JPH06180405A - Semiconductor optical element and te/tm phase matching optical waveguide element formed by using strain super lattice - Google Patents

Abstract

PURPOSE:To provide the waveguide type semiconductor optical element suitable for integration and the optical waveguide element which realizes the perfect mode conversion between a TE wave/TM wave by using a strain super lattice. CONSTITUTION:This semiconductor optical element is constituted of a semiconductor optical element part 10 having an optical waveguide 6a inclined with a substrate 2 surface, an optical element part 12 having an optical waveguide 6c horizontal with the substrate 2 surface and a juncture which has the optical waveguide 6b changing continuously in the inclination with the substrate 2 surface from 45 deg. to 0 deg. and smoothly connect the two optical waveguides 6a, 6c. The lattice constant of the well layer of the optical waveguide for which the structure of the semiconductor strain super lattice is used is made smaller than that of a barrier layer. An intra-surface tensile stress is applied to the optical waveguide to make the base level of light holes stabler than that of heavy holes. The optical transition probability between the light holes and the base level of the transmission band atoms is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type semiconductor optical device which operates stably against the influence of return light, and an optical integrated circuit used for optical communication, optical information processing, optical measuring equipment and the like. The present invention relates to an optical waveguide device in which phase matching between a wave and a TM wave is achieved. The optical waveguide element is applied to a reciprocal or non-reciprocal TE / TM mode converter, and in particular, the non-reciprocal mode converter is applied to an optical isolator that blocks return light and does not induce noise.

[0002]

2. Description of the Related Art At present, advanced information technology in society is rapidly developing, and it is required to process a large amount of information at high speed. Under such circumstances, information processing technology using light for communication and recording has been widely used because of its characteristics such as high speed and large capacity. Among the information processing technology using the light, the semiconductor laser is widely used as a light source for optical communication and optical disks,
It is now an indispensable device. But,
Since this semiconductor laser is essentially an optical oscillator,
There is a problem that it is weak against return light and causes unstable operation and increase in noise when the light emitted from itself returns.

Further, since the semiconductor optical amplifier amplifies an optical signal without converting it into an electric signal, it can suppress the deterioration of the signal and is an important device in optical communication. On the other hand, there was a problem that it was weak and noise increased. An optical isolator is generally used as a measure for returning light to the semiconductor laser and the semiconductor optical amplifier. This optical isolator functions as a diode in light, has a function of allowing light to pass through in only one direction, and conventionally is generally constituted by utilizing a magneto-optical effect.

This optical isolator is roughly classified into 1. Bulk type isolator 2. There is a guided wave isolator. 1. The bulk type isolator has a simple structure and has no particular problem in terms of performance, and has already been put to practical use, but it is considerably larger than a semiconductor laser and is not suitable for integration. Also, 2. Is a waveguide type isolator, but the output from the isolator is
Alternatively, a structure having a non-reciprocal portion and a reciprocal portion has been proposed in order to make TM polarized light. However, various methods such as a method of forming the non-reciprocal portion and the reciprocal portion, an epitaxial growth technique, and the like have been proposed. Currently, there are technical difficulties and it is far from practical use.

By the way, since many integrated optical circuits have waveguide type devices, it is advantageous for a semiconductor optical device considering integration that the output light is a TE mode or a TM mode (generally, TE mode). Further, as described above, the semiconductor laser, the semiconductor optical amplifier, and the like are weak against the return light, and an optical isolator is used as a countermeasure against this. A conceptual diagram of the optical isolator is shown in FIG. Light incident on the optical isolator becomes linearly polarized by the light source side polarizer,
The non-reciprocal portion (generally, a Faraday rotator utilizing the magneto-optical effect is used) is rotated by 45 °, and the light is emitted through the polarizer on the output side. The returned light passes through the output side polarizer and is rotated by 45 ° in the same direction at the non-reciprocal part, and because the polarization plane is rotated by 90 ° from when it was incident, it cannot pass through the light source side polarizer and reaches the light source. There is no return. Since the waveguide type device is usually TE polarized light, it is desirable that both the light source side and the output side be TE polarized light. However, as seen in FIG. 8, the polarization states on the light source side and the output side are inclined by 45 °.

