω _P −ω _S , so that the wavelength λ _S of the signal light 6 becomes the wavelength λ _S of the pump light 5.
_{When the} wavelength is shorter than _P, the wavelength λ _C of the converted light 7 is
The wavelength becomes longer than the wavelength λ _S of the signal light 6, and conversely,
In the case of the wavelength lambda _S is a longer wavelength than the wavelength lambda _P of the pump light 5, the wavelength lambda _C of the converted light 7, since the shorter wavelength than the wavelength lambda _S of the signal light 6, the wavelength dependence of the propagation velocity Can be used as a polarization independent dispersion compensator for compensating for changes in the optical pulse waveform caused by the above.

(2) In the present invention, in the above (1), the (n +＋ １) wavelength plate 3 is arranged so that the crystal orientation is inclined by 45 ° with respect to the semiconductor crystal forming the gain waveguide 2. A semiconductor optical waveguide is used.

As described above, the semiconductor optical waveguide arranged so that the crystal orientation is inclined by 45 ° with respect to the semiconductor crystal forming the gain waveguide 2 can be used as the (n + ／) wavelength plate 3. Note that the length L of the semiconductor optical waveguide in this case is
_W is λ is the wavelength of light in a vacuum, n ₁ and n ₂ are the effective refractive indexes of two eigenpropagation modes, and Δn = n ₁ −n ₂
In this case, it is necessary to set L = (n + ／) λ / Δn.

(3) Further, according to the present invention, in the above (2), the semiconductor optical waveguide arranged so that the crystal orientation is inclined by 45 ° with respect to the semiconductor crystal forming the gain waveguide 2 is formed by using a step substrate. It is characterized by comprising.

As described above, the semiconductor optical waveguide acting as the (n + ／) wavelength plate 3 is a step substrate, that is, TS (T
The substrate can be easily formed by using an erased substrate.

(4) In the present invention, in the above (1), as the (n + ／) wavelength plate 3, a diffraction grating having asymmetry in a direction perpendicular to the waveguide direction is periodically arranged. It is characterized by using an optical waveguide.

As described above, an optical waveguide in which diffraction gratings having asymmetry in a direction perpendicular to the waveguide direction are periodically arranged may be used as the (n + ／) wavelength plate 3. In this case, the length L _c of the diffraction grating is set such that λ is the wavelength of light in a vacuum, and n ₁ and n ₂ are two eigenpropagation modes in order to provide constructive coherence between the diffraction gratings. L = λ / Δn where Δn = n ₁ −n ₂
Need to be

(5) The present invention is characterized in that, in any one of the above (1) to (4), the directional coupler 1 is constituted by a semiconductor optical waveguide structure.

As described above, the directional coupler 1 may be constituted by a semiconductor optical waveguide structure. In particular, when the entire device is integrated, or the directional coupler 1 itself has a gain. This is necessary in the case, and by giving the directional coupler 1 itself a gain, it is possible to prevent attenuation when propagating through the directional coupler 1.

(6) Further, according to the present invention, in any one of the above (1) to (5), at least the directional coupler 1, the gain waveguide 2, and the (n + ／) wavelength plate 3
It is characterized in that it is formed monolithically on the same semiconductor substrate.

As described above, since the directional coupler 1, the gain waveguide 2, and the (n + ／) wavelength plate 3 are monolithically formed on the same semiconductor substrate, the overall configuration can be extremely reduced in size. And the optical axis alignment step is not required.

(7) The present invention is characterized in that, in the above (6), the reflecting mirror 4 is monolithically integrated on the same semiconductor substrate by forming the reflecting mirror 4 by a distributed Bragg reflector. I do.

As described above, by making the reflecting mirror 4 a distributed Bragg reflector (DBR), the entire device can be monolithically integrated, and the step of depositing a multilayer reflective film becomes unnecessary.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, referring to FIGS. 2 and 3, a gain waveguide section and a (n + ／) λ plate section, which are main parts of a first embodiment of the present invention, will be described. The manufacturing process will be described. First, a part of the n-type InP substrate 11 is selectively removed to form a step substrate (TS substrate) having a terrace 12.

