JPS6257276A - Semiconductor laser array device - Google Patents

Abstract

PURPOSE:To convert the guided light of 180 deg. phase mode into the laser light emitting with the same phase and to make it possible to operate up to a high output region a stable single mode oscillation with a radiation pattern having a far-field pattern of single peak, by providing waveguides whose thickness is different with one another an output end surface of a plurality of active waveguides. CONSTITUTION:Thin films whose thickness is alternately different with one another are formed on each output end surface of a plurality of active wavegides. For example, a thin film 2a of Al2O3 is formed on the end surface of a resonator O composed of semiconductor laser array, and the window opening of resist is made on the confronted parts of this film with an active layer 20 and clad layers 19 and 21 of laser stripes 4, 6 and 8 out of five laser stripes 4-8 of the resonator O wherein stripes 4 and 8 are made on both sides and the stripes 6 at the center. Next, the thin film of Al2O3 and that of SiO2 are formed successively, and unnecessary parts of thin films are eliminated. Then the thin film of two layers composed of thin film 26 of Al2O3 and thin film 3 of SiO2 on thin film 2a of Al2O3 is formed on the confronting parts with active waveguides 4, 6 and 8. The single layer composed of only a thin film 2a, and the thin film of a plurality of layers composed of thin films 2a and 2b and a thin film 3 are alternately and periodically formed on the output end surfaces of active waveguides 4-8.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a semiconductor laser array device in which a plurality of semiconductor lasers are formed in parallel on the same substrate to achieve high output.

<Conventional technology> Considering practicality, the output of a semiconductor laser alone is 8.
The limit is about 0 mW. Therefore, research is being conducted on semiconductor laser arrays in which a plurality of semiconductor lasers are arranged in parallel on the same substrate to increase output.

FIG. 5 shows the phase waveform of guided light in the semiconductor laser array. When a plurality of semiconductor lasers are arranged in parallel with optical coupling, and a uniform gain is given to each laser, the phase of each laser beam is synchronized with the same phase, that is, the phase power is 80 from 0° phase mode a. °Reverse state i.e. 1
Easy to oscillate in 80° phase mode b. This is 18o°
This is because in the phase mode, the intensity distribution of the laser beam matches the gain distribution better than in the O° phase mode, and less gain is required for oscillation.

<Problems to be Solved by the Invention> Figures 6 and 7 show far-field images of the radiation pattern of a 1144-body radar array. In the 0-layer phase mode, the peak is unimodal, and in this case, the laser beam can be focused on a single spot with a lens. On the other hand, 180
The layer phase modulus 1 has a multimodal peak, and cannot be focused on a single spot by a lens. In this case, it cannot be used as a light source for optical discs, etc. Therefore, it is desirable that the emitted light from the semiconductor laser array be in the same phase.

<Means for Solving the Problems> The present invention provides a semiconductor laser array device having a plurality of optically coupled active waveguides, in which the emission end faces of the plurality of active waveguides have alternately different film thicknesses. It is characterized by forming a thin film.

<Principle> In the present invention, a thin film is formed on the emission end face of a semiconductor laser array, and laser light guided in a 180-layer phase mode is converted into laser light emitted in the same phase.

FIG. 2 shows a schematic configuration of a semiconductor laser array device in which a thin film is formed on the output end face of a plurality of active waveguides.
, 6, 7. This activation on the output end face 9 of 8! alli4.
5. . . , 8, thin films 1 having alternately different film thicknesses are formed. Active waveguides 4, 5. . . , 8, the laser light of the 180-layer phase mode 1b is guided.

Now, if the wavelength of the laser beam in vacuum is λ0, the refractive index of thin film 1 is n, the smaller thickness of thin film 1 is d, the larger thickness is d, and 10d2, then the following formula is satisfied. do.

O (However, p-1+ 3.5....)---(+
1 This is because when the laser beam in the 180-layer phase mode propagates through the thin film l, the phase difference between adjacent laser beams changes by an odd multiple of 180°, and the laser beams with the same phase at the output end face 10 of the thin film l change. is the condition for emission.

Furthermore, when the laser beam propagates through the thin film 1 and is reflected at the thicker end face 11 and the thinner end face 12 of the thin film l, respectively, and returns to the end face 9, the laser light between adjacent waveguides is The conditions for stable laser oscillation with the phase difference of the light matching the phase difference of the laser beam when it enters WJ191 are the following formula 7% (however, q = 1.2.3...) - (21 Equation (1) above. (From 21, the condition that the refractive index n of U*1 satisfies is n. (q-p)-q (q>p)--(3)
becomes.