Therefore, as the waveguide type isolator, there has been proposed a structure in which the reciprocal portion is used after the non-reciprocal portion to rotate in the opposite direction to the non-reciprocal portion so that the light source side has the same polarization state. (FIG. 9). In FIG. 9, 96 and 98 are TE
It is a vapor-deposited metal film having a structure in which a metal film is loaded on an optical waveguide which is a mode pass filter or a TE selection unit. Reference numeral 100 denotes a non-reciprocal mode conversion waveguide or a non-reciprocal portion, which is formed of a magneto-optical crystal having a Faraday effect (having a magnetic moment M in the light traveling direction), an incident light 94 and a return light 108.
The polarization planes of are rotated non-reciprocally by 45 degrees. 102
Is a reciprocal mode conversion waveguide or a reciprocal part, and is a magneto-optical crystal having the Cotton-Mouton effect or Voigt effect (in the plane perpendicular to the light traveling direction, the direction perpendicular to the waveguide and θ _m
With a magnetic moment M in the direction
The polarization planes of the incident light 94 and the return light 108 are rotated by 45 degrees in opposite directions. These elements are applied to the magneto-optical thin film on the substrate 92 from the light incident side, the TE mode pass filter 96, the nonreciprocal mode conversion waveguide 100, and the reciprocal mode conversion waveguide 10.
2. The TE mode pass filter 98 is arranged in this order to form an integrated optical isolator. The incident light 94 becomes TE-mode guided light by the filter 96, and the polarization directions of the non-reciprocal mode conversion waveguide 100 and the reciprocal mode conversion waveguide 102 are opposite to each other.
After passing through 0 and 102, it becomes TE mode again, and passes through the filter 98 to become emitted light 106. On the other hand, in the return light 108, the rotation of the polarization plane by the nonreciprocal mode conversion waveguide 100 and the reciprocal mode conversion waveguide 102 is in the forward direction, and therefore, after passing through these waveguides 100 and 102, TM
Mode and blocked by filter 96.

However, the reciprocal portion 102 and the non-reciprocal portion 100 are usually different in the material used and the magnetic field application direction, and it is technically very difficult to make them in the same region, and they have been realized. Absent. A semiconductor laser integrated with an isolator for only the non-reciprocal portion has been proposed, but since the incident light is incident in the TE mode from the semiconductor laser, the emitted light is inclined at 45 ° with respect to the substrate, This is an unsuitable state for integration, and it was necessary to correct the polarization state vertically or horizontally with respect to the substrate by some method.

In recent years, optical systems such as optical fiber communication and optical disk memory have been developed in accordance with the speeding up of information transmission and the large capacity of information recording. Then, compact and low-cost optical integrated devices are being developed by integrating the optical devices used in these systems. One of the important techniques for realizing this integrated device is the TE / TM wave phase matching technique. In particular, the integrated optical isolator, which is a non-reciprocal TE / TM mode converter, is considered to be one of the key devices.

In the following, the description will be limited to the optical isolator. In optical communication systems, there are main-line medium and long distance transmission systems that use wavelengths of 1.3 or 1.5 μm and short-distance transmission systems such as LANs (local area networks) that use the 0.8 μm band. In either case, the light emitted from the semiconductor laser is focused on the end face of the fiber and guided in the fiber. At this time, the light reflected by the end faces of the fiber and other optical components returns to the active layer of the semiconductor laser. As a result, the oscillation of the semiconductor laser becomes unstable, causing power fluctuation and wavelength fluctuation. Especially DB
R (distributed reflection type) lasers and DFB (distributed feedback type) lasers are greatly affected by a single mode becoming multimode. Further, the coherent optical communication, which is attracting attention as a future communication system, only changes the phase without turning ON / OFF the light, and therefore the influence of the returning light is particularly large.

Further, in the optical disk memory, in addition to the reflected light from the optical components, the reflected light from the disk substrate returns to the semiconductor laser to induce the above-mentioned instability and noise. In this wavelength range, a simple optical isolator in which a quarter-wave plate and a polarization beam splitter are combined may be used, but the isolation ratio is only about 20 dB at the maximum. In addition, if the polarization plane of the return light changes, the isolation ratio becomes smaller, so in systems that detect the rotation of the polarization plane of the reflected light from the disk as a signal, such as a magneto-optical disk, The impact is more serious. Therefore, a high frequency signal of several 100 MHz is superposed on the semiconductor laser to oscillate the laser in multiple modes,
Symptomatic treatment is used so that the laser is not affected by the returning light. As described above, the generation of noise due to the returning light increases the error rate of the transmission signal in the optical communication and causes the deterioration of the reproduction signal in the optical disk memory.

The only element that removes the return light to the semiconductor laser is an optical isolator. The optical isolator has an irreversible transmission characteristic and completely blocks the returning light to prevent the returning light from re-incident on the active layer of the semiconductor laser. An optical isolator is an essential component in an optical integrated circuit in which a light emitting element and a light receiving element are formed on the same substrate.

