JPH10200196A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enlarge the optical spot size by performing gain wave guide in a region close to the emission end face of laser light and the performing refrac tive index wave guide in the central region of the laser thereby increasing the divergence angle of a far-sighted light pattern. SOLUTION: The semiconductor laser 1 emits laser light while confining the laser light within the width of a stripe structure 5 defined by a constriction layer 4 of a buried layer on a laser light wave guide layer 3 formed on an active layer 2 emitting the laser light. The semiconductor laser 1 comprises a refractive index wave guide region 6 and a gain wave guide region 7. Gain wave guide is performed in the vicinity of an edge emitting laser light and refractive index wave guide as performed in the major emission part of laser light, i.e., the central region. According to the structure, divergence angle of the far-sighted light pattern can be increased and the size of edge emission light spot can be enlarged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having, for example, a ridge type cross-sectional structure and guiding emitted laser light.

[0002]

2. Description of the Related Art FIG. 4 is a perspective view showing an example of a conventional semiconductor laser. This semiconductor laser 31 has a waveguide layer 33 formed of a so-called cladding layer, a guide layer, or the like that guides laser light on an active layer 32 that emits laser light, and is formed on the waveguide layer 33. , Constriction layer 34 by buried layer
The laser light is confined within the width of the stripe structure 35 and emitted by the stripe structure 35 regulated by the above. FIG. 4 shows an example having a stripe structure 35 formed in a trapezoidal shape by etching or the like, that is, a stripe structure 35 having a so-called ridge structure. 36 is
This is a contact layer for making contact with the electrode.

In such a conventional semiconductor laser, light is guided by either one of refractive index guide and gain guide.

[0004] Refractive index semiconductor lasers and gain waveguide semiconductor lasers have the following characteristics, respectively.

[0005] refractive index waveguide: the threshold current I _th is low, astigmatism is small, a single mode oscillation, a small light spot at the end face. Gain guided type: multimode oscillation, low noise, large divergence angle θ‖ in the direction parallel to the junction of the far-field pattern (FFP), and large light spot on the end face.

An optical pickup used for a high-density optical disc such as a DVD is required to have low noise, a large divergence angle θ‖ of a far-field pattern, a small astigmatic difference, and a high output.

The low noise can be easily dealt with by the so-called high frequency superposition method, and the astigmatism can be easily corrected by correcting the laser beam by providing an oblique glass. On the other hand, it is required that the semiconductor laser side cope with increasing the divergence angle θ‖ of the far-field pattern and increasing the output.

[0008]

However, in general, when a refractive index guided semiconductor laser is applied to an optical pickup, the divergence angle θ 遠 of the far-field pattern is often an obstacle. Basically, in order to increase the divergence angle θ‖ of the far-field pattern, it is necessary to reduce the width W of the stripe structure 35 in the structure of the conventional semiconductor laser 31 shown in FIG. However, when the width W of the stripe structure 35 is reduced as described above, the light spot on the end face is reduced, so that the light density is increased and the destruction level of the end face is reduced.

In general, when the width W of the stripe structure is reduced, the threshold current density J _th is increased. _Therefore , there is a high possibility that the reliability is also lowered.

On the other hand, the gain-guided semiconductor laser is effective in increasing the divergence angle θ‖ of the far-field pattern, but increases the drive current density J _op , causing an output that causes a bend in the current-optical output characteristics. There is a problem that the so-called kink level is low and the amount of heat generated is not suitable for increasing the output.

In order to solve the above-mentioned problem, according to the present invention, the divergence angle in the far-field pattern is large, and the size of the light spot on the end face is enlarged, so that high output can be achieved. The present invention provides a semiconductor laser suitable for application.

[0012]

The semiconductor laser according to the present invention has a configuration in which a gain waveguide is provided in a region near an emitting end face of a laser beam and a refractive index is guided in a central region of the laser.

According to the configuration of the present invention described above, since the refractive index is guided in the central region of the laser, the threshold current can be reduced and the transverse mode of the laser beam can be stabilized.
Further, since the gain waveguide is provided in the region near the exit end face, the size of the light spot on the end face can be enlarged, and the divergence angle of the far-field pattern can be increased.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is a semiconductor laser in which a gain guide is provided in a region near a laser light emitting end face and a refractive index guide is provided in a laser central region.

