SEMICONDUCTOR LASER DEVICE, METHOD FOR MANUFACTURING A SEMICONDUCTOR LASER DEVICE AND PROJECTION DEVICE

Abstract

A semiconductor laser device is specified, the semiconductor laser device comprising an active layer having a main extension plane, a first cladding layer and a second cladding layer, the active layer being arranged between the first and second cladding layer in a direction perpendicular to the main extension plane, a light-outcoupling surface parallel to the main extension direction and arranged on a side of the second cladding layer opposite to the active layer, a photonic crystal layer arranged in the first cladding layer or in the second cladding layer, and an integrated optical element directly fixed to the light-outcoupling surface. Furthermore, a method for manufacturing a semiconductor laser device and a projection device are specified.

Claims

1. A semiconductor laser device comprising: an active layer having a main extension plane; a first cladding layer and a second cladding layer, the active layer being arranged between the first and second cladding layer in a direction perpendicular to the main extension plane; a light-outcoupling surface parallel to the main extension direction and arranged on a side of the second cladding layer opposite to the active layer; a photonic crystal layer arranged in the first cladding layer or in the second cladding layer; and an integrated optical element directly fixed to the light-outcoupling surface.

2. The semiconductor laser device according to claim 1, wherein the integrated optical element comprises a wavelength filter.

3. The semiconductor laser device according to claim 1, wherein the integrated optical element comprises a volume Bragg grating.

4. The semiconductor laser device according to claim 1, wherein the integrated optical element comprises an optical isolator.

5. The semiconductor laser device according to claim 1, wherein the integrated optical element comprises a polarization converter.

6. The semiconductor laser device according to claim 1, wherein the integrated optical element comprises a plate element with an input surface facing the light-outcoupling surface and an output surface facing away from the light-outcoupling surface.

7. The semiconductor laser device according to claim 6, wherein the input surface is directly mounted onto the light-outcoupling surface.

8. The semiconductor laser device according to claim 6, wherein the integrated optical element comprises a spacer element on the input surface of the plate element, the spacer element being directly mounted onto the light-outcoupling surface.

9. The semiconductor laser device according to claim 8, wherein the spacer element has a plate-like form or a frame-like form.

10. The semiconductor laser device according to claim 8, wherein the spacer element comprises glass.

11. The semiconductor laser device according to claim 1, wherein the semiconductor laser device comprises at least one first emission region and at least one second emission region arranged next to each other in a direction parallel to the main extension plane.

12. The semiconductor laser device according to claim 11, wherein the integrated optical element is arranged on both the at least one first emission region and the at least one second emission region.

13. The semiconductor laser device according to claim 11, wherein a first integrated optical element is arranged on the at least one first emission region and a second integrated optical element is arranged on the at least one second emission region.

14. The semiconductor laser device according to claim 13, wherein the first integrated optical element and the second integrated optical element comprise different wavelength filters.

15. The semiconductor laser device according to claim 11, wherein the photonic crystal layer comprises a first photonic crystal structure in the first emission region and a second photonic crystal structure in the second emission region, wherein the first and the second photonic crystal structures are different.

16. A method for manufacturing a semiconductor laser device, wherein a semiconductor layer sequence is provided, the semiconductor layer sequence comprising an active layer having a main extension plane, a first cladding layer and a second cladding layer, the active layer being arranged between the first and second cladding layer in a direction perpendicular to the main extension plane, a light-outcoupling surface parallel to the main extension direction and arranged on a side of the second cladding layer opposite to the active layer, and a photonic crystal layer arranged in the first cladding layer or in the second cladding layer, wherein an integrated optical element is directly fixed to the light-outcoupling surface, and wherein at least a part of the integrated optical element is manufactured on the light-outcoupling surface.

17. A projection device comprising a plurality of semiconductor laser devices according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] FIGS. 1A and 1B show schematic illustrations of a semiconductor laser device and a method for manufacturing a semiconductor laser device according to several embodiments;

[0053] FIGS. 2A to 2C show schematic illustrations of a semiconductor laser device according to further embodiments;

[0054] FIGS. 3A to 3C show schematic illustrations of partial views of a semiconductor laser device according to further embodiments;

[0055] FIGS. 4A and 4B show schematic illustrations of partial views of a semiconductor laser device according to further embodiments;

[0056] FIGS. 5A and 5B show schematic illustrations of partial views of a semiconductor laser device according to further embodiments;

[0057] FIG. 6 shows a schematic illustration of a projection device according to a further embodiment;

[0058] FIGS. 7A to 7C show schematic illustrations of a p semiconductor laser device and a projection device according to further embodiments.

