JP2000357789A - Optical integrated element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To integrate into each other easily by a direct coupling ridge and buried optical waveguides having respectively desired characteristics and functions, by forming the core layers of at least one of the optical waveguides in the top and bottom portions of a mesa type region. SOLUTION: The height of an active layer 12 of a DFB-LD formed previously and the height of a core layer 19 of the upper portion of the ridge of an optical waveguide formed posteriorly by a regrowth are made equal to each other. Since the light emitted from the DFB-LD is coupled directly to the core layer 19, a large coupling efficiency is obtained. Also, by forming simultaneously a ridge in the optical waveguide region too through the ridge forming process of the DFB-LD, this ridge is utilized to form the buried structure of the optical waveguide by an etching and a regrowth. Therefore, the ridge and buried optical waveguides can be created by very simple processes to make possible the cutting-down and simplification of their manufacturing processes. In this way, an optical waveguide integrated element can be manufactured easily wherein the different optical confinement structures from each other of the ridge and buried optical waveguides are directly coupled to each other, and their high coupling effects are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated optical device in which two or more optical waveguides are integrated by direct coupling, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Various optical elements such as a semiconductor laser, a light receiving element, an optical modulator, and an optical waveguide are used in various systems. In particular, for the purpose of miniaturization, low power consumption, low cost, and the like, development of an optical integrated device in which these optical devices are monolithically integrated on the same semiconductor substrate has been active. Among them, integrating two or more optical waveguides and coupling light efficiently is an important technique.

As a typical method for coupling two waveguides, two optical waveguides shown in FIG. 11A are stacked close to each other and vertically coupled, and one optical waveguide shown in FIG. There is a method of directly coupling the other optical waveguide at the end face of the optical waveguide.

The method shown in FIG. 11A is easy to manufacture because two optical waveguides can be grown and formed at the same time, but has a problem of low coupling efficiency.

In order to increase the coupling efficiency in the structure shown in FIG. 11A, it is necessary to reduce the distance between the two waveguide layers. In this case, the thickness of the upper cladding layer in the second optical waveguide is increased. And it becomes difficult to design a desired light distribution. Further, the first optical waveguide has
Since there are two waveguide layers, light spreads and the light density of the first waveguide layer decreases. Thus, FIG.
In the method described in (1), structural restrictions are increased, and it is difficult to obtain sufficient characteristics as an integrated device.

The method shown in FIG. 11B can increase the coupling efficiency. However, since two waveguides need to be formed separately, the number of times of growth increases, and furthermore, each of the waveguides needs to be formed. Since it is necessary to match the process, there is a problem that the manufacturing process becomes complicated, such as the necessity of mask alignment.

Next, a typical ridge type optical waveguide and a buried type optical waveguide will be described as a method of confining light in the lateral direction of the optical waveguide.

The ridge-type optical waveguide is a method of confining light in the ridge portion by forming a ridge stripe and making the effective refractive index of the ridge portion larger than the effective refractive index of a region other than the ridge portion. . The ridge type optical waveguide is
A single optical waveguide can be manufactured by etching away both sides while leaving only the central portion of the slab waveguide, and is easy to manufacture. Another advantage is that there is no regrowth interface in the core layer.

The buried optical waveguide is a method in which light is confined by burying both sides above and below the active region with a cladding layer. In the buried optical waveguide, usually, a DH structure is grown on a plane, a mesa is formed, and a clad layer is regrown on both sides of the core to be buried. Therefore, on both sides of the core layer of the buried optical waveguide, the cladding layer is re-grown after being once exposed to air, and an oxide film is formed on the re-growth interface. There is a problem that it is significantly reduced. Although the buried optical waveguide has a complicated manufacturing process as compared with the ridge-type optical waveguide, it has a large degree of freedom in structural design such as a core width, a layer thickness, a mixed crystal ratio, and a small waveguide loss. There are advantages.

In the case of an optical integrated device in which two or more optical waveguides are integrated, each optical waveguide must have a different waveguide structure and optical confinement structure so that each optical waveguide has a function. However, this leads to an improvement in the characteristics and functions of the optical integrated device. Specifically, each optical waveguide is designed such that the cladding layer, the mixed crystal ratio of the core layer, the layer thickness, the width of the waveguide, and the like are obtained in order to obtain a desired light distribution and shape. In a laser, an active layer is designed to be thin to reduce a threshold current.

Therefore, each element must be designed to have an optimal structure according to the purpose of use. Therefore, in the case of an optical integrated element in which optical waveguides having different functions are integrated, it is necessary to make each element have a different structure. desirable. Furthermore, when coupling two waveguides, it is necessary to align the optical axes of the two waveguides, and it is desirable to form the optical axes in a self-aligned manner without mask alignment.

As an optical integrated device in which optical waveguides having different functions are integrated, for example, Japanese Patent Application Laid-Open No. 7-142699 describes an example in which a ridge type optical waveguide and a buried type optical waveguide are integrated (conventionally). Example 1).

The method of manufacturing the optical integrated device of the prior art example 1 is described below.
This will be described below with reference to FIG.

First, as shown in FIG. 12A, an optical waveguide layer 4 serving as a core layer of a ridge type optical waveguide 2 and an optical waveguide layer 5 serving as a core layer of a buried optical waveguide 3 are formed on a semiconductor substrate 1. It is formed in the same substrate plane by a known method.

Next, as shown in FIG.
A silicon oxide film (SiO ₂ ) 6 is formed thereon by ordinary chemical vapor deposition and photolithography.

Next, as shown in FIG. 12C, a photoresist pattern 7 for forming the ridge type optical waveguide 2 and the buried type optical waveguide 3 is simultaneously formed using the same photomask.

Next, as shown in FIG. 12D, the optical waveguide layer 5 is mesa-processed using the photoresist pattern 7 as an etching mask. At that time, the optical waveguide layer 4 is made of SiO 2
_{(2) Since} it is covered with the insulating film 6, no etching process is performed. Further, using the photoresist pattern 7 as a mask, the SiO ₂ insulating film 6 on the optical waveguide layer 4 is patterned using, for example, diluted hydrofluoric acid. In this state,
When the photoresist pattern 7 is removed, a mask pattern 8 as shown in FIG. 12E is obtained.

Next, a semiconductor 9 having a lower refractive index than the semiconductor forming the optical waveguide layers 4 and 5 is crystal-grown on the substrate by using, for example, a metal organic chemical vapor deposition method. In this case, since crystal growth does not occur on the mask patterning 8, the ridge-loaded optical waveguide 2 is formed on the optical waveguide 4 along the mask patterning 8 during the crystal growth as shown in FIG. On the other hand, the mesa-processed optical waveguide 5 becomes the embedded optical waveguide 3 embedded with the low-refractive-index semiconductor 9 during the crystal growth.

