JPH0410582A - Semiconductor optical element - Google Patents

Abstract

PURPOSE:To obtain a semiconductor optical element where outgoing light rays and an optical fiber are coupled well by a method wherein a relation between an outgoing direction in which light rays are emitted and a direction of an optical waveguide which guides light rays is set conforming to a Snell's law. CONSTITUTION:An InP buffer layer 13, an active layer 14, and a clad layer 15 are successively grown in crystal on a substrate to form a double hetero substrate, a mesa 10 tilted against the direction of a cleavage plane 4 is formed on the substrate, an InP second conductive layer 17 and an InP first conductive layer 18 are successively grown to fill, a dielectric layer 10 is deposited, an etching process is carried out, electrode materials 21 on patterns evaporated on both the sides of the substrate are lifted off, which are thermally treated into electrodes 22, and a dielectric layer 23 is evaporated again. Then, the dielectric layer 23 is removed, grooves 27 are provided through etching, and the substrate is split into slant optical waveguide elements 25. The element 25 is die-bonded, a wire 28 is bonded to the element 25 to finish an SLD, an SLA is set as long as the overall length of the slant optical waveguide element 25 and a heat sink 12, and the element 25 is arranged between an output optical fiber 29 and an input optical fiber 31. In result, an optical fiber and light rays can be easily coupled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical waveguide provided on a semiconductor substrate.

That is, the present invention relates to a semiconductor optical device in which the angle of the end face of an optical waveguide is set according to Snell's law so that light is emitted perpendicularly or parallel to a reference plane.

[Conventional technology]

Low coherent light emitting device (5upper Lum1nes)
centDiode (so-called SLD), semiconductor optical direct amplification device (Semiconductor La5er)
An outline of Amplifier (so-called SLA) will be explained below.

Low coherent light emitting device (hereinafter referred to as SLD).

) is an element that has a leading wavepath with optical gain and suppresses laser oscillation. As a result, in the stage before the laser emits light, a light emitting diode (Light Es+itting Dio
hereafter referred to as LED. ), higher light output can be obtained. Since this SLD has low coherence, it is essentially less likely to generate return optical noise or speckle noise that causes interference in a light source, optical fiber, optical disk, etc. In addition, it has a wide optical spectrum width and can be used as an approximate white light source, so it has been actively developed for optical measurement in recent years.

In addition, a semiconductor optical direct amplification element (hereinafter referred to as SLA)
gives optical gain to the optical waveguide by current injection, and
This is an element that suppresses laser oscillation, and is placed in the middle of an optical transmission line. Currently, SLA can directly amplify an optical signal by about 20 dB even including fiber coupling loss with an optical transmission line. This SLA is capable of wide-band optical amplification due to its optical spectral characteristics, and can be integrated with a semiconductor laser (hereinafter referred to as LD) made from the same material. Therefore, there is an urgent need to develop it as a core element for long-distance, high-speed, large-capacity optical communication networks, including future optical switching systems.

The basic operation of the SLD and SLA described above is performed under the condition that the component coupled to the optical waveguide of the light reflection at the end face of the optical waveguide of the LD is suppressed. Furthermore, they have in common that even when the injection density is increased, it is necessary to prevent laser oscillation from occurring.

As described above, the basic operation of an SLD etc. needs to be performed under a condition in which the component coupled to the optical waveguide Q of the light reflection at the end face of the optical waveguide of the LD is suppressed.

In order to suppress the components coupled to the optical waveguide, that is, to reduce the coupling reflectance of the optical waveguide, the following four methods are generally known.

■ Apply an anti-reflection film to the end face of the LD optical waveguide.

■ A light absorption region is provided at the end of the optical waveguide to absorb reflected light.

■ A so-called window area is created by embedding a material that does not absorb light at the end of the optical waveguide, and the light emitted from the optical waveguide,
and diffuse the light reflected within the window area. This suppresses the components of the reflected light that are coupled to the optical waveguide.

(2) The optical waveguide is provided at an angle with respect to the end face that emits light, and the component reflected from the end face and coupled to the optical waveguide is suppressed.

However, the methods from ■ to ■ have the following problems.

Regarding ■, there are the following problems.

