JPH0680862B2 - Semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to an external resonator type semiconductor laser device,
By constructing a resonator using a birefringent substrate provided with a predetermined recess and a single-mode waveguide region, and incorporating a semiconductor laser in this resonator, the assembly and adjustment of the above-mentioned device can be simplified. In addition to reducing the possibility of aging, the resonator efficiency is also improved.

[Industrial application field]

The present invention relates to a semiconductor laser device used as a dual-frequency light source, and more particularly to an external resonator type semiconductor laser device in which all the components are integrated.

Along with the development of optical communication technology, the technology for integrating various optical circuit devices is rapidly advancing, and the technology is used not only in the devices that make up the optical communication system but also in fields other than the optical communication. It has spread to various optical devices. For example, a semiconductor laser device used as a dual-frequency light source in the optical measurement field is no exception, and a resonator composed of a polarization plane control element such as a half-wave plate and a quarter-wave plate and a reflecting mirror, and a semiconductor laser are also included. It is required that the assembly and adjustment of the device be facilitated and the characteristics be stabilized by integrating the light sources of the above.

[Conventional technology]

Recently, the number of optical measurement devices that use laser light is increasing in the field of measurement such as distance measurement and velocity measurement, but in order to efficiently perform such measurement using the optical heterodyne method, which is one of them, a stable frequency Two lights with a difference are needed.

A conventional external resonator type semiconductor laser device is configured by disposing a semiconductor laser that outputs light of a single frequency (ω) in a resonator that is separate from the semiconductor laser. The resonator is a plurality of polarization plane control elements such as a quarter-wave plate, or a reflecting mirror respectively arranged outside the polarization plane control element,
It also has various optical components such as lenses, and these components are all fixed on one substrate with an adhesive.

Such an external resonator type semiconductor laser device can output two lights having a slight frequency difference by the action of the semiconductor laser and the resonator. For example, when the frequency of the light output from the semiconductor laser is ω, the external resonator type semiconductor laser device outputs light of frequency ω + Δω and light of frequency ω−Δω, and the frequency difference between the two lights is 2Δ
becomes ω.

[Problems to be solved by the invention]

However, in the conventional semiconductor laser device, the components constituting the resonator, that is, the lens, the quarter-wave plate, the reflecting mirror, etc. are arranged in the space together with the semiconductor lens and fixed to the substrate with an adhesive or the like as described above. . Therefore, it is difficult to adjust the distance between each component and the optical axis, and there is a large “variation” in accuracy, and in addition, significant time and manpower are required for assembly and adjustment. Moreover, the characteristics of the adhesive may change over time due to aging, and even in a semiconductor laser device having high accuracy immediately after assembly and adjustment, the accuracy may gradually decrease with time. There was a problem.

In view of the above problems, it is an object of the present invention to provide an external resonator type semiconductor laser device which is easy to assemble and adjust, has little possibility of aging, and has good resonator efficiency. .

[Means for solving problems]

In the present invention, a birefringent substrate, the optical axis of which is 45 degrees with respect to the TE polarization plane of the semiconductor laser in a plane perpendicular to the laser optical axis.
It uses a tilted substrate. In this substrate, a concave portion for mounting and fixing a semiconductor laser, and a single mode waveguide region that faces the active layer surface of the semiconductor laser and extends from both sides of the concave portion toward both sides, one of which acts as a quarter-wave plate And are provided. Further, by providing a reflecting surface on each of both end faces outside the single mode waveguide region, a resonator including the recess and the single mode waveguide region is formed between the reflecting faces. .

[Action]

By configuring the resonator in one substrate as described above, all the components are integrated, the semiconductor laser device can be easily assembled and adjusted, and the accuracy can be stabilized. In addition, since a material such as an adhesive that may change over time is not used, high accuracy after assembly can be maintained for a long period of time. Moreover, since the emitted light of the semiconductor laser is confined in the single-mode waveguide region and does not spread to the surroundings, a large amount of reflected light can be returned to the semiconductor laser, and therefore very good resonator efficiency can be achieved. Is obtained.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1 (a), (b), and (c) are a perspective view, a side view, and a front view, respectively, showing an embodiment of the present invention. In this embodiment, a recess 2 and single mode waveguide regions 3 and 4 are formed on the upper surface of a birefringent substrate 1, and the single mode waveguide regions are further formed.
The resonators are integrally formed by providing reflecting surfaces 5 and 6 on the outer end surfaces of the resonators 3 and 4, respectively, and by incorporating the semiconductor laser 7 into the recess 2 of the resonator, an external resonator type This is a structure of a semiconductor laser device. A more specific description will be given below.