In the optical integrated device of the prior art 1, the ridge-loaded optical waveguide 2 and the buried optical waveguide 3 having different optical confinement structures are integrated and formed, and the optical axes are aligned in a self-aligned manner. .

[0020]

However, in the case of Conventional Example 1 described above, the aim is to simplify the manufacturing process.
Since the upper cladding layers 9 of the two optical waveguides are formed at the same time, the two optical waveguides cannot be independently designed.

For this reason, the waveguide structures of the respective optical waveguides are mutually restricted, and the degree of freedom of design is reduced, so that an integrated element in which two different optical waveguides having desired characteristics and functions are integrated cannot be obtained. The problem arises.

Further, since the core layer and the upper cladding layer of the two optical waveguides are separately formed, the number of times of growth increases, the manufacturing process becomes complicated, and the yield of the device decreases. Occurs.

In addition, in the step of forming the SiO ₂ film 6 shown in FIG. 12B and the step of forming the photoresist pattern 7 shown in FIG. 12C, it is necessary to perform mask alignment at the boundary between the two optical waveguide regions. As a result, there is a problem that the yield of the device is reduced.

The present invention solves the above-mentioned problems of the prior art, and provides an optical integrated device capable of easily integrating optical waveguides having desired characteristics and functions by direct coupling, and a method of manufacturing the same. The purpose is to provide.

Another object of the present invention is to reduce the number of times of growth of each layer constituting the optical waveguide and to eliminate the need for mask alignment at the boundary of each optical waveguide region, thereby reducing and simplifying the manufacturing process. An object of the present invention is to provide a method for manufacturing an optical integrated device that can be achieved.

[0026]

The optical integrated device of the present invention comprises:
In an optical integrated device in which at least two optical waveguides are integrated by direct coupling, the core layer of at least one optical waveguide is present at the top and the bottom of the mesa shape, thereby achieving the above object.

Another optical integrated device of the present invention has at least two optical integrated devices.
In an optical integrated device in which two optical waveguides are integrated by direct coupling, the core layer of one optical waveguide exists at the top and bottom of the mesa shape, and the core layer of the other optical waveguide exists planarly below the mesa. Thereby, the above object is achieved.

According to another optical integrated device of the present invention, at least two
In an optical integrated device in which two optical waveguides are integrated by direct coupling, both core layers of the optical waveguide are present at the top and bottom of the mesa shape, thereby achieving the above object.

One of the optical waveguides may be a distributed feedback semiconductor laser.

According to the method of manufacturing an optical integrated device of the present invention, there is provided a method of manufacturing an optical integrated device in which at least two optical waveguides are integrated by direct coupling, wherein a first optical waveguide having a mesa shape is formed; A step of masking the first optical waveguide region, a step of etching the second optical waveguide region while substantially maintaining the mesa shape, and a step of regrowing and forming the second optical waveguide. Thereby, the above object is achieved.

In the method of manufacturing an optical integrated device described above, a step of growing the first optical waveguide on a plane and a step of etching the first optical waveguide into a mesa shape may be included. .

In the above-described method for manufacturing an optical integrated device, a step of growing the first optical waveguide on a substrate having a mesa shape while reflecting the mesa shape may be included.

The operation of the present invention will be described below.

According to the above configuration, in an optical integrated device in which at least two optical waveguides are integrated by direct coupling,
At least one optical waveguide core layer is present on the top and bottom of the mesa shape. For this reason, the entire periphery of the core layer is surrounded by the cladding layer, and the buried optical waveguide is formed, so that the waveguide loss can be reduced. Moreover, in this configuration, since there is no regrowth interface on both sides of the core layer, there is no scattering or absorption of light by the natural oxide film formed on the regrowth interface, and the waveguide loss is further reduced.

The two optical waveguides that are directly coupled can be formed separately, and are not subject to structural restrictions. For example, a buried optical waveguide and a ridge optical waveguide having different characteristics are combined. Even in such a case, it is possible to design each of them into an optimum structure, and it is possible to easily integrate the optical waveguides having desired characteristics and functions by direct coupling.

In an optical integrated device in which at least two optical waveguides are integrated by direct coupling, the core layer of one optical waveguide exists at the top and bottom of the mesa shape, and the core layer of the other optical waveguide has a planar shape below the mesa. With the configuration that exists in
For example, by forming the core layer of the optical waveguide existing planarly below the mesa thinly as the active region of the semiconductor laser, a highly reliable ridge-type semiconductor laser having a low threshold and no regrowth interface can be obtained. The optical integrated device which integrated the type | mold optical waveguide is obtained.

In an optical integrated device in which at least two optical waveguides are integrated by direct coupling, if both core layers of the optical waveguide are present at the top and bottom of the mesa shape, for example, a low threshold voltage excellent in reliability can be obtained. An optical integrated device in which the buried semiconductor laser and the buried optical waveguide are integrated is obtained.

If one of the above optical waveguides is a distributed feedback semiconductor laser, the end face does not have to be a reflecting surface, so that the optical waveguide can be directly grown and formed on the etched surface of the semiconductor laser region. It becomes easy to integrate the semiconductor laser and the optical integrated device of the optical waveguide.

In a method for manufacturing an optical integrated device in which at least two optical waveguides are integrated by direct coupling, a step of forming a first optical waveguide having a mesa shape, a step of masking the first optical waveguide region, According to the method for manufacturing an optical integrated device, the method includes a step of etching the second optical waveguide region while maintaining the mesa shape substantially, and a step of regrowing and forming the second optical waveguide. By the mesa forming process of the waveguide, a mesa is simultaneously formed in the second optical waveguide region, and the buried structure of the second optical waveguide can be formed by etching and regrowth using the mesa.

More specifically, for example, when the mesa shape is dry-etched, the etching proceeds while maintaining the mesa shape, and the surface after the etching also becomes the mesa shape. In addition, when the crystal is grown on the mesa shape, the growth proceeds reflecting the mesa shape. Therefore, by dry-etching and regrowing the mesa shape, a regrown layer reflecting the mesa shape can be formed.

On the other hand, when the optical waveguide is grown on the mesa shape, the growth proceeds reflecting the mesa shape, so that the core layer grows on the top and bottom of the mesa. Furthermore, since the upper clad layer grows covering the core layer, the clad layer is simultaneously formed on the upper side and both sides of the core layer above the mesa. A mold optical waveguide is formed.

Therefore, an optical integrated device in which at least two optical waveguides are directly coupled can be manufactured by a very simple process.
Since the second buried optical waveguide can also be formed by one growth,
It is possible to reduce and simplify the manufacturing process.

Further, the boundary between the first optical waveguide region and the second optical waveguide region does not require mask alignment, and each is arranged in a self-aligned manner. Note that it is not necessary to perform mask alignment for aligning the optical axes of the first optical waveguide and the second optical waveguide, and the optical axes can be aligned in a self-aligned manner.

Thus, in an optical integrated device in which at least two optical waveguides are integrated by direct coupling, an optical integrated device in which the core layer of at least one optical waveguide exists at the top and bottom of the mesa shape can be easily manufactured. , And the yield is improved.