Next, as shown in FIG. 2 (b), the n-type InP cladding layer 13 and the PL wavelength composition were set to 1.2 by MOVPE (metal organic chemical vapor deposition).
3 μm n-type InGaAsP light guide layer, PL wavelength composition 1.46 μm i-type InGaAsP core layer, and PL
An optical waveguide layer 14 made of a p-type InGaAsPSCH layer having a wavelength composition of 1.15 μm and a p-type InP clad layer 15 are sequentially epitaxially grown. In this case, the crystal growth direction of the optical waveguide layer 14 at the edge of the terrace 12, that is, at the stepped portion, is about 4 ° away from the main surface of the n-type InP substrate 11.
The state is inclined by 5 °.

Next, referring to FIG. 2C, the p-type InP clad layer 15 to the n-type InP clad layer 12 deposited in the region where the terrace 12 was not formed are selectively used by using an SiO ₂ mask (not shown) as a mask. To form a gain waveguide section.

Next, referring to FIG. 3D, using the SiO ₂ mask as a selective growth mask, an n-type InP is formed on the removed portion 16 by MOVPE.
Cladding layer 17, n-type I having PL wavelength composition of 1.23 μm
nGaAsP light guide layer, PL wavelength composition is 1.55 μm
I-type InGaAsP core layer having a PL wavelength composition of 1.
A gain waveguide layer 18 made of a 15 μm p-type InGaAsPSCH layer and a p-type InP clad layer 19 are sequentially epitaxially grown.

Next, after removing the SiO ₂ mask, a new mask is used to perform mesa etching in a stripe shape, thereby forming the (n + ／) λ plate portion 20 in the stripe shape and the stripe shape. By forming the gain waveguide section 21, the basic configuration of the main part of the present invention is completed. In order to make the gain waveguide section 21 function as a gain waveguide, p-type In
A p-side electrode is provided on the surface of the P clad layer 19,
It is necessary to form an n-side electrode on the back surface of the n-type InP substrate 11 and perform current injection.

In this case, the optical waveguide layer 14 of the (n + ／) λ plate portion 20 and the gain waveguide 18 of the gain waveguide portion 21 have a butt joint structure. And the main crystal axis of the gain waveguide layer 18 are inclined by about 45 ° with respect to each other, so that the (n + ／) λ plate portion 20
The length L of the optical waveguide layer 14 in the optical axis direction is
4, when the effective refractive indices of TE polarized light and TM polarized light having a wavelength λ are n _TE and n _TM , and the difference is Δn, L = (n + ／) λ / Δn (where n = 0 or a natural number) Is satisfied, the optical waveguide layer 14
Effectively acts as an (n + ／) λ plate.

Next, the overall structure of the polarization-independent optical semiconductor device according to the first embodiment of the present invention will be described with reference to FIG. FIG. 4 is a schematic perspective view of a polarization-independent optical semiconductor device according to the first embodiment of the present invention, in which a removing portion 16 is formed as shown in FIGS. After that, n
-Type InP cladding layer 17, gain waveguide layer 18, and p
When the type InP cladding layer 19 is grown, it is grown over a wide area, and when the (n + ／) λ plate portion 20 and the gain waveguide portion 21 are formed by mesa etching, a mask for forming the gain waveguide portion 21 is formed. By using a mask formed of a forked-branch type fork-like pattern connected to the substrate, a multilayer structure including the n-type InP cladding layer 17, the gain waveguide layer 18, and the p-type InP cladding layer 19 is collectively etched. The directional coupler 24 is also formed monolithically at the same time. In this case, in order to form a reflecting mirror, a multilayer reflective film 22 made of a dielectric material is coated on the exposed end face of the (n + ／) λ plate portion 20 to have a high reflectance.