DETAILED DESCRIPTION

[0059] In the embodiments and figures, identical, similar or identically acting elements are provided in each case with the same reference numerals. The elements illustrated and their size ratios to one another should not be regarded as being to scale, but rather individual elements, such as for example layers, components, devices and regions, may have been made exaggeratedly large to illustrate them better and/or to aid comprehension.

[0060] FIGS. 1A and 1B show schematic illustrations of an embodiment of a semiconductor laser device 100 and a method for manufacturing the semiconductor laser device 100.

[0061] As shown in FIG. 1A, the semiconductor laser device 100 comprises an active layer 1 that is intended and embodied to generate light in at least one active region during operation of the semiconductor laser device 100. The emitted light with its main radiation emission direction is indicated by the arrow labelled by the reference numeral 99 in FIG. 1A.

[0062] The active layer 1 is a part of a semiconductor layer sequence 10 comprising a plurality of semiconductor layers and has a main extension plane perpendicular to an arrangement direction of the layers of the semiconductor layer sequence. In particular, the semiconductor laser device 100 is embodied as a semiconductor laser diode that has a light-outcoupling surface 11. The light 99 generated in the active layer 1 of the semiconductor layer sequence 10 during operation of the semiconductor laser device 100 is emitted via the light-outcoupling surface 11.

[0063] Furthermore, the semiconductor laser device 100 comprises an integrated optical element 20 that is directly fixed to the light-outcoupling surface 11. Light 99 emitted by the active layer 1 during operation is emitted from the light-outcoupling surface 11 through the integrated optical element 20.

[0064] As explained above in the general part, the integrated optical element 20 is an integral part of the semiconductor laser device 100 and is fixedly connected to the semiconductor layer sequence 10. The optical element 20 is fixed to light-outcoupling surface 11 in such way that, under normal conditions, the light-outcoupling surface 11 and the optical element 20 are permanently connected with each other and that the integrated optical element is not intended to and, under normal operating conditions, cannot be removed from the light-outcoupling surface 11 without destroying at least a part of the light-outcoupling surface 11 and/or the optical element 20.

[0065] For manufacturing the semiconductor laser device 100 the semiconductor layer sequence 11 is provided in a first method step 101, as indicated in FIG. 1B, wherein the semiconductor layer sequence 11 comprises the active layer 1 and the light-outcoupling surface 11. An optical element is directly fixed to the light-outcoupling surface, so that the optical element forms the integrated optical element 20 in the semiconductor laser device 100, as indicated in method step 102.

[0066] For instance, the integrated optical element 20 can be separately manufactured and can be fixed to the light-outcoupling surface 11, for example by a layer comprising or being made of a glue, a solder or a sinter material. Alternatively, the integrated optical element 20 can be fixed to the light-outcoupling surface 11 by a direct-bonding method, for instance direct wafer bonding, without using an intermediate layer. Furthermore, at least a part of the integrated optical element 20 can be manufactured on the light-outcoupling surface 11. For instance, at least one layer or element of the integrated optical element 20 can be directly applied to the light-outcoupling surface 11, for instance by a depositing process like an evaporation process or spin coating. It can also be possible that the integrated optical element 20 is completely manufactured on the light-outcoupling surface 11 by performing all method steps for manufacturing the optical element on the light-outcoupling surface.

[0067] The semiconductor laser device 100 is preferably manufactured in a wafer-based process, wherein a plurality of laser device units comprising the semiconductor layer sequence are manufactured by a growth process on a common growth substrate, thereby producing a laser device unit compound. Furthermore, an integral optical element 20 can be fixed to the light-outcoupling surface of each of the plurality of laser device units while still being connected to each other in the compound. Afterwards, the compound can be singulated to separate the semiconductor laser devices from each other.

[0068] Further features and embodiments of the semiconductor laser device and the method for manufacturing the semiconductor laser device are described in connection with the following figures.