However, the most important problem in the waveguide type optical isolator using the thin film waveguide is the reduction of the mode conversion efficiency due to the difference in the propagation constants of the TE wave and the TM wave. TE
Δβ = 2π / λ · (n _TE −n _TM ) (1), where Δβ is the propagation constant difference between the TM wave and the TM wave, and the mode conversion efficiency R from the TE wave to the TM wave is R = θ ² _F / { It is given as θ ² _F + (Δβ / 2) ² } · sin ² {θ ² _F + (Δβ / 2) ² l} ^1/2 (2). Here, θ _F is the Faraday rotation angle per unit length, and l is the waveguide distance. As is clear from the above equation, it is found that complete mode conversion cannot be realized if there is a propagation constant difference.

The above-mentioned change of polarization is shown in FIG. 16 when a Poincare sphere is used. As the linearly polarized wave (TE wave) represented by the point A is guided, the point M on the longitude 0 °
And the center O of the sphere are circled on the spherical surface with the line connecting them as the central axis.
The angle θ from the equatorial plane to the point M is given by tan θ = θ _F / (Δβ / 2) (3). As is apparent from FIG. 16, as long as Δβ is finite, the linearly polarized wave (TE wave) represented by the point A can be linearly polarized at 45 degrees simply by following the same path no matter how guided. It can be seen that point E on the equator cannot be reached. In order to obtain this 45-degree linearly polarized wave, it is necessary to match the propagation constants of the TE wave and the TM wave so that Δβ becomes zero.

Magnetic garnets and II-VI group magnetic semiconductors, which have been studied as waveguide type isolators, are cubic systems. In a thin film waveguide made of such an isotropic material, due to the shape birefringence, FIG.
As shown in (a) and (b), when the film thickness is finite, TE
Since the refractive index (n _TE ) for waves is larger than that for TM waves (n _TM ), it is difficult to achieve phase matching. Therefore, the waveguide type optical isolator has not been realized.

As described above, in the conventional waveguide type optical isolator using the thin film waveguide, how to compensate the phase mismatch due to the shape birefringence has been the most important issue.

In view of the above, the first object of the present invention is to realize integration in which the structure is simple, strong against return light, stable in operation, and the polarization of the emitted light output is perfect TE or TM mode. An object of the present invention is to provide a suitable waveguide type semiconductor optical device and an optical communication system using the semiconductor optical device.

A second object of the present invention is to solve the above-mentioned problem of phase mismatch due to shape birefringence by using a strained superlattice and realize complete mode conversion between TE wave and TM wave. An object is to provide an optical waveguide device and an optical communication system using the same.

[0018]

In a semiconductor optical device that achieves the first object of the present invention, it is 45 ° with respect to the substrate surface.
A semiconductor optical element section having an inclined optical waveguide, an optical element section having an optical waveguide horizontal to the substrate surface, and an optical element whose inclination with respect to the substrate surface continuously changes from 45 ° to 0 °. It is characterized in that it has a waveguide and a connecting portion that smoothly connects the two optical waveguides inclined at 45 ° to each other, and that the emitted light has a plane of polarization completely vertical or horizontal to the substrate surface. .

According to the first aspect of the present invention, the above-mentioned optical device is obtained by growing the active layer of the semiconductor laser section or the semiconductor optical amplifier section at an angle of 45 ° with respect to the substrate by using surface-selective etching and surface-selective doping. It is possible to configure the isolator part, which is a part, with only the non-reciprocal part, and the emitted light can be TE polarized light or TM polarized light that is completely polarized with respect to the substrate. By using the active layer inclined at 45 ° with respect to the substrate, the polarization state of the light incident on the isolator portion is also the polarization state having an inclination of 45 ° with respect to the substrate, and the polarization state at the non-reciprocal portion of the isolator is 45 °. When it is rotated and emitted, it becomes a perfect TE or TM polarized wave with respect to the substrate. Whether TE or TM depends on the oscillation mode of the semiconductor laser section or the like. If the laser section oscillates in the TE mode (relative to the active layer of the laser), the light emitted from the isolator section is TE. If the laser section oscillates in the TM mode (relative to the substrate) and the TM mode (relative to the active layer of the laser), the mode becomes the TM mode (relative to the substrate). In a normal semiconductor laser, the reflectance at the end face is larger in the TE mode than in the TM mode, and it is common that the semiconductor device oscillates in the TE mode. Since many waveguide devices operate in the TE mode, In the embodiment of the first mode of the present invention, only the TE mode will be described.

To further sum up the first aspect of the present invention,
A first element portion having an optical waveguide extending in a first direction,
It has a second element portion having an optical waveguide extending in a second direction inclined with respect to the first direction and an optical waveguide having an inclination continuously changing from the first direction to the second direction. , A semiconductor optical device comprising a connection portion that smoothly connects the two optical waveguides inclined by 45 ° to each other.

