RELIABLE LIGHT CONVERSION DEVICE FOR LASER-BASED LIGHT SOURCES

Abstract

The invention describes a light conversion device comprising: a light converter, wherein the light converter is adapted to convert primary light to converted light, wherein a peak emission wavelength of the converted light is in a longer wavelength range than a peak emission wavelength of the primary light, a reflective structure coupled to at least a part of a coupling surface of the light converter, wherein the reflective structure is a narrowband reflector in the sense that is arranged to reflect at least 55% of the primary light impinging on the reflective structure and to transmit at least 50% of the converted light impinging on the reflective structure.

The invention further describes a laser-based light source comprising such a light conversion device. The invention further relates to a vehicle headlight comprising the laser-based light source.

Claims

1. A light conversion device comprising: a light converter, wherein the light converter is adapted to convert primary light to converted light, wherein a peak emission wavelength of the converted light is in a longer wavelength range than a peak emission wavelength of the primary light, a reflective structure coupled to at least a part of a coupling surface of the light converter, wherein the reflective structure is a narrowband reflector in the sense that it is arranged to reflect at least 55% of the primary light impinging on the reflective structure and to transmit at least 50% of the converted light impinging on the reflective structure.

2. The light conversion device according to claim 1, wherein the light converter is mechanically coupled by means of a coupling layer to a heatsink, wherein the heatsink comprises a mirror structure, wherein the mirror structure is arranged to reflect at least 90% of the converted light impinging on the mirror structure back to the light converter, and wherein the reflective structure is arranged between the coupling surface of the light converter and the mirror structure.

3. The light conversion device according to claim 2, wherein the reflective structure comprises at least one layer deposited on the coupling surface such that the coupling layer is arranged between the reflective structure and the mirror structure.

4. The light conversion device according to claim 2, wherein the reflective structure comprises at least one layer deposited on top of the mirror structure such that the coupling layer is arranged between the reflective structure and the light converter.

5. The light conversion device according to claim 1, wherein the coupling surface is arranged opposite to a light emission surface of the light converter.

6. The light conversion device according to claim 1, wherein the reflective structure comprises a dielectric mirror.

7. The light conversion device according to claim 2, wherein the mirror structure comprises a silver layer deposited on a side of the heatsink next to the light converter.

8. A laser-based light source comprising: at least one laser, wherein the at least one laser is adapted to emit the primary light, and a light conversion device according to claim 1.

9. A vehicle headlight comprising a laser-based light source according to claim 8.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0029] The invention will now be described, by way of example, based on embodiments with reference to the accompanying drawings.

[0030] In the drawings:

[0031] FIG. 1 shows a principal sketch of a first embodiment of a laser-based light source comprising a first light conversion device.

[0032] FIG. 2 shows a principal sketch of a second embodiment of a laser-based light source comprising a second light conversion device.

[0033] In the Figures, like numbers refer to like objects throughout. Objects in the Figures are not necessarily drawn to scale.

DETAILED DESCRIPTION OF EMBODIMENTS

[0034] Various embodiments of the invention will now be described by means of the Figures.

[0035] FIG. 1 shows a principal sketch of a first embodiment of a laser-based light source 100 which comprises a laser 110 and a first light conversion device 130. The first light conversion device 130 comprises a light converter 132 with a light emission surface 131 and a narrowband reflective structure 134 attached to a coupling surface of the light converter 132 (back surface of the light converter 132 opposite to the light emission surface 131 in this case). The light converter 132 is mechanically coupled (glued) by means of a coupling layer 136 to a heatsink 140 such that the coupling layer 136 is arranged between the narrowband reflective structure 134 and the heatsink 140. At least part of the surface of the heatsink 140 is reflective, preferably highly reflective at least in the wavelength range of the converted light 20. The laser 110 emits primary light 10 (e.g. blue laser light) to the light conversion device 130. The blue laser light enters the light converter 132 via the light emission surface 131. A part of the blue laser light is converted to yellow converted light 20 by means of the light converting material of the light converter 132. A part of the converted light 20 impinges on the mirror structure 138 comprised by the heatsink 140 after traversing the narrowband reflective structure 134 and the coupling layer 136. Essentially all of the converted light 20 impinging on the mirror structure 138 is reflected back to the light converter 132. The coupling layer 136 should therefore be transparent at least in the wavelength range of the converted light 20. Primary light 10 that is not converted within the light converter 132 may impinge on the narrowband reflective structure 134. The narrowband reflective structure 134 comprises in this case a layer which reflects 98-99% of the primary light 10 impinging on the narrowband reflective structure 134 such that reflected primary light 12 is emitted via the light emission surface 131 together with converted light 20.

[0036] The narrowband reflective structure 134 is essentially transparent within the wavelength range of the converted light 20. The narrowband reflective structure 134 reduces the intensity of the blue primary light 10 behind the narrowband reflective structure 134 such that degradation of the coupling layer 136 is inhibited or at least delayed. The light converting device 130 is arranged to emit 26% blue laser light and 74% yellow converted light via the light emission surface 131 such that essentially white light is emitted by the light emission surface 131.

[0037] FIG. 2 shows a principal sketch of a second embodiment of the laser-based light source 100 comprising a laser 110 and a second light conversion device 130. The general configuration is very similar to the embodiment discussed with respect to FIG. 1. The light conversion device 130 also comprises a heatsink 140 coupled to a coupling surface of the light converter 132. The heatsink 140 comprises a mirror structure 138 which is a silver layer deposited on the heatsink. But, in difference to FIG. 1, here the heatsink 140 comprises the narrowband reflective structure 134.

[0038] The narrowband reflective structure 134 comprises a stack of thin layers with high and low refractive index in an alternating order being deposited on top of the silver layer, yielding a dielectric mirror with a reflectivity of 97% in the wavelength range of the primary light within a range of angles of incidence of +/−60° with respect to a normal to the surface of the narrowband reflective structure. The narrowband reflective structure 134 may be essentially transparent in the wavelength range of the converted light 20.

[0039] The light converter 132 is a yellow phosphor garnet (YAG:Ce) which is bonded by means of a coupling layer 136 on top of the narrowband reflective structure 134 such that the coupling layer 136 is arranged between the light converter 132 and the narrowband reflective structure 134. The coupling layer 136 is in this case transparent in the wavelength range of the primary light 10 and in the wavelength range of the converted light 20. The dielectric mirror 134 deposited on top of the silver layer 138 most likely also inhibits diffusion of silver atoms or ions to the coupling layer 136, the silver atoms may be having been ionized by means of the primary light. The converted light 20 is nearly to 100% reflected by the silver layer 138 but is nearly completely transmitted by the narrowband reflective structure 134.

[0040] While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive.

[0041] From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the art and which may be used instead of or in addition to features already described herein.

[0042] Variations to the disclosed embodiments can be understood and effected by those skilled in the art, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality of elements or steps. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0043] Any reference signs in the claims should not be construed as limiting the scope thereof.

LIST OF REFERENCE NUMERALS

[0044] 10 primary light [0045] 12 reflected primary light [0046] 20 converted light [0047] 100 laser-based light source [0048] 110 laser [0049] 130 light conversion device [0050] 131 light emission surface [0051] 132 light converter [0052] 134 narrowband reflective structure [0053] 136 coupling layer [0054] 138 mirror structure [0055] 140 heatsink