Also, since the gain waveguide section 21 is a slab type optical waveguide, the TE polarized light and the TM polarized light are made to be effective eigen propagation modes, so that the polarization states of the TE polarized light and the TM polarized light are well preserved. That is, by providing an electrode 23 for injecting a current in the gain waveguide section 21 and injecting the current, the gain is provided in at least either the TE polarized light or the TM polarized light. Note that the gain waveguide section 2
Since both end faces of 1 are crystallinely continuous with the (n + ／) λ plate section 20 and the directional coupler section 24, they become non-reflection end faces and do not constitute an optical resonator.

The operation of the polarization independent optical semiconductor device will be described.
Pump light (angular frequency ω _P ) whose polarization plane is controlled so that the polarization component and the TM polarization component are linearly polarized at 45 ° to the TE polarization and the TM polarization so that the polarization component and the TM polarization component are equal to each other is incident. When signal light (angular frequency ω _s ) is incident from the other port of the sexual coupler unit 24, the gain waveguide unit 21
At ω _C , the angular frequency ω _C becomes ω _C = 2ω due to four-wave mixing.
Phase conjugate wave _P - [omega] _S is obtained as converted light.

In this case, the TE-polarized light component of the pump light stays TE-polarized (n +
１ ／) enters the λ plate portion 20 where the polarization state is changed to, for example, clockwise circularly polarized light, and then the multilayer reflective film 2
The light is reflected at 2 and becomes counterclockwise circularly polarized light, and is (n +＋ １).
By propagating through the λ plate section 20 in the opposite direction, it is converted into TM polarized light, enters the gain waveguide section 21, and is emitted from the directional coupler section 24 while maintaining the polarization state.

The same applies to the case of the TM polarization component.
Since the light is output as polarized light, regardless of the polarization state when the light enters the directional coupler 24, the gain waveguide 2
Since the gain for the TE polarized light and the gain for the TM polarized light at 1 will be felt equally, the two polarization components,
That is, the light is emitted as light containing the TE polarization component and the TM polarization component equally.

On the other hand, for the signal light and the converted light, the polarization state at the time of output differs depending on the polarization state at the time of incidence of the signal light, but the linear gain perceived as a whole while reciprocating through the gain waveguide section 21 is changed to the polarization state. Because it does not depend on the polarization state of the signal light, converted light having an intensity that does not depend on the polarization state of the signal light can be obtained.

Also, since this converted light is a phase conjugate wave, a polarization-independent type that compensates for a change in waveform caused by the wavelength dependence of the propagation speed when propagating through the optical fiber as described above. It can be used as a dispersion compensator.

As described above, in the first embodiment of the present invention, one pump light and one signal light are nonlinearly interacted with each other by a simple configuration, so that the polarization depends on the polarization of one signal light. It is possible to output only the converted light which is not used, and therefore, only three wavelengths are handled, so that the handling is simplified.

Also, in the first embodiment of the present invention, the entire structure is monolithically made of a semiconductor except for the reflector, that is, the multilayer dielectric film, so that the whole structure is simplified and the size is small. In addition to this, there is an advantage that a process such as optical axis alignment becomes unnecessary as compared with the case of the hybrid configuration.

Next, a second embodiment of the present invention will be described with reference to FIG. 5. In this second embodiment, an optical waveguide having a TS structure is used as an (n + ／) λ plate portion. Since a diffraction grating having asymmetry with respect to the waveguide direction is used instead of the waveguide, only the configuration of the (n + ／) λ plate portion will be described. FIG. 5 is a conceptual configuration diagram of a diffraction grating element constituting the (n + ／) λ plate portion.
5A is a plan view of a portion provided with a diffraction grating element, and FIG. 5B is a cross-sectional view taken along a dashed-dotted line connecting AA ′ in FIG. FIG. 6 is a cross-sectional view taken along a dashed line connecting BB ′ in FIG.

