Semiconductor laser arrangement for high output power in the lateral dominant mode.

p0001The maximum output power of AlGaAs laser is generally limited by an irreversible damage mirror employing at a particular light power density. In order to increase the output power of the emission surface can be widened parallel to the active zone, so that with the same maximum power density increases, the emitted light power. Possible ways to do this, for example, laser array structures with several optically coupled single stripe lasers or so-called broad area laser. This laser structures generally have the property that a plurality of lateral modes of the general structure are capable of propagation and vibrate simultaneously. This leads to wide lateral far fields with multiple lobes. A diffraction limited to the smallest spot diameter is not possible with such a lateral multimode structures.

p0002There are a number of array structures, which have a strong mode selection for the fundamental lateral mode. Due to technical reasons and unevenness due to the strong interaction of light output and waveguide but a stable lateral mode can be maintained only with difficulty over a wide power range.

p0003In the patent US 4,713,821, a semiconductor laser is described which consists of a laser range with an active laser stripe and which are separated by a narrow coupling region reinforcement area in which the active layer is widened trapezoidal. The coupled-in radiation gain region is expanded laterally and emerges at the end face of the component. This component is prepared by a substrate having the grown semiconductor layers is fixed on a flat reference surface and then along a lattice plane forming the boundary between the laser portion and the amplifier region, is cleaved. This gap forms the coupling region.

p0004In the patent US 4,773,076, a semiconductor laser is described in which a continuously running waveguide is formed as an active layer with a different width in two different areas. In Fig. 1b of this patent, the lateral dimensioning of the active layer is shown with dashed lines. The second existing area is used here not as a gain region, but as a second laser resonator is coupled to the first resonator. Because of the continuously running active layer and accordingly existing resonator end, these are practically one in two areas divided with different resonator laser.

p0005Object of the present invention is to provide an easily manufacturable semiconductor laser structure in which the lateral fundamental mode is stable and the emission surface is as large as possible.

p0006This object is achieved with a semiconductor laser array according to the invention with the features of Ansprüches. 1

p0007Following is a description of a semiconductor laser array according to the invention with reference to Figures 1 to. 5<ul><li>Fig. 1 shows a semiconductor laser array according to the invention in a section through the waveguide parallel to the overgrown substrate surface.</li><li>Fig. 2 shows a first embodiment of a semiconductor laser array according to the invention in longitudinal section.</li><li>Fig. 3 shows the propagation of the wave fronts of the laser radiation in a semiconductor laser according to the invention in the section corresponding to FIG. 1</li><li>Fig. 4 shows a second embodiment in the cutout.</li><li>Fig. 5 shows a third embodiment in the cutout.</li></ul> The invention consists of a semiconductor laser device in which are integrated on a common substrate 1:<ul><li>1. A laser area A, which consists in the in FIGS. 1 and 2 embodiment, of a single-stripe laser with a lateral and vertical waveguide shown,</li><li>2. a coupling region B and</li><li>3. a reinforcing area C, in which the lateral wave guidance is canceled.</li></ul>

p0008In the embodiment described here, the individual lasers is, for example, as a BH laser (buried heterostructure) or formed as MCRW laser. The lateral wave guiding is effected by lateral regions 9 define the waveguide 4 laterally from it suitable semiconductor material. The waveguide 4 and the active layer 5 located therein are dimensioned such that the generated laser radiation that is laterally and vertically, swings into two perpendicular to the direction of propagation directions, in the fundamental mode.

p0009In the reinforcing member C lacks the lateral wave guide, or at least greatly reduced; a wave guide is only in the vertical direction, ie the conduct of the active layer is perpendicular 5. Between the laser region A and the gain region C a relatively narrow dimensioned coupling region B. This coupling region B is required in order both to ensure that the resonance condition in the laser stripe by a reflection at the end faces, ie, the first resonator boundary surface 2 and the second resonator boundary surface 3 is given in figure 1. On the other hand is a the required coupling coefficient corresponding proportion of the laser radiation can be coupled into the gain region C.