Further, in the semiconductor laser according to the present invention, in the region where the gain waveguide is formed, the stripe has a tapered shape in which the width of the stripe becomes narrower toward the laser light emission side.

An embodiment of a semiconductor laser according to the present invention will be described below with reference to the drawings. FIG. 1A shows a perspective view of an embodiment of the semiconductor laser of the present invention. In this semiconductor laser 1, a waveguide layer 3 made of a so-called cladding layer, a guide layer, or the like that guides laser light is formed on an active layer 2 that emits laser light, and is formed on the waveguide layer 3. The laser light is confined to the width of the stripe structure 5 and emitted by the stripe structure 5 regulated by the narrowing layer 4 by the buried layer. FIG. 1 shows an example having a stripe structure 5 formed in a trapezoidal shape by etching or the like, that is, a stripe structure 5 of a so-called ridge structure. 8 is a contact layer for making contact with the electrode.

In this embodiment, the semiconductor laser 1 is formed from the refractive index waveguide region 6 and the gain waveguide region 7, and the gain is guided near the end face from which the laser light is emitted (gain waveguide region 7). In the central region, which is the main light generation portion, refractive index waveguide is used (refractive index waveguide region 6).

As shown in FIG. 1B, which is a cross-sectional view of the refractive index waveguide region 6, in this case, in the refractive index waveguide region 6 in the central region,
The step of the ridge structure of the waveguide layer 3 is set to be larger than the step of the ridge structure of the waveguide layer 3 in the gain waveguide region 7 near the end face (that is, the thickness di on both sides of the ridge structure in the refractive index waveguide region 6).
Is the thickness d on both sides of the ridge structure in the gain waveguide region 7.
g), the refractive index guiding becomes dominant. In the gain waveguide region 6 near the end face, the gain waveguide becomes dominant by setting the step of the ridge structure of the waveguide layer 3 small.

According to the semiconductor laser 1 of the present embodiment, the refractive index waveguide region 6 and the gain waveguide region 7 make up the laser beam generation mainly by the refractive index waveguide region 6. _Therefore , the threshold current Ith is kept low and the stability of the transverse mode is maintained. In addition, since the gain waveguide region 7 is formed near the end face, the effect of gain guide, that is, spherical wave guide occurs, so that the divergence angle θ‖ of the far-field pattern and the size of the end face light spot increase. Done.

This spherical wave waveguide will be described with reference to FIG. 3 in comparison with a conventional example. As shown on the left side of FIG. 3, in the conventional refractive index guided semiconductor laser, the laser light is emitted as a plane wave, so that the divergence angle θ‖ is small. On the other hand, as shown in the right side of FIG. 3, in the semiconductor laser 1 of the present embodiment, when the wave enters the gain waveguide region 7 near the end face from the refractive index waveguide region 6 in the central region, the wavefront changes from a plane wave to a spherical wave. . Therefore, the laser light emitted from the end face spreads, and the divergence angle θ‖ increases.

At the connection between the refractive index waveguide region 6 and the gain waveguide region 7, it is necessary to convert the mode, so that reflection and scattering may occur here, which may cause coupling loss. By not taking too large a difference between the thickness di of the waveguide layer 3 of the refractive index waveguide region 6 and the thickness dg of the waveguide layer 3 of the gain waveguide region, the refractive index waveguide region 6 and the gain waveguide region 7 can be connected smoothly.

In general, in a gain type semiconductor laser or a refractive index waveguide type semiconductor laser, for example, the thickness d of a gain type waveguide layer
g is 500 nm or more, and the thickness di of the waveguide layer of the refractive index guide type.
In many cases, a value of 300 nm or less is used. On the other hand, in the present example, since the expansion of the divergence angle θ で き る can be ensured by performing gain guiding, the width W of the stripe structure 5 of the refractive index waveguide region 6 is forcibly reduced or the refractive index is reduced. It is no longer necessary to aim for an increase in the difference Δn.

