Optical converter colour wheel

Abstract

A light converter comprises: a solid-state optical member configured to absorb light of an excitation wavelength and generate light of an emission wavelength; a base; and a mechanical fastener attaching the solid-state optical member to the base. The light converter may be part of a light engine, a phosphor wheel or an automotive headlight. A method of manufacturing such a phosphor wheel is also provided.

Claims

1. A light converter comprising: a solid-state optical member configured to absorb light of an excitation wavelength and generate light of an emission wavelength, wherein the optical member is an annulus having a planar front, a planar rear, an inner surface, and an outer surface, and wherein the optical member comprises a ceramic phosphor; a base having a seat surface for receiving the planar rear of the optical member such that the seat surface supports the entire planar rear of the optical member between the inner and outer surface of the annulus, the base having a step formed thereon for fixing the optical member relative to the base; and a mechanical fastener attaching the solid-state optical member to the base, and the mechanical fastener applying force to an inner rim of the optical member; wherein no adhesive is used to join the optical member to the base.

2. The light converter of claim 1, wherein the mechanical fastener rigidly attaches the solid-state optical member to the base.

3. The light converter of claim 1, wherein the mechanical fastener removably attaches the solid state optical member to the base.

4. The light converter of claim 1, wherein the mechanical fastener comprises a longitudinal part that engages with a corresponding engaging point to allow coupling of the mechanical fastener to the base.

5. The light converter of claim 4, wherein the mechanical fastener further comprises a front plate, the optical member being between the front plate and the base and the longitudinal part fixing the front plate to the engaging point, thereby to attach the optical member to the base.

6. The light converter of claim 4, wherein the engaging point is in the base, or in a bracing component, distinct from the base.

7. The light converter of claim 1, wherein the base or the mechanical fastener further comprise a plurality of projections, each engaging with a complementary anchor point on the fastener or the base respectively.

8. The light converter of claim 7, wherein each of the projections comprises a deformable clip.

9. The light converter of claim 7, wherein each of the complementary anchor points comprises one of: a ridge; a groove; or a lip.

10. The light converter of claim 8, wherein the deformable clips are spring members, each exerting a force on their respective anchor point, thereby holding the mechanical fastener in place.

11. The light converter of claim 7, wherein each of the projections comprises a projecting plug and each of the anchor points is a respective notch.

12. The light converter of claim 1, wherein the mechanical fastener comprises a cover plate attached to the base and the optical member is between the cover plate and the base.

13. The light converter of claim 12, wherein the cover plate is attached to the base by spot welding.

14. The light converter of claim 1, wherein the mechanical fastener comprises an elastic material.

15. The light converter of claim 1, wherein the optical member is configured to absorb blue light.

16. The light converter of claim 1, wherein the optical member is configured to generate yellow light or green light.

17. The light converter of claim 1, wherein the optical member further comprises: an anti-reflection coating; or a high-reflection coating.

18. The light converter of claim 17, wherein the anti-reflection coating or the high-reflection coating is a thin film coatings.

19. A phosphor wheel comprising: the light converter of claim 1; and a motor arranged to rotate the base around an axis passing through the base and normal to a planar surface of the solid-state optical member.

20. A light engine comprising: A light source; and a light converter including: a solid-state optical member configured to absorb light of an excitation wavelength and generate light of an emission wavelength, wherein the optical member is an annulus having a planar front, a planar rear, an inner surface, and an outer surface, and wherein the optical member comprises a ceramic phosphor; a base having a seat surface for receiving the planar rear of the optical member such that the seat surface supports the entire planar rear of the optical member between the inner and outer surface of the annulus, the base having a step formed thereon for fixing the optical member relative to the base; and a mechanical fastener attaching the solid-state optical member to the base, and the mechanical fastener applying force to an inner rim of the optical member; wherein no adhesive is used to join the optical member to the base; wherein the light source is arranged to apply exciting light to the light converter.

21. The light engine of claim 20, wherein the light source is a laser-based illumination source.

22. The light engine of claim 20 further comprising: a motor arranged to rotate the base around an axis passing through the base and normal to a planar surface of the solid-state optical member.