[0069] FIGS. 2A to 2C show schematic illustrations of the semiconductor layer sequence 10 of the semiconductor laser device 100 shown in FIG. 1A. In particular, the semiconductor laser device comprises a photonic crystal layer with at least one photonic crystal structure, thus the semiconductor laser device can also be referred to as photonic-crystal semiconductor laser device 100 in the following. FIGS. 2A and 2B show sectional views of the photonic crystal semiconductor laser device 100 and FIG. 2C shows a sectional view of the photonic crystal structure 50 of the photonic crystal semiconductor laser device 100, wherein in FIG. 2C a position of an electrical contact layer is also indicated. The following description equally applies to all FIGS. 2A to 2C.

[0070] As already described in connection with FIG. 1A, the semiconductor laser device 100 comprises the active layer 1 for generating light 99 in an active region during operation of the semiconductor laser device 100. The active region determines an emission region 9 of the semiconductor laser device 100, wherein the emission region 9 can be configured to emit a light beam having an aperture with a diameter of more than 100 μm or, preferably, more than 200 μm. Consequently, the radiation characteristics of the emitted light can be substantially diffraction limited, resulting, preferably, in an almost perfectly collimated beam.

[0071] The active layer 1 that is a part of the semiconductor layer sequence 10 can comprise a plurality of semiconductor layers, as indicated in FIGS. 2A and 2B, and has a main extension plane, indicated by the dot-dashed line, perpendicular to an arrangement direction of the layers of the semiconductor layer sequence 10. Directions parallel to the main extension plane of the active layer 1 are denoted as lateral directions, while the arrangement direction of the layers of the semiconductor layer sequence 10 can be denoted as vertical direction. The light generated in the active layer 1 and especially in the active region during operation of the photonic crystal semiconductor laser diode 100 can be emitted via the light-outcoupling surface 11, with a main radiation emission direction along the vertical direction.

[0072] For example, the active layer 1 can have exactly one active region and can comprise, for instance, an MQW structure for generating light. The active region can at least partly be defined by a contact surface of one or more electrical contact layers 2, 2′ with the semiconductor layer sequence 10, i.e., at least partly by a surface through which current is injected into the semiconductor layer sequence 10 and thus into the active layer 1. Although not shown in the figures, the active region can additionally be defined at least partially by structured semiconductor layers like, for instance, current-spreading and/or current-delimiting layers in the semiconductor layer sequence 10. Moreover, the photonic crystal semiconductor laser device 100 can have one or more reflective layers that can contribute to the definition of an active region.

[0073] The semiconductor layer sequence 10 can, in particular, be epitaxially grown. The semiconductor layers of the semiconductor layer sequence 10 can be arranged on a substrate 12 and can comprise a first cladding layer 3 and a second cladding layer 4. The active layer 1 is arranged between the first and the second cladding layer 3, 4 in a direction perpendicular to the main extension plane, i.e., along the vertical direction. The light-outcoupling surface 11 is arranged on a side of the second cladding layer 4 opposite to the active layer 1. The first cladding layer 3 is arranged between a rear surface 13, which can be a mounting surface of the photonic crystal semiconductor laser device 100, and the active layer 1, and the second cladding layer 4 is arranged between the active layer 1 and the light-outcoupling surface 11.

[0074] The semiconductor layer sequence 10 can comprise further semiconductor layers like, for example, a buffer layer 14 and a semiconductor contact layer 15 as well as other semiconductor layers (not shown) like waveguide layers. The layers of the semiconductor layer sequence 10 can be based on a III-V compound semiconductor material system and, furthermore, can comprise further features as described above in the general part.

[0075] The semiconductor layer sequence 10 further comprises a photonic crystal layer 5 with a photonic crystal structure 50. The photonic crystal 5 layer is preferably arranged in one of the cladding layers 3, 4. Accordingly, the photonic crystal layer 5 can be arranged in the first cladding layer 3 as shown in FIG. 2A or in the second cladding layer 4 as shown in FIG. 2B. Although here and in the following the semiconductor laser device 100 is described having exactly one photonic crystal layer 5, the photonic crystal semiconductor laser device 100 can also comprise more than one photonic crystal layer, which can be arranged in the same or in different cladding layers 3, 4 and, thus, on the same side or on different sides as seen from the active layer 1. In case the photonic crystal semiconductor laser device 100 comprises more than one photonic crystal layer, the photonic crystal layers can comprise the same or similar features or different features.

