Color mixing in laser-based light source

Abstract

The invention provides a lighting device (1) lighting device (10) comprising: (I) a first light source (110) configured to provide first light source light (101); (II) a luminescent material (200) configured to convert at least part of the first light source light (101) into luminescent material light (201); (III) a beam shaping optical element (300) having a light entrance side (341) and a light exit side (342), and a wall (347) bridging a distance between the light entrance side (341) and the light exit side (342), wherein at least part of the wall (347) is reflective for the luminescent material light (201), wherein the beam shaping optical element (300) is configured to receive at least part of the luminescent material light (201) at the light entrance side (341) and to provide beam shaped luminescent material light (201) at the light exit side (342); (IV) an elongated light transmissive body (100) having a first face (141) and a second face (142) defining a length (L) of the light transmissive body (100), and having one or more side faces (147) bridging the length (L) between the first face (141) and the second face (142), the light transmissive body (100) comprising a radiation input face (111) and a first radiation exit window (112), wherein the first face (141) comprises the radiation input face (111) and wherein the second face (142) comprises the first radiation exit window (112), wherein the radiation input face (111) is configured to receive at least part of the beam shaped light luminescent material light (201); (V) a second light source (120) configured to provide second light source light (121); wherein the elongated light transmissive body (100) is configured to receive at least part of the second light source light (121) via one or more of (i) incoupling of the second light source light (121) via the wall (347) of the beam shaping optical element (300), (ii) incoupling of the second light source light (121) via part of the first face (141) of the elongated light transmissive body (100), and (iii) incoupling of the second light source light (121) via part of the of the one or more side faces (147) of the elongated light transmissive body (100).

Claims

1. A lighting device comprising: a first light source configured to provide first light source light; a luminescent material configured to convert at least part of the first light source light into luminescent material light; a beam shaping optical element having a light entrance side and a light exit side, and a wall bridging a distance between the light entrance side and the light exit side, wherein at least part of the wall is reflective for the luminescent material light, wherein the beam shaping optical element is configured to receive at least part of the luminescent material light at the light entrance side and to provide beam shaped luminescent material light at the light exit side; an elongated light transmissive body having a first face and a second face defining a length (L) of the light transmissive body, and having one or more side faces bridging the length (L) between the first face and the second face, the light transmissive body comprising a radiation input face and a first radiation exit window, wherein the first face comprises the radiation input face and wherein the second face comprises the first radiation exit window, wherein the radiation input face is configured to receive at least part of the beam shaped light luminescent material light; a second light source configured to provide second light source light, wherein the second light source comprises a laser light source; wherein: the elongated light transmissive body is configured to receive at least part of the second light source light via one or more of (i) incoupling of the second light source light via the wall of the beam shaping optical element, (ii) incoupling of the second light source light via part of the first face of the elongated light transmissive body, and (iii) incoupling of the second light source light via part of the of the one or more side faces of the elongated light transmissive body; and wherein the optical axis (O.sub.11) of the first light source light, the optical (O.sub.C) axis of the beam shaping element, the optical axis of the (O.sub.121) of the second light source light and the body axis (BA) of the elongated light transmissive body are being essentially parallel to each other with a deviation from parallelism that is less than 15 degrees.

2. The lighting device according to claim 1, wherein the first light source comprises a laser light source.

3. The lighting device according to claim 1, further comprising an optical fiber, configured to receive at one fiber side the first light source light, and wherein a second side of the fiber is optically coupled to the luminescent material.

4. The lighting device according to claim 1, wherein the beam shaping optical element comprises a compound parabolic concentrator.

5. The lighting device according to claim 1, wherein the elongated light transmissive body has an aspect ratio of at least 5, and wherein the elongated light transmissive body comprises one or more of a polymeric material, a ceramic material, a glass material, and a single crystalline material.

6. The lighting device according to claim 1, wherein the first face comprises a first area (A1) being larger than a second area (A2) of the light exit side of the beam shaping optical element, thereby defining a remaining area (A3) of the first face, and wherein the second light source is optically coupled to the remaining area (A3) for incoupling of the second light source light via part of the first face of the elongated light transmissive body.

7. The lighting device according to claim 1, wherein the elongated light transmissive body has a hexagonal cross-section.

