Semiconductor laser arrangement and projector

Abstract

A semiconductor laser arrangement and a projector are disclosed. In an embodiment the semiconductor laser arrangement includes at least two electrically pumped active zones, each active zone configured to emit laser radiation of a different emission wavelength and a semiconductor-based waveguide structure, wherein the active zones are electrically independently operable of one another, wherein the active zones optically follow directly one another along a beam direction and are arranged in a descending manner with regard to their emission wavelengths, wherein at least in a region of a last active zone along the beam direction, a laser radiation of all active zones jointly runs through the waveguide structure, wherein at least the last active zone comprises a plurality of waveguides which are stacked one above the other and are oriented parallel to one another, wherein one of the waveguides is configured for the radiation emitted by the last active zone.

Claims

1. A semiconductor laser arrangement comprising: at least two electrically pumped active zones, each active zone configured to emit laser radiation of a different emission wavelength during operation by recombination of charge carriers in at least one semiconductor material; and a semiconductor-based waveguide structure, wherein the active zones are electrically independently operable of one another, wherein the active zones follow directly one another optically along a beam direction along a straight line and are arranged in the semiconductor laser arrangement in a descending manner with regard to their emission wavelengths, wherein at least in a region of the last active zone along the beam direction, a laser radiation of all active zones jointly runs through the waveguide structure, wherein at least the last active zone comprises a plurality of waveguides which are stacked one above the other and are oriented parallel to one another, the waveguides being part of the waveguide structure, wherein one of the waveguides is configured for the radiation emitted by the last active zone, the at least one active zone that precedes the last active zone radiates into a different one of the waveguides than the last active zone, wherein the waveguides which are assigned to the last active zone, taken together in the direction perpendicular to the beam direction and viewed in cross-section, have an extent of at most 10 m, and wherein the waveguide structure is configured to guide the laser radiation generated during operation in the active zones by internal total reflection so that the waveguides in each case comprise a core material having a high refractive index for the corresponding laser radiation and the core material is surrounded by at least one layer made of a material having a lower refractive index.

2. The semiconductor laser arrangement according to claim 1, wherein each of the active zones is accommodated in a separate edge-emitting semiconductor laser chip.

3. The semiconductor laser arrangement according to claim 2, wherein precisely one of the semiconductor laser chips has exactly one waveguide.

4. The semiconductor laser arrangement according to claim 2, wherein at least a last semiconductor laser chip comprises a plurality of stacked waveguides which are aligned parallel to one another, wherein the stacked waveguides are part of the waveguide structure, wherein one of the waveguides is provided for the active zone of the last semiconductor laser chip, wherein the at least one semiconductor laser chip preceding the last semiconductor laser chip radiates into a different one of the waveguides than the active zone of the last semiconductor laser chip, and wherein the waveguides of the last semiconductor laser chip, taken together in the direction perpendicular to the beam direction and viewed in cross-section, have an extent of at most 4 m.

5. The semiconductor laser arrangement according to claim 2, wherein a distance between at least one of radiation exit surfaces or facets of adjacent semiconductor laser chips is at most 50 m, and wherein a space between the adjacent semiconductor laser chips is free of a waveguide for the laser radiation.

6. The semiconductor laser arrangement according to claim 1, wherein all active zones are produced on a common growth substrate, and wherein a relative difference between at least two of the emission wavelengths is at least a factor of 1.05.

7. The semiconductor laser arrangement according to claim 6, wherein all active zones, along a growth direction of a semiconductor layer sequence with the active zones, are stacked one above the other so that no two active zones are located at the same height in the direction parallel to the growth direction.

8. The semiconductor laser arrangement according to claim 1, wherein a number of the waveguides, which are assigned to the respective active zone in the direction parallel to a growth direction of a semiconductor layer sequence, increases in a strictly monotonic manner along the beam direction.

9. The semiconductor laser arrangement according to claim 6, wherein precisely one of the waveguides extends over all active zones with a constant extent and along a straight line.

10. The semiconductor laser arrangement according to claim 1, wherein, between adjacent active zones and along the beam direction, at least one of a wavelength-selective mirror or a wavelength-selective optical grating are located.

11. The semiconductor laser arrangement according to claim 1, wherein the waveguide structure essentially consists of one or more semiconductor materials.