[0076] The photonic crystal structure 50 comprises a two-dimensional lattice-like matrix of discontinuities 51 in the photonic crystal layer 5 as shown in FIG. 2C. The discontinuities 51 are formed by discrete cylindrical structures extending in the vertical direction and are distributed in lateral directions in the photonic crystal layer 5. The discontinuities 51 and, thus, the photonic crystal layer 5 can have a height, measured in the vertical direction, that is equal to or preferably smaller than a thickness, measured in the vertical direction, of the cladding layer 3, 4 in which the photonic crystal layer 5 is arranged.

[0077] The matrix of the discontinuities 51 can be arranged, for example, in a rectangular lattice as shown in FIG. 2C. Alternatively, other lattice structures are possible, for instance a hexagonal lattice, a rotational lattice or an oblique lattice. The size and distance of the discontinuities 51 with respect to their closest neighbors is on the order of the wavelength of the light produced in the active layer 1.

[0078] The discontinuities 51 have a first refractive index, whereas the medium surrounding the discontinuities 51, i.e., the material of the photonic crystal layer 5, has a second refractive index that is different from the first refractive index. Preferably, the second refractive index is greater than the first refractive index. The medium surrounding the discontinuities 51, i.e., the bulk material of the photonic crystal layer 5, can, in particular, be formed of a semiconductor material of the semiconductor layer sequence 10. The discontinuities 51 can comprise or be made of, for instance, SiO.sub.2 or air or another gas. In case of air or another gas, the discontinuities 51 can be formed by holes in the material of the photonic crystal layer 5.

[0079] The photonic crystal layer 5 can be a separate layer, meaning that the cladding layer 3, 4 with the photonic crystal layer 5 comprises the photonic crystal layer 5 as sublayer, as indicated by the dashed lines in FIGS. 2A and 2B, and at least one additional sublayer that is different from the photonic crystal layer, for instance in regard to the material. Alternatively, the photonic crystal layer 5 can be an integral part of a cladding layer 3, 4, meaning that the cladding layer 3, 4 including the photonic crystal layer 5 and the material of the photonic crystal layer 5 surrounding the discontinuities 51 are the same material.

[0080] The distribution, shape and size of the discontinuities 51 can be regular, as shown in FIGS. 2A to 2C, or irregular. A regular size, as shown for example in FIG. 2C, can mean that the discontinuities 51 have a substantially similar size, which can be, in particular, one or more or all chosen from a length, a width, a diameter and an area measured along one or more lateral directions. An irregular size can mean that the discontinuities have different sizes, in particular with respect to their respective closest neighbors. A regular shape, as shown in FIG. 2C, can mean that all discontinuities 51 have a similar shape, for instance a column-like shape with a round or polygonal cross-section in a plane parallel to the main extension plane of the active layer. An irregular shape can mean that the discontinuities have different sizes, in particular with respect to their respective closest neighbors. A regular distribution can for instance mean that the discontinuities are arranged at similar distances with respect to the respective closest neighbors in the lattice-like structure. Here, the discontinuities 51 can be arranged in a lattice-like manner with a lattice constant 59. An irregular distribution can mean that the lattice-like matrix can be characterized by regularly distributed similar unit cells with a lattice constant, each unit cell containing a discontinuity, wherein the positions of the discontinuities in the unit cells vary from unit cell to unit cell.

[0081] The photonic crystal layer 5 provides an optical nanostructure having a periodic or nearly periodic refractive index distribution with dimensions nearly equal to the wavelength of the light produced in the active layer 1. In the semiconductor layer sequence 10 light is amplified and diffracted by the photonic crystal layer 5 arranged in the vicinity of the active layer 1. Particularly preferably, the photonic crystal layer 5 is arranged close to the active layer 1. For example, an additional reflector layer below the active layer 1 can enhance the output power of the light produced in the semiconductor layer sequence 10. However, it can also be possible that no additional resonator or mirror is necessary.

