Laser based illumination device, and vehicle headlamp with such laser based illumination device

Abstract

An illumination device comprises at least a laser (1) emitting a laser beam (6) of light of a first wavelength, a wavelength converting member (5) converting at least part of the light of the first wavelength into light of a second wavelength, a scanning unit (4) adapted to scan the laser beam (6) across the wavelength converting member (5) and an imaging optics (2) imaging a light emitting face of the laser (1) via the scanning unit (4) onto the wavelength converting member (5). In the proposed device, the laser beam (6) is guided via reflection at a reflective member (3) to the wavelength converting member (5). The reflective member (3) comprises a combination of at least a first and a second reflective element (8, 9), wherein the first and second reflective elements (8, 9) are formed and arranged such that the light emitting face of the laser (1) is imaged as a mirror-inverted image on the wavelength converting member (5) via the first reflective element (8) and as a non-mirror-inverted image via the second reflective element (9), both images being superimposed on the wavelength converting member (5). Due to this reflective member, intensity fluctuations in the image of the light emitting face on the wavelength converting member are reduced without enlarging the image.

Claims

1. An illumination device, comprising: at least one laser emitting a first laser beam light of a first wavelength or wavelength range, a wavelength converting member converting at least part of the first laser beam light into a second light of a second wavelength or wavelength range, a scanning unit adapted to scan the first laser beam across the wavelength converting member in order to generate an illumination pattern formed at least of the second light, an imaging optics adapted to form a laser spot to be scanned by the scanning unit onto the wavelength converting member by imaging a light emitting face of the at least one laser, and a reflective member adapted to guide via reflection the first laser beam to the wavelength converting member, said reflective member comprising a combination of at least a first and a second reflective element, said first and second reflective elements formed and arranged such that the light emitting face of said at least one laser is imaged as a mirror-inverted image on the wavelength converting member via the first reflective element and as a non-mirror-inverted image via the second reflective element, both images being superimposed on the wavelength converting member.

2. The illumination device according to claim 1, wherein said reflective member comprises a combination of at least one flat mirror face as said first reflective element and at least one prismatic structure using two reflective faces for reflection as the second reflective element, said first and second reflective elements being arranged side by side.

3. The illumination device according to claim 2, wherein said reflective member is formed of a triangular 90° prism, said at least one flat mirror face being formed by an inner surface of a hypotenuse of the prism and said at least one prismatic structure being attached to or formed out of an outer surface of the hypotenuse of the prism.

4. The illumination device according to claim 2, wherein said two reflective faces of said prismatic structure are oriented at an angle of 90° to one another.

5. The illumination device according to claim 1, wherein said reflective member is formed of a plurality of said first and second reflecting elements, such that several of said first and second reflecting elements contribute to the reflection of the first laser beam.

6. The illumination device according to claim 1, wherein said device comprises a second imaging optics imaging said illumination pattern to the far field.

7. The illumination device according to claim 1, wherein said reflective member is arranged between the laser and the scanning unit.

8. The illumination device according to claim 1, wherein said reflective member is part of the scanning unit.

9. The illumination device according to claim 1, wherein said laser is formed of a laser diode or of a stack or bar of laser diodes.

10. The illumination device according to claim 1, wherein said reflective member comprises a combination of at least one flat mirror face as a first reflective element and at least one prismatic structure using two reflective faces for reflection as a second reflective element, said first and second reflective elements being arranged side by side.

11. The illumination device according to claim 10, wherein said reflective member is formed of a triangular 90° prism, said at least one flat mirror face being formed by an inner surface of a hypotenuse of the prism and said at least one prismatic structure being attached to or formed out of an outer surface of the hypotenuse of the prism.

12. The illumination device according to claim 10, wherein said two reflective faces of said prismatic structure are oriented at an angle of 90° to one another.

13. The illumination device according to claim 10, wherein said reflective member comprises a plurality of said first and second reflecting elements side by side.

14. A headlamp for a vehicle, comprising an illumination device according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is described in the following by way of examples in connection with the accompanying figures. The figures show:

(2) FIG. 1 a schematic sketch of an example of the proposed illumination device;

(3) FIG. 2 a cross-sectional view of an exemplary design of the reflective member according to the invention;

(4) FIG. 3 a cross-sectional view of the reflective member of FIG. 2 in a plane perpendicular to the cross-sectional plane of FIG. 2;

(5) FIG. 4 a plan view on the reflective member of FIGS. 2 and 3; and

(6) FIG. 5 a further exemplary design of the reflective member according to the invention in three different views