In the above method for manufacturing an optical integrated device, the step of growing the first optical waveguide on a plane and the step of etching the first optical waveguide into a mesa shape include high coupling. It is possible to easily manufacture an optical waveguide integrated device of a direct coupling type of a ridge type optical waveguide and a buried type optical waveguide having high efficiency, and the yield is improved. That is, according to this manufacturing method, in an optical integrated device in which at least two optical waveguides are integrated by direct coupling, the core layer of one optical waveguide exists at the top and bottom of the mesa shape, and the core layer of the other optical waveguide forms the mesa. An optical integrated device existing in a plane below is obtained.

In the above-described method for manufacturing an optical integrated device, a step of growing the first optical waveguide on a substrate having a mesa shape while reflecting the mesa shape is included. It becomes possible to be embedded type. In addition, the first optical waveguide and the second optical waveguide can each be formed by a single growth, and can be formed by a total of two crystal growths.

Accordingly, a buried optical waveguide having a high coupling efficiency and a directly coupled optical waveguide integrated device of the buried optical waveguide can be easily manufactured, and the yield is improved. That is, according to this manufacturing method, in an optical integrated device in which at least two optical waveguides are integrated by direct coupling, an optical integrated device in which both core layers of the optical waveguide exist at the top and the bottom of the mesa shape is obtained.

[0048]

Embodiments of the present invention will be specifically described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows an example of the configuration of an optical integrated device according to Embodiment 1 of the present invention.
It has a structure in which the FB-LD and the embedded optical waveguide are integrated, and can be manufactured by the manufacturing method shown in FIG.

Hereinafter, a method of manufacturing the optical integrated device according to the first embodiment shown in FIG. 1 will be specifically described with reference to FIG.

First, as shown in FIG. 2A, n-GaAs
On the substrate 10, 1 μm thick n-Al_0.6Ga_0.4Asku
Lad layer 11, 0.08 μm thick Al_0.14Ga_0.86A
s active layer 12, 0.2 μm thick p-Al_0.5Ga_0.5A
s carrier barrier layer 13, p-Al having a thickness of 0.1 μm
_0.23Ga_0.77As guide layer 14, 0.02 μm thick n
-Forming the GaAs light absorbing layer 15 sequentially by MOCVD
To achieve. Next, n-GaAs light absorption, which is the uppermost layer of the growth layer, is performed.
The two-beam interference exposure method and the etching
After engraving a concave and convex shape having a period of 0 nm, a thickness of 0.
8 μm p-Al _0.6G_0.4As clad layer 16, thickness
A 0.5 μm p-GaAs contact layer 17 is
Regrowth by VD method to form DFB-LD structure
You.

Next, as shown in FIG. 2B, a stripe-shaped mask 21 is formed, and p-Al
Etching is performed halfway through the _0.6 Ga _0.4 As cladding layer 16 to form a ridge stripe. The ridge stripe is used to confine light in the lateral direction of the DFB-LD. At that time, a ridge is formed simultaneously on the DFB-LD, which is a region where the optical waveguide structure is grown after the etching removal after the ridge stripe for the DFB-LD. The ridge in the waveguide region of the optical waveguide need not be straight, but may be smoothly curved, may have a desired shape if necessary, and the width of the ridge is constant. There is no need to be, and the width may be changed. Therefore, by changing the ridge width between the DFB-LD region and the optical waveguide region, the width of each waveguide can be independently designed.

Next, as shown in FIG. 2C, after removing the mask 21, a mask 22 is formed in the LD region. The mask 22 has a pattern of an SiO ₂ film formed by a sputtering method and ordinary photolithography. In this photolithography, if the previously formed ridge stripe is included therein, there is no need to perform mask alignment, and the region where the mask 22 is formed is self-aligned with the DFB-LD as the first optical waveguide. Area.

When the ridge width is changed between the DFB-LD region and the optical waveguide region, the mask 22 may be aligned with the boundary where the ridge width changes, or the mask 22 may be changed from the boundary where the ridge width changes. The mask 22 may be shifted, but desirably, if the mask 22 is shifted to the DFB-LD region side from the boundary where the ridge width is changed, strict mask alignment is not required, and the optical coupling between the DFB-LD and the optical waveguide is also excellent. Done.

Next, as shown in FIG.
The region other than 2 is etched by 3.5 μm by the RIBE method. The etched region becomes a second optical waveguide region in a self-aligned manner. At the time of this etching, the shape of the ridge is taken over as it is, and the surface after the etching also has a ridge shape. This etching is performed by RI
Dry etching or wet etching other than the BE method may be used, but it is desirable that the etching end face be vertical.

Next, as shown in FIG. 2E, the optical waveguide structure is formed by regrowth using the mask 22 in the LD region as a selective growth mask. The optical waveguide structure has a thickness of 1.6 μm.
Al _0.33 Ga _0.67 As lower cladding layer 18, thickness 0.5
μm Al _0.3 Ga _0.7 As core layer 19, thickness 1.4 μm
Of the upper cladding layer 20 of Al _0.33 Ga _0.67 As. At this time, since it is grown reflecting the ridge shape of the substrate,
The core layer 19 is formed on the top and bottom of the ridge, and the side surface of the core layer 19 on the top of the ridge is covered with an upper cladding layer 20 on the bottom of the ridge.
It is surrounded by 8 and 19 to form a buried optical waveguide. Here, the optical waveguide is directly grown and formed on the etched surface of the DFB-LD region. However, since the optical waveguide is a DFB-LD, the optical waveguide operates as a DFB-LD even if the end surface is not a reflection surface. In particular, in the first embodiment, the gain-coupled DFB-
Since it is an LD and there is no need to match the phase of the end face, the manufacturing yield is improved.

Next, the mask on the ridge above the LD region is removed, and electrodes are deposited on the ridge above the LD region and on the back surface of the substrate (not shown) to complete the optical integrated device.

As shown in FIG. 1, the DFB-
The active layer 12 of the LD and the core layer 19 on the ridge of the optical waveguide formed by regrowth later are located at the same height,
Since the light generated by the B-LD is directly coupled to the core layer 19, a large coupling efficiency was obtained.

In the first embodiment, a ridge is simultaneously formed in the optical waveguide region by the ridge forming process of the DFB-LD, and the buried structure of the optical waveguide is formed by etching and regrowth using the ridge. Therefore, the following effects can be obtained.

(1-1) After the DFB-LD structure is grown, it can be manufactured by a very simple process of one ridge formation process, etching, and regrowth, so that the number of manufacturing steps can be reduced and simplified.

(1-2) The second buried optical waveguide can be formed by one growth.

(1-3) The boundary between the DFB-LD region and the optical waveguide region does not require mask alignment, and is arranged in a self-aligned manner.