Further, in the optical waveguide device which achieves the second object of the present invention, in the optical waveguide using the semiconductor strained superlattice structure, the lattice constant of the well layer is made smaller than that of the barrier layer, and Refractive index of TM wave by applying internal tensile stress to stabilize the ground level of light holes more than that of heavy holes and increase the optical transition probability between light holes and ground level of conduction band electrons. Is larger than the refractive index of the TE wave, and the optical waveguide is set to a thickness such that the propagation constants of the TE wave and the TM wave match due to anisotropy due to shape birefringence. .

The principle of the second aspect of the present invention will be described. First, the refractive index of the superlattice (the lattice constant a _W of the quantum well 111 and the lattice constant a _B of the barrier layer 112 are equal) in the absence of strain will be described. As shown in FIG. 10A, in the quantum well 111 sandwiched between the barrier layers 112 on both sides, the quantum well 111 shown in FIG.
The energy level is discretized by quantum confinement like 0 (b), and due to the difference in effective mass, the ground level hh1 for heavy holes hh and that for light holes lh
1 and are separated. The density of states at that time is shown in FIG.

In the case of the ground level separation by quantum confinement, as shown in FIG. 10B, the ground level hh1 caused by the heavy hole hh is always the ground level lh caused by the light hole lh.
1 (in FIGS. 10 (b) and 10 (c), the energy of electrons is high and low, so that the energy level of holes is lower in the upper level). This is because the wave function of the heavy hole hh is flat in a donut shape in the plane perpendicular to the confining direction, so that the repulsion from the barrier layer 112 is reduced by the light hole l.
This is because it is more difficult to receive than h and is energy stable.

Therefore, in such a lattice matching system,
The absorption and the refractive index near the band edge or the absorption edge wavelength are dominated by the optical transition between the ground level hh1 of heavy holes and the ground level e1 of the conduction band. Due to the symmetry of the wave function with respect to the optical transition between these two levels, only the TE wave whose electric field vector is parallel to the plane of the well 111 has a finite value, and it becomes zero for the vertical TM wave. As a result, in the lattice-matched quantum well structure, as shown in FIG. 11, the refractive index n _TE for the TE wave is TM near the band edge (indicated by λ ₀ ).
A polarization plane peculiar to a quantum well occurs that it is always larger than n _TM for waves.

Next, a strained superlattice according to the second embodiment of the present invention will be described. Consider a strained superlattice in which the lattice constant a _B of the barrier layer 112 is larger than the lattice constant a _W of the well layer 111 as shown in FIG. At this time, due to the difference in lattice constant, in-plane compressive stress and in-plane tensile stress act on the barrier layer 112 and the well layer 111, respectively, as shown in FIG. Light hole lh against in-plane tensile stress
Is more stable than the heavy holes hh, and is opposite to the in-plane compressive stress. As a result, the energy band of the superlattice becomes as shown in FIG. That is, in the well layer 111, the light holes lh come above the heavy holes hh, and in the barrier layer 112, the opposite occurs. The respective ground levels lh1 and hh1 formed in the well layer 111 are also in this order. Therefore, the lattice constant of the barrier layer 112 is different from that of the well layer 111.
In the larger strained superlattice, the e1-lh1 transition is dominant. This transition is caused by the TM in which the electric field vector is perpendicular to the well surface.
Since it has a large oscillator strength for waves and is small for TE waves, the refractive index near the absorption edge is as shown in FIG. Thus, by using the strained superlattice, the refractive index n _TM for TM waves can be made larger than the refractive index n _TE for TE waves.

FIG. 15 shows the dependence of the effective refractive index of an optical waveguide having such a strained superlattice as a core layer on the waveguide thickness.
As described above, since the refractive index of the strained superlattice itself is anisotropic, it is larger for the TM wave when the waveguide is sufficiently thick (see FIG. 13). On the contrary, when the waveguide becomes very thin, the effect of shape birefringence becomes large, and the refractive index n _TE for TE waves becomes larger than that for TM waves (n _TM ).
(See (b)). Therefore, there always exists a certain finite film thickness d _{0 with} which the effective refractive indices of both are the same. Therefore, TE wave and T
The propagation constant difference Δβ with the M wave becomes zero, and the phase matching of the TE / TM wave is performed in this waveguide.
In the Poincare sphere of, it will rotate around the north pole (N) (angle θ from the equatorial plane to point M is 9
Point A corresponding to the horizontal polarization is on the equator,
That is, it is possible to reach the point E of 45-degree polarized light with the linearly polarized light as it is.

