JPH06163874A - Optical device - Google Patents

Abstract

PURPOSE:To improve the coupling efficiency between a semiconductor laser and optical waveguide by forming the core sections of the laser and waveguide in tapered states having narrow core widths near a groove. CONSTITUTION:The cores 3 and 4 of a semiconductor laser 1 and wavequide section 2 are narrowed (tapered cores 6) in core width toward a groove 5 when they are viewed from the top so that their core widths can become about 1/5 of their proper core widths near the groove 5. Therefore, the mode field diameter of the light guided from the laser 1 is enlarged on the end face of the core of the laser 1 on the side wall of the groove 5 without causing any propagation loss owing to the tapered core 6 and the diffracting effect is reduced. On the other hand, since the core width on the waveguide 2 side also gradually increases as going farther from the groove 5, the mode field diameter enlarged on the side face of the groove 5 again returns to the size decided by the size of the waveguide core 4. Therefore, the coupling efficiency between the laser 1 and waveguide section 2 can be improved, because the enlarged beams are coupled to each other near the groove 5.

Description

Detailed Description of the Invention

[0001]

The present invention relates to optical communication or optical measurement /
The present invention relates to a semiconductor integrated light source used for optical switching and the like.

[0002]

2. Description of the Related Art A semiconductor laser is used as a light source in the fields of optical communication and optical measurement, but in order to improve its 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 hybridly integrated and an optical fiber is coupled. However, the technique of modularizing the semiconductor light emitting element and the 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 on the semiconductor substrate in a unified manner. For that purpose, it is necessary to establish a simple manufacturing process of the semiconductor functional element and to integrate the semiconductor optical functional element with each other. It is necessary to increase the coupling efficiency of.

When a semiconductor laser is integrated on a semiconductor substrate, it is necessary to introduce a cleaved surface or a diffraction grating as a reflecting mirror because it is necessary to construct a resonator to oscillate the semiconductor laser. . In this case, the introduction of the diffraction grating complicates the manufacturing process. Therefore, the Fabry-Perot laser using the crystal facet is advantageous from the viewpoint of manufacturing process and cost. However, forming a semiconductor laser having a crystal facet in the production of an integrated circuit of an optical functional element results in the formation of a groove for forming the facet, so that the semiconductor laser is directly coupled to the optical waveguide or the light receiving element. Is not possible, and a large loss of light intensity will occur at the joint.

FIG. 6 is an integrated structure of a semiconductor laser 1 and an optical waveguide 2 having a conventional structure, and is a plan view (a) and a sectional view (b) schematically showing coupling through a groove 5. is there. Here, the optical waveguide 2 is shown on one side of the semiconductor laser 1, but there are cases where an optical waveguide portion is formed on both sides or a waveguide type light receiving element portion is formed on the other side. And an optical waveguide 2 on one side thereof are shown.

[0005]

In the coupling of the semiconductor laser 1 and the optical waveguide 2 as described above, the refractive index of the semiconductor material forming the cores 3 and 4 is 3.0 or more, which is higher than that of air. Therefore, as the beam diameter propagating through the semiconductor material is smaller, the light wave emitted from the groove for forming the reflecting end face into the air is greatly diffracted and spreads radially. Therefore, scattered light increases in the end face forming groove portion 5, 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 emission wavelength of 1.5 μm, the coupling efficiency becomes 10% or less when the groove interval is 5 μm.