[0082] The photonic crystal layer 5 and, in particular, the photonic crystal structure 50, i.e., the size, shape and distribution of the discontinuities 51, determine the emission characteristic. In other words, the wavelength of the emitted light 99 can be tuned by the properties of the photonic crystal structure 50, for instance by one or more of distribution, size and shape of the discontinuities 51 and lattice constant 59 of the matrix. The amplified light is output via the light-outcoupling surface 11 as a laser beam. Even with a large area of the active region and, thus, the emission region 9, which can be more than 100 μm or more than 200 μm in diameter, the photonic crystal semiconductor laser device 100 can provide a narrow spot beam pattern, having a narrow beam spread angle of less than 1° and with a circular shape, and a narrow spectral linewidth.

[0083] The electrical contact layers 2 on the light-outcoupling surface 11 and on the rear side of the semiconductor layer sequence 11 can be applied continuously or patterned. In the shown embodiment, a first electrical contact layer 2 on the light-outcoupling surface 11 is formed in a disk shape for defining the active region in the active layer 1, while a second electrical contact layer 2′ on the rear side is applied continuously over a large area. However, depending on the electrical contact layer 2 on the light-outcoupling surface 10 the light-outcoupling surface 10 to which the integrated optical element 20 is fixed can vary, as shown in FIGS. 4A to 4C.

[0084] As shown in FIG. 3A, f the light produced in the active layer 1 is emitted through the first electrical contact layer 2, the first electrical contact layer 2 can form the light-outcoupling surface 11 of the semiconductor layer sequence 10 as also indicated in FIGS. 2A and 2B. Preferably, the first electrical contact layer 2 can comprise or be made from a transparent conducting material like a transparent conductive oxide. The integrated optical element 20 is directly fixed to the first electrical contact layer 2. The electrical contact layer 2 can comprise conductor track or similar that leads out from under the integrated optical element and that is not covered by the integrated optical element 20 so that the first electrical contact layer 2 can be connected to an external current source.

[0085] Alternatively, the first electrical contact layer 2 can be patterned as indicated in FIGS. 4B and 4C. For example, the first electrical contact layer 2 can be patterned to at least partly have a ring shape (FIG. 3B) or form a grid (FIG. 3C). The light produced in the active layer during operation can be emitted from one or more regions that are not covered with material of the first electrical contact layer 2, so that the semiconductor layer sequence 10 forms the light-outcoupling surface 11. In this case, the first electrical contact layer 2 can comprise or be made of an oblique material like a metal or a metal layer stack.

[0086] The integrated optical element 20 comprises one or more optical functions like wavelength filtering, polarization filtering, polarization conversion, optical isolation and can comprise one or more chosen from a wavelength filter, a polarization filter, polarization converter, optical isolator.

[0087] As shown in FIG. 4A, the integrated optical element 20 can comprise or be a wavelength filter. The wavelength filter can comprise a grating structure 21 having, along the light emission direction, alternately stacked regions with different refractive indices. Particularly preferably, the integrated optical element comprises a volume Bragg grating (VBG). The volume Bragg grating comprises a photosensitive transparent material 22 having a periodic modulation of the refractive index formed by the grating structure 21 that can be produced, for example, by irradiating the material 22 with ultraviolet light in the spatial shape of a standing wave pattern. The photosensitive material 22 can, for example, comprise or be a photosensitive glass, like silica which can contain one or more dopants, or a photosensitive polymer. The volume Bragg grating can be manufactured separately and fixed to the light-outcoupling surface 11. Preferably, the photosensitive material 22 can be applied as film to the light-outcoupling surface 11, for instance by spin-coating. Afterwards, the grating structure 21 can be written into the applied film formed by the material 22 by holographic writing.

[0088] The combination of a photonic crystal laser structure in the semiconductor layer sequence with its diffraction limited collimated beam with an integrated VBG can lead to an external-cavity-laser-like structure with a stable and narrow optical emission, but without additional optics downstream the laser diode, so that a compact device can be achieved and no active alignment process is necessary.