To further explain the second aspect of the present invention,
In the optical waveguide using the semiconductor strained superlattice structure, by making the lattice constant of the well layer smaller than that of the barrier layer,
Refraction of TM waves by applying in-plane tensile stress to stabilize the ground level of light holes more than that of heavy holes and increasing the optical transition probability between light holes and the ground level of conduction band electrons. It is based on the fact that the index is made larger than the refractive index of TE waves.

[0028]

[Embodiment 1] FIG. 1 is a conceptual diagram of Embodiment 1 of an integrated semiconductor laser constructed by using the present invention. The light generated by the semiconductor laser portion 10 is incident on the waveguide 6b of the connection portion 11 at AA 'in FIG. 1A, but the emitted light at this time is
Since the active layer 4 (only the cross section is shown) is formed with an inclination of 45 ° with respect to the substrate 2, the field distribution, reflecting the inclination,
Both the plane of polarization (plane of polarization) is inclined by 45 ° with respect to the substrate 2. However, in A-A ', the connecting portion 1
Since the optical waveguide 6b of No. 1 is also inclined at 45 ° with respect to the substrate 2 and is parallel to the active layer 4 of the semiconductor laser unit 10,
The optical output from the optical waveguide 6a of the semiconductor laser section 10 can be incident on the optical waveguide 6b of the connection section 11 with almost no loss.

In the state shown on the left side of FIG.
The light incident on the optical waveguide 6 b of No. 1 is 45
The optical waveguide 6 of the connecting portion 11 while maintaining the tilted polarization state
Although it propagates through b, the inclination of the optical waveguide 6b of the connection portion 11 changes smoothly from the state of being inclined by 45 ° with respect to the substrate 2 to the state of being parallel to the substrate 2, so the inclination of the field distribution is It changes as it propagates through the optical waveguide 6b and becomes parallel to the substrate 2 when entering the optical waveguide 6c of the isolator portion 12 at BB ', as shown in the central portion of FIG. 1 (d). Has become. Since the optical waveguide 6c of the isolator section 12 is parallel to the substrate 2, the output light from the connection section 11 whose field distribution is parallel to the substrate 2 enters the optical waveguide 6c of the isolator section 12 with almost no loss. ,
Magneto-optical effect (Faraday rotation, etc.) in the process of propagating through the optical waveguide 6c of the non-reciprocal portion 8 of the isolator portion 12.
The polarization plane is rotated by (see the right side of FIG. 1D), the field distribution is parallel to the surface of the substrate 2, and the polarization direction becomes the complete TE mode and the light is emitted from the mode selector 14. The inclination and polarization state of each optical waveguide in AA 'and CC' are shown in FIGS. 1 (b) and 1 (c). Further, as described above, the entrance of the connecting portion 11 (A-
A '), the outlet of the connecting portion 11 (BB'), the outlet (C-
The field distribution and polarization state in C ') are shown in Fig. 1 (d).

When the length of the nonreciprocal portion 8 of the isolator portion 12 is 1 and the strength of the applied magnetic field 16 is H, the rotation angle θ of the plane of polarization is θ = V1H. Here, V is a proportional coefficient unique to a substance called Verde constant. The length of the non-reciprocal portion 8 of the isolator portion 12 and the strength of the applied magnetic field 16 are set at the oscillation wavelength of the semiconductor laser portion 10 in consideration of the Verdet constant V of the magnetic semiconductor forming the non-reciprocal portion 8 of the isolator portion 12. θ = 45
It is set to be °. In this way, the light emitted from the non-reciprocal portion 8 of the isolator portion 12 is a completely TE-polarized light, and its field distribution is parallel to the surface of the substrate 2. Finally, the light is emitted through the mode selector 14, but since it is a complete TE mode, it can be emitted from C-C 'as the emitted light 18 without any loss.

The emitted light 18 is C for some reason.
Suppose you have returned to -C '. Only the TE polarization component of the return light 20 passes through the mode selector 14 and when it passes through the non-reciprocal portion 8 of the isolator portion 12, the Faraday effect causes an additional 45 ° (in the same direction as for the emitted light). Is incident on the connection portion 11 of BB '. BB '
Since the return light that has entered is incident on the AA ′ emission port of the semiconductor laser section 10, it has a polarization state (TM mode) orthogonal to the oscillation mode (TE mode) of the semiconductor laser section 10 ( (Refer to incident light in FIG. 1B), it cannot be combined with the oscillation mode of the semiconductor laser unit 10,
There is no adverse effect on the operation of the semiconductor laser unit 10.