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

[0007]

In order to achieve the above object, a semiconductor laser having a groove forming one end of a cavity end face on a semiconductor substrate, and an optical waveguide coupled to the semiconductor laser through the groove. In an optical device having a waveguide, the invention according to claim 1 has a structure in which the core widths of the semiconductor laser and the optical waveguide are tapered in the vicinity of the groove, and the invention according to claim 2 is The semiconductor laser and the core of the optical waveguide have a double core structure composed of a first inner core and a second outer core, and the first core width is tapered in the vicinity of the groove. According to the invention of claim 3, the core widths of the semiconductor laser and the optical waveguide are tapered in the vicinity of the groove, and the end surface of the groove on the semiconductor laser side is perpendicular to the optical axis, and Waveguide in the groove An optical device having a structure in which a side end face is inclined with respect to the optical axis, and further comprising a semiconductor laser on a semiconductor substrate and an optical waveguide coupled to the semiconductor laser, wherein the invention according to claim 4 is: ,
The core widths of the semiconductor laser and the optical waveguide are connected while reducing in a tapered shape at the coupling portion, the semiconductor laser side has an end face perpendicular to the optical axis at the coupling portion, and the coupling is performed on the optical waveguide side. The invention according to claim 5 has a groove that is closer to the tapered core as it approaches the portion.
The core widths of the semiconductor laser and the optical waveguide are connected while being reduced in a tapered shape at the coupling portion, the semiconductor laser side has an end face perpendicular to the optical axis at the coupling portion, and the semiconductor substrate at the waveguide side. Characterized by having V-shaped grooves in the thickness direction.

[0008]

With the above structure, the existence of the tapered core in the groove for forming the end face increases the mode field diameter of the guided light to reduce the diffraction effect.
It realizes high coupling efficiency between the semiconductor laser and the waveguide.

[0009]

Embodiments will be described in detail below with reference to FIGS. 1 to 5. (Embodiment 1) FIG. 1 is a plan view (a) and a sectional view (b) showing an embodiment of the first invention, showing a core 3 of a semiconductor laser 1.
And the core 4 of the waveguide portion 2 both have a narrower core width when viewed from the plane as they go in the direction of the groove 5 (hereinafter, the tapered core 6
Called. ), The core width in the vicinity of the groove 5 has a structure reduced to about one fifth of the original width.

Therefore, the guided light from the semiconductor laser 1 does not cause a propagation loss due to the tapered core 6, and the mode field diameter is remarkably enlarged at the end surface of the groove 5. Since the mode field diameter is enlarged, the guided light emitted to the groove 5 has a small diffraction effect during propagation of the groove 5, and the mode field diameter at the end face of the groove 5 on the waveguide side is the mode field before being emitted to the groove 5. Almost does not change with the diameter. On the other hand, since the core width on the waveguide side gradually widens with increasing distance from the groove 5 as on the semiconductor laser 1 side, the mode field diameter enlarged at the end surface of the groove 5 is again determined by the size of the waveguide core 4. Return to size. Therefore, since the expanded beams are coupled in the vicinity of the groove 5, the coupling efficiency is significantly improved as compared with the conventional core having the same size. If you only want to reduce the diffraction effect,
The core 3 of the semiconductor laser 1 may be tapered, but the coupling efficiency is remarkably improved by matching the mode shape with the waveguide 2 side and taking a loose opening angle, so that the groove on the waveguide 2 side is also improved. The taper core 6 is provided on the 5 side.

In this embodiment, the laser resonator has a structure in which one end face is the end face of the groove 5 on the laser side and the other end face is a normal cleaved end face. However, the groove 5 is formed on both sides of the laser. May be. Actually, the thickness of the active layer is 0.25 μm
In the InP-based laser having a core width of 1.5 μm, a tapered core having a core width of 0.25 μm in the groove 3 was produced, and as a result, no increase in coupling loss was observed up to a groove interval of 5 μm.

(Embodiment 2) FIG. 2 is a plan view (a) and a sectional view (b) showing an embodiment of the second invention. In this embodiment, the semiconductor laser 1 and the taper connection are shown for simplicity of manufacture. Department,
An example in which a double waveguide structure is adopted over the entire waveguide 2 is shown. That is, it is composed of the first inner core 3 and the core 4 and the second outer core 7 surrounding the inner cores 3 and 4,
The first inner cores 3 and 4 each become a tapered core 6 near the groove 5, and the first cores 3 and 4 disappear at the ends of the groove 5.

