JPH0281493A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To radiate a specific laser beam to the outside at a low output and to reduce a noise by a method wherein a transparent plate having the following is installed in a radiation direction of the laser beam: a waveguide; a grating coupler designed so as to couple the specific laser beam out of a plurality of laser beams to the waveguide. CONSTITUTION:In a radiating direction of a semiconductor layer chip 1, a transparent plate 2 where a waveguide 3 and a grating coupler 4 have been manufactured on its surface is installed perpendicularly to an optical axis of a laser beam. The semiconductor laser chip 1 is driven; one part of a beam 9a on the left side is coupled to the waveguide 3 by using the grating coupler 4; it is transformed into a waveguide beam 9b; the remaining part is transmitted through the transparent plate 2 and is transformed into a transmitted beam 9c. After the waveguide beam 9b has been propagated in the waveguide 3, it is absorbed by a light absorber 5. An angle of incidence of two (center and right) beams other than the left beam is different from that of the left beam; they are not coupled to the waveguide 3 and are transmitted through the transparent plate 2; an output of the beams is changed little.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a semiconductor laser device used in an optical disk device, etc., and more specifically, to a multi-beam semiconductor laser device that emits a plurality of laser beams. be.

[Prior Art] A 3-beam semiconductor laser is an example of a multi-beam semiconductor laser that emits multiple laser beams.Since the 3-beam semiconductor laser can drive each of the three beams independently, it has an override function. In a magneto-optical disk device with
mW) for erasing and writing, and the remaining one has a low output (~5 mW) and is used for reproduction.

3 and 4 are perspective views showing a conventional three-beam semiconductor laser, and FIG. 3 shows a single laser chip 1 in which three laser elements are integrated on a submount 11. Fig. 4 shows a monolithic three-beam semiconductor laser having a configuration in which three separate and independent laser chips la,
A hybrid three-beam semiconductor laser is shown in which lb and lc are arranged side by side on a submount ll. In both figures, 6 indicates the active layer of the laser element, 7 also indicates the light emitting point, and 8 indicates the electrode.

The monolithic three-beam semiconductor laser shown in FIG.
This is an improved version of the hybrid three-beam semiconductor laser shown in Figure 4, and since three laser elements are monolithically integrated into one chip, the precision of each beam spacing is high, making it easy to manufacture. It has the advantage of good yield.

[Problem to be solved by the invention]

In both types of conventional 3-beam semiconductor lasers as described above, in order to obtain high output power (~301) from each beam, the reflectance of the rear end facet of the laser chip is increased and the reflectance of the front facet is increased. lowering the rate. A semiconductor laser that emits a high-output laser beam due to the difference in reflectance between both end faces is known to have noise characteristics as shown in FIG. 5. In FIG. 5, the vertical axis represents the amount of noise, and the horizontal axis represents the optical output. As can be understood from FIG. 5, the noise characteristics deteriorate during low output operation (FIG. 5A) compared to high output operation (FIG. 5B). Therefore, as described above, when one of the three laser beams is operated at low output, the required noise characteristics are barely satisfied.

By the way, in a hybrid three-beam semiconductor laser, only the laser chip used at low output has low output and low noise, that is, only its front facet reflectance is different from the front facet reflectance of the other two laser chips. By doing so, the above-mentioned problem can be easily solved.

However, monolithic three-beam semiconductor lasers have the disadvantage that it is difficult to manufacture and change the reflectance of the front facet only in the portion corresponding to one laser beam, and the yield of good products is reduced. This point will be explained below. When manufacturing a monolithic three-beam semiconductor laser, the characteristics of each laser element are inspected in the form of a bar in which multiple laser elements are lined up horizontally, and the three consecutive laser elements are separated by folds to form a single bar. We have obtained several laser chips. Laser chip 1 as shown in fat in FIG.
), from a bar 13 like fbl on which high reflectance parts 12 are already formed at equal intervals, 1
On the other hand, two chips can be obtained from a bar 13 as shown in (C) in which the end face reflectance is constant over the entire area. As described above, the method of partially changing the end face reflectance in a monolithic three-beam semiconductor laser has a low yield and cannot be said to be a preferable method.

The present invention has been made in view of the above circumstances, and includes a transparent plate having a waveguide and a grating coupler so as to couple only one specific laser beam out of three laser beams to the waveguide. A semiconductor laser device that can emit a specific laser beam to the outside at a low output without reducing the yield by lowering the output of that specific laser beam to the outside, and can also reduce the noise at that time. The purpose is to provide

[Means to solve the problem]

A semiconductor laser device according to the present invention is a semiconductor laser device in which a plurality of semiconductor laser elements are integrated in order to emit a plurality of laser beams in the same direction. The present invention is characterized by comprising a transparent plate having a grating coupler designed to couple a specific laser beam among the laser beams to the waveguide.

[Effect]

In the semiconductor laser device of the present invention, the waveguide and the specific laser beam are designed based on the incident angle of the specific laser beam so that only the laser beam is coupled to the waveguide in the emission direction of the laser beam. A grating coupler is provided. Therefore, only the specific laser beam is coupled to the waveguide, but other laser beams are not coupled to the waveguide because they do not satisfy the incident angle condition.

Then, only the specific laser beam is selectively emitted to the outside with its output reduced. At this time, since the specific laser beam is actually operated at high output, its noise characteristics do not deteriorate.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on drawings showing embodiments thereof.