It is needless to say that the optical axis can be self-aligned without the need for mask alignment for aligning the optical axis of the DFB-LD with the optical waveguide.

As described above, the ridge type optical waveguide (DFB
A direct-coupling optical waveguide integrated device having a different light confinement structure, ie, an LD region) and a buried optical waveguide (optical waveguide region), can be easily manufactured, yield can be improved, and high light coupling efficiency can be obtained. Was.

In the first embodiment, the DFB-LD
Since the optical waveguide and the optical waveguide are separately formed, the DFB-LD and the optical waveguide can be designed to have optimal structures without any structural restrictions, thereby improving the degree of freedom in design. This makes it possible to achieve both design flexibility and ease of manufacture.

In the first embodiment, the active region is relatively thin in the DFB-LD region in order to lower the threshold current. On the other hand, in the optical waveguide region, the core layer is thickened,
The beam shape is optimized. Thus, DF
Since the active layer of the B-LD and the core layer of the optical waveguide have different thicknesses and mixed crystal ratios, it is necessary to change the mixed crystal ratios of the cladding layers.

In the first conventional example, the upper cladding layers of the first optical waveguide and the second optical waveguide are formed at the same time. Therefore, the structure is restricted, and the degree of freedom in designing the optical integrated device is reduced. However, each waveguide cannot be optimized as in the first embodiment.

On the other hand, in the first embodiment, the DFB-
The active layer, the core layer, and the cladding layer of the LD and the optical waveguide can be designed to have the optimum mixed crystal ratio and layer thickness, respectively, and the function as an optical integrated device can be sufficiently brought out.

The DFB-LD as the first optical waveguide is a ridge-type optical waveguide, so that a highly reliable DFB-LD device having no regrowth interface in the active layer is obtained.

Since the second optical waveguide is a buried optical waveguide, both sides are covered with a cladding layer having a relatively close refractive index, so that the single mode is maintained even if the ridge width is increased. The degree of freedom of the ridge width increases. Therefore, when the optical waveguide structure is grown, it grows reflecting the ridge shape, so that the ridge width increases as the growth proceeds, and the single mode is maintained even if the width of the core layer increases. Further, since there is no air having a large difference in refractive index near the core layer, the waveguide is not affected by the air and the waveguide loss is reduced.

In the buried optical waveguide, a DH structure is usually grown on a plane, a mesa is formed, and a cladding layer is regrown on both sides of the core to be buried. Therefore, both sides of the core layer of the buried optical waveguide are once exposed to air, and then the cladding layer is regrown, an oxide film is formed at the regrowth interface, and light absorption and scattering increase. Propagation loss has increased, leading to deterioration of element characteristics and reduction in yield.

However, in the first embodiment, since there is no regrowth interface on both sides of the core layer, light is not scattered or absorbed by the natural oxide film formed on the regrowth interface, and the waveguide loss is further reduced.

When the ridge stripe is formed by dry etching, no eaves are formed in the ridge shape. Therefore, in a later process, the mask material does not go deep into the eaves, and the mask material is not removed. As a result, the mask material can be completely removed, and the etching of the optical waveguide portion and the regrowth of the optical waveguide are performed satisfactorily.

After forming the second optical waveguide, the DF
It is needless to say that a region other than the ridge of the B-LD region embedded with a semiconductor, a resin or the like is also included in the optical integrated device of the present invention.

(Embodiment 2) FIG. 3 shows a configuration example of an optical integrated device according to Embodiment 2 of the present invention.
It has a structure in which a B-LD and a buried optical waveguide are integrated, and can be manufactured by the manufacturing method shown in FIG.

Hereinafter, a method for manufacturing the optical integrated device according to the second embodiment shown in FIG. 3 will be described in detail with reference to FIG.

First, as shown in FIG. 4A, a diffraction grating having a period of 240 nm and a depth of 100 nm is imprinted on the p-InP substrate 30 by two-beam interference exposure and etching.

Next, as shown in FIG. 4B, a mesa shape having a height of 1 μm is simultaneously formed on both the LD forming region and the optical waveguide forming region on the substrate by ordinary photolithography and a bromine-based etchant. As a result, the diffraction grating remains at the top of the mesa, but the shape of the diffraction grating gradually decreases during etching, and the diffraction grating disappears at the bottom of the mesa.

Here, the mesa of the waveguide region of the optical waveguide need not be a straight line, but may be smoothly curved.
The desired shape can be obtained as required, and the width of the mesa does not need to be constant, but may be changed. For example, by changing the mesa width between the DFB-LD region and the optical waveguide region, the width of each waveguide can be independently designed.

Next, as shown in FIG. 4C, a 0.2 μm-thick n-InGaAs is formed on the mesa substrate shown in FIG. 4B.
A P guide layer 31 (energy wavelength: 1.25 μm), a multiple quantum well active layer 32, a 1.5 μm-thick p-InP clad layer 33, and a 0.5 μm-thick p ⁺ -InGaAsP contact layer 34 are formed by MOCVD. D
An FB-LD structure is formed.

Here, the multiple quantum well active layer 32 has a well layer of InGaAs (In composition 0.5) having a thickness of 7 nm.
3) The barrier layer was composed of a 3-nm-thick five-layer well of InGaAsP (energy wavelength: 1.1 μm), and the energy wavelength measured by photoluminescence measurement was 1.55 μm.

The active layer 32 is formed on the top and bottom of the mesa because it is grown reflecting the mesa shape of the substrate. The side surface of the active layer 32 above the mesa is covered with the upper cladding layer 33 at the bottom of the mesa, and the entire periphery of the active layer 32 is surrounded by the cladding layer 33, thereby forming a buried DFB-LD. . Since the growth proceeds in accordance with the mesa shape of the substrate, the outermost surface of the growth also has a mesa shape.

Next, as shown in FIG. 4D, a mask 38 is formed in the LD region. The mask 38 has a pattern of an SiNx film formed by a plasma CVD method and ordinary photolithography. In this photolithography, if the mesa previously formed is included, it is not necessary to perform mask alignment, and the region where the mask 38 is formed is self-aligned with the DFB as the first optical waveguide.
-It becomes an LD region.

When the mesa width is changed between the DFB-LD region and the optical waveguide region, the mask 38 may be aligned with the boundary where the mesa width changes, or the mask 38 may be changed from the boundary where the mesa width changes. It may be shifted. Desirably, when the mask 38 is shifted to the DFB-LD region side from the boundary where the mesa width is changed, strict mask alignment is not required, and the optical coupling between the DFB-LD and the optical waveguide is performed well.

Next, as shown in FIG.
When a region other than 8 is etched by 3 μm by the RIBE method, the region takes over the shape of the mesa as it is, and becomes a second optical waveguide region in a self-aligned manner, and a mesa shape is formed on the etched surface. .