12. The semiconductor laser arrangement according to claim 1, wherein the semiconductor laser arrangement is free of phosphors and free of optically pumped laser structures.

13. The semiconductor laser arrangement according to claim 1, wherein the semiconductor laser arrangement comprises one active zone for generating blue light, one active zone for generating green light and one active zone for generating red light.

14. The semiconductor laser arrangement according to claim 1, wherein the semiconductor laser arrangement comprises one active zone for generating blue light or ultraviolet radiation and one active zone for generating near-infrared radiation.

15. The semiconductor laser arrangement according to claim 1, wherein for each one of the different emission wavelengths an own plane parallel to a support is present, in which planes the respective radiation is guided, the planes have mutually different distances to the support.

16. A projector for projecting variable color images comprising: a semiconductor laser arrangement according to claim 1; and an imaging optical system, wherein the projector is designed to emit laser radiation having an average luminous flux of at least 10 lm, and wherein the semiconductor laser arrangement takes a volume of at most 10 mm3 mm3 mm in the projector.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, laser arrangements described here and projectors described here are explained in more detail with reference to the drawing on the basis of exemplary embodiments. Identical reference signs indicate the same elements in the individual figures. In this case, however, no relationships to scale are illustrated; rather, individual elements can be represented with an exaggerated size in order to afford a better understanding.

(2) In the figures:

(3) FIGS. 1 to 8 show schematic sectional representations of exemplary embodiments of projectors described here with semiconductor laser arrangements described here;

(4) FIGS. 9 and 10 show schematic plan views of exemplary embodiments of projectors described here with semiconductor laser arrangements described here; and

(5) FIG. 11 shows a schematic representation of spectral properties of mirrors for semiconductor laser arrangements described here.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(6) FIG. 1 shows an exemplary embodiment of a projector 10. The projector 10 comprises a semiconductor laser arrangement 1 and an imaging optical system 6. The imaging optical system 6 comprises collimating optics in the form of a converging lens.

(7) The semiconductor laser arrangement 1 has a support 7. Three semiconductor laser chips 2 are mounted on the support 7. The semiconductor laser chips 2 each comprise an active zone 31, 32, 33 and a waveguide 41, 42, 43. In total, a laser radiation R is emitted by the semiconductor laser arrangement 1.

(8) A radiation having an emission wavelength L1 is generated in the active zone 31. The radiation having the emission wavelength L1 is, for example, red light. Said radiation having the wavelength L1 is guided within the semiconductor laser chip 2 that comprises the active zone 31 in the waveguide 41. The active zone 31, as well as the other active zones 32, 33, is located in a not separately drawn resonator. Correspondingly, radiation having the emission wavelength L2, for example, green light, is emitted in the active zone 32, and in the active zone 33 a radiation having the emission wavelength L3, for example, blue light, is generated.

(9) The radiation emitted in the active zone 31 leaves the associated semiconductor laser chip 2 in the direction towards the adjacent semiconductor laser chip 2 and enters the waveguide 42 of the semiconductor chip 2 with the active zone 32. The radiations having the emission wavelengths L1 and L2 are thus guided in the waveguide 32. These radiations L1, L2 subsequently enter the semiconductor laser chip 2 with the active zone 33. Thus, the radiations having the emission wavelengths L1, L2, L3 are jointly guided in the waveguide 43 and are jointly coupled out of the semiconductor laser arrangement 1.

(10) Consequently, in the intended use the radiation R exits from the semiconductor laser arrangement 1 only at a single region. A collimation and beam shaping is thereby possible by means of a comparatively simple imaging optical system 6, for example, by means of a single converging lens. Optionally, as well as in all other exemplary embodiments, the imaging optical system 6 can include an aperture for preventing scattered light from leaving the projector 10.

(11) In other words, the semiconductor laser chips 2 are arranged optically directly one behind the other along a beam direction x within the semiconductor laser arrangement 1 and couple the generated radiation directly into the subsequent semiconductor laser chip 2. All generated radiation components are thus emitted at the same time from the same waveguide 43 towards an outside area.