p0010The inventive design of the coupling region B provides in particular three embodiments: In FIG. 2, a coupling region B is shown in longitudinal section, wherein the interface between the laser region A and the coupling region B (ie, the second resonator boundary surface 3) and the interface between the coupling region B and the Ver reinforcing area C (that is, the entrance surface 7 for the entry of radiation into the gain region C) each consist of a plane perpendicular to the propagation direction of the radiation mirror surface. These mirror surfaces can be prepared by etching the semiconductor layer structure. The laser range A and the gain region C are not completely separated from each other; by only partial removal (etching) of the transverse waveguide structure is formed, an incision which constitutes a longitudinal disturbance of the continuous waveguide 4th This part of the light output in the laser stripe is reflected back, namely by the laser field A partially bounding specular second resonator boundary 3. The other portion is effectively coupled into the gain region C.

p0011Targeted partial reflection can also be done by installing a longitudinal grating structure in the wave guiding region. Such a built-in into the waveguide 4 (DBR) lattice 10 is shown in Fig. 4. Such a DBR (distributed Bragg reflector) also has a wavelength-selective feedback, making it possible to achieve that the narrow stripe laser oscillates and longitudinally single mode. Through the depth and other configuration of the grid 10 to the desired Reflxionsgrad be adjusted.

p0012Fig. 5 shows a third embodiment in which the entrance surface 17, which delimits the coupling region B of the reinforcing area C is at least partially inclined, extends to the propagation direction of the radiation. Particularly advantageous is the embodiment shown, in which the plane of the entrance face is rotated 17 relative to the plane of the second resonator boundary surface 3 about a meaning specified perpendicular to the propagation direction, and that laterally in the above-extending axis, and such that the width of the coupling region B increases in points away from the substrate 1 direction. By this embodiment of the oblique entry surface 17 of the reinforcement member C reflections of the optical wave to be avoided during coupling, which could lead to undesired Fabry-Perot resonances in the coupling region B. The sloped entrance surface 17 can be produced by ion beam etching, for example.

p0013It is also possible to combine existing in the embodiments described characteristics with each other. Thus, for example in the embodiment of FIG. 2, in addition a grating 10 can be installed as in Fig. 4. It can furthermore be provided with a coating for. Example of dielectric material, the second resonator boundary surface 3 of the laser region A and the entrance surface 7 in the gain region C. It must in this case be only ensures that the coupling region B has a sufficient reflection of a few percent of the narrow stripe laser in the laser area A, so that in the laser, the feedback condition is satisfied for the oscillation of the laser oscillation. Secondly, it must be ensured that the emerging from the laser region A light output can be effectively injected into the gain region C.

p0014The laser cavity in the laser region A is provided on the first resonator boundary 2 with a highly reflective layer (eg, metal, dielectric mirror of Al₂O₃-Si layers). The exiting at the second resonator boundary surface 3 in the coupling region B light is coupled in via the inlet face 7 in the gain region C. This gain range C, the lateral wave guidance is at least reduced; It is also possible that extending the waveguide layer in the gain region C over the entire width of the structure.

p0015A first metal contact 11 is deposited on the surface of the lasing region A, a second metal contact 12 is located on the underside of the substrate 1, and a third contact 13 is applied to the reinforcing area C. This third contact 13 is designed such that it allows a current injection into the area in which the light coming from the laser light propagates under broadening of the beam path. The exit surface 8 of the gain region C is characterized by a dielectric coating (such as Al₂O₃-layers) antireflective coating of the semiconductor body, so that no reflection of the radiation can be carried back into the laser active region.

p0016The optical wave, which is coupled by narrow laser stripe in the laser region A via the coupling region B in the gain region C, swinging in the lateral fundamental mode because of the dimension of the waveguide 4 in the laser region A and spreads laterally in quasi free jet (opening angle 5 to 10 °) from, as the amplification of C no or a reduced lateral wave guide has. With the widening of the beam up to the exit surface 8 towards the lateral fundamental mode (3 Fig.) Is maintained. In the vertical direction the wave is guided through the vertical layer structure of the waveguide 4th This guide is also available in the gain region C. By suitable current injection into the gain region C on the third contact 13 is in this gain region C, which has the same vertical layer structure as the laser region A, caused by stimulated emission an optical gain which amplifies the continuous optical wave to the outlet surface 8 down. This principle and the lateral expansion of the wave is high output power while maintaining the fundamental lateral mode can be achieved.

p0017The laser device according to the invention is particularly easy to manufacture because the laser region (A) and the reinforcing region (C) is grown on a common substrate 1 and the coupling region (B) by a subsequent etching step or the incorporation of a DBR grating easily in a provided for the function optimized shape can be formed. Therefore, the laser device of the invention can in addition to the improved functioning of a higher percent yield of functional elements in the production than conventional embodiments expect.