JPS62171180A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To manufacture a semiconductor laser having structure in which the improvement of a laser outgoing shape and the stabilization of an oscillation mode can also be expected even when an output is enhanced by thickening an active layer by obliquely forming at least one end surface of both end surfaces of said active layer at an angle smaller than perpendicularity to an optical axis along the longitudinal direction of said active layer. CONSTITUTION:At least one end surface 15 of both end surfaces of an active layer 11 constituting an optical resonator is formed as an inclined plane shaping the inclination of an angle thetaa smaller than perpendicularity to an axis Az. The conditions of resonance are satisfied only by upward plane waves W1 vertically projected to the active-layer end surface 15 in plane waves wave- guiding in the active layer 11, and downward plane waves W2 are absorbed through a clad layer 12 as shown in a virtual line or at least the conditions of resonance are not satisfied. Accordingly, phase phi on the laser outgoing end surface 15 is equalized, and a far-field pattern Ir is also changed into a unimodal pattern, in which a peak is positioned at the center, and stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to improvements in the geometrical shape involved in the oscillation effect of semiconductor lasers, and particularly to improvements that are effective for high-power semiconductor lasers.

<Prior Art> Generally, as shown in FIG. 7, a semiconductor laser has an active layer 11 with a refractive index of na, which is sandwiched above and below the active layer 11, and has a refractive index nc of the active layer with the refractive index na of the active layer. Both end surfaces 13.13 of the active layer 11, which is composed of a pair of cladding layers 12 and 12 smaller than the cladding layers 12 and 12 and which form an optical resonator, are generally formed by crevices.

However, when increasing the output of such a semiconductor laser 10, there is a method for increasing the thickness of the active layer 11 and increasing the area of the laser emitting end faces 13, 13.

<Problems to be Solved by the Invention> It is true that increasing the laser beam output by expanding the area of the emission end faces 13, 13 as described above is regarded as one of the simplest methods. can do.

However, on the other hand, when such a method is used, the output end face 13
, 13, the presence of high-order standing waves is allowed in the thickened active layer 11, which eliminates the drawback that the far-field pattern of the emitted laser becomes multimodal and the oscillation mode becomes unstable. The disadvantage of stability has arisen.

That is, for example, in the case of a conventional double heterojunction laser (DH laser), the optical resonance mode in the active layer 11 is located in the optical resonator or the output end face 1, as shown in FIG.
Two plane waves Wl each incident on 3 with an incident angle θ,
It can be thought of as a superposition of W2 (in this book, "incident angle '° is defined as the angle between the surface on which a light wave is incident and the light wave)".

Therefore, if the thickness of the active layer 11 is made to be sufficiently thick compared to the wavelength (for example, about 0.3Mn) in the optical medium in accordance with the above-mentioned demand for high output, the output end face in FIG. As schematically shown on the right hand side of 13, the phase φ of the emitted light is reversed in positive and negative directions in the X direction along the emitting end surface.

Since the light from this exit surface becomes aligned in phase as a plane wave in an oblique direction, its far-field image Ir becomes multimodal, as schematically shown at the rightmost end in Fig. 7. Become.

In particular, the two illustrated plane waves Wl and W2 have a critical angle (
GaAs/AIo, 3Gao, and 7As interfaces can exist if the standing wave condition is satisfied within a range of approximately 30 degrees (inclination from the interface), but as the active layer 11 becomes thicker, a large number of incident Since the standing wave condition is satisfied at the corners, as the thickness is increased to achieve higher output, the oscillation mode becomes even more unstable.

The present invention was made to eliminate these drawbacks that are particularly common in conventional high-output lasers.Basically, even if high output is achieved by thickening the active layer, the laser emission shape The present invention aims to provide a semiconductor laser with a structure that can be expected to improve the oscillation mode and stabilize the oscillation mode.

<Means for Solving the Problems> In order to achieve the above object, the present invention has considered the structural and geometric shapes of existing semiconductor lasers.

As described above, in most of the semiconductor lasers that have been developed so far, the emission end face is formed between folds, and thus is formed as a face perpendicular to the active layer 11. However, because of this, it can be considered that the problem of multiple standing waves being superimposed as described above has arisen.

Based on these findings, the present invention provides a semiconductor laser having the following configuration.

A pair of cladding layers sandwich the active layer from above and below, and
In a semiconductor laser in which both end faces of the active layer are used as optical resonators, at least one end face of the above-mentioned both end faces of the active layer is
A semiconductor laser characterized in that the active layer is formed obliquely at an angle less than perpendicular to the optical axis along the length direction of the active layer.

<Operations and Effects> In the semiconductor laser of the present invention configured as described above, among a plurality of plane waves that may exist in the active layer, a specific angle (preferably Only plane waves that are incident vertically are allowed to resonate, and other plane waves are absorbed, for example, through the cladding layer.

The phase of the laser beam becomes uniform, the two oscillation modes become stable, and the far-field pattern becomes unimodal.

