Light conversion device with constrained light converter
阅读说明:本技术 具有受约束的光转换器的光转换设备 (Light conversion device with constrained light converter ) 是由 U·黑希特菲舍尔 F·黑林 于 2019-02-12 设计创作,主要内容包括:本发明描述了一种光转换设备,包括:-具有入光面与发光面的光转换器(130),其中该转换器(130)被布置成将在所述入光面上进行扫描的激光(10)转换为转换光(20),其中所述转换光(20)的峰值发射波长处于比所述激光(10)的激光峰值发射波长更长的波长范围内;-包封所述光转换器(130)的约束结构(150),其中该约束结构(150)被布置成在所述光转换器(130)发生机械故障的情况下保持所述光转换器(130)的几何形状。本发明还描述了包括这种光转换设备(130)的基于激光器的光源。本发明最后描述了包括这种基于激光器的光源的车辆头灯。(The invention describes a light conversion device comprising: -a light converter (130) having an entrance face and an emission face, wherein the converter (130) is arranged to convert laser light (10) scanned over the entrance face into converted light (20), wherein a peak emission wavelength of the converted light (20) is in a longer wavelength range than a laser peak emission wavelength of the laser light (10); -a confinement structure (150) encapsulating the light converter (130), wherein the confinement structure (150) is arranged to maintain the geometry of the light converter (130) in case of a mechanical failure of the light converter (130). The invention also describes a laser-based light source comprising such a light conversion device (130). The invention finally describes a vehicle headlamp comprising such a laser-based light source.)
1. A light conversion device comprising:
-a light converter (130) having an entrance face and an exit face, wherein the light converter is arranged to convert laser light (10) scanned over the entrance face into converted light (20), wherein a peak emission wavelength of the converted light (20) is in a longer wavelength range than a laser peak emission wavelength of the laser light (10),
-a constraint structure (150) encapsulating the light converter, wherein the constraint structure (150) is arranged to maintain the geometry of the light converter (130) in case of a mechanical failure of the light converter (130), thereby improving the eye safety of the light conversion device.
2. The light conversion device according to claim 1, wherein the light converter (130) is characterized by a thickness d perpendicular to the light entry surface, wherein the confinement structure (150) is arranged to hold a damaged portion (131) of the light converter (130) having the thickness d perpendicular to the light entry surface in a position of mechanical failure of the light converter (130).
3. The light conversion device of claim 1 or 2, wherein the confinement structure (150) is arranged such that there is a gap between the confinement structure (150) and the light entry face or between the confinement structure (150) and the light emission face, wherein the gap has a width g perpendicular to the light entry face or the light emission face of less than 2 μm.
4. A light conversion device according to claim 3, wherein the gap is arranged such that there is mechanical contact and no optical contact between the confinement structure (150) and the light-in face or the confinement structure (150) and the light-emitting face.
5. A light conversion device according to claim 1 or 2, wherein the confinement structure (150) comprises a substrate (115) and a confinement cap (140), wherein the light converter (130) is confined between the substrate (115) and the confinement cap (140).
6. The light conversion device of claim 5, wherein the substrate (115) is transparent over a range of wavelengths including the peak emission wavelength of the laser light, wherein the light incident face is disposed proximate to the substrate (115), wherein the light emitting face is different from the light incident face, and wherein the light emitting face is disposed proximate to a surface of the confinement cap (140).
7. The light conversion device of claim 6, wherein the substrate (115) is in mechanical contact with the light incident surface but not in optical contact.
8. The light conversion device of claim 6, wherein the containment hood (140) is in mechanical contact with the light emitting face but not in optical contact.
9. The light conversion device according to claim 5, wherein the substrate (115) is coupled to a reflective structure (137), wherein the reflective structure (137) is arranged to reflect laser light (11) and converted light (20) received via the entrance face of the light converter (130) to the emission face.
10. Light conversion device according to claim 1 or 2, comprising a failure sensor (210), wherein the failure sensor (210) is arranged to detect damage of the confinement structure (150).
11. The light conversion device according to claim 10, wherein the confinement structure (150) comprises a substrate (115) and a confinement cap (140), wherein the light converter (130) is confined between the substrate (115) and the confinement cap (140), and wherein the fault sensor (210) is arranged to detect a relative movement of the confinement cap (140) with respect to the substrate (115).
12. A laser-based light source, comprising:
-a light conversion device according to any of claims 1-11, and
-a laser (110) adapted to emit the laser light (10).
