JPH09197154A - Optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of reflected light on a joint face and to prevent a buildup in the joint face by forming the joint face between optical waveguides in such a manner that the joining face crosses the optical waveguide plane and the plane perpendicular to the optical waveguide plane. SOLUTION: Core layer 11 of a first waveguide is grown by an epitaxial method on a substrate 10. Then, a SiO2 film 12 is grown in a region including the region where the first waveguide is to be formed, in a size about 20μm wide and about 300μm long which is the same length as the first waveguide and the SiO2 film 12 is used as a mask for etching to remove the core layer in the first waveguide region and to form an island of the core layer 11 of the first waveguide. In this process, the island of the core layer 11 is formed in such a manner that at least the joining face with a second waveguide crosses the plane of laminated layers in the optical waveguide direction, namely in <110> direction, and with the plane in <001> direction, that is perpendicular to the laminated layer plane in the optical waveguide direction (shown is Fig b-1).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an optical waveguide device, and specifically, an optical waveguide in which two or more kinds of optical waveguides having different refractive index distributions are cascade-connected in the optical axis direction. It concerns a waveguide.

[0002]

2. Description of the Related Art It has been attempted to improve the performance of a semiconductor optical device by connecting optical waveguides having different refractive index distributions in cascade in the optical axis direction of the optical waveguides. The structure used in that case is shown in FIG. 5 as an example of a semiconductor laser. In FIG. 5, reference numeral 20 is a gain waveguide, 21 is a guide waveguide, 22 is a joint surface between the gain waveguide 20 and the guide waveguide 21, 23 is a laser emission end face, 30 is a substrate, and 35 is a laser cladding layer. Each is illustrated.

In order to fabricate a semiconductor laser module in which an optical fiber is coupled to a semiconductor laser, it is important that the optical axis adjustment in coupling the semiconductor laser and the optical fiber is coupled with high efficiency and with high tolerance. Is.

Therefore, the structure of the optical waveguide as shown in FIG. 5 is used. That is, a bandgap energy (refractive index becomes low) larger than that of the gain waveguide 20 on one end side of the gain waveguide 20 that produces a gain by current injection.
The guide waveguide 21 constituted by the core layer having the is connected via the joint surface 22.

At this time, the shape of the guide waveguide 21 is shown in FIG.
As shown in (1), the tapered structure has a width that gradually narrows toward the laser emission end face 23 side, and the light confinement efficiency in the waveguide is loosened toward the laser emission end face 23, so that the laser emission end face 23 is emitted. This structure is designed to expand the size of laser light.

As described above, the gain waveguide 20 and the guide waveguide 21 having a bandgap energy larger than that of the gain waveguide 20 are provided.
When manufacturing the joint surface 22 with, the manufacturing process generally shown in FIGS. 6 and 7 has been used. That is, as shown in FIG. 6A, first, the core layer 31 of the gain waveguide is epitaxially grown on the substrate 30. Next, as shown in FIG. 6B, the width including the region where the gain waveguide 20 is formed is 20 μm.
m, the SiO ₂ film 32 formed in a region having a length of about 300 μm, which is equal to the length of the gain waveguide, is used as an etching mask to remove the core layer 31 of the gain waveguide in the region other than this region. , The island 33 of the core layer of the gain waveguide is formed. Next, as shown in FIG. 6C, the core layer 34 of the guide waveguide is formed in a region other than the island 33 of the core layer of the gain waveguide.
To grow the layer forming. Next, as shown in FIG. 7A, the S remaining on the island 33 of the core layer of the gain waveguide.
After removing the iO ₂ film 32, the island 3 of the core layer of the gain waveguide is formed.
3 and the core layer 34 of the guide waveguide are processed into the shapes of the gain waveguide 20 and the guide waveguide 21 as shown in FIG. Next, as shown in FIG. 7B, a cladding layer 35 of the laser is grown, and the gain waveguide 20 and the guide waveguide 21 are formed.
Forming a laser waveguide, and forming an electrode 36 for current injection.
To provide a laser.