DESCRIPTION OF EMBODIMENTS

(7) The proposed illumination device comprises at least one laser, a laser scanning unit, a wavelength converting member, imaging optics and a reflecting member. FIG. 1 shows an exemplary example of such an illumination device which can be used within an adaptive headlamp of a vehicle. The figure shows the laser 1 emitting a laser beam 6 in the blue wavelength range. The laser beam 6 is directed to a scanner 4, which scans the laser beam 6 across a wavelength converting member 5 to generate an illumination pattern of converted light in the yellow wavelength range. The scanning unit 4 is controlled by a control unit to scan the converting layer of the wavelength converting member 5 with a laser spot to generate the desired pattern. The illumination pattern is then projected with a second imaging optics 7 to the far field. The wavelength converting member 5 in this example is formed of an optically transparent ceramic plate containing a wavelength converting material like phosphor. The laser spot scanned over the wavelength converting member 5 is formed by an imaging optics 2 which images the emitting face of the laser 1 via the scanning unit 4 to the wavelength converting member 5. In the present invention the laser beam 6 emitted by the laser 1 is guided by reflection at a reflecting member 3 via the scanning unit 4 to the wavelength converting member 5. This reflective member 3 can be identified in FIG. 1. According to the present invention, this reflective member 3 has a special design of its reflective area such that the reflective area generates a mirror-inverted image and a non-mirror-inverted image exactly superimposed on the wavelength converting member 5.

(8) FIG. 2 shows an exemplary design of such a reflecting member 3. The figure shows a cross-sectional view through a portion of the reflective area of the reflective member 3. As can be seen from FIG. 2, in this cross-sectional view, flat mirror areas 8 alternate with prismatic structures 9 in the reflective area. The prismatic structures 9 comprise two reflecting faces oriented perpendicular to one another similar to the situation in a rectangular prism. Therefore, two different imaging paths are combined with such a reflecting member. Using the imaging path through the 90° prism structure instead of that of the flat mirror the image is mirrored along the axis of the top edge of the prism. This results in a non-mirror-inverted image. The reflection on the flat mirror, on the other hand, results in a mirror-inverted image. With such a reflective member 3, thus, two images are created—one is mirrored, one is not—and superimposed on the same spot on the wavelength converting member 5. If the intensity fluctuation is not strictly symmetric it will be reduced with this effect. The remaining fluctuation then will be strictly symmetric after reflection at the reflecting element 3. Preferably, instead of one prism an array of small prisms or prismatic structures 9 with flat mirror areas 8 in-between are used to achieve the same effect. The figure also shows three exemplary reflecting paths of the laser beam 6, one reflecting at the flat mirror area 8 and the other two reflecting at the prismatic structure 9. From this perspective, the reflective member 3, due to the prismatic structures 9, has a retroreflective behavior such that the member 3, with respect to the dimension visible in this perspective, should be oriented perpendicular or nearly perpendicular to the impinging laser beam 6.

(9) FIG. 3 shows a cross-sectional view of this reflecting member 3 in a cross-sectional plane perpendicular to the plane of FIG. 2. As can be seen from this figure, the reflection in the dimension visible in such perpendicular perspective is not retroreflective so that the reflecting member 3 may be arranged within the laser beam as indicated for example in FIG. 1.

(10) FIG. 4 shows a plan view of the reflective member 3 of FIGS. 2 and 3 in which the alternating prismatic structures 9 and flat mirror areas 8 can be clearly recognized.

(11) FIG. 5 shows, in three different views, a further exemplary design of a reflecting member according to the invention. In this example, the reflecting member is formed of a triangular 90° prism 10. The inner surface of the hypotenuse 11 of this prism 10 serves as a reflecting face. The incoming laser beam 6 is reflected at this surface by internal total reflection as schematically shown in FIG. 3B). By forming out or applying prismatic structures—as already described with FIGS. 2 to 4—of or to the hypotenuse 11, a structure of alternating prismatic structures 9 and flat mirror areas 8 (areas of internal reflection) is achieved. FIG. 3C) is a plan view on the hypotenuse 11 of the prism 10 from which this structure can be recognized. FIG. 3A) shows a side view in which only the prismatic structures 9 are visible at the hypotenuse 11.

(12) For the application of the illumination device within an adaptive headlamp in the automotive sector, laser diodes having emitter faces with typical dimensions in the range of 30 to 40 micrometers can be used. The image of these emitter faces on the converter element is typically approximately ten times enlarged, i.e., has dimensions of several 100 micrometers. The imaging optics has a diameter of typically 3 to 4 mm, the reflective area of the reflecting member then comprises several mm.sup.2. On this reflective area, preferably, between 10 and 100 first and second reflective elements are arranged side by side. This is only an example of dimensioning such an illumination device. Depending on the application and desired reduction of intensity fluctuations, also completely other dimensions and numbers of first and second reflecting elements may be used.

(13) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, 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. 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. Any reference signs in the claims should not be construed as limiting the scope of the invention.

LIST OF REFERENCE SIGNS

(14) 1 Laser 2 Imaging optics 3 Reflective member 4 Scanning unit 5 Wavelength converting member 6 Laser beam 7 Second imaging optics 8 Flat mirror area 9 Prismatic structure 10 Triangular 90° prism 11 Hypotenuse