[0089] Furthermore, the integrated optical element 20 can comprise or be a polarization filter, for example a polarizer comprising or being made from a metal grid. For instance, as shown in FIG. 4B, the integrated optical element 20 can comprise a first polarizer 23, a second polarizer 23′ and a polarization-effecting material 24 between the two polarizers 23, 23′. Preferably, at least the first polarizer 23 is directly manufactured on the light-outcoupling surface 11, for instance by depositing a metal grid on the light-outcoupling surface 11. The material 24 and the second polarizer 23′ can preferably also be manufactured by depositing the respective material.

[0090] For example, the integrated optical element 20 can be an optical isolator, having the first polarizer 23 and the second polarizer 23′ that is rotated by 45° with respect to the first polarizer 23, wherein a polarization rotating material 24 like a Faraday element is arranged between the first and second polarizer 23, 23′. Materials for the Faraday element can be, for example, bismuth-substituted rare-earth iron garnets. For instance, a thickness of about 480 μm can be suitable for a wavelength of 1550 nm. Consequently, the semiconductor laser device 100 can have a built-in optical isolator that can prevent optical feedback and ensure a stable low linewidth without the need for an additional external optical isolator.

[0091] For some application, linear polarized light is difficult to operate with, for instance because it causes speckle in projection or AR/VR applications. Thus, alternatively or additionally, the integrated optical element 20 can comprise as material 24 a polarization converter having a quarter-wave-plate element between the first and second polarizer 23, 23′. This integrated on-chip-setup can transform linear polarized light emitted from the semiconductor layer sequence directly into circularly polarized light and also act simultaneously as an optical isolator. The quarter-wave-plate element can comprise or be a birefringent material comprising or formed by a glass foil or an ultra thin glass, crystal or plastic plate, for instance having a thickness of less than 100 μm, making on-chip integration easy as no magnetic field is needed.

[0092] Thus, the integrated optical element 20 can provide a compact solution of a laser source with the required optical isolation and/or polarization conversion within one small and compact device and without active alignment and additional optics.

[0093] As shown in FIGS. 4A and 4B, the integrated optical element 20 can comprise or be formed as a plate element 29 with an input surface 25 facing the light-outcoupling surface 11 and an output surface 26 facing away from the light-outcoupling surface 11. The plate element 29 can have one or more of the optical functions as described before. As described before, the input surface 25 can be directly mounted onto the light-outcoupling surface 11. Particularly preferably, the input surface 25 can be formed by manufacturing at least a part of the integrated optical element 20 directly on the light-outcoupling surface 11.

[0094] Alternatively, the integrated optical element 20 can comprise a spacer element 27 on the input surface 25 of the plate element 29 as shown in FIGS. 5A and 5B, wherein the spacer element 27 is directly mounted onto the light-outcoupling surface 11. For instance, the spacer element 27 can have a plate-like form (FIG. 5A) or a frame-like form (5B). Preferably, the spacer element 27 comprises glass or is made of glass. Particularly preferably, the spacer element 27 is directly manufactured on the light-outcoupling surface 11, for instance by spin coating and, if applicable, by patterning and curing the applied material. In case the spacer element 27 is formed as frame as shown in FIG. 5B, the emitted light beam of the semiconductor laser device can be laterally surrounded by the frame. Between the plate element 29 and the light-outcoupling surface 11 can be a gap 28 that is surrounded by the frame and that can contain a gas like air or an inert gas or a vacuum.

[0095] In FIG. 6 a projection device 1000 is shown, which comprises at least one photonic crystal semiconductor laser device 100 and, preferably, a plurality of semiconductor laser devices 100 as described in connection with any of the foregoing embodiments. For instance, the projection device 1000 can have three photonic crystal semiconductor laser devices 100, 100′, 100″ as shown in FIG. 6.

[0096] Each of the photonic crystal semiconductor laser devices 100, 100′, 100″ of the projection device 1000 emits light with a certain color that is preferably different from the colors of the other respective photonic crystal semiconductor laser devices 100, 100′, 100″. Accordingly, the projection device 1000 comprises a plurality of photonic crystal semiconductor laser devices 100, 100′, 100″, wherein the plurality of photonic crystal semiconductor laser devices 100, 100′, 100″ comprises at least a first photonic crystal semiconductor laser device 100 emitting, during operation, light with a first color, at least a second photonic crystal semiconductor laser device 100′ emitting, during operation, light with a second color being different form the first color, and at least a third photonic crystal semiconductor laser device 100″ emitting, during operation, light with a third color being different form the first and second color. For example, the first color can be red, the second color can be green and the third color can be blue, so that the projection device 1000 can be an RGB projector. The projection device 1000 can preferably be used in consumer, industry and automotive applications. For instance, the projection device 1000 can be implemented in a virtual reality (VR) or augmented reality (AR) projection system.