In the above process, since the laser end face 23 is produced by the cleavage process, the laser waveguide has a direction orthogonal to this cleavage face. That is, since the cleavage occurs along the [110] plane, which is the crystallographic plane orientation, the laser waveguide necessarily takes the <110> direction orthogonal to the [110] plane. At this time, the island 33 of the core layer of the gain waveguide is <110> as shown in FIG.
A rectangular shape having four sides parallel to the direction or a direction crystallographically equivalent to this direction has been used.

The reason is that, as shown in FIG. 6B, as a method for removing the core layer 31 of the gain waveguide in a region other than the region where the gain waveguide is formed, for example, a wet etching method using a chemical solution such as hydrochloric acid is used. To use.

This means that when the sides of the island 33 are deviated from the <110> direction, a crystallographically unstable surface is formed on the side surface of the island, resulting in a non-uniform joint surface. This is because the desired results cannot be obtained because they are formed. Therefore, the side surface of the island formed by the wet etching method is formed by four crystallographically stable [110] planes,
In order to form a uniform joint surface, the shape of the island 33 should be <11.
The rectangle has four sides parallel to the 0> direction or the direction crystallographically equivalent to this direction.

[0010]

However, even in the case described above, the optical inconvenience caused by the fact that the joint surface 22 has a positional relationship perpendicular to the optical axis of the waveguide, and the side surface of the island 33 has a growth rate. The problem is that the shape is inconvenient due to the fast [110] plane. Here, the optical inconvenience means that the reflected light generated at the joint surface causes unstable operation of the laser, and the geometrical inconvenience means that the side surface having a fast growth rate causes bulge at the joint part. That is, the laser characteristics are deteriorated.

As described above, the two optical waveguides 20 and 21
When they are connected in tandem, the guided light is reflected due to the mismatch of the refractive index distributions of these connection surfaces 22, causing various inconveniences such as instability of laser oscillation.

Further, when the optical waveguide is a single crystal such as a semiconductor, the cleaved end face can be formed only with a low index face, so that the direction of the optical waveguide is limited to the direction perpendicular to this, and in the end, the bonding surface is formed. Will correspond to this low index plane.
In this case, abnormal crystal growth may occur at the junction end face, causing an abnormal shape of the optical waveguide.

In view of the above problems, the present invention can prevent the generation of reflected light at the joint surface in an optical waveguide having a joint portion, or prevent the rise of the joint portion which is a cause of geometrical inconvenience. An object is to provide an optical waveguide that can be used.

[0014]

In the optical waveguide of the present invention for achieving the above object, a plurality of optical waveguides having different refractive index distributions in the stacking direction are connected in series in the light guiding direction of the waveguide. In the optical waveguide, the joint surface of the plurality of optical waveguides is
It is characterized in that it intersects with a laminated surface in the waveguide direction of the light and a surface orthogonal to the laminated surface in the waveguide direction.

In the above optical waveguide, the joint surface intersects with the stacking direction.

In the above optical waveguide, the plurality of optical waveguides are formed of a semiconductor.

In the optical waveguide according to the present invention, the joint surface between the optical waveguides intersects with the waveguide surface of the light and the surface orthogonal to the waveguide surface. Therefore, since the guided light reflected by the joint surface is radiated to the outside of the waveguide, the guided light does not enter the waveguide again and return to the original direction, and therefore the disadvantage due to the reflected light does not occur.

Further, when the waveguide is made of a single crystal material, it is possible to make the junction surface not a low index surface where abnormal growth easily occurs, and it is possible to prevent the shape of the optical waveguide from being abnormal.

[0019]

Embodiments of the present invention will be described below.

<First Embodiment> FIGS. 1 to 3 show an optical waveguide and a method of manufacturing the same according to a first embodiment of the present invention. First, as shown in FIG. 1A, the core layer 11 of the first waveguide is epitaxially grown on the substrate 10.

Next, FIG. 1 (b)-(1) and FIG. 1 (b)-
As shown in (2), the SiO ₂ film 1 including a region for forming the first waveguide has a width of about 20 μm and a length of about 300 μm which is equal to the length of the first waveguide.
Using 2 as an etching mask, the core layer of the first waveguide in the region other than this region is removed to form the island 13 of the core layer of the first waveguide.