Next, plane selective doping (plane-s)
selective doping and plane-selective substrata
A method of manufacturing the semiconductor laser 10 having the active layer 4 tilted by 45 ° by using the technique of etching will be described. Si
In MBE growth of doped GaAs and AlGaAs, the conductivity type is GaAs depending on the growth conditions.
In some cases, the plane orientation dependency on the substrate 2 may be exhibited. For example, MB
E-grown Si-doped GaAs is (111) A, (2
11) A and (311) growth on the A plane (the plane on which the group III element mainly appears) shows p-type conductivity, and (10
It exhibits n-type conductivity when grown on the (0) plane.
Then, the GaAs (100) substrate is processed into (111)
A semiconductor laser having an active layer 4 tilted at 45 ° with respect to the substrate can be manufactured by allowing the A plane and the (100) plane to exist and growing while controlling the growth conditions.

FIG. 2 shows a substrate processing method using a photoresist and wet etching. A stripe is formed on the substrate 2 using a photoresist in the [011] direction. In that state, a plane that is effective to bring out the (111) A plane-
selective etchant, for example, H ₃ PO _4:
Etching was carried out using an etchant of H ₂ O ₂ = 1: 10, and stripe-shaped (11
1) A plane tilt is prepared. Then the photoresist is removed, an ammonia-based etchant _{(NH 4 OH: H 2 O} 2:
After etching with H ₂ O = 1: 1: 10) for about 5 seconds and thoroughly washing with pure water, it is introduced into the MBE apparatus and grown. At this time, by controlling the substrate temperature and the flux ratio (the ratio of the number of flying molecules of V group and III group), S on the (111) A surface
It is possible to control the conductivity of i-doped GaAs and AlGaAs.

FIG. 3 shows a sectional view of a semiconductor laser having a current blocking layer 50 produced by controlling conductivity. The layer structure is as shown in FIG. In FIG. 3, Si-doped n
-Like the AlGaAs layer 24 (100), (111)
When the n-type conductivity is given to both the A faces, the growth is performed at a substrate temperature of 580 ° C. and As ₄ / Ga = 18 (pressure ratio), and the Si-doped n-AlGaAs layer 3 shown in FIG.
2. Si-doped p-AlGaAs layer 44, Si-doped n-AlGaAs layer 36, Si-doped p-AlGa
In the (100) plane as the As layer 42, n-type,
On the (111) A plane, when p-type is obtained, growth is performed at a substrate temperature of 670 ° C. and As ₄ / Ga = 18. N ⁺ -GaAs patterned as described in FIG.
Growth is performed on the substrate 22 by controlling the substrate temperature and the like, and (1
11) A double hetero (DH) structure having the current blocking layer 50 can be formed by selectively performing p-type doping on the A surface.

The problem here is that the growth on the (111) A plane is carried out smoothly. Even if the DH structure is created by simply controlling the substrate temperature and the like, the growth on the (111) A plane is generally not so smooth, and a rough non-planar surface is likely to be formed instead of a smooth flat surface. Like this (111)
If the surface A, that is, the GaAs active layer 28 has roughness, optical loss is large and laser operation cannot be expected. Therefore, by irradiating only the (111) A surface with a He-Ne laser or an Ar laser during growth to promote migration on the (111) A surface,
It is possible to realize smooth surface growth with little optical loss on the A surface (see FIG. 4).

[0036]

Second Embodiment Since the emitted light of the semiconductor light emitting device of the present invention is a perfect TE mode or a perfect TM mode, it can be effectively integrated with other waveguide type optical devices. 5 and 6 are conceptual diagrams of an optical communication system configured using the semiconductor light emitting device of the present invention. FIG. 5 is an overall view of an optical communication system configured using the semiconductor light emitting device of the present invention. In FIG. 5, 72 is an optical transmission line such as an optical fiber, 60, 62 and 64 are terminals that perform communication using this optical transmission line 72, and 66, 68 and 70 convert electric signals from the terminals into optical signals. Is an integrated type terminal station device that transmits the optical signal from the optical transmission line 72 into an electric signal and transmits the electric signal to the terminal.

