Illumination module

Abstract

An illumination module comprises a semiconductor light source and a light guide, which comprises a solid body with essentially parallel entry and exit faces and side faces extending between the entry and exit faces; and wherein the entry face receives light emitted by the semiconductor light source; the exit face is offset from the entry face and the area of the exit face exceeds the area of the entry face; a first side face comprises a uniform plane subtending an angle of inclination to the entry face; a second side face, opposite to the first side face, comprises a plurality of offset sub-faces, each sub-face subtends an angle of inclination relative to the entry face; and the inclined faces are formed so that the direction of light leaving the exit face is essentially the same as the direction of light entering the entry face.

Claims

1. A light guide comprising: a solid body comprising: an entry face, an exit face parallel to the entry face, the exit face having an area that exceeds an area of the entry face, a first inclined side face extending from the entry face to the exit face and comprising a uniform plane subtending a first angle of inclination to the entry face, and a second inclined side face extending from the entry face to the exit face and comprising a plurality of offset sub-faces, each of the plurality of offset sub-faces subtending a second angle of inclination relative to the entry face.

2. The light guide of claim 1, wherein the solid body is shaped such that a perpendicular extending from the entry face does not pass through the exit face, and a direction of light leaving the exit face is essentially the same as the direction of light entering the entry face.

3. The light guide according to claim 1, wherein the area of the exit face exceeds the area of the entry face by at least 500%.

4. The light guide according to claim 1, wherein the area of the exit face exceeds the area of the entry face by at least 1000%.

5. The light guide according to claim 1, wherein the first angle of inclination is chosen to redirect a light ray toward the second inclined side face.

6. The light guide according to claim 1, wherein the plurality of offset sub-faces comprises at least 5 sub-faces.

7. The light guide according to claim 1, wherein the plurality of offset sub-faces comprises at least 10 sub-faces.

8. The light guide according to claim 1, wherein the second angle of inclination is arranged to redirect a light ray out through the exit face.

9. The light guide according to claim 1, wherein the second angle of inclination is the same for each of the plurality of offset sub-faces.

10. The light guide according to claim 1, wherein the first angle of inclination is the same as the second angle of inclination.

11. The light guide according to claim 1, wherein the first angle of inclination and the second angle of inclination are each between 45° and 60°.

12. The light guide according to claim 1, wherein the entry face and the exit face are rectangular in shape.

13. An illumination system comprising: a semiconductor light source; and a light guide comprising a solid body that comprises: an entry face adjacent the semiconductor light source, an exit face parallel to the entry face, the exit face having an area that exceeds an area of the entry face, a first inclined side face extending from the entry face to the exit face and comprising a uniform plane subtending a first angle of inclination to the entry face, and a second inclined side face extending from the entry face to the exit face and comprising a plurality of offset sub-faces, each of the plurality of offset sub-faces subtending a second angle of inclination relative to the entry face.

14. The illumination system according to claim 13, wherein the light guide is arranged such that the entry face receives essentially all light originating from the semiconductor light source.

15. The illumination system according to claim 13, wherein the area of the exit face exceeds the area of the entry face by at least 500%.

16. The illumination system according to claim 13, wherein the first angle of inclination and the second angle of inclination are each between 45° and 60°.

17. The illumination system according to claim 13, wherein the semiconductor light source comprises at least one vertical-cavity surface-emitting laser (VCSEL).

18. An imaging system comprising: a camera; and an illumination module, the illumination module comprising: a semiconductor light source, and a light guide comprising a solid body that comprises: an entry face adjacent the semiconductor light source, an exit face parallel to the entry face, the exit face having an area that exceeds an area of the entry face, a first inclined side face extending from the entry face to the exit face and comprising a uniform plane subtending a first angle of inclination to the entry face, and a second inclined side face extending from the entry face to the exit face and comprising a plurality of offset sub-faces, each of the plurality of offset sub-faces subtending a second angle of inclination relative to the entry face.

19. The imaging system according to claim 18, wherein the first angle of inclination and the second angle of inclination are each between 45° and 60°.

20. The imaging system according to claim 18, wherein the semiconductor light source comprises at least one vertical-cavity surface-emitting laser (VCSEL).

Description

BRIEF DESCRIPTION OF THE DRAWING(S)

(1) FIG. 1 shows a side view of an embodiment of the inventive light guide;

(2) FIG. 2 shows a plan view of the light guide of FIG. 1 when viewed from above;

(3) FIG. 3 shows a plan view of the light guide of FIG. 1 when viewed from below;

(4) FIG. 4 shows a perspective view of an embodiment of the inventive illumination module;

(5) FIG. 5 shows a handheld device incorporating an embodiment of the inventive illumination module;

(6) FIG. 6 shows an alternative embodiment of the inventive light guide;

(7) FIG. 7 shows an alternative embodiment of the inventive light guide.

(8) In the drawings, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

(9) FIG. 1 shows a side view of an embodiment of the inventive light guide 1 as used with a VCSEL array die 2 as light source 2 in an illumination module 3. The diagram shows the light guide 1 to have an entry face F.sub.in arranged vis-à-vis the light source 2, an exit face F.sub.ex, and first and second side faces 10, 11 extending between the entry face F.sub.in and exit face F.sub.ex.

(10) The entry face F.sub.in is arranged essentially directly above the emission surface of the VCSEL array 2 so that light L leaving the VCSEL array 2 will pass through the entry face F.sub.in into the body of the light guide 1. Since a VCSEL emits essentially perpendicularly from its emission surface, all light rays R initially travel directly upwards into the light guide 1 (in reality the light will exhibit a small spread, but for the sake of clarity the diagram shows parallel light rays leaving the emission surface). In this embodiment, the angle of inclination α of the first side face 10 is 45°, so that when a light ray R arrives at the slanted or inclined side face 10, its path undergoes a 90° redirection.