At this time, in the case shown in FIGS. 1 (b)-(1), the island shape of the core layer 11 of the first waveguide is set so that at least the joint surface 14 with the second waveguide is in the light guiding direction. Ie <1
A plane is formed so as to intersect with the stacking plane in the 10> direction and the plane in the <001> direction orthogonal to the stacking plane in the waveguide direction. 1 (b)-(1), the bonding surface 14 is a surface orthogonal to the substrate 10.

Another example is shown in FIGS. 1 (b)-(2).
As shown in, the shape of the island 13 of the core layer of the first waveguide is formed so that at least the bonding surface 16 with the second waveguide intersects the stacking direction, that is, <001> to form a tapered surface. I have to.

Next, as shown in FIG.
As a continuation of (1), a layer for forming the core layer 17 of the second waveguide is grown in a region other than the island 13 of the core layer of the first waveguide.

Next, as shown in FIG. 2B, the SiO ₂ film 12 remaining on the island 13 of the core layer of the first waveguide.
After removing the first waveguide core island 13 and the second waveguide core layer 17, the first waveguide 18 and the second waveguide 18 having the same shape as shown in FIG. The waveguide 19 is formed. Next, as shown in FIG. 2C, the cladding layer 101 is grown.

<Second Embodiment> A second embodiment of the present invention will be described with reference to FIGS. 3 and 4 by taking a semiconductor laser having a guide waveguide structure as an example.

First, as shown in FIG. 3A, the substrate 40
The core layer 41 of the gain waveguide is epitaxially grown thereon. Next, as shown in FIGS. 3 (b)-(1) and 3 (b)-(2), a width 20 including a region for forming a gain waveguide is provided.
μm, the length is equal to the gain waveguide length, 300 μ
Using the SiO ₂ film 42 formed in the m region as an etching mask, the core layer of the gain waveguide in the region other than this region is removed to form the island 43 of the core layer of the gain waveguide.
At this time, as shown in FIG. 3B- (1), the shape of the island 43 of the core layer of the gain waveguide is set so that at least the joint surface 44 with the guide waveguide is in the light guiding direction, that is, the <110> direction. Is formed so as to intersect with the surface of the <001> direction orthogonal to the surface of the waveguide and the surface of the <001> direction orthogonal to the surface of the waveguide. In addition, in FIG. 3B- (1), the joint surface 44
Is a plane orthogonal to the substrate 40.

Another example is shown in FIGS. 3 (b)-(2).
, The shape of the island 43 of the core layer of the gain waveguide is
At least the joint surface 46 with the guide waveguide is in the stacking direction <0.
01> to form a tapered surface.

Reactive ion etching was used to form the islands 43 of the core layer of the gain waveguide.
Since the reactive ion etching method enables etching with excellent directivity, the side wall of the island of the core layer with good uniformity,
That is, the joint surface 44 could be obtained. Furthermore, by utilizing the directionality of the ions, it was possible to form the joint surface 46 that is inclined also in the thickness direction of the substrate. The angle of inclination can be set to an arbitrary angle by setting the angle between the substrate and the directional ions. Further, the etching depth when the core layer of the gain waveguide in the region other than the region where the gain waveguide is formed is removed is about 0.3 μm deeper than the core layer.

Next, as shown in FIG. 4A, a core layer 47 of the guide waveguide is grown in a region other than the island 43 of the core layer of the gain waveguide. At this time, the core layer 47 of the guide waveguide
Prior to the growth of, the intermediate layer 48 was grown such that the position of the core layer 47 of the guide waveguide was aligned with the position of the core layer 41 of the gain waveguide. The thickness of the intermediate layer 48 is such that the etching depth when the core layer of the gain waveguide in the region other than the region where the gain waveguide is formed is removed is about 0.
Based on the fact that the depth was about 3 μm, it was set to about 0.3 μm. As a result, the quality of the core layer 47 of the guide waveguide can be improved, and as a result, the characteristics of the manufactured laser are improved. Further, since the [110] plane having a high growth rate does not form the side wall of the island 43 of the core layer of the gain waveguide, the core layer 47 of the guide waveguide could be grown in a state without swelling.

Next, as shown in FIG. 4B, after removing the remaining SiO ₂ film 42 on the island 43 of the core layer of the gain waveguide, the island 43 of the core layer of the gain waveguide is removed. The core layer 47 of the guide waveguide was processed to form the gain waveguide 49 and the guide waveguide 50.

Next, as shown in FIG. 4C, after growing a cladding layer 51, an electrode 52 for current injection was formed to obtain a semiconductor laser with a guide structure. In this laser, since the joint surface 44 or the joint surface 46 is not in a positional relationship such that it is orthogonal to the optical axis of the gain waveguide, the reflected light on these joint surfaces propagates to the region other than the waveguide in the element and is absorbed. Therefore, the operation of the laser could be stabilized.

In the above embodiments, the semiconductor laser with the guide structure has been described as an example, but it is obvious that the invention can be applied to other semiconductor waveguide devices and dielectric waveguide devices.

An example of the dielectric waveguide element is a SiO ₂ waveguide on a Si substrate. In this case, SiO ₂
Since is amorphous, there is no abnormal growth derived from the crystal structure, but it has the effect of eliminating the adverse effect of light reflection at the joint surface.

[0035]

As described above, by using the junction structure of the present invention, a semiconductor having excellent optical characteristics and excellent shape characteristics in connecting two types of waveguides having different refractive index distributions. A laser or other semiconductor waveguide device or a dielectric optical waveguide device could be obtained.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a manufacturing process of an optical waveguide and a structure thereof according to the present invention.

2A to 2D are schematic explanatory views of a manufacturing process of an optical waveguide and a structure thereof according to the present invention.

FIG. 3 is a schematic explanatory diagram of a manufacturing process of a semiconductor laser with a guide waveguide structure having an optical waveguide according to the present invention.

FIG. 4 is a schematic explanatory diagram of a manufacturing process of a semiconductor laser with a guide waveguide structure having an optical waveguide according to the present invention.

FIG. 5 is a schematic explanatory view of a semiconductor laser with a guide waveguide structure having a conventional optical waveguide structure.

FIG. 6 is a schematic explanatory diagram of a manufacturing process of a semiconductor laser with a guide waveguide structure having a conventional optical waveguide structure.

FIG. 7 is a schematic explanatory diagram of a manufacturing process of a semiconductor laser with a guide waveguide structure having a conventional optical waveguide structure.

[Explanation of symbols]

10 Substrate 11 Core Layer of First Waveguide 12 Etching Mask SiO ₂ 13 Island of Core Layer of First Waveguide 14 Bonding Surface 15 Sides That Form Bonding Surface 16 Bonding Surface 17 Core Layer of Second Waveguide 18 1st waveguide 19 2nd waveguide 20 Gain waveguide 21 Guide waveguide 22 Junction surface 23 Laser emission end face 30 Substrate 31 Gain waveguide core layer 32 Etching mask SiO ₂ 33 Island of gain waveguide core layer 34 Guide Waveguide Core Layer 35 Laser Clad Layer 36 Electrode 40 Substrate 41 Gain Waveguide Core Layer 42 Etching Mask SiO ₂ 43 Island of the Gain Waveguide Core Layer 44 Bonding Surface 45 Bonding Side Edge 46 Bonding Surface 47 Core Layer of Guide Waveguide 48 Intermediate Layer 49 Gain Waveguide 50 Guide Waveguide 51 Clad Layer 52 Electrode 101 Clad Layer

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Naoto Yoshimoto 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Susumu Kondo 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo No. within Nippon Telegraph and Telephone Corporation (72) Inventor Hiroshi Okamoto 3-19-3 Nishishinjuku, Shinjuku-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Inventor Yoshio Itaya 3-chome Nishishinjuku, Shinjuku-ku, Tokyo No. within Nippon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. An optical waveguide in which a plurality of optical waveguides having different refractive index distributions in the stacking direction are connected in series in the waveguide direction of light of the waveguide, the joint surface of the plurality of optical waveguides is An optical waveguide characterized by intersecting a laminated surface in the light guiding direction and a surface orthogonal to the laminated surface in the light guiding direction. 2. The optical waveguide according to claim 1, wherein the bonding surface intersects with the stacking direction. 3. The optical waveguide according to claim 1, wherein the plurality of optical waveguides are made of semiconductor.