Lighting device with fluorescent wheel and excitation radiation source

Abstract

Lighting device (100; 110; 120), comprising a. an excitation radiation source (101; 121) for the emission of excitation radiation (1), b. a fluorescent wheel (102) comprising a carrier substrate (7) with a front (5) and a back (6), wherein the fluorescent wheel (102) is arranged in a beam path of the excitation radiation (1) such that the excitation radiation (1) can reach the front (5), and wherein the fluorescent wheel (102) further comprises: i. at least one phosphor arranged on the front (5) for irradiation with excitation radiation (1) and wavelength conversion of the excitation radiation into wavelength-converted radiation (2), ii. at least one phosphor arranged on the back (6) for irradiation with excitation radiation (1) and wavelength conversion of the excitation radiation into wavelength-converted radiation (3), iii. a first region (5b, 6b) transparent to the excitation radiation (1) and designed to allow the excitation radiation to reach the back side (6), c. and wherein the illumination device (100; 110; 120) further comprises an optical device (11, 12) designed to deflect the excitation radiation (1) illuminating the front (5) of the support substrate (7) and radiating through its first transparent area (5b, 6b) to the back (6) of the support substrate (7); wherein the support substrate (7) comprises a second and a third region (5a, 6a; 5a', 6a') transparent to the excitation radiation and the illumination device (100) is designed such that the excitation radiation (1) illuminating the front (5) of the support substrate (7) can pass through the second transparent region (5a, 6a), is deflected to the back (6) of the support substrate (7) by means of the optical device (11, 12) and passes through the third transparent region (6a, 6a'); and wherein the first transparent area (5b, 6b) and / or any further or each transparent area (5a, 6a; 5a', 6a') is provided with a color or polarization filter or a polarization-rotating optical element.

Description

Technical area

[0001] The invention is based on a lighting device with an excitation radiation source and a phosphor wheel for converting at least part of the excitation radiation into wavelength-converted radiation, the latter usually in the visible range of the electromagnetic spectrum ("conversion light").

[0002] Such a lighting device can be used in particular as a light-generating unit in a projector, e.g. for video projectors or data projectors.

[0003] The invention also relates to a method for operating the lighting device according to the invention. State of the art

[0004] From the prior art, for example, document US 2010 / 0245777 A1, illumination devices for projection applications are known, which comprise a disk-shaped phosphor wheel with one or more phosphors. These illumination devices comprise an excitation radiation source that excites the phosphor to emit light at a wavelength different from the excitation radiation wavelength (wavelength conversion of the excitation radiation by means of a phosphor). Typically, the phosphors are arranged one after the other on one side of the phosphor wheel in the direction of rotation, so that the light emitted by the respective phosphor (converted light) is generated sequentially in time and fed to the imaging system.

[0005] Lasers, such as laser diodes, are preferably used as the excitation radiation source. In this case, the technology is also known as LARP (Laser Activated Remote Phosphor).

[0006] Document CN 102385233 A shows an illumination device for a projector with an excitation laser, a phosphor wheel for wavelength conversion of the excitation laser light into conversion light, and a filter wheel for spectral filtering of the conversion light. The excitation laser light is directed onto the phosphor wheel using a dichroic mirror. The conversion light reflected by the phosphor wheel passes through the dichroic mirror and strikes the filter wheel. The excitation laser light can pass through a transparent segment in the phosphor wheel and is guided to the dichroic mirror via a wrap-around loop. The dichroic mirror reflects the excitation laser light to the filter wheel. The filter wheel and the phosphor wheel are arranged on a common axis and thus rotate synchronously at the same speed.In this way, the conversion light generated sequentially by a phosphor segment of the phosphor wheel is spectrally filtered by an associated filter segment of the filter wheel.

[0007] EP 2 530 520 A1 discloses an illumination device for use in a projector. The illumination device has a phosphor wheel coated on one side, consisting of a transparent, circular-disk-shaped carrier material, three-quarters of the front side of which is coated with various phosphors. The uncoated quarter serves as a transparent segment. The laser radiation is passed through this transparent segment and deflected by mirrors onto the back of the phosphor wheel. There, the laser beam passes through the transparent carrier material and excites a blue phosphor applied behind it in a quarter segment on the front side to emit blue light. The blue phosphor conversion thus occurs in transmission. The other two quarter segments are coated with green phosphor. The green phosphor conversion here occurs in reflection.However, a reflective layer is required between each phosphor layer and the transparent substrate so that the light converted by the respective phosphor can be radiated from the front side and combined in a common direction. Otherwise, part of the converted light would be lost through the transparent substrate in the opposite direction. At least for the blue phosphor segment (transmission mode), the reflective layer must also be transparent to the laser radiation. For the red light channel, red light from a separate light-emitting diode (LED) is added.