8. The lighting device according to claim 1, further comprising a second elongated light transmissive body having a first face of the second elongated light transmissive body and a second face of the second elongated light transmissive body defining a second length (L2) of the second light transmissive body, and having one or more side faces of the second elongated light transmissive body bridging the second length (L2) between the first face of the second elongated light transmissive body and the second face of the second elongated light transmissive body, wherein the second light transmissive body comprises a radiation input face of the second elongated light transmissive body and a first radiation exit window of the second elongated light transmissive body, wherein the first face of the second elongated light transmissive body comprises the radiation input face of the second elongated light transmissive body and at least one of the one or more side faces of the second elongated light transmissive body comprises the first radiation exit window, wherein the radiation input face of the second elongated light transmissive body is configured to receive at least part of the second light source light, and wherein a first part the at least one of the one or more side faces of the second elongated light transmissive body is optically coupled to one or more side faces of the elongated light transmissive body, for incoupling of the second light source light via part of the first face of the elongated light transmissive body.

9. The lighting device according to claim 8, wherein the second elongated light transmissive body tapers over at least part of the second length (L2) for facilitating coupling of the second light source light into the elongated light transmissive body.

10. The lighting device according to claim 1, wherein the wall of the beam shaping optical element comprises an opening for receiving at least part of the second light source light for incoupling of the second light source light via the wall of the beam shaping optical element.

11. The lighting device according to claim 3, wherein the optical axis of the optical fiber is essentially parallel to the optical axis of the first light source light with a deviation from parallelism that is less than 15 degrees.

12. The lighting device according to claim 1, further comprising a second optical fiber, configured to receive at a first fiber side of the second optical fiber the second light source light, and wherein a second side of the second optical fiber is optically coupled to one or more of (i) the wall of the beam shaping optical element, (ii) the part of the first face of the elongated light transmissive body, and (iii) the part of the of the one or more side faces of the elongated light transmissive body.

13. The lighting device according to claim 1, wherein the luminescent material is configured to provide one or more of green and yellow luminescent material light, and wherein the second light source is configured to provide one or more of blue and red second light source light.

14. The lighting device according to claim 1, comprising a plurality of second light sources comprising two or more second light sources configured to provide different second spectral distributions, differing with a difference in peak maxima of at least 20 nm.

15. A lighting system comprising the lighting device according to claim 1, wherein the lighting system comprises a spot lighting system or an image projection system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

(2) FIGS. 1a-1b schematically depict some aspects of the invention; and

(3) FIGS. 2a-2d schematically depict some embodiments.

(4) The schematic drawings are not necessarily on scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(5) A light emitting device according to the invention may be used in applications including but not being limited to a lamp, a light module, a luminaire, a spot light, a flash light, a projector, a (digital) projection device, automotive lighting such as e.g. a headlight or a taillight of a motor vehicle, arena lighting, theater lighting and architectural lighting.

(6) Light sources which are part of the embodiments according to the invention as set forth below, may be adapted for, in operation, emitting light with a first spectral distribution. This light is subsequently coupled into a light guide or waveguide; here the light transmissive body. The light guide or waveguide may convert the light of the first spectral distribution to another spectral distribution and guides the light to an exit surface.

(7) FIG. 1a schematically depicts some embodiments of possible bodies, such as ceramic bodies or crystals as waveguides. The faces are indicated with references 141-146. The first variant, a plate-like or beam-like light transmissive body has the faces 141-146. Light sources, which are not shown, may be arranged at one or more of the faces 143-146 (general indication of the edge faces is reference 147). The second variant is a tubular rod, with first and second faces 141 and 142, and a circumferential face 143. Light sources, not shown, may be arranged at one or more positions around the light transmissive body. Such light transmissive body will have a (substantially) circular or round cross-section. The third variant is substantially a combination of the two former variants, with two curved and two flat side faces. Especially, the body has a cross-section deviating from round (see first and third variant).

(8) In the context of the present application, a lateral surface of the light guide should be understood as the outer surface or face of the light guide along the extension thereof. For example in case the light guide would be in form of a cylinder, with the first base surface at one of the ends of the light guide being constituted by the bottom surface of the cylinder and the second base surface at the other end of the light guide being constituted by the top surface of the cylinder, the lateral surface is the side surface of the cylinder. Herein, a lateral surface is also indicated with the term edge faces or side 140.