(12) A distance between the adjacent semiconductor laser chips 2 is preferably very small, for example, smaller than 10 m. In contrast to the illustration, the semiconductor laser chips 2 preferably abut one another, so that there is no or no significant distance between the adjacent semiconductor laser chips 2. Furthermore, the individual semiconductor laser chips 2 and thus the active zones 31, 32, 33 can be controlled electrically independently of one another.

(13) Further components of the projector 10, such as power supply lines, control electronics or a housing, are not drawn in each case in order to simplify the illustration.

(14) In the exemplary embodiment of FIG. 2, the semiconductor laser arrangement 1 of the projector 10 is formed only from a single semiconductor laser chip 2. The semiconductor laser chip 2 comprises a growth substrate 30, which also functions as the support 7. Proceeding from the growth substrate 30, semiconductor layer sequences are provided for the active zones 31, 32, 33 along a growth direction G, in particular epitaxially. As in FIG. 1, according to FIG. 2 the waveguides 41, 42, 43, which together form the waveguide structure 4, run in a straight line and at a constant distance from the growth substrate 30.

(15) A wavelength-selective mirror 51 is located between adjacent active zones 31, 32, 33. The radiation having the wavelength L1 passes through the mirror 51, the radiations having the wavelengths L1, L2 pass through the mirror 52. The mirrors 51, 52 are formed, for example, as dielectric mirrors having a layer sequence having layers of alternately high and low refractive indices. It is likewise possible for the mirrors 51, 52 to be designed as Bragg gratings.

(16) According to FIG. 2, as is also possible in all other exemplary embodiments, the imaging optical system 6 comprises a directional component 6b, in addition to the collimating optical system 6a. The component 6b is, for example, a movable micromirror by means of which individual pixels of an image to be generated can be projected.

(17) FIG. 3 shows a detail from a semiconductor laser chip 2 in which the active zones 31, 32 are grown in a continuous manner. The associated semiconductor layer sequence comprises a mask layer 39, for instance made of silicon dioxide. The mask layer 39 has openings of different sizes, from which pyramid-shaped structures with accordingly different sizes grow.

(18) The semiconductor layer sequence is preferably based on the material system AlInGaN. The different sizes of the pyramids also result in different growth conditions on the pyramids. As a result, quantum well structures 38 with different thicknesses are formed on the pyramids. Different emission wavelengths can thus be obtained in the active zones 31, 32. Such a semiconductor laser chip 2 can be used, for example, in the exemplary embodiment according to FIG. 2, wherein the mirrors 51, 52 are preferably introduced subsequently.

(19) A further exemplary embodiment is shown in FIG. 4. The semiconductor laser arrangement 1 is formed from a single semiconductor laser chip 2. The active zones 31, 32, 33 are monolithically integrated in a semiconductor layer sequence and follow one another along the growth direction G. The growth direction G is at the same time the beam direction x. Adjacent active zones 31, 32, 33 are connected to one another, for example, by tunnel diodes. The mirrors 51, 52 are located between adjacent active zones 31, 32, 33. The waveguide structure 4 extends continuously over all active zones 31, 32, 33 and runs parallel to the growth direction G.

(20) Particularly preferably, the active zones 31, 32, 33 can be electrically controlled individually. This can be achieved, for example, in that the associated semiconductor layer sequence is partially removed, for example, by etching, not shown, so that separate electrical contacts can be attached to the associated active zones 31, 32, 33.

(21) In the exemplary embodiment of FIG. 5, a plurality of semiconductor laser chips 2 are present which abut directly against each other and which are mounted on the support 7 without gaps. At least the semiconductor laser chips 2 with the active zones 32, 33 have a plurality of waveguides 41, 42, 43 which are arranged stacked one on top of the other along the growth direction G. As in all other exemplary embodiments, along the growth direction G a thickness of the individual waveguides 41, 42, 43 is preferably at most twice the respective vacuum emission wavelength L1, L2, L3. In this way, an extent of the waveguide structure 4 along the growth direction G is, for example, at most 20 m.

(22) For each radiation having the emission wavelengths L1, L2, L3 thus its own plane is provided parallel to the carrier 7, in which the respective radiation is guided. The individual waveguides 41, 42, 43 can thus be optimized for the respective emission wavelengths L1, L2, L3. Due to the very small extension of the waveguide structure 4 along the growth direction G, the total emitted laser radiation R can thus appear as homogeneously mixed light in a projected image point.