In FIG. 6 showing an example of the configuration of the integrated type terminal device, 74 is a semiconductor laser section for converting an electric signal from a terminal into an optical signal and transmitting it to the optical transmission lines 88 and 90, and its active layer. Is tilted at 45 ° with respect to the substrate. Reference numeral 76 denotes an optical isolator section, which is composed only of a non-reciprocal section having a waveguide parallel to the substrate surface. The polarization plane is rotated so that the incident light and the outgoing light are orthogonal to each other, and the semiconductor laser section 74 is provided.
It prevents the return light to. Reference numeral 75 denotes a connection portion in which the optical waveguide changes smoothly, and connects the waveguides of the semiconductor laser portion 74 and the optical isolator portion 76 smoothly. 80
Converts the optical signal transmitted through the optical transmission lines 88 and 90 into an electric signal, and transmits the signal to the connection terminal if the converted signal is transmitted to the terminal connected to the own terminal station. The semiconductor photodetector (having the same structure as the above-mentioned semiconductor laser), and the waveguide is tilted at 45 ° with respect to the substrate. Reference numeral 78 denotes an optical isolator section similar to the optical isolator section 76, which prevents signals from returning to the optical transmission paths 88 and 90. 79 is an optical isolator section 78 similar to the connection section 75.
And a waveguide of the semiconductor photodetector 80 are smoothly connected. Further, 82 is a semiconductor optical amplifier having a semiconductor laser structure, 84 is a T-shaped coupler for guiding a part of the optical signal transmitted through the optical transmission lines 88, 90 to the semiconductor photodetector 80, and 86 is a semiconductor laser 74. T-shaped couplers 88 and 90 for guiding the optical signals to the optical transmission lines 88 and 90 are optical transmission lines such as optical fibers.

By the way, in the semiconductor optical device of the present invention, since the waveguides which are inclined by 45 ° are connected by the connecting portion having the waveguide whose inclination is gradually changed, almost all of the loss is caused. A waveguide structure that does not exist can be formed. Figure 7
An example of producing a connection part having a waveguide whose inclination changes gradually by an ion beam is shown in FIG. While the ion beam is scanned in the long axis direction of the waveguide, the ion beam is moved in the short axis direction of the waveguide to form a waveguide structure on the substrate or a laminated portion (shown as a sample in FIG. 7) on the substrate. The waveguide structure can be formed by gradually changing the inclination by changing the ion current in synchronization with the scanning during the scanning in the axial direction. The optical waveguide is formed in the substrate or the laminated portion in the above-described groove portion 91 in which the inclination is gradually changed.
It is formed by laminating an appropriate film on.

In the above, the materials constituting the semiconductor laser, semiconductor optical amplifier or semiconductor photodetector are GaAs, AlGaAs, ZnCdSe, InP and In.
GaAs, ZnCdSSe, InGaAsP, etc., and the optical isolator is CdTe, CdMnTe, ZnS.
e, ZnMnSe, YIG and the like.

[0040]

Third Embodiment In the present embodiment of the second aspect of the present invention, Ga
ZnSe buffer and ZnMnSe / Z on As substrate
After forming the nSe superlattice buffer layer, a three-layer waveguide structure is formed. The waveguide has a structure in which a ZnMnSe / ZnSe superlattice core layer (for example, a stack of ZnSe well layers 60Å / ZnMnSe barrier layers 40Å) is sandwiched between upper and lower ZnMnSe cladding layers. 20% Mn composition of core layer
Then, the misfit of the lattice constant between the well layer 111 and the barrier layer 112 becomes 0.8%, and the in-plane tensile stress acts on the well layer 111. As a result, the refractive index n _TM for TM waves
Is larger than n _TE for TE waves, and the film itself has anisotropy. Therefore, a phase matching waveguide can be obtained by determining the thickness of the core layer so that the shape birefringence compensates for the anisotropy of the refractive index anisotropy (Fig. 15).

The optical waveguide has CdTe as a well layer,
The barrier layer may be made of CdMnTe. At that time, the materials of the buffer, the superlattice buffer layer, and the cladding layer may be changed accordingly.

This semiconductor optical device is also used as an optical isolator or the like in the optical communication system as described with reference to FIGS.

[0043]

As described above, according to the present invention, for example, a device such as a semiconductor laser section or a semiconductor photodetector is formed by growing a waveguide with an inclination of 45 ° with respect to a substrate. As a result, even if the isolator section is composed of only the non-reciprocal section, the emitted light is completely TE-polarized light, and an integrated semiconductor optical device that is hardly affected by the presence of return light can be obtained.

Further, according to the present invention, a waveguide device (for example, an optical isolator) that requires TE / TM phase matching is used.
Can be realized.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a first embodiment of the present invention.

FIG. 2: (100) GaAs using face-selective etching
It is a figure explaining the processing method for making a (111) A surface inclination in a board.

FIG. 3 is a cross-sectional view of a semiconductor laser portion configured by using face-selective etching and face-selective doping.

FIG. 4 is a diagram illustrating a method of reducing roughness on a (111) A plane.

FIG. 5 is a diagram showing an example in which the device of the present invention is applied to an optical communication system.

FIG. 6 is a conceptual diagram of an integrated type terminal device configured using the element of the present invention.

FIG. 7 is a diagram illustrating a method of manufacturing a connection portion in which the inclination of the waveguide is changed.

FIG. 8 is a conceptual diagram of an optical isolator.

FIG. 9 is a conceptual diagram of a conventional waveguide type isolator.