[0097] The projection device comprises an optics system arranged directly downstream of the semiconductor laser devices 100, 100′, 100″ for directing the emitted light onto an image plane. As described above, the semiconductor laser devices 100, 100′, 100″ can preferably emit light beams with a very low beam divergence, for example of much less than 1°, with the emission regions having diameters of more than 100 μm and preferably more than 200 μm. Thus, since the semiconductor laser devices 100, 100′, 100″ provide already collimated light and each comprise an integrated optical element 20, which can, for instance, comprise or be an optical isolator and/or a wavelength filter, the optics system can be simplified in comparison to usual projection systems based, for instance, on edge-emitting laser diodes, and can be, in particular, free of any collimating optics and polarization-modifying optics arranged downstream of the semiconductor laser devices. For instance, the optics system can comprise beam combining elements 31 and one or more scanning mirrors 32, i.e., one or more movable mirrors that can be used to scan the light beams of the photonic crystal semiconductor laser devices 100, 100′, 100″ over an image region. Preferably, the one or more scanning mirrors are based on MEMS (microelectromechanical system) technology. Alternatively or additionally, the light of the semiconductor laser devices 100, 100′, 100″ can be coupled into a lightguide or fiber optics, onto an LCoS (liquid crystal on silicon) or onto a DMD (digital micro-mirror device).

[0098] FIGS. 7A, 7B and 7C show semiconductor laser devices 100 and a projection device 1000 with such semiconductor laser devices.

[0099] FIG. 7A shows a schematic illustration of a photonic crystal semiconductor laser device 100 that has two separated electrical contact layers 2, resulting in two emission regions 9, 9′. Thus, the photonic crystal semiconductor laser device can have the first emission region 9 and the second emission region 9′ arranged next to each other in a lateral direction, wherein each of the emission regions 9, 9′ can be operated to emit light via the light-outcoupling surface. For example, the at least two emission regions 9, 9′ can be operated independently from each other. Alternatively, the at least two emission regions 9, 9′ can be operated simultaneously.

[0100] In FIG. 7B, a semiconductor laser device 100 is shown that has a first photonic crystal structure 50 in the first emission region 9 and a second photonic crystal structure 50′ in the second emission region 9′, wherein the first and the second photonic crystal structures 50, 50′ are different. In particular, the first photonic crystal structure 50 can comprise a two-dimensional lattice-like first matrix of discontinuities 51 in the photonic crystal layer 5 and the second photonic crystal structure 50′ can comprise a two-dimensional lattice-like second matrix of discontinuities 51 in the photonic crystal layer 5, wherein the first and the second two-dimensional matrices differ regarding one or more parameters chosen from a lattice constant 59, 59′, a density of discontinuities 51, a mean size of the discontinuities 51, a material of the discontinuities. The mean size of the discontinuities 51 of each of the photonic crystal structures 50, 50′ can be, for instance, an average diameter or an average area, measured in a plane parallel to the main extension plane of the active layer, of the discontinuities 51 of the respective photonic crystal structure 50, 50′. In the embodiment shown in FIG. 7B, the first and second photonic crystal structures 50, 50′ differ, by way of example, with regard to the lattice constants 59, 59′.

[0101] Since the wavelength of the light produced in the active layer and amplified in the semiconductor laser device 100 depends on the properties of the photonic crystal structure in an active region, the photonic crystal semiconductor laser device 100 shown in FIG. 7B can produce and emit light with a first wavelength from the first emission region 9 and light with a second wavelength different from the first wavelength from the second emission region 9′. Due to the more than one photonic crystal structures 50, 50′ in the photonic crystal layer 5, the photonic crystal semiconductor laser device 100 can thus be configured as a multi-wavelength emitter emitting at least two light beams with different wavelengths. In particular, the second wavelength can be slightly detuned with respect to the first wavelength.

