JPH0736046B2 - Method for manufacturing optical waveguide device - Google Patents

Description

The present invention relates to an optical waveguide device that guides light by a laminated structure. In particular, it relates to the structure of an optical waveguide device. The present invention is suitable for use as a waveguide of a semiconductor laser and its peripheral optical circuit.

〔Overview〕

According to the present invention, in an optical waveguide device having a laminated structure, by embedding a layer for giving a lateral refractive index in this laminated structure with another material, the refractive index difference caused by this layer is controlled with high accuracy. Is.

[Conventional technology]

Conventionally, various structures of optical waveguide elements have been proposed and manufactured. The ones used for semiconductor lasers are:
Rib type optical waveguide devices are well known.

In the rib type optical waveguide device, a passive optical waveguide layer is provided adjacent to an active optical waveguide layer (active layer in a semiconductor laser) for propagating light, a part of the passive optical waveguide layer is etched, and a difference in thickness is obtained. This makes the effective refractive index of the layer structure including the active optical waveguide layer different. Therefore, the refractive index difference in the layer structure including the active optical waveguide layer is determined by the thickness of the passive optical waveguide layer, that is, the etching amount.

[Problems to be Solved by the Invention]

However, in order to obtain transverse mode unity, the refractive index difference Δn is set to 10
It is common to set the waveguide width W to ^-2 to 10 ^-3 and the waveguide width W to ² to ⁴ μm. For this purpose, the etching amount of the passive optical waveguide layer is
It should be about 20 to 30 nm. Therefore, it is difficult to control the etching amount, and it is difficult to obtain in-plane uniformity.

It is another object of the present invention to solve the above problems and provide a method for manufacturing an optical waveguide device capable of setting the refractive index difference with good reproducibility and controllability.

[Means for Solving the Problems]

The method for producing an optical waveguide element of the present invention is a method of stacking a first layer and a second layer, each of which has a refractive index different from that of an adjacent layer, with a third layer in between, and a layer structure including the first layer. In the method of manufacturing an optical waveguide element in which the second layer is etched according to the waveguide pattern to be set to, the third layer is exposed through the second layer by etching, and the third layer left by this etching is exposed. The second layer is embedded with a material having a refractive index substantially equal to that of the third layer.

In the following description, the first layer is called an active optical waveguide layer or an active layer (in the case of a semiconductor laser), the second layer is called a passive optical waveguide layer or a guide layer, and the third layer is called a block layer.

[Action]

The difference in the refractive index in the layer structure including the active optical waveguide layer is determined by the difference in the thickness of the passive optical waveguide layer, but if the structure in which the passive optical waveguide layer is left only along the waveguide pattern is used, The thickness of the wave layer directly becomes the difference in the thickness of the passive optical waveguide layer.

In this case, since the etching penetrates the passive optical waveguide layer, the underlying layer of the passive optical waveguide layer is also etched. Therefore, a block layer is provided between the active optical waveguide layer and the passive optical waveguide layer. The etching amount with respect to the block layer varies depending on the conditions at that time, but if it is filled with a material having the same refractive index after etching, there is no effect. Therefore, the etching conditions need not be set so strictly.

By controlling the film thickness and the refractive index (composition) of each of the passive optical waveguide layer and the block layer in this manner, the refractive index difference in the layer structure including the active optical waveguide layer can be set with good reproducibility.

〔Example〕

FIG. 1 is a perspective view showing a first embodiment of the present invention, a part of which is cut away.

In this embodiment, the present invention is implemented by a semiconductor laser, and an active layer 4 is provided as a first layer having a refractive index different from that of an adjacent layer, and effective refraction in a layer structure including the active layer 4 is performed. The guide layer 6 is provided as a second layer that sets the distribution of the rates and defines the propagation path of light in this layer structure. More specifically, the buffer layer 2, the clad layer 3, the active layer 4, the block layer 5, the guide layer 6, the clad layer 7, the cap layer 8, the SiO ₂ insulating layer 9, and the Cr / Au electrode 10 are formed on the substrate 1. An AuGe / Au electrode 11 is provided on the back surface of the substrate 1 which is laminated.

The active layer 4 in this embodiment has a quantum well structure, and includes a quantum well layer 42 and GRIN (graded index) layers 41 and 43 sandwiching the quantum well layer 42.

The guide layer 6 is a layer that sets an effective refractive index distribution in the layer structure including the active layer 4 and defines the optical propagation path, that is, the optical waveguide portion 44, and is cut along the optical waveguide portion 44. It has a formed shape, that is, a shape in which a portion corresponding to the periphery of the optical waveguide section 44 is removed.

The block layer 5 and the cladding layer 7 are made of materials having the same refractive index, and the guide layer 6 is embedded with these two layers. The refractive index of the block layer 5 and the cladding layer 7 is the guide layer 6
Choose one with a lower refractive index.

The clad layer 7 and the cap layer 8 are provided with grooves corresponding to the portions where the guide layer 6 is removed. The groove and the cap layer 8 are covered with the SiO ₂ insulating layer 9 except for the portion corresponding to the waveguide pattern. Therefore, the electrode 10
The electric current supplied from is passed through the guide layer 6 defining the waveguide pattern and injected into the active layer 5.