13. The laser-based light source according to claim 12, comprising the light conversion device according to claim 11, the laser-based light source further comprising a fault detector (200), wherein the fault detector (200) is coupled with the fault sensor (210), wherein the fault detector (200) is arranged to generate a control signal upon detection of damage of the confinement structure (150), and wherein the laser-based light source is arranged to switch off the laser (110) upon detection of the control signal during operation of the laser-based light source.
14. A vehicle headlamp comprising the laser-based light source of claim 12 or 13.
Technical Field
The present invention relates to a light conversion device with a constrained light converter, a laser-based light source comprising such a light conversion device, and a vehicle headlamp comprising such a laser-based light source.
Background
In high brightness light sources, light conversion devices are often used which are excited by blue light emitted by a laser, for example. The phosphor of the light conversion device is adhered to the heat sink by means of a glue layer or a solder layer, which is placed between the heat sink and the phosphor. The high intensity of the laser, particularly the blue laser, and the high temperature caused by the light conversion by the phosphor may cause reliability and safety problems.
Disclosure of Invention
It is an object of the present invention to provide a light conversion device with improved reliability.
According to a first aspect, a light conversion device is provided. The light conversion device includes a light converter having a light incident surface and a light emitting surface. The light converter is arranged to convert the laser light into converted light. The peak emission wavelength of the converted light is in a longer wavelength range than the laser peak emission wavelength of the laser light. The light conversion device further comprises a confinement structure encapsulating the light converter. The confinement structure is arranged to maintain the geometry of the light converter in case of a mechanical failure of the light converter, thereby improving the eye safety of the light conversion device.
Laser-based (white light) light sources for vehicles, in particular for headlights of cars, are currently under investigation because of their approximately 1 Gcd/m2Due to high brightness. In such laser-based light sources, the intense blue pump laser beam is sent to a light converter ("phosphor") that converts the intense blue pump laser beam to white light comprising about 75% (yellow) converted light and 25% (scattered) unconverted laser light. A well-known problem with such light sources is laser safety. In a fault situation, if the pump laser beam leaves the laser-based light source unscattered, it may cause eye damage. Therefore, the integrity of the converter must be guaranteed.
Ensuring the integrity of the light converter is most challenging, not for small converters in static light sources (ii)<1mm2) For large scale converters (-1 cm) in laser scanner systems2) In laser scanner systems, a pump laser beam is scanned over a light converter by a micromirror.
The confinement structure constrains or encapsulates the light converter such that the integrity of the light converter with respect to eye safety is not compromised even by material imperfections of the converter material that may cause the light converter to break during operation (e.g., caused by thermal loading during light conversion). The geometry of the light converter is substantially maintained. The integrity of the light conversion device may be determined by reference measurements after encapsulating the light converter in the confinement structure. For optical reasons, it may not be desirable to embed the light converter in the confinement structure such that there is an optical interface between the light converter and the material of the confinement structure (see below).
The light converter may further be arranged to convert the collimated laser light into converted light such that when the emission direction of the collimated laser light is perpendicularAt the light incident surface of the light converter, the light guide plate has a size of 10000 μm2The intensity of unconverted laser light emitted by surface elements of the light emitting face is less than a specified intensity percentage of the collimated laser light across the light emitting face. The confinement structure is arranged to confine the light converter therein such that, in case of mechanical failure of the light converter, the confinement structure is bounded by a dimension of 10000 μm2The intensity of the unconverted laser light emitted by the surface elements of the light emitting surface is less than 10% of the specified intensity percentage of the collimated laser light, more preferably less than 5% of the specified intensity percentage of the collimated laser light.
For example, the light conversion device may be arranged such that a prescribed 25% of the unconverted laser light is emitted by the light emitting face according to the above described example. The percentage depends on the intended color point and the converter material of the light converter. The specified percentage may be in the range between 18% and 32%, preferably between 20% and 30%, and most preferably between 22% and 28%. The light converter is constrained by a constraint structure such that relative movement between portions of the light converter is limited. From 10000 μm2The intensity of the unconverted laser light emitted by the reference surface, e.g. comprising a crack between two parts of the light converter due to relative movement between said two parts, is below 35%, preferably below 30%.
The light converter is characterized by a thickness d perpendicular to the light-in surface. The confinement structure is arranged to hold a broken portion of the light converter having said thickness d perpendicular to the light entry surface in a position of mechanical failure of the light converter.
The geometrical boundary conditions imposed by the constraint structure, which are necessary to guarantee eye safety, even in the event of a fatal failure of the light converter, may depend on the size, thickness and shape (e.g., rectangular or circular) of the light converter. Thus, the confinement structure may be arranged such that a broken portion of the material of the light converter is held close to its original position in the undamaged light converter. The thickness d may typically be between 20 and 100 microns.