When using a non-reflective film, it is necessary to control the layer thickness to within 5 nm and the refractive index to within 0.05 in order to achieve a reflectance of 10-'& (e.g., IEICE technical research report 0QE84). -93, pp, 29-pp, 36 Saito, Mukaiben, Mikami) It has also been reported that both TE and TM modes cannot be reduced to the same level at the same time (for example,
G, A, AIphonese etal, Applie
d Physics Letters, Vol 55,
No. 22 27 November 1989 pp
, 2289-pp, 2291).

Furthermore, since this method of using a non-reflective film relies on the resonance phenomenon of light waves, it is not possible to achieve a stable low reflectance over a wide range of light wavelengths.

Regarding ■, there are the following problems.

When a light absorption region is provided at the end of an optical waveguide, this region acts as a saturable absorber (therefore, the absorption changes rapidly after reaching the optical density threshold in the optical waveguide, and this change occurs due to the crystal Crystal defects that are unintentionally introduced during growth and device formation become non-emissive recrystallization centers.
Variations occur in the light absorption characteristics and their characteristics over time, making it difficult to obtain stable device characteristics. Furthermore, not only this, but also an optical direct amplification element cannot be obtained because the input or output signal light is attenuated due to the optical absorption 2-2 region formed at the end of the leading waveguide.

Regarding ■, there are the following problems.

The window region is made of the same material that forms the optical waveguide in order to eliminate light reflection at the boundary between the end of the optical waveguide and the window region, or
Refers to a region formed by a substance having a very similar refractive index so as to be in contact with the end face of an optical waveguide, and to have a termination face separated by a certain length from the end face of the optical waveguide. The function of this window area is that light that enters the window area from the end face of the optical waveguide in contact with the window area diffuses through the window area and returns to the end face of the optical waveguide via the end face of the window area. By its diffusion, the component that passes through the end face of the optical waveguide and returns into the optical waveguide is significantly suppressed.

However, for example, GaxIn+- which has an embedded structure
In the XAsy P+-y/InP compound semiconductor optical device, a window region is formed by crystal growth using the compound semiconductor, but the crystal growth of the compound semiconductor on the end face of the optical waveguide generally has poor reproducibility. Therefore, light reflection at the boundary between the optical waveguide end face and the window region cannot be sufficiently suppressed. In addition, since the transmission of light is disturbed at the boundary between the optical waveguide end face and the window region, a near-field image and a far-field image are disturbed in the light emitted from the end face of the window region.

Therefore, when the emitted light is incident on the optical fiber, there is a problem that the proportion of the emitted light that is incident on the optical fiber decreases.

[Problem to be solved by the invention] Compared to the above methods from ■ to ■, the method of ■ is to provide the optical waveguide at an angle with respect to the light emitting end face, and to suppress the component coupled to the optical waveguide due to the end face reflection. The method is simple and feasible.

However, ■ also has the following problems.

First, a method for forming an element with an inclined optical waveguide is, for example, in the case of an element employing a refractive index waveguide structure, a Ga
X I nl-x As, P+-v /InP active layer,
A stripe-shaped etching mask is formed on a double hetero substrate made by sequential crystal growth of second conductivity type JnP, and then a mesa-shaped etching mask is etched to include the active layer.
Form a mesa stripe that will later become a refractive index waveguide. At this time, the direction of the mesa stripe is set so as not to coincide with the surface direction of the light emitting end face.

Subsequently, the second conductivity type 1nP and the second conductivity type 1nP are sequentially grown on the mesa stripe except for the portion covered by the mask, thereby forming a buried layer and completing the device structure. In such a configuration, a ray emitted from within the optical waveguide after passing through the end face of the optical waveguide is determined by the sine of the angle with respect to the virtual normal to the end face of the optical waveguide and the sine of the medium before and after passing through the end face of the optical waveguide. Satisfies Snell's law that the product of refractive index is conserved.

Therefore, the inclination angle of the optical waveguide and the light output angle are in a relationship such that as the inclination angle of the optical waveguide increases in order to obtain a lower reflectance, the direction of the output light moves away from the normal direction of the light output end face. .

This relationship is shown in FIGS. 9 and 10.