Furthermore, in the conventional method, in order to form a steep surface perpendicular to the active layer, it was necessary to use the space between the folds, which made two-dimensional integration extremely difficult. In the case of forming the active layer end face obliquely as in the invention, the existing wet etching method has good processing accuracy and is less likely to cause damage to the workpiece, and can also form a smooth molding surface. Since the process can also be used, it becomes easy to two-dimensionally integrate a plurality of pieces on a suitable substrate.

In particular, in the semiconductor laser of the present invention, the emitted laser beam is directed in an oblique direction.
The distance between adjacent semiconductor lasers can be sufficiently shortened without the beam being physically blocked by other adjacent semiconductor lasers, and high concentration can also be achieved.

<Embodiment> FIG. 1 shows a principle diagram of the present invention and a basic embodiment of a semiconductor laser IO constructed in accordance with the present invention. Regarding the reference numerals in Fig. 1, the same reference numerals are given to those functionally corresponding to those in the conventional semiconductor laser shown in Fig. The end face or optical resonator has been changed to 15.

In the semiconductor laser 10 of the present invention, as only one of them is shown in FIG. It is formed as an oblique surface having an angle θa less than perpendicular to the axis Az along the length direction.

When both end surfaces 15 and 15 are oblique surfaces, the semiconductor laser of the present invention has a trapezoidal shape when viewed as a whole.

In this way, only one of the plane waves guided in the active layer 11, for example, the upward plane wave W1 that is incident perpendicularly to the active layer end face 15, satisfies the resonance condition, and the downward plane wave W2 is shown by an imaginary line. As such, it is absorbed through the cladding layer 12, or at least the resonance condition is no longer satisfied.

Therefore, as shown in FIG. 1, the active layer end face 15,
That is, the phase φ at the laser emission end face 15 becomes uniform, and the far-field image Ir also becomes stable with a single peak having a peak at the center.

After all, in the semiconductor laser of the present invention, only a specific plane wave corresponding to the emission facet inclination θa can be allowed to resonate under the resonance condition. Therefore, even if the output of the semiconductor laser is increased and the active layer is thickened, Single-longitudinal mode oscillation may be possible.

However, even in the semiconductor laser 10 of the present invention having an optical resonator formed by the oblique end face 15, if the waveguide path in the active layer is also considered, the total reflection mirror formed by the end face 15 as shown in FIG. 15 and a total reflection mirror 15°9100 due to the boundary between the active layer and the cladding layer. Since it can be seen as a collection of , it naturally does not have the function of converging light.

Equivalently, as shown in FIG. 2 CB), plane mirrors 15, 15 are simply opposed to each other.

Therefore, in order to reduce the loss of the optical resonator, it is necessary to make the luminous flux sufficiently large compared to the wavelength within the tube, for example, 111 m or 3 g.
It is desirable to set it to about 1.

However, if necessary, as shown in FIG. 2(C), the end face 1
It is effective to use curved surfaces at 5° and 15° because the light can be converged.

When the end face of the active layer is formed obliquely as in the present invention, the slope θa is limited by the critical angle θimaz at the boundary between the active layer 11 and the cladding layer 12.

That is, the incident angle θ of the plane wave Wl with respect to the cladding layer 12 when the resonance condition is satisfied in FIG.
Regarding i, it is limited by the maximum value θimax at which total reflection is observed. Of course, if the plane wave is perpendicularly incident on the oblique end face 15 as in the case shown in FIG. 1, θa=90′−θi.

However, for example, GaAs and A I G, 3 Ga
When O, 7A s is used as the active layer 11 and cladding layer 12, respectively, the above critical angle is about 30'', so the lower limit of the inclination θd of the active layer end face 15 is about 70°; Since light is not effectively confined near the corners, the practical upper limit of the incident angle θi is about 20'', and therefore the lower limit of the end face inclination θa is about 80'.

However, in the case of the semiconductor laser of the present invention, since the end faces of the active layer are not formed vertically as in the prior art, there is no necessity to use the inter-fold process.

Taking advantage of this difference, it is possible to easily cut out an etched surface with a specific plane orientation as an end surface of the active layer.

This method is not only simple, but also has an extremely low risk of damaging the cut out surface, so it can significantly improve yield compared to the crease method.

Furthermore, the important task of two-dimensional integration of semiconductor lasers on a suitable mechanical support substrate, which could not be achieved using the interfold method, can be achieved.

That is, as shown in a schematic construction example in FIG. 3, a global structure consisting of a series of cladding layers, active layers, and cladding layers is first formed on almost the entire surface of a suitable support substrate 20, as shown by imaginary lines. After forming the laser structure layer 21, it is etched according to a desired pattern to form a plurality of individual semiconductor lasers 10. , , , can be extracted. In such a case, the active layer end faces 15, 15 of these individual semiconductor lasers 10 may be formed according to the idea of the present invention.
It is formed diagonally.

Furthermore, since the distance between adjacent semiconductor lasers to and to can be made sufficiently close to each other in a device having an oblique emission end face 15 as in the present invention, it is possible to increase the distance sufficiently if two-dimensional integration density is required. Collateral effects also occur.