As the composition and film thickness of the block layer 5, the guide layer 6 and the cladding layer 7, for example, the block layer 5 Al _0.6 Ga _0.4 As 100 nm guide layer 6 Al _0.3 Ga _0.7 As 50 nm cladding layer 7 Al _0.6 Ga _0.4 As − , The refractive index difference Δn =
An optical waveguide portion 44 of 0.005 is obtained.

FIG. 2 shows a method of manufacturing this device, where (a) is the first growth step, (b) is the pattern formation step, (c) is the etching and resist removal step, and (d) is the second growth step.
(E) shows an electrode formation process, respectively.

First, in the first growth step, the buffer layer 2, the cladding layer 3, the active layer 4, the block layer 5 and the guide layer 6 are crystal-grown on the substrate 1. The film thicknesses of the block layer 5 and the guide layer 6 are controlled particularly accurately.

Then, a pattern formation process is performed. In this process,
A resist is applied to the surface of the guide layer 6, and pattern exposure and development are performed according to the waveguide pattern to be formed in the layer structure including the active layer 4. As a result, the resist mask 12 is formed.

In the etching and resist removing process, the guide layer 6 is etched using the resist mask 12 until the block layer 5 is reached. As a result, the guide layer 6 becomes the optical waveguide portion.
The shape is cut along 44.

In the second growth step, the clad layer 7 and the cap layer 8 are regrown on the etched guide layer 6.
The clad layer 7 has the same refractive index (composition) as the block layer 5. As a result, the guide layer 6 is embedded, and the presence or absence of the guide layer 6 causes an effective refractive index difference in the active layer 4. Due to this difference in refractive index, the optical waveguide portion 44 is defined in the layer structure including the active layer 4.

Then, as an electrode forming step, the cap layer 8 and the cladding layer 7 are etched, the SiO ₂ insulating layer 9 is formed and etched, and the electrode 10 is formed, and the electrode 11 is provided on the back surface of the substrate 1.

FIG. 3 is a perspective view showing a second embodiment of the present invention, and is shown with a part cut away as in FIG. This embodiment also implements the present invention with a semiconductor laser, and differs from the first embodiment in that the guide layer 6 is provided with the diffraction grating 61.

FIG. 4 shows the oscillation characteristics of the device prototyped according to the structure of the second embodiment.

For the composition and film thickness of the block layer 5, the guide layer 6, and the cladding layer 7 in this device, the values exemplified in the description of the first embodiment were used. The resonator length is 350 μm. Further, the etching conditions of the guide layer 6 (film thickness 50 nm) are as follows: etchant sulfuric acid / hydrogen peroxide 4: H ₂ SO ₄ +1: H ₂ O ₂ +90: H _{2 O} temperature 5 ° C. etching rate 30 nm / min etching time 2 minutes And

The distribution of the threshold current of the prototyped device is shown in the following table.

[Effects of the Invention] As described above, according to the present invention, since the refractive index can be controlled by controlling the film thickness of the passive optical waveguide layer and the block layer during crystal growth, the optical waveguide having a uniform refractive index difference. There is an effect that the structure can be manufactured with good reproducibility.

Further, since it is not necessary to set the thickness of the passive optical waveguide layer by etching and the passive optical waveguide layer may be completely removed by etching, there is an effect that the tolerance of etching is large and the manufacturing process is simplified.

Further, when the structure of the present invention is used for a semiconductor laser, the active layer and the regrowth interface are separated from each other, so that the device characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first embodiment of the present invention, in which a part is cut away. FIG. 2 is a view showing the manufacturing method of this embodiment. FIG. 3 is a perspective view showing a second embodiment of the present invention, in which a part is cut away. FIG. 4 is a diagram showing oscillation characteristics of a device prototyped according to the structure of the second embodiment. 1 ... Substrate, 2 ... Buffer layer, 3 ... Clad layer, 4
...... Active layer, 5 ... Block layer, 6 ... Guide layer, 7 ...
… Cladding layer, 8 …… Cap layer, 9 …… SiO ₂ insulating layer,
10, 11 …… Electrode, 12 …… Resist mask, 41,43 …… GR
IN layer, 42 ... Quantum well layer, 44 ... Optical waveguide section.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Haruo Hosomatsu Inventor Haruo Hosomatsu 2-11-13 Nakamachi, Musashino City, Tokyo Photometer Measurement Technology Development Co., Ltd. (56) Reference JP-A-52-77741 (JP, A) JP-A-54-34847 (JP, A)

Claims (1)

[Claims] 1. An attempt is made to stack a first layer and a second layer, each of which has a refractive index different from that of an adjacent layer, through a third layer, and to set the layer structure including the first layer. In the method of manufacturing an optical waveguide element, which etches the second layer according to a waveguide pattern, the third layer is exposed by penetrating the second layer by the etching, and the third layer left by this etching. A method for manufacturing an optical waveguide device, characterized in that the second layer is embedded with a material having a refractive index substantially equal to that of the third layer.