[0008] The document US 2012 / 0243205 A1 also discloses an illumination device for use in a projector. In one variant, a phosphor wheel runs in a slot in a curved reflector, specifically through the reflector's focal point. The phosphor wheel has a region provided with phosphor on both sides, i.e., on both sides of the usually circular support disk of the phosphor wheel. This is intended to increase the light intensity of the arrangement. However, two separate excitation radiation sources are provided for this purpose, with each of the two sides of the phosphor wheel being irradiated in the region of the focal point by means of a respective excitation radiation source through corresponding openings in the reflector. The document US 2013 / 0021582 A1 discloses an illumination device with a phosphor arranged on the front of the phosphor wheel and a phosphor arranged on the back of the phosphor wheel.The document US 2013 / 0100417 A1 discloses a phosphor wheel with a region permeable to the excitation radiation. Description of the invention

[0009] The object of the present invention is to at least partially overcome the disadvantages of the prior art and to provide a lighting device, in particular a lighting device for projection applications, with the most efficient, compact and cost-effective design possible.

[0010] A further aspect of the invention is the possibility, in contrast to the prior art, of generating a temporally sequential sequence of differently filtered conversion light without a filter wheel, but with at least one static filter.

[0011] This object is achieved by a lighting device according to the claims. Such a lighting device comprises an excitation radiation source for the emission of excitation radiation, a phosphor wheel comprising a carrier substrate with a front side and a back side, wherein the phosphor wheel is arranged in a beam path of the excitation radiation such that the excitation radiation can reach the front side, and wherein the phosphor wheel further comprises the following: at least one phosphor arranged on the front side for irradiation with excitation radiation and wavelength conversion of the excitation radiation into wavelength-converted radiation, at least one phosphor arranged on the back side for irradiation with excitation radiation and wavelength conversion of the excitation radiation into wavelength-converted radiation, a first region permeable to the excitation radiation, which is designed tothat the excitation radiation can reach the rear side, and wherein the illumination device further comprises an optical device designed to redirect the excitation radiation irradiating the front side of the carrier substrate and passing through its first transmissive region to the rear side of the carrier substrate.

[0012] Particularly advantageous embodiments can be found in the dependent claims.

[0013] Furthermore, the object is achieved with regard to its aspects for operating the lighting device according to the invention by a method having the features of the independent method claim.

[0014] The features, advantages and functionalities described below for the lighting device according to the invention and its design options also apply, where applicable, analogously to the method according to the invention and vice versa.

[0015] The basic idea of ​​the present invention is to provide at least one phosphor on each of the two sides of a disk-shaped phosphor wheel, i.e. on the "front side" as well as on the opposite "back side", and to excite these two-sided phosphors sequentially in time, i.e. to irradiate the front and back of this "two-sided phosphor wheel" alternately with the excitation radiation.

[0016] The conversion of excitation radiation into conversion light preferably occurs from a shorter wavelength to a longer wavelength ("downconversion"), as this does not require additional energy. In this case, the wavelength of the excitation radiation is therefore shorter than the wavelengths of the conversion light. For example, the excitation radiation from the excitation radiation source can comprise blue laser radiation and / or blue-violet and / or ultraviolet laser radiation.

[0017] Using blue laser radiation as excitation radiation has the advantage that a portion can be used unconverted as blue light (wrap-around light path). A blue phosphor for the blue light channel is therefore not required in this case.

[0018] Lasers are particularly preferred as excitation radiation sources due to the high power densities they enable. A suitable laser device can, in particular, comprise at least one semiconductor laser, in particular a diode laser or laser diode. Several similar and / or different laser diodes can also be operated together in groups, e.g., as a stack (laser stack) or matrix.

[0019] A phosphor can be understood as any substance, especially a solid, that enables wavelength conversion. Wavelength conversion can be based, for example, on fluorescence or phosphorescence.