For example, the confinement structure may be arranged to limit a lateral offset parallel to the entrance face of the damaged portion with respect to an initial position of the damaged portion in the light converter to less than 3 μm, preferably less than 2 μm, most preferably less than 1 μm. Avoiding or at least limiting the lateral offset reduces the maximum possible size of a slit or slit in the light converter through which unconverted laser light not scattered by the light converter can reach the subsequent optical device and ultimately enter the human eye.
The constraining structure may be arranged such that there is a gap between the constraining structure and the light-in face or between the constraining structure and the light-emitting face. The width of the gap perpendicular to the light-incident or light-emitting surface may be less than 2 μm, preferably less than 1 μm and most preferably less than 0.5 μm. The gap may optically decouple between the surface of the light converter and the adjacent surface of the confinement structure, thereby reducing optical loss. For example, the gap may be arranged such that there is mechanical contact but no optical contact between the constraining structure and the light-in surface or between the constraining structure and the light-emitting surface. By no or substantially no optical contact is meant that at least a micro gap exists between the confinement structure and the corresponding surface of the light converter. There may be mechanical contact, but the surface roughness of the corresponding surface of the confinement structure or the light converter avoids a smooth interface between the material of the light converter and the confinement structure that may simultaneously act as an optical device of the laser-based light source.
The confinement structure may include a base and a confinement cap. The light converter is constrained between the substrate and the confinement shield. Constraining the light converter between at least two separate components may simplify the mechanical and optical construction of the light conversion device. For example, the confinement shield may include an optical element, which may be a lens or the like, for optical manipulation of the converted and unconverted laser light. The optical element may be integrated into an optical arrangement of a laser-based light source, and in particular into an optical arrangement of a vehicle headlight. The optical arrangement may be arranged to image the converted and unconverted laser light on an image plane, which may be arranged at a distance of several meters away.
According to one embodiment, the substrate may be transparent at least in a wavelength range including a peak emission wavelength of the laser. The light incident surface may be disposed proximate to the substrate. In this embodiment, the light emitting surface is different from the light incident surface. The light emitting face is disposed proximate to a surface of the containment hood. In this transmission scheme, the light incident surface and the light emitting surface are separated. Laser light enters the light converter through an entrance face adjacent the substrate, and the converted and unconverted laser light generally exits the emission face after a single pass through the light converter. The light-incident surface and the light-emitting surface are generally parallel to each other.
As discussed above, the substrate may be in mechanical contact with the light-in surface but not in optical contact. Optical contact between the input surface and the substrate may increase light loss because back reflection of converted and, in particular, unconverted laser light, to the substrate may increase. Alternatively, the light-entering face may be covered by a mirror layer which is reflective in the wavelength range of the converted light and transmissive in the wavelength range of the laser light.
Alternatively or additionally, the optical element may be in mechanical contact with the light emitting face but not in optical contact with the light emitting face. In case of optical contact between the light converter and the optical element comprised by the confinement structure, the relatively high refractive index of the optical element compared to air may increase the emission numerical aperture of the light converter. Therefore, in the case of optical contact, the optical element needs to have a higher numerical aperture in order to avoid optical loss. Avoiding such optical contact thus enables an efficient (no optical losses) and cost-effective laser-based light source (requirement for a reduction of the numerical aperture of the optical device).
According to an alternative embodiment, the substrate of the light conversion device may be coupled to the reflective structure. The reflective structure is arranged to reflect laser light received through the entrance face of the light converter and the converted light. The light incident surface and the light emitting surface may be at least partially identical. In this embodiment, the light conversion device is arranged according to a so-called reflection scheme. A portion of the converted light and unconverted laser light may pass through the light converter at least twice. In such a reflective arrangement, the confinement shield may only provide part of the solution, as the integrity of the light converter is insufficient, compared to a transmissive solution. The pump laser light may still be deflected out of the light source due to, for example, offset pump optics (e.g., a lens arranged to focus the laser light to the light converter), or due to reflective particles on the light converter.
The light conversion device according to any of the embodiments described above may comprise a failure sensor. The failure sensor is arranged to detect damage to the constraint structure. For example, in the event of mechanical damage to the constraining structure, the fault sensor may be arranged to detect a change in resistance, capacitance or temperature. In contrast to the light converter, the confinement structure may for example comprise a strong transparent material, such as glass, in or on which the wires or metal surfaces can easily be provided.