The reason is that the output laser beam from each semiconductor laser IO is emitted obliquely upward as shown in the third diagram, so even if the adjacent semiconductor laser IO is located nearby, This is because they can easily overcome heights.

Furthermore, if necessary, by shifting the adjacent semiconductor lasers 10, 10 in a direction perpendicular to the plane of the drawing, it is possible to prevent the laser beams emitted from them from intersecting each other in space.

Note that, in the gist of the present invention, only the end face 15 of the active layer 11 may be formed obliquely.

When the etching method is actually applied, it goes without saying that the end faces of the upper and lower cladding layers 12 and 12 will also be cut obliquely in series.

Another embodiment of the invention is shown in FIG.

The basic structure is of course the same as that shown in FIG. 1, but the refractive index distribution of the cladding layer 12.12 has been devised so that it decreases as it moves away from the active layer 11 in the thickness direction. .

The technology to do this is already established in the field of optical waveguides, so there is no problem, but this results in a function similar to a type of selfoc lens, increasing the angle of incidence of the waveguide defined by the active layer. can do.

FIG. 5 roughly shows another embodiment of the present invention, in which the cladding layers 12 and 12 are composed of a hetero multilayer film.

That is, the cladding layer 1 formed above and below the active layer 11
In this embodiment, 2.12 is made into a multilayer film structure of a first layer 12-1 and a second layer 12-2, which are alternately laminated and superimposed with IO to 20 layers each.

Specifically, for example, when the active layer 11 is made of GaAs, the first and second layers 12-1 and 12-2 are made of AlGaAs/GaAs.
Should it be As?

AIo, 3Gao, 7As/ AlO, tGao-sA
s etc.

In such a case, the wave number component in the thickness direction of each layer of film H is 17
Therefore, for example, 1100n
When the angle of incidence is set so that the angle of incidence is within the range of 100 to 200 nm, the phases of the reflected waves in each layer of the multilayer film are matched, so that a high reflectance can be obtained at a relatively deep angle of incidence.

Figure 6 (A) and (B) show AIo, 3Gao, and 7A at angles of 30@ and 25@ from the GaAs active layer to the interface.
It shows the number of times the multilayer film is superimposed and the reflectance when light is incident on the multilayer cladding layer of s/Ala, tGan, and sAs.

When the thickness of the active layer is 2 mm and the laser length is 100 gF, about 100 reflections are repeated during the round trip of the optical path, but in the case of a normal DH laser, the reflectance of the interfold surface is 0. 3
2, the resonator loss [In(1/R)1 is 1.14.

The condition for the reflection loss due to the hetero multilayer film to be less than half of the resonator loss due to end face reflection is that the resonator loss due to reflection of two layers of the multilayer film is 1/100 or less.

Therefore, when reading the number of times of superimposition that satisfies this condition, in the case of 30° incidence in Fig. 6(A), 15 times (film thickness 4,
5 wn ), and in the case of 25° incidence as shown in FIG. 6(B), the number of times is 10 (film thickness: 4 mm).

Incidentally, the virtual lines in Fig. 6 indicate the reflectance when the light beam is incident from the GaAs active layer to the A IQ, 3 Gao, and 7 As cladding layers at each incident angle. , the reflectance is 0.1, respectively.
4B, the reflectance is as low as 0.247, and there is no practical problem considering that a satisfactory optical waveguide has been formed.
It can be seen that this can only be realized using a semiconductor heteromultilayer film.

Of course, as with the excitation mechanism of existing semiconductor lasers, p-type and n-type conductivity types may be selected for the cladding layer, and even with regard to such an operation mechanism, according to the present invention, the excitation current density is not reduced. By increasing the thickness of the active layer, it is possible to achieve high output.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of the principle or basic embodiment of the semiconductor laser of the present invention, FIG. 2 is an explanatory diagram of the optical resonator of the semiconductor laser of the present invention, and FIG. 3 is a diagram of the second embodiment of the semiconductor laser of the present invention. 4 and 5 are schematic diagrams of other embodiments of the present invention, FIG. 6 is a characteristic diagram of the cladding layer of the embodiment shown in FIG. 5, and FIG. The figure is a schematic diagram of a conventional semiconductor laser that utilizes interfold surfaces for active layer end surfaces or optical resonators. In the figure, 10 is the semiconductor laser as a whole, 11 is an active layer, 12 is a cladding layer, 13 is an end face of the active layer formed perpendicularly by conventional folds, and 15 is an end face of the active layer formed obliquely according to the present invention. Or an optical resonator. Figure 2 Figure 3

Claims (1)

[Claims] The active layer is sandwiched between the upper and lower sides by a pair of cladding layers, and
In a semiconductor laser in which both end faces of the active layer are used as optical resonators, at least one end face of the above-mentioned both end faces of the active layer is
A semiconductor laser characterized in that the active layer is formed obliquely at an angle less than perpendicular to the optical axis along the length direction of the active layer.