Therefore, for example, the thickness di of the waveguide layer 3 in the refractive index waveguide region 6 is set to 350 nm or less, the thickness dg of the waveguide layer 3 in the gain waveguide region 7 is set to 450 nm or more, and these thicknesses di are set. , Dg can be reduced.

In order to make the thickness di of the waveguide layer 3 in the refractive index waveguide region 6 different from the thickness dg of the waveguide layer 3 in the gain waveguide region 7 as described above, for example, After growing 3,
The refractive index waveguide region 6 where the waveguide layer 3 is to be formed thinner may be lightly etched by, for example, photolithography. Other parts can be manufactured by a known manufacturing method.

Considering the deterioration of the astigmatic difference, it is not preferable to increase the length Lg of the gain waveguide region 7 with respect to the length Li of the refractive index waveguide region 6. Therefore, in order to secure the gain waveguide property, the length Lg of the gain waveguide region 7 is set to L
g <100 μm.

Next, another embodiment of the semiconductor laser according to the present invention will be described. In gain waveguide, the far-field pattern may have a bad phenomenon of so-called bimodalization having two peaks. In this example, a configuration for preventing such a bimodal state is shown.

FIG. 2 is a perspective view of another embodiment of the semiconductor laser according to the present invention. The semiconductor laser 11 has a so-called tapered shape in which the width W of the stripe structure 5 of the gain waveguide region 7 is reduced as approaching the end face in order to prevent the above-mentioned double-peak phenomenon. Thereby, the peak of the far-field pattern becomes one due to the wavefront shaping effect of the region having the tapered shape.

In this example, as in the above example, the threshold current can be kept low, the stability of the transverse mode of the laser beam can be maintained, and the divergence angle θ‖ of the far-field pattern can be increased.

In the above-described example, the semiconductor laser having a stripe structure of a ridge structure is applied. However, the semiconductor laser of the present invention is similarly applied to a semiconductor laser having a stripe structure formed by another structure. hand,
By forming the refractive index waveguide region and the gain waveguide region, the divergence angle θ‖ of the far-field pattern can be increased, and the output of the semiconductor laser can be increased. The stripe structure of the ridge structure is more suitable for application to the semiconductor laser of the present invention because the parameter change in the refractive index waveguide region 6 and the gain waveguide region 7 can be reduced.

The semiconductor laser of the present invention is not limited to the above-described example, but may take various other configurations without departing from the gist of the present invention.

[0031]

According to the above-described semiconductor laser according to the present invention, gain guiding is performed in the region near the emitting end face of the laser beam, and refractive index guiding is performed in the central region of the laser. The divergence angle of the far-field pattern is enlarged by the effect of the wave, which is suitable for application to an optical pickup.

Further, since the size of the light spot on the end face can be enlarged by the effect of the gain waveguide, a high output operation can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a semiconductor laser according to the present invention. A is a perspective view. B is a cross-sectional view of the refractive index guide region.

FIG. 2 is a schematic configuration diagram (perspective view) of another embodiment of the semiconductor laser according to the present invention.

FIG. 3 is a diagram comparing a waveguide state and a divergence angle between a conventional example and an example.

FIG. 4 is a schematic configuration diagram (perspective view) of a conventional semiconductor laser.

[Explanation of symbols]

1,11 semiconductor laser, 2 active layer, 3 waveguide layer, 4
Constriction layer, 5 stripe structure, 6 refractive index waveguide region,
7 gain waveguide region, 8 contact layer, 31 semiconductor laser, 32 active layer, 33 waveguide layer, 34 constriction layer, 35
Stripe structure, 36 contact layer, width of W stripe structure, θ‖ divergence angle of far-field pattern, di film thickness of waveguide layer in refractive index waveguide region, dg film thickness of waveguide layer in gain waveguide region, Li Length of refractive index guide region, length of Lg gain guide region

Claims (2)

[Claims] 1. A semiconductor laser, wherein a gain guide is provided in a region near an emission end face of a laser beam, and a refractive index guide is provided in a central region of the laser beam. 2. In the region where the gain waveguide is formed,
2. The semiconductor laser according to claim 1, wherein the stripe has a tapered shape in which a width decreases toward an emission side of the laser beam.