In this structure, the refractive index difference between the outer core 7 and the clad 8 is extremely small, so that the guided light is confined in the inner cores 3 and 4 by feeling the outer core 7 as the clad 8 in the semiconductor laser 1 and the waveguide 2. However, since the inner core disappears at the connecting portion, it is confined in the outer core 7. That is, even when the core disappears at the tip of the taper 6, the waveguide structure is maintained and the single mode condition is maintained on both sides of the groove 5.

The width and thickness of the outer core 5 are 10 to 20 μm.
Since it can be set to m, the mode field diameter of the guided light can be made larger than the mode field diameter of the semiconductor laser 1 by one digit or more, and the diffraction at the groove 5 can be reduced to improve the coupling efficiency.

(Embodiment 3) FIG. 3 is a plan view (a) and a sectional view (b) showing an embodiment of the third invention. In this embodiment, the end surface of the groove 5 on the waveguide 2 side is slightly inclined with respect to the axis of the core 3 of the laser 1, and the axis of the waveguide core 4 is inclined with respect to the axis of the laser core 3. . Also in this embodiment, the widths of the cores 3 and 4 near the groove 5 are reduced like the tapered core 6. In this embodiment, the waveguide 2 end of the groove 5 is formed by slightly inclining the waveguide side end surface of the groove 5.
It is possible to reduce the rate at which the light reflected by the side facets is recombined with the semiconductor laser core 3.

As shown in FIG. 3, when the optical axis of the waveguide core 4 is set in accordance with the refraction angle of the guided light due to the inclination angle θ of the end face of the groove 5 on the waveguide side, the optical axis is guided from the laser core 3. Excessive loss due to the inclination angle θ in coupling to the waveguide core 4 can be ignored, and the coupling efficiency to the waveguide core can be improved. However, because of the arrangement of the semiconductor laser 1 and the waveguide 2, it is possible to reduce the recombination to the core 3 due to the reflected light only by providing the end face of the waveguide without inclining the optical axis of the waveguide 2. . In this embodiment, the tilt angle θ is given as shown in FIG. 3A when viewed from the plane, but the tilt angle may be given as shown in FIG. 3B when viewed from the side. Further, the present embodiment can be applied to the double core structure shown in FIG. The most significant feature of this embodiment is that in the first embodiment, the light emitted to the groove 5 is reflected also at the boundary with the waveguide portion, so that the semiconductor laser portion has a composite structure in which both end faces of the groove 5 are reflection surfaces. The resonator structure causes variations in the semiconductor laser oscillation threshold current, but this embodiment is intended to prevent the deterioration of this characteristic.

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

In such a structure, the guided light from the semiconductor laser 1 propagates through 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 surface of the cut groove 5 functions as a reflection surface for the light intensity distribution leached from the tapered core 6H region. on the other hand,
The waveguide side boundary surface of the groove 5 which is not perpendicular to the axis of the core 4 of the waveguide 2 couples the light wave emitted into the space of the groove 5 to the core 4 of the waveguide 2 by the lens effect.

In FIG. 4, in order to increase the coupling efficiency by matching the distribution of light that has passed through the groove 5 and reaches the optical waveguide portion 2 in the expanded mode field diameter, the waveguide 4 is used.
In the example, 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 formed in the clad layer instead of the core layer. In general, the core layer is often a multiple quantum well layer or the like, and the cladding layer is InP or In.
It is often composed of a material having a uniform composition such as GaAsP. Therefore, the structure of this embodiment has an advantage that only the clad layer, which is easy to process, needs to be processed. Even if the groove 5 penetrates into the tapered core 6F and the semiconductor laser 1 and the waveguide 2 are separated by the gap, the basic operation of the present invention is performed.