To explain with reference to FIG. 9, the light emitting end face 7 is formed by cleavage. Then, in the process of joining the element with the inclined optical waveguide 6 to the heat sink 12 such as a diamond, the separated end face is used as a reference for setting the direction. According to Snell's law, the light 9 propagating inside the optical waveguide 6 which is inclined θi with respect to the normal direction 8 of the separated end faces is
The output light 5 has an angle of θr in the figure. As a result,
It becomes difficult to couple an element in which the optical waveguide 6 is inclined with an optical fiber running along an optical transmission line parallel to the normal direction 8.

In addition, when the inclination of the leading waveguide 6 is made large in this way, the optical fiber receiving the emitted light 5 is also inevitably inclined, so in order to improve the light reception efficiency of the optical fiber, it is necessary to
For example, the light emitting end face 7 and the optical fiber end are tilted.
It is necessary to bring them close to each other by about 10 μm. However, in this case, the end of the optical fiber comes into contact with the light emitting end surface 7.

The present invention provides SLDs and SLAs with inclined leading wavepaths.
This was done in view of the above-mentioned circumstances, and the object of the present invention is to provide a semiconductor optical device in which the coupling reflectance of the optical waveguide is strongly suppressed and the coupling between the emitted light and the optical fiber is good. do.

[Failure to solve the problem]

In order to solve the above problems, the semiconductor optical device of the present invention has a configuration in which the relationship between the direction of the leading waveguide through which the light is guided and the direction of the exit surface from which the light is emitted is set in accordance with Spearl's law. And so.

In other words, one end face of this semiconductor optical device is arranged at an angle such that guided light emits or introduces light in a direction parallel or perpendicular to the reference plane determined by Snell's law. A first optical waveguide is formed on a semiconductor substrate, and a first optical waveguide defined as described above is introduced or emitted from an end face of the first optical waveguide.
and a second reference plane disposed parallel or perpendicular to the reference plane.

〔Example〕

An embodiment of the semiconductor optical device of the present invention will be described below with reference to the drawings.

Here, the first optical waveguide is simply an optical waveguide 6, and the second optical waveguide is
The optical waveguide will be described below as the second optical waveguide 3.

In the configuration of the first embodiment, FIG. 1 shows an overhead view, and FIG. 2 shows a schematic sketch.

First, there is light 9 that travels parallel to the optical waveguide 6 , and the light 9 becomes output light 5 at the light output waveguide end face 2 of the optical waveguide 6 . The emitted light 5 forms a vertical light emitting optical waveguide end face 2 so that the emitted light 5 is in an arbitrary direction, horizontally or vertically, with respect to the cleavage plane 4 as the first reference plane. The formation of this light output optical waveguide end face 2 is performed by wet or dry etching. Next, the emitted light 5 is incident perpendicularly to the second reference plane 1 of the second optical waveguide 3 located parallel or perpendicular to the cleavage plane 4, and travels inside the second optical waveguide 3 in parallel. move on.

Then, the condition that the direction of the output light 5 from the light output optical waveguide end face 2 coincides with the normal direction 8 of the cleavage plane 4 is set, for example, by G
a When applicable to InAsP/InP (Ag-1°55 μm), the relationship established between the light 9 and the light output optical waveguide end face 2 is shown in FIGS. 3 and 4.

Angle in Figure 3: θn is the normal XH of the end face 2 of the light output optical waveguide
It is the inclination of the light 9 with respect to ".

Angle: θf is the light output optical waveguide end face 2 with respect to the normal direction 8
is the slope of

Angle: θi is the inclination of the light 9 with respect to the normal direction 8°.

An example of the ratio (optical waveguide coupling reflectance) of the light 9 at the light output optical waveguide end face 2 returning to the original optical waveguide 6 with such a configuration is the ratio of the light 9 to the light output optical waveguide end face 2.
The inclination angle of is shown in FIG. 8 as a function of θn. The optical waveguide coupling reflectance decreases rapidly with θn. For example, in the crystal system shown in FIG. 5X I also in the refractive index optical waveguide structure as a coupled reflectance
It can be seen that less than O-' can be obtained (indicated by a broken line).