23. A projector comprising the light engine of claim 22.

24. An automotive headlight comprising the light engine of claim 20.

25. A light converter comprising: a solid-state optical member configured to absorb light of an excitation wavelength and generate light of an emission wavelength, wherein the optical member is an annulus and has a planar front and a planar rear, and wherein the optical member comprises a ceramic phosphor; a base for supporting the planar rear of the optical member between an inner surface and an outer surface of the annulus, the base having a step formed thereon for fixing the optical member relative to the base; and a mechanical fastener attaching the solid-state optical member to the base, wherein the base or the mechanical fastener further comprises a plurality of projections each of the projections engaging with a complementary anchor point on the fastener or the base respectively, and each of the projections comprising a deformable clip.

26. The light converter of claim 25, wherein the deformable clips are spring members, each exerting a force on their respective anchor point, thereby holding the mechanical fastener in place.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention may be put into practice in a number of ways, and preferred embodiments will now be described by way of example only and with reference to the accompanying drawings, in which:

(2) FIG. 1 shows an example of a known reflective phosphor-in-silicone-glue colour wheel;

(3) FIG. 2 shows an example of a reflective phosphor ceramic-glue color wheel;

(4) FIG. 3 shows an exploded perspective view of a first embodiment in accordance with the disclosure;

(5) FIG. 4 schematically illustrates a cross-section view of a first embodiment in accordance with the disclosure;

(6) FIG. 5 shows an assembly view of an alternative first embodiment in accordance with the disclosure;

(7) FIG. 6 schematically illustrates a cross-section view of the alternative first embodiment in accordance with the disclosure;

(8) FIG. 7 shows an assembly view of a second embodiment in accordance with the disclosure;

(9) FIG. 8 shows a perspective view of a second embodiment in accordance with the disclosure;

(10) FIG. 9 schematically illustrates a cross-section view of a second embodiment in accordance with the disclosure;

(11) FIG. 10 schematically illustrates a cross-section view of a third embodiment in accordance with the disclosure;

(12) FIG. 11A shows a first assembly view of a third embodiment in accordance with the disclosure;

(13) FIG. 11B shows a second assembly view of a third embodiment in accordance with the disclosure;

(14) FIG. 12 schematically illustrates a cross-section view of a fourth embodiment in accordance with the disclosure; and

(15) FIG. 13A shows a first assembly view of a fourth embodiment in accordance with the disclosure.

(16) FIG. 13B shows a second assembly view of a fourth embodiment in accordance with the disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(17) Light converters convert exciting light in one wavelength range to another emission light in another wavelength range. For example, a light converter (which may comprise a phosphor wheel) may convert blue light to green/yellow light. To generate a desired colour sequence, the phosphor wheel may comprise colour segments with different conversion properties. To achieve the desired light output and alleviate localized heating of the conversion material in the laser spot area, fast rotation of the phosphor wheel is recommended.

(18) To increase the conversion light output, in many cases, phosphor wheels are designed to reflect light that is converted. With optical converters that comprise anti-reflection/high reflection (AR/HR) coating, metal disks with mirror coating are no longer required.

(19) Some performance characteristics such as conversion light output, colour, and lifetime are direct functions of working temperature. At higher operating temperatures, the conversion light output may decrease, the colour may shift, and the lifetime of phosphor wheel may be decreased. Under normal operating conditions, approximately 50%-60% of the input power is output as heat, while the rest of the input power is converted to light. Particularly, when the input laser power reaches as high as several hundred watts, the heat generation during the conversion will cause high temperature more than 200 degrees Celsius (200? C.). Thermal effect considerations must be therefore be taken into the product structure design. This is at least so that the solid optical converter can dissipate the heat by effective heat conduction. In order to increase the heat dissipation from the working optical converter, while also reducing weight loading of motor and decreasing the cost, a substrate to support or clamp optical converters may use metals with high thermal conductivity. Aluminium/aluminium alloy may be used as the substrate and manufactured in a cost efficient way of stamping or punching.