(Embodiment 5) FIG. 5 shows a plan view (a) and a sectional view (b) of an embodiment of the fifth invention. In this embodiment, the cores of the semiconductor laser 1 and the waveguide 2 are made thinner by a tapered core 6 and are connected by a predetermined minimum width core 9 at a coupling portion. Furthermore, in the coupling portion, an end face perpendicular to the optical axis is formed on the semiconductor laser side,
In addition, a V-shaped cutout is formed on the semiconductor substrate on the waveguide side as shown in the figure.
The V-shaped groove 5 is formed in the thickness direction. In such a structure, the reflecting surface of the semiconductor laser can be formed and the coupling between the semiconductor laser and the waveguide can be enhanced, as in the fourth embodiment.

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

The taper structure may be asymmetric between the semiconductor laser side and the waveguide side. Further, in the embodiment, the configuration example in which only the waveguide width is tapered is shown, but both the waveguide width and the thickness may be tapered by increasing the mode field diameter. Further, although the changes in the width of the tapered waveguide of the semiconductor laser and the waveguide are linearly changed, they may be in the form of a function such as a parabola or an exponential function.

[0024]

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

[Brief description of drawings]

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

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

FIG. 3 is a plan view and a sectional view showing a third embodiment.

FIG. 4 is a plan view and a sectional view showing a fourth embodiment.

FIG. 5 is a plan view and a sectional view showing a fifth embodiment.

6A and 6B are a plan view and a cross-sectional view showing coupling between a semiconductor laser having a conventional configuration and a waveguide.

[Explanation of symbols]

 1 Semiconductor Laser 2 Waveguide 3 Laser Core 4 Waveguide Core 5 Groove 6, 6H, 6F Tapered Core 7 External Core 8 Cladding 9 Minimum Width Core

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Suzuki 1-6, Uchiyuki-cho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Osamu Mitomi 1-1-6, Uchiyuki-cho, Chiyoda-ku, Tokyo No. Japan Telegraph and Telephone Corp. (72) Inventor Mitsuru Naganuma 1-6 No. 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp.

Claims (5)

[Claims] 1. An optical device comprising: a semiconductor laser having a groove forming one end of a cavity end face on a semiconductor substrate; and a waveguide coupled to the semiconductor laser via the groove, the semiconductor laser comprising: An optical device having a structure in which a core width of each of the waveguide and the core is reduced in a tapered shape in the vicinity of the groove. 2. An optical device having a semiconductor laser having a groove forming one end of a cavity end face on a semiconductor substrate, and a waveguide coupled to the semiconductor laser via the groove. Each core of the waveguide has a dual core structure consisting of a first inner core and a second outer core surrounding the inner core, and the first core width is tapered near the groove. An optical device characterized by being downsized. 3. An optical device having a semiconductor laser having a groove forming one end of a cavity end face on a semiconductor substrate, and a waveguide coupled to the semiconductor laser via the groove, wherein the semiconductor laser and Each core width of the waveguide is tapered in the vicinity of the groove, the semiconductor laser side end face of the groove is perpendicular to the optical axis, and the waveguide side end face of the groove is inclined with respect to the optical axis. An optical device having a structured structure. 4. An optical device comprising a semiconductor laser on a semiconductor substrate and a waveguide coupled to the semiconductor laser, wherein the core width of each of the semiconductor laser and the waveguide is tapered at the coupling portion. And a groove that is connected and forms an end face perpendicular to the optical axis on the semiconductor laser side at the coupling portion, and has a groove that is closer to the tapered core as it approaches the coupling portion on the waveguide side. And optical device. 5. An optical device comprising a semiconductor laser on a semiconductor substrate and a waveguide coupled to the semiconductor laser, wherein the core width of each of the semiconductor laser and the waveguide is tapered at the coupling portion. A light which is connected and forms an end face perpendicular to the optical axis on the semiconductor laser side at the coupling portion, and has a V-shaped groove in the thickness direction of the semiconductor substrate on the waveguide side. device.