(9) The variants shown in FIG. 1a are not limitative. More shapes are possible; i.e. for instance referred to WO2006/054203, which is incorporated herein by reference. The ceramic bodies or crystals, which are used as light guides, generally may be rod shaped or bar shaped light guides comprising a height H, a width W, and a length L extending in mutually perpendicular directions and are in embodiments transparent, or transparent and luminescent. The light is guided generally in the length L direction. The height H is in embodiments <10 mm, in other embodiments <5 mm, in yet other embodiments <2 mm. The width W is in embodiments <10 mm, in other embodiments <5 mm, in yet embodiments <2 mm. The length L is in embodiments larger than the width W and the height H, in other embodiments at least 2 times the width W or 2 times the height H, in yet other embodiments at least 3 times the width W or 3 times the height H. Hence, the aspect ratio (of length/width) is especially larger than 1, such as equal to or larger than 2, such as at least 5, like even more especially in the range of 10-300, such as 10-100, like 10-60, like 10-20. Unless indicated otherwise, the term aspect ratio refers to the ratio length/width. FIG. 1a schematically depicts an embodiment with four long side faces, of which e.g. two or four may be irradiated with light source light.

(10) The aspect ratio of the height H:width W is typically 1:1 (for e.g. general light source applications) or 1:2, 1:3 or 1:4 (for e.g. special light source applications such as headlamps) or 4:3, 16:10, 16:9 or 256:135 (for e.g. display applications). The light guides generally comprise a light input surface and a light exit surface which are not arranged in parallel planes, and in embodiments the light input surface is perpendicular to the light exit surface. In order to achieve a high brightness, concentrated, light output, the area of light exit surface may be smaller than the area of the light input surface. The light exit surface can have any shape, but is in an embodiment shaped as a square, rectangle, round, oval, triangle, pentagon, or hexagon.

(11) Note that in all embodiments schematically depicted herein, the radiation exit window is especially configured perpendicular to the radiation input face(s). Hence, in embodiments the radiation exit window and radiation input face(s) are configured perpendicular. In yet other embodiments, the radiation exit window may be configured relative to one or more radiation input faces with an angle smaller or larger than 90.

(12) Note that, in particular for embodiments using a laser light source to provide light source light, the radiation exit window might be configured opposite to the radiation input face(s), while the mirror 21 may consist of a mirror having a hole to allow the laser light to pass the mirror while converted light has a high probability to reflect at mirror 21. Alternatively or additionally, a mirror may comprise a dichroic mirror.

(13) FIG. 1b schematically depicts an embodiment of a lighting device 10. The lighting device comprises a first light source 110 configured to provide first light source light 101, especially a laser light source. The first light source light 101 may have an optical axis O.sub.11. Further, the device 10 comprises a luminescent material 200 configured to convert at least part of the first light source light 101 into luminescent material light 201. The device 10 further comprises a beam shaping optical element 300 having a light entrance side 341 and a light exit side 342, and a wall 347 bridging a distance d between the light entrance side 341 and the light exit side 342 of the beam shaping optical element 300, wherein at least part of the wall 347 is reflective for the luminescent material light 201, wherein the beam shaping optical element 300 is configured to receive at least part of the luminescent material light 201 at the light entrance side 341 and to provide beam shaped luminescent material light 201 at the light exit side 342. The beam shaping element may be a CPC like collimator. The beam shaping element 300 may have an optical axis O.sub.C. Reference A.sub.2 indicates (the area of) the light exit side 342 of the beam shaping optical element 300.

(14) The device 10 yet further comprises an elongated light transmissive body 100, such as a ceramic or a crystal, having a first face 141 and a second face 142 defining a length L of the light transmissive body 100, and having one or more side faces 147 bridging the length L between the first face 141 and the second face 142, the light transmissive body 100 comprising a radiation input face 111 and a first radiation exit window 112, wherein the first face 141 comprises the radiation input face 111 and wherein the second face 142 comprises the first radiation exit window 112, wherein the radiation input face 111 is configured to receive at least part of the beam shaped light luminescent material light 201. Luminescent material light 201 propagates through the body 100 to the light exit side 342 and escapes therefrom.

(15) The device 10 further comprises second light source 120 configured to provide second light source light 121 having a second spectral distribution. The second light source 120 is especially also a laser light source. The second light source light may have an optical axis O.sub.121. The optical axes of the first light source light 101, the second light source light 121 and the beam shaping element 300 as well as the body axis BA of the light transmissive body 100 are essentially parallel. Advantage of such a configuration is that it reduces the angular distribution of the light that exits the light transmissive body 100. At the exit of the light transmissive body 100 the spatial uniformity is improved, as the incident angle of the light relative to the side face 147 when entering the light transmissive body 100 is reduced. A relatively narrow exit beam of the light is advantageous for a number of applications, such as for digital projection, spot lights and automotive head lights. In addition, it allows to reduce the size of the lighting system that comprises a lighting device according to the invention. In specific embodiments, the optical axes of the light source light 101, the beam shaping element 300 and a body axis BA of the light transmissive body 100 are essentially in line with each other (over at least part of their lengths coincide).