By setting the refractive index n and film thicknesses al and a2 of the thin film 1 so as to satisfy the above conditions, it is possible to convert the laser light guided in the 180-layer phase mode into the laser light emitted in the same phase.

The semiconductor laser array device shown in FIG. 3 includes a plurality of active waveguides 4.5. . . , a thin film consisting of a plurality of layers and a thin film consisting of a single layer are formed on the output end face 9 of the active waveguides 4, 5 .・
. . , 8 are formed alternately. thin film 2
are active waveguides 4, 5 . . Thin film 2 and thin film 3 have different refractive indexes.

Now, the refractive index of the first thin film 2 is nl, the thickness of the smaller one of the thin films 2 is dl, the thickness of the larger one is di + d2, and the second
The refractive index of the WIi-film 3 of the layer is n2, and the thickness of the thin film 3 is d.
Set it to 3. However, the two-layer thin film 2°3 is selected to have a relatively small difference in refractive index. In this case, the condition for making the laser light of the 180-layer phase mode into the same phase emitted light at the emitting end face 13 of the thin film 2.3 is as follows: =p-n.-(4). Furthermore, the laser beam propagates through the thin films 2 and 3 and the thin film 2
, 3 and return to the end surface 9, the phase difference between the laser beams between adjacent waveguides matches the phase difference when the laser beam is incident on the thin film 2, so that the laser becomes stable. The conditions for oscillation are expressed by the following equation.

A C+ From the above equation (4), ff1l, the film thickness (12, (13) is obtained by solving the following simultaneous equations.

= ~ (6) nl ・d2 +n2− d3 = −−−−−λ0 Therefore, when the refractive index n1ln2 of the thin films 2 and 3 is determined,
By determining appropriate variables p and q, the film thickness a2. d3
is determined.

In general, by forming a thin film in which the number of thin film layers or the film thickness and refractive index of each layer are alternately and periodically different for each active waveguide, 1) guided light in the 180" phase mode can be outputted in the same phase; 2) Stable laser oscillation even if a thin film is added
If the thickness of the thin film is set to satisfy two conditions, 1
Laser light oscillated in 80° phase mode can be converted into emitted light having the same phase at the emitting end face.

<Example> Hereinafter, as an example of the present invention, V −
channeled 5ubstrate 1nner
In addition to applying a 5tripe laser (VSIS laser), Al2O3 and 5i02 are applied to the output end face of the waveguide.
A semiconductor laser array device formed by forming a thin film consisting of the following will be described.

FIG. 4 shows a cross-sectional structure of a semiconductor laser array.

The manufacturing method for this semiconductor laser array begins with p-GaAs
N-Ga, which forms a reverse polarity junction, is grown on the substrate 16 by a crystal growth method such as a liquid phase epitaxial growth method (1, PE method).
As current■Current layer 1 stops. Next, by photolithography and etching techniques, five parallel stripes of square-shaped grooves 18 are formed from the surface of the current blocking layer 17 to a depth reaching into the substrate 16. This ■-shaped groove 18
By forming this, the portion where the current blocking layer 17 is removed from the substrate 16-1- becomes a current path.

Using the LPE method again, one layer 17 and a full 1 layer were added to the current barrier 1.
8, a p-A I xGa(-xAs cladding layer 1
9, p- or n-AIyGa+ -yAs active layer 20,
The n-A I xGal-XAS cladding ff121 is sequentially grown to obtain the active layer 20 via a double heterojunction. Note that x>y. Furthermore, on top of this, n”GaA
The s-camp layer 22 is continuously grown to form a multilayer crystal structure for laser operation, a p-type resistive electrode 23 is formed on the substrate 16 side, and an n-type resistor is formed on the growth layer side, that is, the camp layer 22. After forming the sexual electrode 24, the resonator length is 200~
A laser plane mirror is formed by a cleavage method in a direction perpendicular to the stripes so that the thickness is 300 μm.

First, a thin film of Al2O3 is deposited on both end faces of the resonator consisting of the semiconductor laser array manufactured by the above method to a thickness d+ equal to half the oscillation wavelength λe of the semiconductor laser array.
=0.34λe). Note that the oscillation wavelength λe of this semiconductor laser array is 780 nm, and the refractive index n1 of Al2O3 at this time is 1.76. and,
The resonator with this Al2O3 thin film formed thereon is mounted on a Cu block, current is injected into the resonator to cause laser oscillation, and the far-field pattern of the radiation pattern at this time is observed. As shown in Figure 7, the output reaches around 150 mW. A single mode oscillation with a 180° phase mode was obtained with the bimodal pattern shown in FIG.