An example of forming a semiconductor optical device of the present invention will be described below with reference to FIG.

(1) On an InP substrate having a first conductive layer, an InP Hanwha layer 13 as a first conductive layer, an active layer 14, and a cladding layer 15 as a second conductive layer are successively crystal-grown.

(2) The mesa 16 tilted with respect to the four directions of the cleavage plane of the double hetero substrate grown in the step (1) is used as a normal LD.
Formed using the same method as .

(3) Add it to the second conductive layer 17 and the second conductive layer
Filling growth is performed sequentially using nP.

(4) Next, a dielectric layer 19 that will later become an etching mask is deposited on the InP substrate by plasma CVD or the like. Thereafter, taking into consideration the angle between the direction of the mesa 16, which will become the optical waveguide 6, and the light emitting end surface 7, a resist pattern 20 for forming a groove including the light emitting end surface 7 later is formed. Next, the process of forming a groove including the light emitting end surface 7 is shown in FIG.
This will be explained using (a) Karage) at the AA' cross section in the process of ).

(a) Resist pattern 2 on the dielectric layer 19 on the substrate
After etching into a zero shape, electrode material 21 is deposited on both the front and back surfaces of the substrate in accordance with the respective conductivity.

(b) After dissolving the resist pattern 20 with acetone or the like to lift off the electrode material 21 on the pattern, heat treatment is performed to form the electrode 22.

(C) On the substrate on which the electrode 22 is formed in this way,
Again, a dielectric layer 23 is applied.

(d) After applying the resist 24, a window is opened in a region for etching parallel to the resist pattern 20.

(e) Subsequently, the dielectric layer 23 is removed using the resist 24 as a mask.

(f) Then, using the dielectric layer 23 as a mask, Ga
T n As / I n P crystal or Ga1n
Grooves 27 are formed by processing and etching the AsP/InP crystal using a wet method or a dry method.

(5) A substrate having grooves 27 is formed by the process (a) Karaage) above. (See Figure 5 (5)) (6)
Next, an optical waveguide 6 including an active layer is formed in the vertical portion of the groove 27.
The inclined optical waveguide element 25 can be obtained by dividing the InP substrate by cleaving or dicing so that the end faces of the two sides coincide with each other.

And (7), (8) using the semiconductor optical device of the present invention
There are examples of applications.

(Force) Then, this inclined optical waveguide element 25 is attached to the end face of the heat sink 12, such as a diamond, at the cleavage plane 4 of the crystal.
After matching and performing die bonding, wire bonding 28 to the inclined optical waveguide element 25 is performed to complete the SLD.

(8) On the other hand, SLA is completed by making the total lengths of the inclined optical waveguide element 25 and the heat sink 12 approximately the same, and placing them between the output optical fiber 29 and the input optical fiber 31.

The SLD and SLA function by injecting current or electrons into the inclined optical waveguide element 25 through the wire 28.

Up to now, the explanation has been made regarding a Ga1nAsP/InP-based refractive index waveguide structure element, but the present invention also relates to a gain waveguide structure, an optical waveguide structure, and an AlGaAs/GaA
Needless to say, the present invention can also be applied to other crystalline elements such as S-type.

Further, as a second embodiment, an example in which the semiconductor optical device of the present invention is applied to a distributed feedback semiconductor laser (DFB-LD) is shown in FIG.
FIG. 7 shows an example in which this method is applied to a LD.

The DFB-LD includes a guide layer 30 in which a diffraction grating 32 for selecting an oscillation wavelength is carved along the active layer 14 .

On the other hand, the DBR-LD has a structure in which an active layer 14 and a guide layer 30 having a diffraction grating 32 that selectively reflects light are coupled in series. In this side structure, the diffraction grating 32 is
FIG. 5 (1) so that the light is diffracted in the direction of the guide layer 30.
It is formed during the formation of the duffle hetero substrate made in the process of 1, and the subsequent buried growth process is basically the same as that of SLD and SLA in the first embodiment. As described above, the effects when the present invention is applied to DBR-LD or DFB-LD are as follows.