FIG. 10 is a diagram illustrating a distortion-free superlattice.

FIG. 11 is a diagram illustrating a refractive index near a band edge in a phase-matched quantum well.

FIG. 12 is a diagram illustrating a strained superlattice of the present invention.

FIG. 13 is a diagram illustrating a refractive index near a band edge in a superlattice.

FIG. 14 is a diagram illustrating in-plane compressive stress and in-plane tensile stress.

FIG. 15 is a diagram illustrating the waveguide thickness dependence of the effective refractive index of an optical waveguide including a superlattice as a core layer.

FIG. 16 is a diagram of a Poincare sphere for explaining how the polarization changes.

FIG. 17 is a diagram illustrating the refractive index of a thin film waveguide made of an isotropic material.

[Explanation of symbols]

2, 22, 92 ... Substrate 4 ... Active layer 6a, 6b, 6c ... Optical waveguide 8,100 ... Non-reciprocal part 10, 74 ... Laser part 11, 75, 79 ... Connection part 12, 76, 78 ... Isolator part 14, 94, 98 ... Mode selector 16 ... Magnetic field 18 ... Emitted light 19 ... Incident light 24, 32, 36, 46, 48 ... Si-doped n-Al
GaAs layer 26, 30 ... AlGaAs layer 28 ... GaAs active layer 34 ... Be-doped p-AlGaAs layer 38 ... Be-doped p ⁺ -GaAs layer 40 ... Metal contact 50 ... Current blocking layer 60, 62, 64 ...... Terminals 66,68,70 ...... Terminal devices 72,88,90 ...... Optical transmission line 80 ...... Semiconductor photodetector 82 ...... Semiconductor optical amplifiers 84,86 ...... T-coupler 91 ...... Groove 102 ... ... Reciprocal part 104 ... Magneto-optical thin film 111 ... Well layer 112 ... Barrier layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04B 10/02 // G02B 27/28 Z 9120-2K

Claims (11)

[Claims] 1. A semiconductor optical device section having an optical waveguide inclined at 45 ° with respect to a substrate surface, an optical element section having an optical waveguide horizontal to the substrate surface, and an inclination at 45 ° with respect to the substrate surface. It has an optical waveguide that continuously changes from 0 ° to 0 °, and is composed of a connecting part that smoothly connects the two optical waveguides that are inclined to each other by 45 °, and the emitted light is completely perpendicular to the substrate surface. Alternatively, a semiconductor optical device having a horizontal plane of polarization. 2. The semiconductor optical device according to claim 1, wherein the semiconductor optical device portion having an optical waveguide inclined at 45 ° with respect to the substrate surface is a semiconductor laser, a semiconductor optical amplifier or a semiconductor photodetector. . 3. The semiconductor optical device according to claim 1, wherein the optical device portion having an optical waveguide horizontal to the substrate surface is an optical isolator. 4. The semiconductor optical device according to claim 1, wherein the semiconductor optical device portion having an optical waveguide inclined with respect to the substrate is formed by face-selective etching and face-selective doping. 5. The material forming the semiconductor laser, the semiconductor optical amplifier or the semiconductor photodetector is GaAs or AlGa.
As, ZnCdSe, InP, InGaAs, ZnCd
3. A semiconductor optical device according to claim 2, which is a suitable one of SSe and InGaAsP. 6. The optical isolator is CdTe or CdMnT.
4. The semiconductor optical device according to claim 3, wherein the semiconductor optical device is made of an appropriate one of e, ZnSe, ZnMnSe, and YIG. 7. An optical communication system for performing optical communication using an optical communication device configured using the semiconductor optical device according to claim 1. Description: 8. In an optical waveguide using a semiconductor strained superlattice structure, by making the lattice constant of a well layer smaller than that of a barrier layer, in-plane tensile stress is given and the ground state of light holes is changed to heavy holes. The refractive index of the TM wave is made higher than that of the TE wave by increasing the optical transition probability between the light hole and the ground level of the conduction band electron. An optical waveguide in which the TE wave and the TM wave are phase-matched, characterized in that the optical waveguide is set to a thickness such that the propagation constants of the TE wave and the TM wave match due to anisotropy. Waveguide element. 9. The optical waveguide comprises ZnS as a well layer.
The optical waveguide element according to claim 8, wherein the optical waveguide element is made of ZnMnSe as a barrier layer. 10. The optical waveguide comprises CdT as a well layer.
The optical waveguide device according to claim 8, wherein the optical waveguide element is made of e and the barrier layer is made of CdMnTe. 11. An optical communication system for performing optical communication using an optical communication device configured using the semiconductor optical device according to claim 8. Description: