JP3223930B2 - Optical device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated light source used for optical communication, optical measurement, optical exchange, and the like.

[0002]

2. Description of the Related Art A semiconductor laser is used as a light source in the field of optical communication and optical measurement. In order to improve the function, integration of a light source, a waveguide, and a light receiver is required. As a conventional integrated module, for example, there is a pigtail type component in which a PLC circuit formed of a silica-based waveguide, a semiconductor light emitting element, and a semiconductor light receiving element are integrated in a hybrid manner and an optical fiber is coupled. However, this technique of modularizing a semiconductor light emitting element and a light receiving element is expensive because it requires alignment on the order of microns. For this reason, it is desirable to integrate the semiconductor light receiving element, the light emitting element, and the waveguide element integrally on a semiconductor substrate. For this purpose, along with the establishment of a simple semiconductor functional element manufacturing process, the semiconductor optical functional element It is necessary to increase the coupling efficiency of the light.

When a semiconductor laser is integrated on a semiconductor substrate, it is necessary to construct a resonator in order to oscillate the semiconductor laser. Therefore, it is indispensable to introduce an open surface or a diffraction grating which should be a reflecting mirror. is there. In this case, the introduction of the diffraction grating complicates the manufacturing process, and therefore, a Fabry-Perot laser using a crystal end face is advantageous from the viewpoint of the manufacturing process and cost. However, forming a semiconductor laser having a crystal end face in the fabrication of an integrated circuit for an optical functional element results in the formation of a groove for forming the end face, which directly couples the semiconductor laser with the optical waveguide or the light receiving element. And a large loss of light intensity occurs at the joint.

[0004] Figure 3 is an integrated structure of the semiconductor laser 1 and the optical waveguide 2 made of conventional configuration, in plan view schematically illustrating the coupling through the grooves 5 (a) and a cross-sectional view (b) is there. Although the optical waveguide 2 is shown on one side of the semiconductor laser 1 here, an optical waveguide section may be formed on both sides, and a waveguide type light receiving element section may be formed on the other side. And an example of the optical waveguide 2 on one side thereof.

[0005]

In the connection between the semiconductor laser 1 and the optical waveguide 2, the refractive index of the semiconductor material forming each of the cores 3 and 4 is 3.0 or more, which is higher than that of air. Since the beam diameter is large, the smaller the diameter of the beam propagating in the semiconductor material is, the larger the light wave emitted into the air from the groove for forming the reflection end face is to have a larger diffraction effect and spread radially. For this reason, the scattered light increases in the groove 5 for forming the end face, and the coupling efficiency from the semiconductor laser 1 to the waveguide 2 decreases. Specifically, InP is used as a semiconductor material.
In the case of a semiconductor laser having a system light emission wavelength of 1.5 μm, the coupling efficiency is reduced to 10% or less when the groove interval is set to 5 μm.

An object of the present invention is to increase the coupling efficiency between a semiconductor laser having a groove for forming an end face and an optical waveguide when an optical functional element is integrated on a semiconductor substrate.

[0007]

To achieve SUMMARY OF to the above objects, a semiconductor laser on a semi-conductor substrate, wherein the optical device comprising a semiconductor laser and the coupling optical waveguides, a first aspect of the present invention, wherein The core width of the semiconductor laser and the optical waveguide is connected while reducing in a tapered shape at the coupling portion, the semiconductor laser side forms an end face perpendicular to the optical axis at the coupling portion, and the coupling portion at the tip waveguide side. 3. The semiconductor device according to claim 2 , wherein the semiconductor laser and the optical waveguide are connected to each other while the core width of the optical waveguide is reduced in a tapered shape at a coupling portion. The semiconductor laser is characterized in that it has an end face perpendicular to the optical axis on the semiconductor laser side and has a V-shaped groove in the thickness direction of the semiconductor substrate on the waveguide side.

[0008]

With the above construction, the presence of the tapered core in the groove for forming the end face increases the mode field diameter of the guided light, thereby reducing the diffraction effect.
This realizes a high coupling efficiency between the semiconductor laser and the waveguide.

[0009]

EXAMPLES Hereinafter, FIG. 1, also preparative not a have been described in detail in Example with reference to FIG.

[0010]

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

(Embodiment 1 ) FIG. 1 shows a plan view (a) and a sectional view (b) showing an embodiment of the first invention. The core widths 3 and 4 of the semiconductor laser 1 and the waveguide 2 are narrowed as shown by tapered cores 6H and 6F toward the coupling portion, and the cores are connected with a predetermined minimum core width. Further, in the coupling portion, the notch (concave) type groove 5 in the lateral direction of the thin tapered core 6F as shown in the drawing is adjacent to the waveguide 2 at the end face perpendicular to the optical axis on the semiconductor laser 1 side. It is formed in.
The groove 5 can be formed by ion etching using a reactive gas or etching with a chemical solution.

In such a structure, the guided light from the semiconductor laser 1 propagates in the tapered core 6H region with its mode field diameter enlarged without increasing the propagation loss. At this time, since the mode field diameter is enlarged, the end face of the cut groove 5 functions as a reflecting surface for the light intensity distribution oozing out of the tapered core 6H region. on the other hand,
Waveguide side boundary surface of the groove 5 which is not perpendicular to the axis of the waveguide 2 of the core 4, by the lens effect coupling the light wave emitted into the space of the groove 5 to the core 4 of the waveguide 2.

In FIG. 1 , in order to increase the coupling efficiency by matching the distribution of light that passes through the groove 5 and reaches the optical waveguide portion 2 in the enlarged mode field diameter, the waveguide 4 is increased.
2 shows an example in which the core width of the tapered core 6F and the core width of the tapered core 6H of the semiconductor laser 1 are different.

In this embodiment, the groove 5 is not formed in the core layer but formed in the clad layer. Generally, the core layer often uses a multiple quantum well layer or the like, and the cladding layer is made of InP or InP.
Often composed of a material of uniform composition such as GaAsP. Therefore, the structure of this embodiment has an advantage that only the clad layer which is easy to process need be processed. Even if the groove 5 penetrates the tapered core 6F and the semiconductor laser 1 and the waveguide 2 are separated by a gap, the basic operation of the present invention is performed.

(Embodiment 2 ) FIG. 2 shows a plan view (a) and a sectional view (b) of an embodiment of the second invention. In this embodiment, the semiconductor laser 1 and the waveguide 2
The two cores are tapered to reduce their core width by a tapered core 6 and are connected by a predetermined minimum width core 9 at a joint. Further, in the coupling portion, a cut-shaped V-shaped groove 5 is formed in the thickness direction as shown in the figure on the semiconductor substrate on the semiconductor laser side, forming an end face perpendicular to the optical axis, and on the waveguide side. ing. In this structure, in the same manner as in Example 1, to form a reflecting surface of the semiconductor laser, it is possible to increase the coupling between the semiconductor laser and the waveguide.

In the embodiment described above, the reflectivity of the laser resonator can be increased by providing a high-reflection film made of a metal or dielectric multilayer film on the end face of the groove on the side of the semiconductor laser. The threshold current can be reduced.

The tapered structure may be asymmetrical between the semiconductor laser and the waveguide. Further, in the embodiment, the configuration example in which only the waveguide width has a tapered shape is shown. However, if the mode field diameter is increased, both the waveguide width and the thickness may be tapered. Further, although the change in the tapered waveguide width of the semiconductor laser and the waveguide is linearly changed, it may be a function such as a parabola or an exponential function.

[0024]

As described above, according to the present invention, in the integration of a semiconductor optical functional device on a semiconductor substrate,
The coupling between the semiconductor optical functional devices can be realized with high optical coupling efficiency. In particular, since the integration of optical functional elements can be realized by a practical semiconductor manufacturing technique, an inexpensive and highly reliable optical component can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view and a sectional view showing a first embodiment.

FIG. 2 is a plan view and a sectional view showing a second embodiment.

3A and 3B are a plan view and a cross-sectional view illustrating coupling between a semiconductor laser having a conventional configuration and a waveguide.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser 2 waveguide 3 laser core 4 waveguide core 5 groove 6, 6H, 6F taper core 7 external core 8 cladding 9 minimum width core

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuhiro Suzuki 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Osamu Mitomi 1-16-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Mitsuru Naganuma 1-6-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-3-63606 (JP, A) JP-A Sho-64 -32206 (JP, A) JP-A-4-97206 (JP, A) JP-A-5-60929 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/12- 6/14 H01S 5/00-5/50 H01L 27/15 JICST file (JOIS)

Claims (2)

(57) [Claims] In an optical device comprising a semiconductor laser on a semiconductor substrate and a waveguide coupled to the semiconductor laser, the core width of each of the semiconductor laser and the waveguide is reduced in a tapered shape at a coupling portion. Connected to the coupling portion, the semiconductor laser side has an end face perpendicular to the optical axis, and the waveguide side has a groove that is closer to the tapered core as it approaches the coupling portion. And optical devices. 2. An optical device comprising a semiconductor laser on a semiconductor substrate and a waveguide coupled to the semiconductor laser, wherein each core width of the semiconductor laser and the waveguide is reduced in a tapered shape at a coupling portion. A light having a V-shaped groove in the thickness direction of the semiconductor substrate on the side of the waveguide, wherein the groove forms an end face perpendicular to the optical axis on the side of the semiconductor laser at the coupling portion; device.