The substrate 1 is made of a uniaxial birefringent material (for example, crystal) having a high transmittance for laser light. Moreover, as shown in FIG. 1 (c), its optical axis 1a is the laser optical axis 7a.
In the plane perpendicular to ((b) of the figure), the semiconductor laser 7 is inclined by 45 degrees with respect to the TE polarization plane 7b.

The recess 2 is formed in conformity with the shape of the semiconductor laser 7 so that the semiconductor laser 7 can be fixed. Moreover, the depth of the recess 2 is such that when the semiconductor laser 7 is fitted, the single mode waveguide region 3, The positions where 4 and 4 face each other (eg, a depth of several μm) are set.

The single mode waveguide regions 3 and 4 have a ridge type waveguide structure, and extend in a rectangular parallelepiped shape from the recess 2 toward both sides, that is, on the extension of the active layer of the semiconductor laser 7. There is. The sizes of these cross-sectional shapes are determined according to the refractive index of the substrate 1 so that the TE and TM modes are not cut off. For example, when quartz is used as the substrate 1, the cross-sectional shape is about 5 μm square. Further, one of the single mode waveguide regions 3 functions as a quarter wave plate, and its length 1 is determined by the following equation.

In the above formula, λ is the wavelength of the semiconductor laser 7, n _o is the refractive index of the substrate 1 for ordinary rays, and n _e is the refractive index of the substrate 1 for extraordinary rays. The length l'of the other single mode waveguide region 4 can be changed according to the required frequency difference within the range where the above equation is not satisfied.

Further, reflecting surfaces 5 and 6 are formed on the outer end faces of the single mode waveguide regions 3 and 4, respectively, and the inner end face (that is, the face in contact with the semiconductor laser 7) is reflected at the boundary face. Non-reflective surfaces 8 and 9 are formed to eliminate the above.

Next, a method of manufacturing the semiconductor laser device having the above structure will be described with reference to FIG.

First, by using chemical etching, plasma etching, mechanical grinding, etc. together with the substrate 1 of the birefringent material (for example, quartz) having the above-mentioned axial orientation, which is the slab type waveguide, As shown in the figure, the concave portion 2 having a depth of about several μm and the cross-sectional shape of lengths 1 and 1 ′ are 5
Single-mode waveguide regions 3 and 4 of about μm × 5 μm are formed.

Subsequently, a high-reflectance dielectric multilayer film (for example, a film in which a large number of layers of silicon and alumina are stacked) is used to form a single mode waveguide region.
The reflection surfaces 5 and 6 are formed by coating the outer end surfaces of 3 and 4. On the other hand, by coating a low-reflectance dielectric film (for example, a film in which silicon nitride and alumina are laminated in a single layer or two layers) on the inner end faces of the single mode waveguide regions 3 and 4, a non-reflecting surface is obtained. Form 8,9.
The resonator is completed as described above.

Then, next, a metal layer (not shown) is formed on the bottom surface of the recess 2 by vapor deposition, and this is used as an electrode for current injection into the semiconductor laser 7. Finally, a semiconductor laser 7 having an end face having a reflection-free surface similar to that described above is fitted into the recess 2 and aligned with the single mode waveguide regions 3 and 4, and then the semiconductor laser is formed on the metal layer. The electrode of No. 7 is fixed by welding. In practice, in order to improve the heat dissipation effect, the whole is mounted on a heat sink (not shown) made of a high thermal conductive material such as diamond and then wire-bonded to the opposite electrode of the semiconductor laser 7. finish.

In the semiconductor laser device configured as described above, the light emitted from the semiconductor laser 7 to the reflecting surface 5 side passes through the single-mode waveguide region 3 having the length 1 as the quarter-wave plate, and then the reflecting surface. The light is reflected by 5 and again passes through the single mode waveguide region 3 to enter the inside of the semiconductor laser 7. Similarly, the light emitted from the semiconductor laser 7 to the side of the reflecting surface 6 passes through the single mode waveguide region 4 having the length l ′ (≠ 1), is then reflected by the reflecting surface 6, and is again single mode. The light passes through the waveguide region 4 and enters the inside of the semiconductor laser 7.