5 (a) to 5 (c). As shown in FIG. 5, after growing an n-type InP cladding layer 13 on an n-type InP substrate 11, a diffraction grating of length L composed of periodic irregularities 25 is formed. in forming the element 26, the guiding direction indicated by the arrow, i.e., depth t ₁ becomes in a-a 'as depth becomes asymmetrical in the vertical direction with respect to the optical axis, B
Formed such that the depth t ₂ in -B '. In this case, the length L of the diffraction grating element 26 is, with respect to the effective refractive index of the TE mode and the TM mode n _TE and n _TM , with respect to the wavelength λ of the light propagating in the optical waveguide in vacuum. Therefore, it is necessary to set the relation of L = λ / (n _TE −n _TM ).

The present inventor has already proposed a specific method of manufacturing the diffraction grating element 26 having such an asymmetric structure (if necessary, Japanese Patent Application No. 9-261640).
This asymmetry has periodic irregularities 2
5 is not the depth t ₁ , t ₂ , but the ratio of the width w ₁ of the concave portion of the periodic unevenness 25 to the width of the convex portion w ₂ , that is, w ₁ / w ₂ is A−
It may be changed between A 'and BB'.

From one end face of such a diffraction grating element 26, the eigenmode T in the symmetric slab waveguide is obtained.
When the polarized light of the E mode is incident, the intensity of the Bragg reflected lights 27 and 28 becomes asymmetric in AA 'and BB' and shows an asymmetric reflectivity distribution. The part is converted to the TM mode, and conversely, when the TM polarized light is incident, the part is converted to the TE mode, so that it operates in the same manner as the (n + ／) λ plate part.

The embodiments of the present invention have been described above. However, the present invention is not limited to the configurations described in the embodiments, and various modifications are possible. For example, in the description of the above-described embodiment, the current is injected only into the gain waveguide section 21. However, an electrode may be provided in the directional coupler section 24 so that the current is injected to have a gain. The directional coupler unit 24 is good because it has a gain.
Can prevent absorption loss.

In the description of the above embodiment, the semiconductor optical waveguide structure forming the directional coupler section 24 has the same configuration as the semiconductor optical waveguide structure of the gain waveguide section 21, but has a different configuration. Is also good,
In particular, when the directional coupler section 24 does not have gain, an optical waveguide layer made of a semiconductor having a wider bandgap than the gain waveguide layer 18 forming the gain waveguide section 21 in order to reduce absorption loss. It is desirable to use

In the above embodiment, the reflecting mirror is constituted by the multilayer reflecting film 22.
May be replaced by a distributed Bragg reflector (DBR). In this case, the (n + ／) λ plate portion 2
The semiconductor optical waveguide structure is formed on the emission end side of the optical waveguide having the TS structure constituting the optical waveguide structure 0, and a diffraction grating is provided on at least one of the cladding layer, the optical guide layer, and the optical waveguide layer which constitute the semiconductor optical waveguide structure. Just do it.

In the above embodiment, each element is monolithically integrated. However, each element may be formed discretely and the whole may be hybridized. In this case, the gain waveguide It is necessary to coat both end faces of the gain waveguide with anti-reflection so that the optical waveguide does not constitute an optical resonator.

In the case of a hybrid configuration,
The (n + ／) λ plate may be a normal engineering λ / 4 plate, and the directional coupler may be a dielectric directional coupler.

In the above embodiment, the directional coupler is described as a tuning fork-shaped bifurcated directional coupler. However, the present invention is not limited to such a shape. Directional coupler may be used. In short, 2:
Any type of directional coupler may be used.

In the above embodiment, the gain waveguide layer 18 is constituted by using a bulk i-type InGaAsP core layer, but may be constituted by using an MQW (multiple quantum well) structure. For example, a non-doped InGaAsP well layer having a compression strain of 1% at 6 nm and a thickness of, for example, 10 nm and a PL wavelength of 1.1 μm.
An MQW gain waveguide layer having an EL wavelength of 1.3 μm may be formed by alternately growing non-doped, non-doped InGaAsP barrier layers having m compositions.