(20) An improved solution including a phosphor colour wheel can use ceramic phosphors as a converter. In some such devices, transparent silicone glue is applied to join the ceramic converter with a reflective metal disk. FIG. 2 is a schematic view of ceramic phosphor colour wheel of 200 of such a device. The colour segments are changed from the composition of phosphor-in-silicone-glue to the composition of ceramic phosphors. The phosphor ceramic colour ring 201 or colour segments are attached to metal disk with mirror surface 202 by optically transparent silicone glue 203. The figure shows exciting light (input light) 204a e.g. from a laser-based illumination source or other light source (not shown) and emitting/converted reflected light 204b. However, because of the previously mentioned characteristics of the glue, the product cannot work under high temperature. Testing results show that the proper working temperature cannot be higher than 200 degrees Celsius (200? C.). Some devices disclosed herein provide a total solid product solution, avoiding any glue, adhesive or paste. As a result, the product therefore achieves an improved performance and improved durability, even in high power laser projection display systems. Devices disclosed herein may be used in applications where the solid state laser projector can be equipped with laser power in excess of than 100 watts. The working temperature of such devices can reach above 200 degrees Celsius (200? C.) to enable high luminous brightness.

(21) Referring to FIG. 3, there is shown an exploded perspective (assembly) view of such an optical converter colour wheel according to a first embodiment. A structure including a longitudinal member is provided to mechanically fasten the reflective ceramic phosphor colour wheel to the base. The solid optical converter (for example, a phosphor-ceramic based optical converter ring) 303 is secured between the base (or supporting substrate) 304 and the front plate (or cover hub) 302 by a central longitudinal member (for example a screw) 301. A threaded adapter 305 may then join the colour wheel with a motor. To precisely fix the optical converter, a step or a groove is formed on the supporting substrate. The cover hub only presses the optical converter along the inner rim. By such a configuration, a highly radical concentric structure is obtained. Any unbalance can be easily corrected by removing mass from the thicker circular column in the central portion of the cover hub (the hat body of the cover hub) in a subsequent dynamic balancing process. In this way, the material removing balancing process can be easily operated. In this example, the base and front plate 302 and 304 may be formed of the material of 6061 Aluminium alloy. The colour wheel has an outer diameter of 50 mm. Other sizes are possible and may be used.

(22) FIG. 4 shows a sectional view of optical converter colour wheel according to the first embodiment of FIG. 3. In this arrangement, the outer rim ring area 401 of the cover hub 302 may be as thin as 0.2 mm. This advantageously allows the device to be used in light engine systems where the collecting lens system is close to the top surface of phosphor luminous ring. Additionally, jitter of the rotating colour wheel can be reduced in a dynamic balancing process. This is performed in order to avoid contact of the colour wheel with the lens system as a result of jitter.

(23) FIG. 5 shows an assembly view of optical converter colour wheel according to an alternative first embodiment. FIG. 6 shows a sectional view of the same structure. The cover hub in this example is formed by two parts: the hub 502 and the clamping ring 503, as shown in FIG. 5 and FIG. 6. The solid optical converter 504 is secured between a threaded base substrate 505 and a clamp plate 503 by a central longitudinal member 501. In this way, the two parts of the cover hub (the hub and the clamping ring) can be manufactured separately by stamping/punching. As a result, a low cost alternative assembly is produced.

(24) FIG. 7 shows an assembly view of an optical converter colour according to a second embodiment. FIG. 8 shows a perspective view and FIG. 9 shows a sectional view of the same structure. In this type structure, the phosphor-ceramic based optical converter ring 702 is seated on the outer ring shaped area of the base (or supporting substrate) 703. The optical member is clamped against the base 703 by an S-shaped spring 701. The spring is mounted in the slot of the base 703, with its one circular end 701a pressing the inner rim of the optical converter 702 and with its other claw shaped ends 701b holding against in the groove of the central shaft 703a of the supporting substrate 703. The depth and width of the slot, as well the groove height of the central shaft in the optical converter holder substrate 703 may preferably be designed and optimized so that the clamping force is appropriate.

(25) Although an S-shaped spring is shown, other spring configurations are possible. There are 5 spring claws in the example embodiment shown in FIG. 5. Alternatively, the number of claws may be different. The number of claws may be 6 or 8, for example. The material for this spring may be stainless steel, spring steel, brass, or copper. Other alternatives are also possible.