In a DBR-LD or a DFB-LD, the phase of the diffraction grating 32 at the end face of the optical waveguide has a strong influence on the characteristics of laser oscillation. For example, GaI n A s
In the P/I n P optical semiconductor laser, the pinch of the order diffraction grating 32 is as fine as 200 to 250 nm.

For this reason, it is currently impossible to control the phase of the diffraction grating 32 when forming an optical waveguide end face by cleavage or the like. Therefore, in order to stabilize the oscillation characteristics of these LDs, it is necessary to suppress the reflection of light at the end face of the optical waveguide. It is clear from the above description that the present invention is effective in solving such problems.

Furthermore, the configuration according to the present invention can also be applied to a semiconductor laser type optical switch.

The effects in this case are as follows.

In the semiconductor optical device of the present invention, since the light emitting end is shifted in the direction perpendicular to the light incidence, in the switch-off state, incident light to the device, which causes crosstalk, propagates around the active layer. Therefore, there is an advantage that the optical signal component directly output to the light output end can be reduced compared to the conventional one.

〔Effect of the invention〕

According to the configuration of the present invention, the following advantages can be obtained.

First, since the light can be emitted or introduced parallel or perpendicular to the reference plane while suppressing the coupling reflectance, the light can now be easily coupled.

Next, light can be emitted at an easily adjustable angle parallel to or perpendicular to the reference plane of the semiconductor optical device. Therefore, the element can be easily aligned using the cleavage plane other than the light emitting end face, as in a normal semiconductor laser, and therefore manufacturing is easy.

In addition, this reduction in reflectance is achieved using a method that does not have the wavelength dependence of materials such as non-reflective films, so it suppresses Fabry-Perot mode oscillation over a wide range of wavelengths. becomes possible.

[Brief explanation of drawings]

FIG. 1 is an overhead view of the semiconductor optical device of the present invention, FIG. 2 is a sketch diagram schematically showing the semiconductor optical device of the present invention, and FIG. 3 is an enlarged view of the vicinity of the light emitting end face of FIG. 1. FIG. 4 is a diagram explaining the relationship established between the optical waveguide and the light emitting end face, FIG. 5 is a diagram showing the manufacturing process of the semiconductor optical device of the present invention, and FIG. 6 is the diagram of the semiconductor optical device of the present invention. Fig. 7 is an overhead view when the semiconductor optical device of the present invention is used in a DBR-LD, and Fig. 8 shows how the incident light at the light output end face returns to the original light guide. 4 is a diagram showing an example of the rate of feedback to the waveguide (optical waveguide coupling reflectance) as a function of the optical waveguide inclination angle: θn with respect to the end face shown in FIG. 3. FIG. FIG. 9 is an overhead view of a conventional semiconductor optical device, and FIG. 1O is a schematic diagram of a conventional semiconductor optical device. 12, 13, 15, 16, 18, 20, 22, 24, 27, 29, 31 ・Second optical waveguide cleavage plane, 5... Output light, optical waveguide, 7... Light output end face, normal line Direction, 9... Light, Emitted light, 11... Semiconductor substrate heat sink, InP half layer 7, 14... Active layer, crat layer of second conductive layer, Mesa, 17... Second conductive layer layer, first conductive layer, 19... dielectric layer, resist pattern, 21... electrode material, electrode, 23.
...dielectric layer, resist, 25...slanted optical waveguide element, groove, 2B...
・Wire output fiber, 30...guide layer, human power fiber. 32... Diffraction grating. 1...Second reference plane, 2...Light output optical waveguide end surface, Applicant: Anri Co., Ltd. Agent Patent attorney: Ryutabe Koike Figure Figure Figure 64 +00 φr (degrees) Figure Number Fig. θ, + (and Fig. 10

Claims (1)

[Claims] A semiconductor substrate (11) having a first reference surface (4);
An angle formed on the semiconductor substrate (11) such that the light (9) guided by it emits or introduces light in a direction parallel or perpendicular to the first reference plane (4) according to Snell's law. a first optical waveguide (6) with one end face (2) disposed with the first optical waveguide (6); and introducing or introducing light (5) emitted from the end face (2) of the first optical waveguide (6). a second reference plane (4) disposed parallel or perpendicular to the first reference plane (4);
1) and a second optical waveguide (3).