For example, the fault sensor may be arranged to detect relative movement of the containment hood with respect to the base. The failure sensor may be arranged to detect relative movement of all sub-elements or sub-structures of the constraint structure to determine potential damage to the constraint structure and/or the light converter, which may be a risk to eye safety. A faulty sensor may have the following advantages: without imposing limitations on light emission, substantially all potential damage to the light conversion device can be detected.
According to yet another aspect, a laser-based light source is provided. The laser-based light source comprises a light conversion device as described above and at least one laser adapted to emit laser light.
The laser-based light source may comprise two, three, four or more lasers (e.g. arranged in an array) emitting e.g. blue laser light.
The laser-based light source may further comprise a fault detector. The fault detector is coupled to the fault sensor described above. The fault detector is arranged to generate a control signal upon detection of damage to the restraint structure. The laser based light source is arranged to switch off the at least one laser when a control signal is detected during operation of the laser based light source.
According to yet another aspect, a vehicle headlamp is provided. A vehicle headlamp comprisesAt least one laser-based light source as described above. The vehicle headlamp may comprise two, three, four or more laser-based light sources as described above. In this case, the light converter may include or comprise a garnet yellow phosphor (e.g., Y)(3-0.4)Gd0.4AL5O12: ce). A mixture of blue laser light and yellow converted light may be used to produce white light as described above.
It shall be understood that preferred embodiments of the invention may also be any combination of the dependent claims with the respective independent claims.
Further advantageous embodiments are defined below.
Drawings
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.
The invention will now be described by way of example based on embodiments with reference to the accompanying drawings.
In the drawings: fig. 1 shows a schematic sketch of a prior art laser-based light source.
Fig. 2 shows a schematic sketch of a first laser-based light source comprising a light conversion device according to a first embodiment.
Fig. 3 shows a schematic sketch of a mechanical failure of a light converter.
Fig. 4 shows a schematic sketch of a second laser-based light source comprising a light conversion device according to a second embodiment.
Fig. 5 shows a schematic sketch of a third laser-based light source comprising a light conversion device according to a third embodiment.
Fig. 6 shows a schematic sketch of a fourth laser-based light source comprising a light conversion device according to a fourth embodiment.
Fig. 7 shows a schematic sketch of a fifth laser-based light source comprising a light conversion device according to a fifth embodiment.
Fig. 8 shows a schematic sketch of a top view of a light-converting device according to a fifth embodiment.
In the drawings, like reference numerals refer to like elements throughout. The objects in the figures are not necessarily to scale.
Detailed Description
Various embodiments of the invention will now be described with the aid of the accompanying drawings.
Fig. 1 shows a schematic sketch of a prior art laser-based light source in which the
Fig. 2 shows a schematic sketch of a first laser-based light source comprising a
Fig. 3 shows a schematic sketch of a mechanical failure of the
The worst case is very unlikely. For example, polycrystalline materials commonly used for light converters (e.g., ceramic phosphor materials) are less likely to crack in the manner described in fig. 3. Since there is no such straight narrow slit as depicted in fig. 3, the laser light will typically be deflected further. Thus, in a real scenario, the width of the gap g may be larger, without a substantial risk of eye injury, than in the situation discussed with respect to fig. 3.
Fig. 4 shows a schematic sketch of a second laser-based light source comprising a light conversion device according to a second embodiment. The second embodiment is very similar to the first embodiment described with reference to fig. 2. The
Fig. 5 shows a schematic sketch of a third laser-based light source comprising a light conversion device according to a third embodiment. The general configuration remains similar to that described with reference to fig. 2 and 4. In this embodiment, the
Fig. 6 shows a schematic sketch of a fourth laser-based light source comprising a light conversion device according to a fourth embodiment. The
Fig. 7 shows a schematic sketch of a fifth laser-based light source comprising a light conversion device according to a fifth embodiment. The fifth embodiment is a reflective arrangement in which the light incident and light emitting surfaces of the
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.
Other modifications will be apparent to persons skilled in the art upon reading this disclosure. 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.
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.
Any reference signs in the claims shall not be construed as limiting the scope.
List of reference numerals
10 laser
11 unconverted laser light
20 converted light
110 laser
115 substrate, transparent structure
120 coupling layer
130 light converter
131 damaged portion
137 reflection structure
140 restraining shield
141 side restraint
143 optical element
150 restraining structure
200 fault detector
210 fault sensor
a, transverse extent of (largest) damaged part of amax
c width of narrow slit caused by lateral offset of damaged portion
Thickness of d light converter
g width of gap between light emitting face of light converter and confinement structure
Lateral extension of the L-light converter