Next, as shown in FIG. 4F, using the mask 38 in the LD region as a selective growth mask, a thickness of 0.8 μm
InAlAs lower cladding layer 35 (In composition 0.5
2) 0.4 μm thick InGaAlAs core layer 36
(Energy wavelength: 1.3 μm), 1.8 μm thick In
The AlAs upper cladding layer 37 (In composition 0.52) is sequentially regrown to form an optical waveguide structure.

At this time, the core layer 36 is formed on the upper and lower portions of the mesa since the substrate is grown reflecting the mesa shape of the substrate. Will be Therefore, the entire periphery of the core layer 36 is surrounded by the cladding layers 35 and 37, and a buried optical waveguide is formed.

Next, the mask 38 above the mesa in the LD region is removed, and electrodes are deposited (not shown) on the mesa in the LD region and on the back surface of the substrate, thereby completing this optical integrated device.

In the DFB-LD region, since a diffraction grating is formed only on the mesa, light generated by the active layer formed on the mesa acts as a light feedback by the diffraction grating and operates as a DFB-LD. . On the other hand, the active layer formed on the mesa bottom does not perform optical feedback and does not operate as a DFB-LD. Also, since each layer is grown continuously, a buried DFB-LD having no regrowth interface in the active layer is formed.
This is a low threshold DFB-LD with excellent reliability.

As shown in FIG. 3, the DFB-
The active layer 32 of the LD and the core layer 37 above the mesa of the optical waveguide formed by regrowth later are located at the same height,
-Light generated by the LD is directly coupled to the core layer 37, so that high coupling efficiency was obtained. In the first embodiment, the mesa is formed after growing the DFB-LD structure as the first optical waveguide, whereas in the second embodiment, the mesa is formed.
A DFB-LD structure is grown on a substrate on which a mesa is formed.

In the second embodiment, a substrate in which a mesa shape is formed in advance in the DFB-LD region and the optical waveguide region is used, and the DFB-LD and the optical waveguide are grown and formed using the mesa. The effect of is obtained.

(2-1) One-time mesa formation process and D
Fabrication can be performed by very simple steps of FB-LD structure growth, etching, and regrowth, and the number of manufacturing steps can be reduced and simplified.

(2-2) The DFB-LD and the second buried optical waveguide can be formed by a single growth, respectively, and can be formed by a total of two crystal growths.

(2-3) The boundary between the DFB-LD region and the optical waveguide region does not require mask alignment, and is arranged in a self-aligned manner.

It is needless to say that the optical axis can be self-aligned without the need for mask alignment for aligning the optical axis of the DFB-LD with the optical waveguide.

As described above, the embedded optical waveguide (DFB-
A direct coupling type optical waveguide integrated device of an LD region) and a buried optical waveguide (optical waveguide region) could be easily manufactured, yield was improved, and high light coupling efficiency was obtained.

As described above, in the second embodiment, the DFB
-Since the LD and the optical waveguide are formed separately from each other, there is no structural restriction for each, so the DFB-LD
The optical waveguide and the optical waveguide can be designed to have optimal structures, respectively, and the degree of freedom in designing has been improved. This makes it possible to achieve both design flexibility and ease of manufacture.

In the second embodiment, the DFB-L
Although an example in which each upper clad layer of D and the optical waveguide is formed separately has been described, the present invention is not limited to this, and each upper clad layer may be simultaneously grown and formed of the same material.

(Embodiment 3) FIG. 5 shows an example of the configuration of an optical integrated device according to Embodiment 3 of the present invention.
It has a structure in which a B-LD and a buried optical waveguide are integrated, and can be manufactured by the manufacturing method shown in FIG.

Hereinafter, a method of manufacturing the optical integrated device according to the third embodiment shown in FIG. 5 will be described in detail with reference to FIG.

First, as shown in FIG. 6A, n-GaAs
On a substrate 40, an n-In _0.48 Ga _0.52 P cladding layer 41 having a thickness of 1 μm, a multiple quantum well active layer 42, and a thickness of 0.1 μm
m of p-InGaAsP (energy wavelength 850 nm)
The guide layers 43 are sequentially formed by the MOCVD method. Next, the guide layer 43, which is the uppermost layer of the growth layer, is engraved with an irregular shape having a period of 450 nm by two-beam interference exposure and etching, and then p-In _0.48 Ga _0.52 P having a thickness of 0.8 μm is formed.
A cladding layer 44 and a 0.5 μm thick p-GaAs contact layer 45 are regrown by MOCVD to form a DFB-
An LD structure is formed.

Here, the multiple quantum well active layer 42 has a thickness of 8n.
m In _0.2 Ga _0.8 As well layer and 5 nm InGaAs
It was composed of an sP (energy wavelength 850 nm) barrier layer, and the energy wavelength measured by photoluminescence was 980 nm.

Next, as shown in FIG. 6B, the DFB-LD
In order to form a mesa stripe in the region, a stripe-shaped mask 50 is formed, and n-In
Etching is performed halfway through the _0.48 Ga _0.52 P cladding layer 41 to form a mesa stripe. At that time, DFB-L
A mesa shape is also formed on the DFB-LD, which is a region where the optical waveguide structure is grown after the etching removal after the mesa stripe for D, which is performed later.

Here, the mask 50 has a pattern of a SiNx film formed by a plasma CVD method and ordinary photolithography.

The mesa in the waveguide region of the optical waveguide does not need to be straight, but may be smoothly curved, or may have a desired shape if necessary. Need not be constant, and may vary in width. For example, by changing the mesa width between the DFB-LD region and the optical waveguide region, the width of each waveguide can be independently designed.

Next, as shown in FIG. 6C, a mask 51 is formed in the LD region. The mask 51 is obtained by forming a pattern of an SiO ₂ film by a sputtering method and ordinary photolithography. Also, with the mask 50,
Those remaining outside the LD region are also removed at the same time. In this photolithography, if the previously formed mesa stripe is included therein, it is not necessary to perform mask alignment, and the region where the mask 51 is formed is self-aligned with the first optical waveguide DFB-LD. Area.

When the mesa width is changed between the DFB-LD region and the optical waveguide region, the mask 51 may be aligned with the boundary where the mesa width changes, or the mask 51 may be shifted from the boundary where the mesa width changes. Is also good. Preferably, the mask 5 is located closer to the DFB-LD region than the boundary where the mesa width is changed.
Shifting 1 makes precise mask alignment unnecessary, and DF
Optical coupling between the B-LD and the optical waveguide is also performed well.

Next, as shown in FIG.
The region other than 1 is etched by 2 μm by the RIBE method, the region takes over the shape of the mesa as it is, and becomes the second optical waveguide region in a self-aligned manner, and the mesa shape is also formed on the surface after the etching. You.

Next, as shown in FIG. 6E,
With the SiNx mask 50 shown in FIG. 6B remaining, all of the SiO ₂ mask 51 in the LD region other than the upper part of the mesa is removed.