(11) The second face 11 comprises inclined sub-faces 12 offset from each other by offset distances Δ. The length of the offset distance Δ is chosen to obtain a desired width W.sub.ex of the exit face F.sub.ex. For example, the length of the offset distance Δ is chosen to obtain an exit face W.sub.ex that is several times as wide as the entry face width W.sub.in. In this embodiment, the angle of inclination β of each sub-face 12 is also 45°, so that when a light ray R arrives at a slanted or inclined sub-face 12, its path undergoes another 90° re-direction. The light guide 1 is shaped such that a perpendicular P extending from the entry face F.sub.in cannot pass through the exit face F.sub.ex. In other words, it is not possible for any light ray to leave the exit face without being re-directed at least once after entering the light guide at the entry face. The shape of the light guide 1 is such that the light L emitted by the VCSEL array is “diluted” by the time it leaves the exit face F.sub.ex, but its direction of travel is unchanged. The thickness of the light guide 1 is largely given by the thickness T of the portion defined by the side faces 10, 11 and depends on the chosen angle of inclination α of the first side face 10.

(12) In this exemplary embodiment, the VCSEL array may have an emission surface that measures about 0.5 mm along each side. The entry face may have similar dimensions, so that each edge of the entry face F.sub.in has a length of at least 0.5 mm (to ensure that all light is captured). The second face 11 of the light guide 1 can be formed to have 10-15 inclined sub-faces 12 offset by 0.2 mm-0.4 mm, so that the width W.sub.ex of the exit face is 3 to 5 times longer than the width W.sub.in of the entry face F.sub.in.

(13) The light guide can be made of a suitable polymer such as PMMA. When the VCSEL array die 2 comprises infrared-emitting VCSELs, the light guide 1 may include a pigment that blocks visible spectrum wavelengths but is transmissive to infrared wavelengths. To improve the safety of the device and to obtain a desired light distribution, a diffusing element may be arranged in the path of the light L′ leaving the exit face F.sub.ex of the light guide 1. For example, a micro lens array may be arranged over on the exit face F.sub.ex.

(14) FIG. 2 shows a plan view of the light guide 1 of FIG. 1 when viewed from above. The diagram shows the exit face F.sub.ex and the inclined first side face 10, which has a projected area coinciding with the area of the entry face F.sub.in, so that the exit face F.sub.ex appears to lie beside the entry face F.sub.in.

(15) FIG. 3 shows a plan view of the light guide of FIG. 1 when viewed from below. The diagram shows the entry face F.sub.in and the second side face 11, which comprises inclined sub-faces 12 offset from each other by offsets 13. The projected area of the second face 11 coincides with the area of the exit face F.sub.ex.

(16) FIG. 4 shows a perspective view of an embodiment of the inventive illumination module 3. Here, the inclined sub-faces 12 of the second side 11 can be clearly seen through the transparent body of the light guide 1. The diagram also shows that the horizontal “height” of the exit face F.sub.ex of the light guide 1 corresponds to the horizontal “height” of the emission surface of the VCSEL array 2. Only the horizontal width of the light emitted from the emission surface is “stretched” by the light guide 1, and the virtual light source will have the rectangular dimensions of the exit face F.sub.ex.

(17) FIG. 5 shows a handheld device 5 such as a mobile phone with an imaging arrangement incorporating an embodiment of the inventive illumination module 3. The enlarged portion of the diagram shows the exit face F.sub.ex of the light guide 1, and indicates the position of the semiconductor light source 2 underneath the entry face of the light guide 1. The diagram also indicates a camera 4 of the handheld device, which can capture an image of a scene illuminated by the illumination module 3. The handheld device can be manufactured to incorporate such an imaging arrangement at the front and/or rear of the device. An embodiment of the imaging arrangement can be used in an iris scanning application, for example, which can be safely carried out even if the semiconductor light source comprises infrared VCSELs.

(18) FIG. 6 shows a side view of a further embodiment of the inventive light guide 1. Here, the first side face 10 has a steeper angle of inclination, so that the light L entering the light guide 1 undergoes TIR at the first face 10 and then again at the interior of the exit face F.sub.ex, before reaching the second face 11 and being re-directed by the inclined sub-face 12 to exit the exit face F.sub.ex. Here also, the light guide 1 is shaped such that a perpendicular P extending from the entry face F.sub.in cannot pass through the exit face F.sub.ex. For use with an infrared light source 2, the light guide can be made of a suitable material that includes a pigment to block visible spectrum wavelengths but which is transmissive to infrared wavelengths.

(19) FIG. 7 shows an alternative embodiment of the inventive light guide 1. Here, the side faces 10, 11 have been formed without facets or sub-faces. Instead, the side faces 10, 11 are curved in such a way that the light is re-directed by TIR through the body of the light guide 1, and such that a perpendicular P extending from the entry face F.sub.in cannot pass through the exit face F.sub.ex. In this case also, the exit face area is significantly larger than the entry face area, resulting in the desired “spread” or “stretching” of the light to reduce the coherence length of the light and/or to reduce speckle contrast in an image when the light source 2 is used to illuminate a scene to be photographed by a digital camera.

(20) Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

(21) For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements. The mention of a “unit” or a “module” does not preclude the use of more than one unit or module.

REFERENCE SIGNS

(22) light guide 1 side face 10, 11 sub-face 12, offset distance 13 semiconductor light source 2 illumination module 3 camera 4 handheld device 5 entry face F.sub.in exit face F.sub.ex light L, L′ light ray R perpendicular P thickness T angle of inclination α, β