In the above embodiment, since long-distance optical communication is assumed, InGaAsP / InP
Although a system is used, other semiconductors such as a GaAs / AlGaAs system may be used instead of the InGaAsP / InP system.

[0062]

According to the present invention, by combining an (n + ／) λ plate and a reflecting mirror with respect to a gain waveguide, one pump light and one signal light make one polarization independent. Polarization-independent type optical semiconductor device can be realized with a simple configuration, thereby achieving polarization-independent wavelength conversion and polarization-independent dispersion compensation. It greatly contributes to the spread and development of optical fiber communication technology.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of the present invention.

FIG. 2 is an explanatory diagram of a manufacturing process of a part of the first embodiment of the present invention in the middle.

FIG. 3 is an explanatory diagram of a manufacturing process of the main part of the first embodiment of the present invention after FIG. 2;

FIG. 4 is an overall configuration diagram of a polarization independent optical semiconductor device according to the first embodiment of the present invention.

FIG. 5 shows (n + ／) λ according to the second embodiment of the present invention.
It is explanatory drawing of a board part.

FIG. 6 is an explanatory diagram of a spectrum in the conventional polarization independent wavelength conversion.

[Explanation of symbols]

 Reference Signs List 1 directional coupler 2 gain waveguide 3 (n + ／) wavelength plate 4 reflector 5 pump light 6 signal light 7 converted light 11 n-type InP substrate 12 terrace 13 n-type InP cladding layer 14 optical waveguide layer 15 p-type InP Cladding layer 16 Removal part 17 n-type InP cladding layer 18 Gain waveguide layer 19 p-type InP cladding layer 20 (n + ／) λ plate part 21 Gain waveguide part 22 Multilayer reflection film 23 Electrode 24 Directional coupler part 25 Period 26 Irregularity 26 Diffraction grating element 27 Bragg reflected light 28 Bragg reflected light

Claims (7)

[Claims] 1. A directional coupler that couples light of different wavelengths, has two mutually orthogonal linearly polarized lights as effective eigenpropagation modes, and has a gain in at least one of at least two linearly polarized lights by current injection. A gain waveguide that does not constitute an optical resonator, a (n + ／) wavelength plate (where n = 0 or a natural number) for the two linearly polarized lights,
And a pump light composed of a continuous wave laser beam including a reflecting mirror arranged in series along the optical axis in order and equally dividing the two linearly polarized light components from one of the input waveguides of the directional coupler. And a signal light having a wavelength different from that of the pump light is made to enter from the other input waveguide of the directional coupler. 2. The semiconductor optical waveguide according to claim 1, wherein the (n + ／) wavelength plate is a semiconductor optical waveguide arranged such that the crystal orientation is inclined by 45 ° with respect to a semiconductor crystal forming the gain waveguide. Item 2. A polarization independent optical semiconductor device according to item 1. 3. The semiconductor optical waveguide according to claim 2, wherein the semiconductor optical waveguide arranged so that the crystal orientation is inclined by 45 ° with respect to the semiconductor crystal forming the gain waveguide is formed using a stepped substrate. Polarization independent optical semiconductor device. 4. An optical waveguide in which a diffraction grating having asymmetry in a direction perpendicular to a waveguide direction is periodically arranged as the (n + ／) wavelength plate. A polarization independent optical semiconductor device as described in the above. 5. The polarization-independent optical semiconductor device according to claim 1, wherein the directional coupler is constituted by a semiconductor optical waveguide structure. 6. The semiconductor device according to claim 1, wherein at least the directional coupler, the gain waveguide, and the (n + ／) wavelength plate are monolithically formed on the same semiconductor substrate. A polarization independent optical semiconductor device according to any one of the preceding claims. 7. The polarization-independent optical semiconductor according to claim 6, wherein said reflecting mirror is constituted by a distributed Bragg reflector, so that the reflecting mirror is also monolithically integrated on the same semiconductor substrate. apparatus.