Next, as shown in FIG. 6F, the SiNx
Using the mask 50 as a selective growth mask, the p-InGaP lower cladding layer 46 having a thickness of 0.5 μm,
nGaAsP (energy wavelength 700 nm) core layer 4
7. 1.2 μm thick n-InGaP upper cladding layer 48
Are sequentially regrown to form an optical waveguide structure.

At this time, since the optical waveguide is grown reflecting the mesa shape of the substrate, the core layer 47 is formed on the top and bottom of the mesa. This optical waveguide is a first optical waveguide, D
The active layer 42 of the FB-LD is simultaneously grown on the side surface.
The DFB-LD has a bias opposite to the voltage applied to the LD, so that the DFB-LD acts as a current blocking layer and is optically embedded with a layer having a smaller refractive index than the active layer 42. It becomes a built-in DFB-LD.

The mask 50 above the mesa in the LD region is removed, and electrodes are deposited on the mesa in the LD region and on the back surface of the substrate (not shown) to complete this optical integrated device.

As shown in FIG. 5, the DFB-
The active layer 42 of the LD and the core layer 47 above the mesa of the optical waveguide formed by regrowth later are located at the same height,
-Light generated by the LD is directly coupled to the core layer 47, so that high coupling efficiency was obtained.

In the third embodiment, a mesa is simultaneously formed in the optical waveguide region by the mesa forming process of the DFB-LD, and the optical waveguide is formed by etching and regrowth using the mesa. The following effects can be obtained.

(3-1) After the DFB-LD structure is grown, it can be manufactured by a very simple process of once forming a mesa, etching, and regrowing the optical waveguide, and the number of manufacturing steps can be reduced and simplified. it can.

(3-2) The second buried optical waveguide can be formed by one growth.

(3-3) The boundary between the DFB-LD region and the optical waveguide region does not require mask alignment, and each is arranged in a self-aligned manner.

It is needless to say that the optical axis can be self-aligned without the need for mask alignment for aligning the optical axis of the DFB-LD with the optical waveguide.

As described above, a direct coupling type optical waveguide integrated device of a buried type DFB-LD and a buried type optical waveguide can be easily manufactured, the yield is improved, and a high light coupling efficiency is obtained. .

In the third embodiment, the second optical waveguide is
Although the upper cladding layer is also grown on the side surface of the core layer above the mesa, it can be made to hardly grow on the side surface by selecting the plane orientation.

In Embodiments 1 to 3 described above, D
Although the integration of the FB-LD and the optical waveguide has been described, the optical integrated device of the present invention is not limited to this combination. Good. When a semiconductor laser and an optical waveguide are integrated, the DFB-LD does not require a reflection end face.
And a combination of an optical waveguide.

Although the second waveguide may be a DFB-LD, the first growth provides better crystallinity than the second growth.
It is desirable that the B-LD be a first optical waveguide formed by the first growth.

Further, the optical integrated device of the present invention is not limited to the material system shown in each of the above embodiments, but may be applied to material systems other than those shown in the above embodiments. It is needless to say that similar structures can be produced by a simple manufacturing method, and these are included in the present invention.

(Embodiment 4) FIG. 7 shows a configuration example of an optical integrated device according to Embodiment 4 of the present invention, which has a structure in which a buried optical waveguide and a buried optical waveguide are integrated. 8 can be manufactured by the manufacturing method shown in FIG.

The method of manufacturing the optical integrated device according to the fourth embodiment shown in FIG. 7 will be specifically described below with reference to FIG.

First, as shown in FIG. 8A, the semiconductor substrate 6
A first optical layer is formed by vapor-phase growing a first core layer 61 on 0.

Next, as shown in FIG. 8B, a photoresist mask 64 is formed by ordinary photolithography and etching, and a mesa shape is simultaneously formed in both the first optical waveguide forming region and the second optical waveguide forming region. To form

Next, as shown in FIG. 8C, after the photoresist mask 64 is removed, the first optical waveguide region is formed by sputtering and ordinary photolithography.
An SiO ₂ mask 65 is formed.

In this photolithography, if the previously formed mesa shape is included in the inside, there is no need to perform mask alignment, and the region where the mask 65 is formed becomes the first optical waveguide region in a self-aligned manner. .

Next, as shown in FIG.
The region other than 5 is etched, and the region takes over the above-mentioned mesa shape as it is, becomes the second optical waveguide region in a self-aligned manner, and the surface after etching also becomes the mesa shape.

Next, as shown in FIG.
5 is used as a selective growth mask, a second core layer 62 is grown,
A second optical waveguide is formed. At this time, the core layer 62 is formed on the upper portion and the lower portion of the mesa because the core layer 62 grows while reflecting the mesa shape of the substrate.

Next, as shown in FIG. 8F, the mask 65 is removed.

Next, as shown in FIG. 8G, an upper clad layer 63 is grown over the entire first optical waveguide region and the second optical waveguide region to complete this optical integrated device.

Here, in the second optical waveguide, the side surface of the second core layer 62 above the mesa is covered with the upper cladding layer 63 at the bottom of the mesa, and the entire periphery of the second core layer 62 is surrounded by the cladding layer 63. And is a buried optical waveguide.
Also in the first optical waveguide, the side surface of the first core layer 61 above the mesa is covered with the upper cladding layer 63 at the bottom of the mesa,
The entire periphery of the first core layer 61 is surrounded by the cladding layer 63, and the buried optical waveguide is formed.

As shown in FIG. 7, the first core layer 61 of the first optical waveguide formed first and the second core layer formed by regrowth later.
The second core layer 62 above the mesa of the optical waveguide is located at the same height, and light having propagated through the first optical waveguide is directly coupled to the second core layer 62, so that a large coupling efficiency was obtained.

In the fourth embodiment, a mesa is simultaneously formed in the second optical waveguide region by the mesa forming process of the first optical waveguide, and the second optical waveguide is formed by etching and regrowth using the mesa. Therefore, the following effects can be obtained.

(4-1) After growing the first optical waveguide, the first optical waveguide can be manufactured by a very simple process of once forming a mesa, etching and regrowth.

(4-2) The boundary between the first optical waveguide region and the second optical waveguide region does not require mask alignment, and is arranged in a self-aligned manner.

It is needless to say that the optical axes can be aligned in a self-aligning manner without the need for mask alignment for aligning the optical axes of the first optical waveguide and the second optical waveguide.

As described above, a directly coupled optical waveguide integrated device of two buried optical waveguides (the first optical waveguide and the second optical waveguide) can be easily manufactured, the yield is improved, and the high light Coupling efficiency was obtained.

(Embodiment 5) FIG. 9 shows an example of the configuration of an optical integrated device according to Embodiment 5 of the present invention.
It has a structure in which a B-LD and a buried optical waveguide are integrated, and can be manufactured by the manufacturing method shown in FIG.

Hereinafter, the method for manufacturing the optical integrated device according to the fifth embodiment shown in FIG. 9 will be described in detail with reference to FIG.