(26) The spring can be manufactured as thin as 0.15 mm in a cost effective method of stamping. By such a configuration, a highly concentric structure is provided. In such a structure, it is advantageously relatively easy to correct the unbalance by adding mass to the spring at some points. A cheap, simple and configurable assembly is therefore provided.

(27) FIG. 11A shows an assembly view of an optical converter colour wheel according to a third embodiment. FIG. 10 shows a sectional view of the same structure. In this embodiment, the base (supporting substrate) 904, has projecting plugs 904a distributed along the outer flank. The fitting cover ring 901 is made of spring material and has respective notches 901a in positions corresponding to the projecting plugs. The optical converter is held in place between the base and the cover ring by joining the cover ring to the base by the snap-on of plugs and notches. The optical converter 902 may be seated in a recess ring area of the cover ring 901.

(28) One difference in this configuration is that the force is applied to the outer rim of the optical converter. In contrast, in other configurations (such as those described earlier), the clamping force is applied to the inner rim of the optical converter. By a configuration according to this third embodiment, as illustrated in FIG. 11B, individual colour segments 902a can be combined as required in order to generate a desired emission spectrum. They may then be fastened using a cover ring that engages with the outer edges of the segments, without the need for glue. Parts of the cover ring and base may be fabricated by stamping. Advantageously, this method is very cost effective.

(29) FIGS. 10 and 11A-B show projecting plugs on the base and respective notches on the cover ring, however, it will be apparent to the skilled person that alternatives are possible. For example, some or all of the plugs may be on the cover ring with corresponding notches in the base.

(30) FIG. 12 shows a cross-sectional view of optical converter colour wheel and FIGS. 13A and 13B show two different perspective views, according to a fourth embodiment. In this embodiment, a cover plate 1002 is used to attach the optical converter colour wheel 1003 to the base 1004, as an alternative to glue/adhesive. The optical converter 1003 is sandwiched between the base substrate 1004 and the cover plate 1002. The base substrate 1004 and the cover plate 1002 can be made of metals, such as, aluminium alloy, stainless steel etc. The base substrate 1004 and the cover plate 1002 are mechanically attached by means of attaching the metals directly together. For example, the base substrate 1004 and the cover plate 1002 may be attached by welding (for example laser spot welding) or soldering. For the laser spot welding, only the laser spot area 1005 is affected by the heat. The expensive optical converter may therefore not be damaged by this method of fastening.

(31) Although specific embodiments have been described, the skilled person will understand that variations and modifications are possible. For example, the designs may be applicable to all solid-state light converters and not necessarily only those using a ceramic material, for example a glass-based or plastics-based material may be used. The glass-based or plastics-based material may act as a substrate that is coated with a phosphor.

(32) For a reflective phosphor wheel, a layer of thin film coating of anti-reflection (AR) in the wavelength band of emission light, and/or another layer of thin film coating of high reflection (HR) in the wavelength band of emission light after conversion, may be applied to one or both sides of thin ceramic converters. This may be done in order to further improve the light conversion efficiency of ceramic converters. Testing results show that, with the AR/HR coating enhancement, the light conversion output will improved by around 10%. Moreover, AR/HR coating can work reliably under high temperature.

(33) Particularly, with HR coating on the ceramic converters, a high reflective metal disk may not be required. In known reflective phosphor wheel systems, a high reflective metal disk is provided. Such disks are typically composed of coated Silver/Sulphur layers on an aluminium substrate. With such a metal disk based phosphor wheel, after some period of operation, a failure mode of disk corrosion due to Silver oxidation and Sulphur migration among thin film layers may be observed.

(34) The solid optical converter colour wheel may include a colour wheel motor, an optical converter, a converter supporting substrate and a converter clamping component. The optical converter is secured directly by the supporting substrate and the clamping component. By such configurations eliminating or omitting glue/adhesive/paste, light converters can work properly under high temperature. For example, light converters disclosed herein can be used in high power laser projectors.

(35) These reflective phosphor wheels are used to convert exciting light in one wavelength range to another emission in the other wave length range. For example, the colour wheel may convert blue light to yellow or green light, particularly in laser projection display systems. These optical converters may also be used in automotive headlights.

(36) It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. It will be further appreciated that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.