At this time, the light emitted as TE polarized light from the semiconductor laser 7 to the reflecting surface 5 side is a quarter-wave plate (single-mode waveguide region 3) having an optical axis inclined by 45 degrees with respect to the TE polarized surface. By going back and forth, the plane of polarization is rotated by 90 degrees and converted into TM polarized light that is orthogonal to the TE polarized light. On the contrary, the light emitted as TM polarized light is converted into TE polarized light. Therefore, the semiconductor laser 7
On the side including the single mode waveguide region 3, the emitted light travels back and forth through the 1/4 wavelength plate, so that all the anisotropy regarding the polarization plane is canceled, that is, isotropic with respect to various polarization components. It becomes a medium. On the other hand, the single mode waveguide region 4
On the side of, since the length l'is different from l and does not act as a quarter-wave plate, the effective resonator lengths for the above two orthogonal polarizations can be slightly different.
As a result, two orthogonal polarizations (slightly shifted from TE and TM) having slightly different frequencies oscillate, and thus a dual-frequency light source is realized. It should be noted that these frequency differences are determined by the length l'of the single mode waveguide region 4.

Further, during oscillation, the emitted light of the semiconductor laser 7 is limited in the vertical and horizontal directions by the single mode waveguide regions 3 and 4, that is, is confined in this and does not spread to the surroundings. Therefore, almost all the reflected light from the reflecting surfaces 5 and 6 can be returned to the inside of the semiconductor laser 7, and thus very good resonator efficiency can be obtained.

Further, in this embodiment, since the resonator is constituted by the birefringent substrate 1 in which the semiconductor laser 7 is embedded and the reflecting surfaces 5 and 6 formed at both ends thereof, all parts are integrated. . This facilitates the assembly and adjustment of the device and stabilizes the accuracy. Moreover, since a material such as an adhesive that may change over time is not used, high accuracy after assembly can be maintained for a long period of time.

〔The invention's effect〕

According to the semiconductor laser device of the present invention, the assembly and adjustment of the device are simplified, the deterioration of characteristics due to aging is eliminated, and good resonator efficiency is obtained.

[Brief description of drawings]

FIGS. 1 (a), (b), and (c) are perspective views, side views, front views, and FIGS. 2 (a) and (b), respectively, showing a semiconductor laser device according to an embodiment of the present invention. 9A and 9B are a side view and a front view for explaining a method for manufacturing the semiconductor laser device according to the above-described embodiment. 1 ... Substrate, 1a ... Optical axis, 2 ... Concave, 3,4 ... Single mode waveguide region, 5,6 ... Reflecting surface, 7 ... Semiconductor laser, 7a ... Laser optical axis, 7b …… TE polarization plane, 8,9 …… No reflection plane.

Claims (4)

[Claims] 1. A semiconductor laser device of an external cavity type, wherein a semiconductor laser (7) is incorporated in a resonator, wherein the semiconductor is in a plane where an optical axis (1a) is perpendicular to a laser optical axis (7a). On the birefringent substrate (1) inclined by 45 degrees with respect to the TE polarization plane (7b) of the laser, the concave portion (2) for mounting and fixing the semiconductor laser and the active layer surface of the semiconductor laser are opposed to each other. A single-mode waveguide region (3, 4) extending from the recess to both sides and one of which acts as a quarter-wave plate is provided, and reflecting surfaces are provided on both end faces outside the single-mode waveguide region. A semiconductor laser device comprising (5, 6) to constitute the resonator. 2. The semiconductor laser device according to claim 1, wherein the depth of the recess is several μm. 3. The size of the cross-sectional shape of the single mode waveguide region is determined according to the refractive index of the substrate so that the TE and TM modes are not cut off. The semiconductor laser device according to claim 1 or 2. 4. The non-reflective surface (8, 9) is formed on the end face of the single mode waveguide region on the side of the semiconductor laser, as claimed in any one of claims 1 to 3. The semiconductor laser device described in 1.