FIG. 1 shows a perspective structure of a semiconductor laser array device. Five laser stripes 4 and 5 of the resonator 0 are formed on the Al2O3 thin film 2a formed on the end face of the resonator 0 consisting of a semiconductor laser array as described above.

6, 7. Laser stripes at both ends and center of 8 4, 6
．． A window in the resist was opened in a portion facing the active layer 20 and the cladding layer 19, 21 of No. 8 using photolithography technology. Next, in the formula (61, +71) for determining the film thickness of the thin film described in -, the oscillation wavelength λe of the laser array is 780
Refractive index of Al2O3 in nm rz = 1.76 and 5
By substituting the refractive index n2=1.45 of 102, Al2O3
When determining the thickness d2 of the thin film 2b of 5i02 and the thickness d3 of the thin film 3 of 5i02, the variable p=1. When q=3, d2=o, +eλe, d3=o, 84λe. By setting the film thicknesses of Al2O3 and 5i02 in this way,
Thin films of Al2O3 and 5i02 were sequentially formed on the resist l-plane-12. Then, unnecessary portions of the thin film were removed with acetone. As a result, as shown in Figure 1, Al2O3
A two-layer thin film consisting of a thin film 2b of Al2O3 and a thin film 3 of 5i02 is formed on the thin film 2a of , in a portion facing the active waveguides 4, 6.8. A single layer of thin M*2a on the output end face of FJII! 2a,
The structure is such that a plurality of thin films consisting of the thin film 2b and the thin film 3 are alternately and periodically formed.

The semiconductor laser array device configured as described above is
When mounted on the U block and injecting current into resonator 0 to cause laser oscillation, the far-field pattern of the radiation pattern is not shown in Figure 6, and small-mode oscillation with a single peak occurs up to an output of around 150 mW. Obtained. In this way, the laser light guided by the laser array is converted into laser light emitted with the same phase at the emission end face of the thin film, and moreover, stable laser oscillation is possible.

In this example, Al2O3 and 5i02 are used as the thin films formed on the emission end face of the semiconductor laser array, and GaAs-G is used as the material of the semiconductor laser array.
Although the aAlAs system is used, the present invention is not limited thereto, and 'I'iO2 and other materials are used as the thin film, and InP-rnGaAsP is used as the semiconductor laser array.
It goes without saying that various types of materials may be used.

Furthermore, the stripe structure of the semiconductor laser array is
In addition to the TS structure, other internal stripe structures or other element structures can also be applied.

<Effects> As explained above, in the present invention, thin films having alternately different thicknesses are formed on the output end faces of a plurality of active waveguides, thereby creating a laser that emits guided light in the 180° phase mode in the same phase. When converted to light, it produces a radiation pattern with a single-peak far-field pattern, which enables stable single-mode oscillation up to high output.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic perspective structure of a semiconductor laser array device according to an embodiment of the present invention, FIGS. 2 and 3 are diagrams showing a schematic planar configuration of an embodiment of the present invention, and FIG. FIG. 5 is a diagram showing a schematic cross-sectional structure of a semiconductor laser array according to an embodiment of the invention.
The figure shows the phase waveform of guided light in a semiconductor laser array.
6 and 7 are graphs showing far-field images of the radiation pattern of a semiconductor laser array. 1.2.2a, 2b, 3.=thin film 4, 5. 6. 7. 8... Active waveguide 9...
Output end faces 11.12, 14.15... end faces Figure 1 Figure 2 Figure 3 Figure 6

Claims (3)

[Claims] (1) A semiconductor laser array device having a plurality of optically coupled active waveguides, characterized in that thin films having alternately different thicknesses are formed on each of the output end faces of the plurality of active waveguides. Semiconductor laser array device. (2) The semiconductor laser array device according to claim 1, wherein the number of layers and the refractive index of the thin film alternately differ for each of the emission end faces of the plurality of active waveguides. (3) When the phase difference between the laser beams emitted from the adjacent active waveguides changes by 180° and the laser beam reflected from the end face of the thin film returns to the active waveguide, the laser beam between the adjacent active waveguides 3. The semiconductor laser array device according to claim 1, wherein the phase difference of the laser beam coincides with the phase difference of the laser beam when it is incident on the thin film.