[0102] For example, the first emission region can emit light with a central wavelength λ, while the second emission region can emit light with a central wavelength λ+Δλ. Both the light emitted by the first emission region and the light emitted by the second emission region can have a respective spectral width with, for example, an FWHM of several nm, for instance less than 10 nm or less than 5 nm. For example, Δλ can be equal to or greater than the FWHM. This can also mean that Δλ is equal to or greater than 2 nm and less than or equal to 10 nm or less than or equal to 5 nm.

[0103] By overlapping the light beams emitted by the first and second emission region 9, 9′, the wavelength detuning causes a reduction of interference effects like speckle patterns that could be perceived by an observer. To a human observer, the light beams emitted by the different emission regions 9, 9′ can appear to have the same color, so that the photonic crystal semiconductor laser device 100 emits, for a human observer, just several light beams with the same color.

[0104] For instance, for both semiconductor laser devices 100 shown in FIGS. 7A and 7B, respectively, a common integrated optical element can be placed over both emission regions 9, 9′.

[0105] As indicated in the projection device 100 shown in FIG. 7C, however, it can also be possible that a first integrated optical element 20 can be arranged on the first emission region and a second integrated optical element 20′ can be arranged on the second emission region. The first and second integrated optical elements 20, 20′ can be embodied as described before and can be similar or different to each other.

[0106] It can for example be possible that the first and second emission region are embodied similarly as explained in connection with FIG. 7A, while the first and second integrated optical element 20, 20′ are embodied as different wavelength filters. For instance, the first and second integrated optical element 20, 20′ can be embodied as VBGs having different properties so that the first emission region is forced to emit light with a first wavelength and the second emission region is forced to emit light with a second wavelength that is different from the first wavelength.

[0107] For instance, if the wavelength drift over temperature of the semiconductor laser device 100 is too high, one can use, alternatively or in addition to using an active temperature control, a semiconductor laser device 100 with more than one emission region, emitting light with slightly different wavelengths, and can switch, depending on the temperature, between the different emission regions. The emission regions are next to each other, on the same chip, but are slightly detuned in wavelength either by having different integrated optical elements 20, 20′ with different VBG conditions or by having emission regions 9, 9′ with different photonic crystal structures 50, 50′, as explained in connection with FIG. 7B, or both. As there is no additional optics involved, a semiconductor laser device with more than one emission region requires only some more chip space, which is not too expensive in regard to volume and housing.

[0108] Furthermore, when utilizing a semiconductor laser device having more than one emission region in a projection device as a laser beam scanning module, multiple emission regions increase the resolution and help to overcome flicker, particularly for HUD applications which require larger mirrors to accommodate a larger scanning image. Multiple emission regions can also help to overcome problems with a lower than 120 Hz scanning speed.

[0109] Alternatively or additionally to the features described in connection with the figures, the embodiments shown in the figures can comprise further features described in the general part of the description. Moreover, features and embodiments of the figures can be combined with each other, even if such combination is not explicitly described.

[0110] The invention is not restricted by the description on the basis of the exemplary embodiments. Rather, the invention encompasses any new feature and also any combination of features, which in particular comprises any combination of features in the patent claims, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.

REFERENCE NUMERALS

[0111] 1 active layer [0112] 2, 2′ electrical contact layer [0113] 3 first cladding layer [0114] 4 second cladding layer [0115] 5 photonic crystal layer [0116] 9, 9′ emission region [0117] 10 semiconductor layer sequence [0118] 11 light-outcoupling surface [0119] 12 substrate [0120] 13 rear surface [0121] 14 buffer layer [0122] 15 semiconductor contact layer [0123] 20 integrated optical element [0124] 21 grating structure [0125] 22 material [0126] 23, 23′ polarizer [0127] 24 material [0128] 25 input surface [0129] 26 output surface [0130] 27 spacer element [0131] 28 gap [0132] 29 plate element [0133] 31 beam combining element [0134] 32 scanning mirror [0135] 50, 50′ photonic crystal structure [0136] 51 discontinuity [0137] 59, 59′ lattice constant [0138] 99 light [0139] 100, 100′, 100″ semiconductor laser device [0140] 101, 102 method step [0141] 1000 projection device