FIG. 1 is a perspective view showing an embodiment of the semiconductor laser device according to the present invention, which is a monolithic three-beam semiconductor laser. This embodiment is an example in which the beam at one end is used at low output. be. In the figure, l is monolithic type 3
This is a beam semiconductor laser chip, and in the emission direction of the semiconductor laser chip 1, a waveguide 3 made of, for example, Corning #7059 and a grating coupler 4 made of, for example, SiN are arranged on its upper surface (on the opposite width side from the semiconductor laser chip 1). A transparent plate 2 made of, for example, soda glass is provided perpendicularly to the optical axis of the laser beam. An antireflection film (not shown) is provided on the lower surface of the transparent plate 2 to prevent reflection of the beam from the semiconductor laser chip l.

The grating coupler 4 is designed to couple only the left beam 9a in FIG. 1 to the waveguide 3. Specifically, the grating coupler 4
As shown in FIG. 2, the shape of is obtained by setting the surface of the waveguide 3 as an xy plane and setting the xyz coordinates so that the origin is the intersection point P of the optical axis 10 of the beam, which is the Z axis, and the xy plane. , the following (equation 11 is satisfied.

Ny ten X” +y” + f” = mλ+f −(
11 However, N: Effective refractive index of waveguide 3 f: Distance from light emitting point Q (FIG. 1 7) to origin P λ: Wavelength of laser beam m: 0. ±1. ±2. ... If the shape of the grating coupler 4 is determined so as to satisfy the above equation (1), the guided light 9b coupled to the waveguide 3 becomes parallel light.

Further, one end surface of the transparent plate 2 in the traveling direction of the guided light 9b is
In order to prevent reflected light from the guided light 9b, it has a tapered shape, and a light absorber 5 made of silicone resin, for example, is adhered to the end face of the tapered shape, and the guided light 9b passes through the light absorber 5.
It is designed to be absorbed by In the figure, 6 indicates an active layer of the laser element, 7 also indicates a light emitting point, and 8 indicates an electrode.

Next, the operation will be explained.

When the semiconductor laser chip 1 is driven, a portion of the left beam 9a is coupled to the waveguide 3 by the grating coupler 4 to become the guided light 9b, and the rest passes through the transparent plate 2 to become the transmitted light 9C. After the guided light 9b propagates through the waveguide 3, it is absorbed by the light absorber 5. Note that although there is a possibility that a part of the light of the beam 9a is reflected on the lower surface of the transparent plate 2, this reflection is prevented by an antireflection film provided on the lower surface of the transparent plate 2.

The original optical output of the left beam 9a is p, and the optical output of the guided light 9b is P. , and the optical output of the transmitted light 9c is PC, the relationship shown in equation (2) below holds between them.

PM = pb + p, ... (2
) P, and PC depend on the coupling efficiency of the grating coupler 4 to the waveguide 3, but this coupling efficiency can be adjusted to an arbitrary value by adjusting the thickness of the grating coupler 4 (Fig. 2 t). It is possible to set it to a value.

In other words, as t increases, the coupling efficiency increases and PC decreases.

The two beams other than the left (center and right) have different incident angles from the left beam, so they do not satisfy the coupling conditions to the waveguide 3 by the grating coupler 4, and are transparent as they are without being coupled to the waveguide 3. The light passes through the plate 2, and its light output hardly changes.

As described above, only the transmitted light 9c of the left beam 9a has a low output, and the other two transmitted lights have a high output, so that three laser beams having the desired output can be obtained. At this time, the laser element on the left side is actually driven at high output like the other laser elements, so
The noise is small.

In this embodiment, a case has been described in which the shape of the grating coupler 4 is set so that the guided light 9b becomes parallel light, but it is also possible to design the grating coupler 4 so that the guided light 9b becomes diverging light or convergent light. Good too.

Further, unlike this embodiment, a configuration in which the transparent plate 2 is provided at an angle with respect to the optical axis of the laser beam is also possible.
In this case, since aberrations occur in the transmitted light depending on the thickness of the transparent plate 2, a means for correcting the aberrations is required.

In this embodiment, the waveguide 3 and the grating coupler 4 are provided on the upper surface of the transparent plate 2, but both members may be provided on the lower surface of the transparent plate 2.
Both members may be fabricated on the window glass.

Furthermore, although the present embodiment has been described with reference to the case of three beams, the present invention is not limited to this and can of course be similarly applied to a semiconductor laser that emits two or four or more beams.

〔Effect of the invention〕

As described in detail above, in the monolithic semiconductor laser device according to the present invention, the noise of a specific laser beam emitted to the outside at low output can be reduced.

Furthermore, the present invention has excellent effects such as no reduction in yield compared to the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the configuration of a semiconductor laser device according to the present invention, FIG. 2 is a diagram for explaining how to determine coordinates set when designing a grating coupler, and FIG. 3 is a diagram showing a conventional monolithic type 4th perspective view showing the semiconductor laser of
The figure is a perspective view showing a conventional hybrid semiconductor laser, Figure 5 is a graph showing the relationship between optical output and noise in a high-power semiconductor laser, and Figure 6 is a diagram explaining the difference in yield of laser chips. It is. 1... Semiconductor laser chip 2... Transparent plate 3...
・Waveguide 4...Grating coupler patent Applicant: Sanyo Electric Co., Ltd. Representative Patent attorney: Noboru Kono Diagrams

Claims (1)

[Claims] 1. In a semiconductor laser device in which a plurality of semiconductor laser elements are integrated to emit a plurality of laser beams in the same direction, a waveguide and the plurality of lasers are arranged in the emission direction of the laser beam. 1. A semiconductor laser device comprising: a transparent plate having a grating coupler designed so that a specific laser beam among the beams is coupled to the waveguide.