First, as shown in FIG. 10A, n-InP
On a substrate 70, an n-InP cladding layer 71, InGaAs
sP active layer 72 (energy wavelength 1.3 μm), p-I
nGaAsP guide layer 73 (energy wavelength 1.05 μm)
m) are sequentially formed by MOCVD. Next, after forming a 200 nm-period uneven shape on the guide layer 73, which is the uppermost layer of the growth layer, by two-beam interference exposure and etching, the p-InP cladding layer 74 and the p-InGaAs contact layer 75 are formed by MOCVD. Regrow sequentially and D
An FB-LD structure is formed.

Then, as shown in FIG. 10B, a striped SiNx mask 80 is formed, and etching is performed halfway through the n-InP cladding layer 71 to form a mesa stripe. At this time, a mesa is formed simultaneously on the DFB-LD, which is a region where the optical waveguide structure is grown after the etching removal after the mesa stripe for the DFB-LD.

Next, as shown in FIG.
-An SiO ₂ mask 81 is formed in a region other than the LD. At this time, the mask 81 is patterned so that the SiNx mask 80 in the DFB-LD region remains.

Next, as shown in FIG.
And DFB-LD using mask 81 as a selective growth mask
An Fe-doped InP current confinement layer 76 is buried on both sides of the mesa in the region to form a buried DFB-LD.

Next, as shown in FIG.
Then, the mask 81 is removed.

Next, as shown in FIG. 10F, DFB-L
An SiO ₂ mask 82 is formed in the D region. Here, the region where the mask 82 is formed is the DFB which is the first optical waveguide.
-It becomes an LD region.

Next, as shown in FIG. 10G, a region other than the mask 82 is etched by the RIBE method, and the region takes over the above-mentioned mesa shape as it is, and becomes a second optical waveguide region. The surface also has a mesa shape.

Next, as shown in FIG. 10H, using the mask 82 as a selective growth mask, the InP lower cladding layer 7 is formed.
7. InGaAsP core layer 78 (energy wavelength 1.1)
μm), the InP upper cladding layer 79 is sequentially regrown to form an optical waveguide structure. At this time, since the core layer 78 grows reflecting the mesa shape of the substrate, the core layer 78 is formed on the upper and lower portions of the mesa. For this reason, the entire periphery of the core layer 78 is surrounded by the cladding layer 79 to form a buried optical waveguide.

Here, the optical waveguide is grown and formed directly on the etched surface of the DFB-LD region.
Therefore, the end face operates as a DFB-LD even if it does not have to be a reflection surface.

The mask 82 above the mesa in the DFB-LD region is removed in the form of a stripe, and electrodes are deposited on the mesa in the DFB-LD region and on the back surface of the substrate (not shown) to complete this optical integrated device.

As shown in FIG. 9, the DFB-
The active layer 72 of the LD and the core layer 78 formed on the mesa of the optical waveguide formed by regrowth later are located at the same height, and the light generated by the DFB-LD is directly coupled to the core layer 78. Therefore, a large coupling efficiency was obtained.

In the fifth embodiment, a mesa is simultaneously formed in the optical waveguide region by the mesa forming process of the DFB-LD, and the buried structure of the optical waveguide is formed by etching and regrowth using the mesa. Therefore, the following effects can be obtained.

(5-1) After the DFB-LD structure is grown, it can be manufactured by a very simple process of once forming a mesa, etching and regrowth.

(5-2) The second embedded optical waveguide can be formed by one growth.

It is needless to say that the optical axis can be self-aligned without the necessity of mask alignment for aligning the optical axis of the DFB-LD with the optical waveguide.

As described above, it is possible to easily manufacture a direct coupling type optical waveguide integrated device of a buried type optical waveguide (DFB-LD and optical waveguide) having two different structures, to improve the yield and to increase the light output. Was obtained.

The optical integrated device and the method of manufacturing the same according to the present invention are not limited to the specific structures and manufacturing methods described in the first to fifth embodiments. It is needless to say that a configuration having a different thickness or another material system can be used, and further, the configuration and process can be appropriately changed or added.

[0160]

As described above, according to the optical integrated device and the method of manufacturing the same of the present invention, optical waveguides having desired characteristics and functions can be easily integrated by direct coupling. Furthermore, the number of growth steps of each layer constituting the optical waveguide is reduced, and mask alignment at the boundary between the optical waveguide regions is not required, so that the number of manufacturing steps can be reduced and simplified.

More specifically, for example, in an optical integrated device in which at least two optical waveguides are integrated by direct coupling, since the core layer of at least one optical waveguide exists at the top and bottom of the mesa shape, the area around the core layer is reduced. Are all surrounded by the cladding layer and become a buried optical waveguide, so that the waveguide loss can be reduced. Moreover, in this configuration, since there is no regrowth interface on both sides of the core layer, light is not scattered or absorbed by the natural oxide film formed on the regrowth interface, and waveguide loss can be further reduced.

The two optical waveguides that are directly coupled can be formed separately and are not subject to any structural restrictions. For example, a buried optical waveguide and a ridge optical waveguide having different characteristics are combined. In this case, the optical waveguides having the desired characteristics and functions can be easily integrated by direct coupling.

In an optical integrated device in which at least two optical waveguides are integrated by direct coupling, the core layer of one optical waveguide exists at the top and bottom of the mesa shape, and the core layer of the other optical waveguide has a planar shape below the mesa. With the configuration that exists in
For example, by forming the core layer of the optical waveguide existing planarly below the mesa thinly as the active region of the semiconductor laser, a highly reliable ridge-type semiconductor laser having a low threshold and no regrowth interface can be obtained. The optical integrated device which integrated the type | mold optical waveguide is obtained.

In an optical integrated device in which at least two optical waveguides are integrated by direct coupling, if both core layers of the optical waveguide are present at the top and bottom of the mesa shape, for example, a low threshold voltage excellent in reliability can be obtained. An optical integrated device in which the buried semiconductor laser and the buried optical waveguide are integrated is obtained.

If one of the above optical waveguides is a distributed feedback semiconductor laser, the end face does not have to be a reflecting surface, so that the optical waveguide can be directly grown and formed on the etched surface of the semiconductor laser region. It becomes easy to integrate the semiconductor laser and the optical integrated device of the optical waveguide.

In a method for manufacturing an optical integrated device for integrating at least two optical waveguides by direct coupling, a step of forming a first optical waveguide having a mesa shape, a step of masking the first optical waveguide region, According to the method for manufacturing an optical integrated device, the method includes a step of etching the second optical waveguide region while maintaining the mesa shape substantially, and a step of regrowing and forming the second optical waveguide. By the mesa forming process of the waveguide, a mesa is simultaneously formed in the second optical waveguide region, and the buried structure of the second optical waveguide can be formed by etching and regrowth using the mesa.

Therefore, an optical integrated device in which at least two optical waveguides are directly coupled can be manufactured by a very simple process.
Since the second buried optical waveguide can also be formed by one growth,
The number of manufacturing steps can be reduced and simplified.