(16) An optical axis is an imaginary line that defines the path along which light propagates through an element, and is usually parallel to the axis of symmetry. For an optical fiber, the optical axis is also known as the fiber axis.

(17) The wording essentially parallel means that the deviation from parallelism is less that 15 degrees. Preferably, the deviation from parallelism is less than 10 degrees. More preferably, the deviation from parallelism is less than 5 degrees. Even more preferably, the deviation from parallelism is zero degrees.

(18) The elongated light transmissive body 100 is configure to receive at least part of the second light source light 121 via one or more of (i) incoupling of the second light source light 121 via the wall 347 of the beam shaping optical element 300, (ii) incoupling of the second light source light 121 via part of the first face 141 of the elongated light transmissive body 100, and (iii) incoupling of the second light source light 121 via part of the of the one or more side faces 147 of the elongated light transmissive body 100. FIGS. 1b and 2a schematically depict the embodiment of incoupling of the second light source light 121 via part of the first face 141 of the elongated light transmissive body 100.

(19) The lighting device 10 is especially configured to provide lighting device light 11 emanating from the first radiation exit window 112, wherein the lighting device light 11 comprises one or more of the at least part of the luminescent material light 201 and at least part of the second light source light 121.

(20) FIG. 1b also schematically depicts an embodiment wherein the device 10 further comprises an optical fiber 400, configured to receive at one fiber side 411 the first light source light 101. A second side of the fiber 412 is optically coupled to the luminescent material 341 of the beam shaping optical element 300. The optical fibers 411 and/or 412 may especially be used to provide a broader beam shape than provided by the laser light sources 110 and/or 120, respectively, such as by micro-optical structures at the end of the fiber, e.g. surface roughness.

(21) As indicated above, FIG. 2a (also) shows an embodiment wherein incoupling of the second light source light 121 is done via part of the first face 141 of the elongated light transmissive body 100. Here, it is further shown that the first face 141 may comprise a first area A1 being larger than a second area A2 of the light exit side 342 of the beam shaping optical element 300. Thereby, a remaining area A3 of the first face 141 is defined, and wherein the second light source 120 is optically coupled to the remaining area A3 for incoupling of the second light source light 121 via part of the first face 141 of the elongated light transmissive body 100.

(22) Here, by way of example the elongated light transmissive body 100 has a hexagonal cross-section.

(23) Reference 500 indicates an optional rod, such as for beam shaping. Laser light from the fiber can get a broader distribution (broader beam shape). In this way, the luminescent material may irradiated over a larger area.

(24) Alternatively or additionally, other intermediate optical elements may be applied. Such intermediate optical element, like a positive or negative lens or a curved reflector or diffraction grating element may (also) provide some broadening of the beam. Especially, such elements may be configured downstream of the optical fiber (s) for providing a broader beam shape.

(25) FIG. 2b schematically depicts an embodiment of the lighting device 10 which further comprises a second elongated light transmissive body 2100 having a first face 2141 of the second elongated light transmissive body 2100 and a second face 2142 of the second elongated light transmissive body 2100 defining a second length L2 of the second light transmissive body 2100.

(26) The second elongated body 2100 has one or more side faces 2147 of the second elongated light transmissive body 2100 bridging the second length L2 between the first face 2141 of the second elongated light transmissive body 2100 and the second face 2142 of the second elongated light transmissive body 2100.

(27) The second light transmissive body 2100 comprises a radiation input face 2111 of the second elongated light transmissive body 2100 and a first radiation exit window 2112 of the second elongated light transmissive body 2100.

(28) The first face 2141 of the second elongated light transmissive body 2100 comprises the radiation input face 111 of the second elongated light transmissive body 2100 and at least one of the one or more side faces 2147 of the second elongated light transmissive body 2100 comprises the first radiation exit window 112. The radiation input face 2111 of the second elongated light transmissive body 2100 is configured to receive at least part of the second light source light 121. A first part 2148 the at least one of the one or more side faces 2147 of the second elongated light transmissive body 2100 is optically coupled to one or more side faces 147 of the elongated light transmissive body 100, for incoupling of the second light source light 121 via part of the first face 141 of the elongated light transmissive body 100.