(23) Deviating from the illustration in FIG. 5, it is also possible for the laser chips 2 with the active zones 31, 32 to each have all waveguides 41, 42, 43. However, only the waveguides 41, 42, 43 shown in FIG. 5 are preferably used functionally as waveguides.

(24) If the emission wavelengths L1, L2, L3 are only slightly different, it is possible for a plurality of active zones to be grown on top of one another in the waveguide structure 4. Laterally, individual active zones can then be deactivated or turned off, for example, by means of ion implantation or by targeted material damage with laser irradiation in accordance with stealth dicing. Alternatively, the individual waveguides, in which no radiation is generated, can also be grown without an active zone, as is also shown in FIG. 5.

(25) In FIG. 5, the waveguides 41, 42, 43 stacked one above the other are realized in three different semiconductor laser chips 2. Such a stacking of the waveguides 41, 42, 43 is equally possible in only one single semiconductor laser chip 2, analogously to the exemplary embodiment of FIG. 2.

(26) In the exemplary embodiment of FIG. 6, between the individual active zones 31, 32, 33 the mirrors 51, 52 are located. The mirrors 51, 52 are, for example, only in contact with one of the active zones 32, 33 and/or with one of the waveguides 42, 43.

(27) A reflectivity r in percent of the mirrors 51, 52 is preferably designed with regard to a wavelength in nm, as illustrated in FIG. 1i. The two mirrors 51, 52 are thus transmissive to the emission wavelength L1, which lies in the red spectral range. The mirror 52 is additionally transmissive to the emission wavelength L2 lying in the green spectral range. The mirror 52 thus only reflects the emission wavelength L3 lying in the blue spectral range.

(28) In the exemplary embodiment of FIG. 7, the waveguides 41, 42 are present in both semiconductor laser chips 2. However, only the waveguide 42 located closer to the support 7 is functionally used in the semiconductor laser chip 2 with the active zone 32. A control photodiode is provided on a side of the semiconductor laser chips 2 facing away from the imaging optical system 6; thus, the waveguide 42 which is not provided with an active zone can also serve to direct radiation with the wavelength L2 to said control photodiode. The same can apply in the exemplary embodiment of FIG. 5.

(29) The emission wavelength L1 is, for example, in the infrared or near-infrared spectral range. The semiconductor laser chip 2 with the active zone 31 can be a high-power laser diode which is used for material processing, for example, for melting or welding. The semiconductor laser chip 2 having the active zone 32 is designed, for example, to generate ultraviolet or blue radiation having the emission wavelength L2, in order to ensure efficient material processing for instance of gold or copper. The processing of aluminum is also possible with such semiconductor laser arrangements 1. Alternatively, a combination of green laser light with blue and/or ultraviolet laser light can also be used, in particular for material processing.

(30) As in all other exemplary embodiments, for an adaptation of a distance of the waveguides 41, 42 to the support 7 it is possible for an intermediate carrier 8 to be present. Such an intermediate carrier 8 can also function as an additional cooling component.

(31) In the exemplary embodiment of FIG. 8, between adjacent active zones 31, 32, 33 there is in each case an intermediate optical system 91, 92. Via the intermediate optical systems 91, 92, the laser radiation of an active zone 31 preceding in the beam direction x, 32 is coupled or imaged into the following waveguide 42, 43. The optical systems 6, 91, 92 are preferably fixedly connected to the support 7, as can also be the case in all other exemplary embodiments.

(32) According to the plan view of FIG. 9, the semiconductor laser arrangement 1 has a narrow waveguide 41, for example, for monomode operation. The radiation from this narrow waveguide 41 is coupled into a broad stripe laser with the relatively wide waveguide 42. The broad waveguide 42 is preferably designed for multimode operation. In this case, the narrow waveguide 41 can be arranged eccentric to the wide waveguide 42, that is to say can be arranged displaced in the direction perpendicular to the beam direction x relative to a central axis of the wide waveguide 42.

(33) FIG. 10 shows that the waveguides 41, 42 are not arranged parallel to one another, but at an angle. Thus, the laser radiation from the active zone 31 can be efficiently coupled into the waveguide 42 at a Brewster angle.

(34) The invention described here 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 includes in particular 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.