Further, the boundary between the first optical waveguide region and the second optical waveguide region does not require mask alignment, and each is arranged in a self-aligned manner. Note that it is not necessary to perform mask alignment for aligning the optical axes of the first optical waveguide and the second optical waveguide, and the optical axes can be aligned in a self-aligned manner.

Thus, in an optical integrated device in which at least two optical waveguides are integrated by direct coupling, an optical integrated device in which the core layer of at least one optical waveguide exists at the top and bottom of the mesa shape can be easily manufactured. , And the yield is improved.

In the above-described method of manufacturing an optical integrated device, the step of growing the first optical waveguide on a plane and the step of etching the first optical waveguide into a mesa shape include high coupling. It is possible to easily manufacture an optical waveguide integrated device of a direct coupling type of a ridge type optical waveguide and a buried type optical waveguide having high efficiency, and the yield is improved. That is, according to this manufacturing method, in an optical integrated device in which at least two optical waveguides are integrated by direct coupling, the core layer of one optical waveguide exists at the top and bottom of the mesa shape, and the core layer of the other optical waveguide forms the mesa. An optical integrated device existing in a plane below is obtained.

In the above-described method for manufacturing an optical integrated device, the step of growing the first optical waveguide on the substrate having the mesa shape while reflecting the mesa shape is included. It can be embedded. In addition, the first optical waveguide and the second optical waveguide can each be formed by a single growth, and can be formed by a total of two crystal growths.

Accordingly, a buried optical waveguide having a high coupling efficiency and a direct coupling type optical waveguide integrated device of the buried optical waveguide can be easily manufactured, and the yield is improved. That is, according to this manufacturing method, in an optical integrated device in which at least two optical waveguides are integrated by direct coupling, an optical integrated device in which both core layers of the optical waveguide exist at the top and the bottom of the mesa shape is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of an optical integrated device according to a first embodiment of the present invention.

FIG. 2 is a process chart showing a method for manufacturing an optical integrated device according to Embodiment 1 of the present invention.

FIG. 3 is a diagram showing a configuration example of an optical integrated device according to a second embodiment of the present invention.

FIG. 4 is a process chart showing a method for manufacturing an optical integrated device according to Embodiment 2 of the present invention.

FIG. 5 is a diagram showing a configuration example of an optical integrated device according to a third embodiment of the present invention.

FIG. 6 is a process chart showing a method for manufacturing an optical integrated device according to Embodiment 3 of the present invention.

FIG. 7 is a diagram showing a configuration example of an optical integrated device according to a fourth embodiment of the present invention.

FIG. 8 is a process chart showing a method for manufacturing an optical integrated device according to Embodiment 4 of the present invention.

FIG. 9 is a diagram showing a configuration example of an optical integrated device according to a fifth embodiment of the present invention.

FIG. 10 is a process chart showing a method for manufacturing an optical integrated device according to Embodiment 5 of the present invention.

FIG. 11 is a diagram illustrating a method of coupling two optical waveguides.

FIG. 12 is a process chart showing a conventional method for manufacturing an optical integrated device.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 semiconductor substrate 2 ridge-type optical waveguide 3 buried optical waveguide 4, 5 optical waveguide core layer 6 silicon oxide (SiO ₂ ) 7 photoresist pattern 8 mask pattern for selective growth 9 low refractive index semiconductor 10 n-GaAs substrate 11 n-Al _0.6 Ga _0.4 As clad layer 12 Al _0.14 Ga _0.86 As active layer 13 p-Al _0.5 Ga _0.5 As carrier barrier layer 14 p-Al _0.23 Ga _0.77 As guide layer 15 n-GaAs light absorption layer 16 p-Al _0.6 Ga _0.4 As clad layer 17 p-GaAs contact layer 18 Al _0.33 Ga _0.67 As lower clad layer 19 Al _0.3 Ga _0.7 As core layer 20 Al _0.33 Ga _0.67 As upper clad layer 21 Mesa forming mask 22 SiO ₂ mask 30 p-InP Substrate 31 n-InGaAsP guide layer 32 InGaAs / InGaAsP multilayer Quantum well active layer 33 p-InP cladding layer 34 p ⁺ -InGaAsP contact layer 35 InAlAs lower cladding layer (In composition 0.52) 36 InGaAlAs core layer 37 InAlAs upper clad layer (In composition 0.52) 38 SiNx mask 40 n -GaAs substrate 41 n-In _0.48 Ga _0.52 P cladding layer 42 In _0.2 Ga _0.8 As / InGaAsP multiple quantum well active layer 43 p-InGaAsP guide layer 44 p-In _0.48 Ga _0.52 P cladding layer 45 p-GaAs contact layer 46 p -InGaP lower cladding layer 47 InGaAsP core layer 48 n-InGaP upper cladding layer 50 the mesa forming SiNx mask 51 SiO ₂ mask 60 semiconductor substrate 61 the first core layer 62 over the second core layer 63 clad layer 64 the mesa forming a photoresist Disk 65 SiO ₂ mask 70 n-InP substrate 71 n-InP cladding layer 72 InGaAsP active layer 73 p-InGaAsP guide layer 74 p-InP cladding layer 75 p-InGaAs contact layer 76 Fe-doped InP current blocking layer 77 InP lower cladding layer 78 InGaAsP core layer 79 SiO for InP upper cladding layer 80 the mesa forming SiNx mask 81 current confinement layer selective growth ₂ mask 82 waveguide etching / re-growth SiO ₂ mask

Claims (7)

[Claims] 1. An optical integrated device in which at least two optical waveguides are integrated by direct coupling, wherein the core layer of at least one optical waveguide exists at the top and bottom of the mesa shape. 2. An integrated optical device in which at least two optical waveguides are integrated by direct coupling, wherein a core layer of one optical waveguide is present on top and bottom of a mesa shape, and a core layer of the other optical waveguide is located below the mesa. An optical integrated device that exists in a planar shape. 3. An integrated optical device in which at least two optical waveguides are integrated by direct coupling, wherein both core layers of the optical waveguide are present at a top and a bottom of a mesa shape. 4. The optical integrated device according to claim 1, wherein one of said optical waveguides is a distributed feedback semiconductor laser. 5. A method of manufacturing an optical integrated device in which at least two optical waveguides are integrated by direct coupling, a step of forming a first optical waveguide having a mesa shape, and a step of masking the first optical waveguide region. And a step of etching the second optical waveguide region while maintaining the mesa shape substantially, and a step of regrowing and forming the second optical waveguide. 6. The method for manufacturing an optical integrated device according to claim 5, comprising a step of growing said first optical waveguide on a plane and a step of etching said first optical waveguide into a mesa shape. 7. The method according to claim 5, further comprising the step of growing the first optical waveguide on a substrate having a mesa shape while reflecting the mesa shape.