(29) The second length L2 can be identical or can be smaller than the first length. At the second face 2142 a mirror may be configured.

(30) FIG. 2b (and also FIGS. 2c-2d) also shows an embodiment wherein a second optical fiber 2400 is applied. This second optical fiber 2400 may have a function analogous to the first optical fiber 400, but then in relation to the second light source light 121 (of the second light source). The second optical fiber 2400 is especially configured to receive at a first fiber side 2411 of the second optical fiber 2400 the second light source light 121. A second side 2412 of the second optical fiber 2400 is optically coupled to one or more of (i) the wall 347 of the beam shaping optical element 300 (see FIG. 2d), (ii) the part of the first face 141 of the elongated light transmissive body 100 (FIG. 2a), and (iii) the part of the of the one or more side faces 147 of the elongated light transmissive body 100 (FIGS. 2b and 2c). The fibers 400, 2400 may in embodiments have an essentially round cross-section, though other options may also be possible.

(31) FIG. 2c schematically depicts an embodiment with a slanted face. In such embodiment, the second face 2142 and a side face 2147 are essentially the same (such as in especially size and shape). Hence, FIG. 2c shows an embodiment wherein the second elongated light transmissive body 2100 tapers over at least part of the second length L2 for facilitating coupling of the second light source light 121 into the elongated light transmissive body 100.

(32) In FIG. 2b the width of the second elongated light transmissive body 2100 is essentially smaller than the width of the elongated body 100. However, this is not necessarily the case, see e.g. FIG. 2c. Further, also the embodiment of FIG. 2b may comprise in a variant a slanted face 2147 over at least part of its length L2.

(33) Note that the second elongated light transmissive body 2100 may be a separate body, brought in optical contact with the first elongated light transmissive body 100, but may in embodiments may also a part of the body 100, with the elongated body and the second elongated light transmissive body 2100 produced as a single body.

(34) Further, a combination of n second light sources and n second elongated light transmissive bodies 2100 may be provided, wherein n is at least 1, and may in embodiments be in the range of 1-12, such as 1-6.

(35) FIG. 2d schematically depicts an embodiment wherein the wall 347 of the beam shaping optical element comprises an opening 350 for receiving at least part of the second light source light 121 for incoupling of the second light source light 121 via the wall 347 of the beam shaping optical element 300.

(36) Like in FIGS. 2b (and 2c) the area of the light exit side of the beam shaping optical element and the first face (more especially the radiation input face) may essentially be the same.

(37) The four configurations in FIGS. 2a-2d were simulated and the maximum color error over the output area, expressed as delta-uv coordinates d_uv, dimensionless], were calculated, as well as the gradient of the color variations with distance, in units of [delta-uv/meter]. This gradient number is important as a measure for the visibility of the color error, since this is determined by the absolute color error and the distance between points with different color. All four configurations behave relatively similarly. It was further noted that the performance can be improved by choosing longer mixing rods.

(38) TABLE-US-00001 Maximum color color error error d_uv gradient [m-1] 2a: hexagonal 0.040 23.6 2b: sub-rod 0.031 20.5 2c: coupling prism 0.033 19.4 2d: through collimator 0.033 21.1

(39) The term substantially herein, such as in substantially all light or in substantially consists, will be understood by the person skilled in the art. The term substantially may also include embodiments with entirely, completely, all, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term substantially may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. Where stated that an absorption, a reflection or a transmission should be a certain value or within a range of certain values these values are valid for the intended range of wavelengths.

(40) The term comprise includes also embodiments wherein the term comprises means consists of. The term and/or especially relates to one or more of the items mentioned before and after and/or. For instance, a phrase item 1 and/or item 2 and similar phrases may relate to one or more of item 1 and item 2. The term comprising may in an embodiment refer to consisting of but may in another embodiment also refer to containing at least the defined species and optionally one or more other species.

(41) Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

(42) The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

(43) It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb to comprise and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words comprise, comprising, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of including, but not limited to. The article a or an preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. 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.

(44) Practical designs may be further optimized the person skilled in the art using optical ray trace programs, such particular angles and sizes of microstructures (reflective microstructures or refractive microstructures) may be optimized depending on particular dimensions, compositions and positioning of the one or more elongated light transmissive bodies.

(45) The invention further applies to a device comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.