[0020] The phosphor areas can be the same or different on the front and back of the carrier substrate of the phosphor wheel - depending on the application.

[0021] Preferably, the phosphors on the front and rear sides as well as the at least one transmissive region of the carrier substrate, which is intended for the irradiation of the rear side, are formed as circular ring-shaped segments.

[0022] The circular segments on both sides can also be arranged at different radii on the front and back. This provides more flexibility for the different design of the fluorescent segments. If the circular segments on both sides are arranged at the same radius, the fluorescent segments on both sides are necessarily the same size with the same angular extension.

[0023] To ensure that the excitation radiation can be directed not only to the front but also to the back of the phosphor wheel, the carrier substrate has a first region that is permeable to the excitation radiation. This allows the excitation radiation striking the front to be redirected through the permeable region and onto the back. In this way, the excitation radiation is radiated sequentially onto the front and back of the phosphor wheel. With the help of phosphors applied to both sides of the phosphor wheel, for example in the form of phosphor segments, this results in both a front-side conversion light path and a back-side conversion light path.

[0024] By dividing the fluorescent wheel into segments accordingly, i.e. at least one transparent segment and at least one fluorescent segment on each side, three different light paths can be traversed in a specific temporal sequence: ◯ a path for the excitation light, which alternately irradiates the front and back sides (front and back excitation light path), ◯ a path for the light converted by a phosphor segment on the front side (front conversion light path), ◯ a path for the light converted by a phosphor segment on the back (back conversion light path). ◯ Optional: an additional path for the excitation radiation, provided that this excitation radiation is blue light and the phosphor wheel has two additional transmissive segments (wrap-around light path).

[0025] Preferably, one or both conversion light paths have a static filter (wavelength or polarization filter). Due to the two conversion light paths, a temporally sequential sequence of differently filtered conversion light is possible without a filter wheel, but instead with at least one static filter.

[0026] For example, a green phosphor can be provided on the front side and a yellow phosphor on the back of the phosphor wheel. The broadband conversion spectrum of the yellow phosphor is centered in the yellow spectral range, but also exhibits wing-like peripheral regions extending into the red spectral range. Therefore, for example, the yellow light converted on the back side can be filtered to red light using a suitable filter. The green light converted on the front side can be filtered in various ways or remain spectrally unfiltered.

[0027] In another embodiment, a yellow phosphor can be provided on the front side and a green and a red phosphor on the back of the phosphor wheel. With the help of a suitably designed band-stop filter, which filters out the longer wavelengths of the green conversion light and the shorter wavelengths of the red conversion light, the spectrum of the rear conversion light can be modified to expand the resulting color space.

[0028] The advantage of the inventive solution over the prior art is, among other things, that no second wheel (=filter wheel) needs to be synchronized with the phosphor wheel. Furthermore, static filters can be arranged at locations where the light is almost parallel. This allows steep filter edges to be implemented using dichroic layers. Furthermore, the inventive solution with one or more static filters eliminates the spoke effect caused by a filter wheel (the passage of the excitation beam through the rotating transition from one color filter segment to the other).

[0029] The first or each region in the phosphor wheel that is transparent to the excitation radiation can be formed by an opening in the carrier substrate, for example, in the form of a perforated circular ring segment. The opening can also be filled with transparent or translucent material.

[0030] While the first region permeable to the excitation radiation is provided for irradiating a phosphor segment on the back of the phosphor wheel, the carrier substrate can optionally have a second and third region permeable to the excitation radiation, which are provided for a wrap-around light path for the excitation light, which in this case is preferably blue. The two additional permeable regions are designed such that the excitation radiation irradiating the front of the carrier substrate can shine through the second permeable region of the carrier substrate. With the aid of the optical device, the excitation radiation shining through is deflected to the back of the phosphor wheel and thus shines through the third permeable region of the carrier substrate, i.e. reaches the front of the phosphor wheel again. There it can be guided to the light output or output by means of suitable optical elements.with the conversion light paths on both sides. For further details, please refer to the examples.

[0031] The first and / or a further or each transmissive region may also be provided with a color or polarization filter or a polarization-rotating optical element.

[0032] The optical device can be designed such that the conversion light emitted by a phosphor on the back of the carrier substrate (= "back-side conversion light") radiates back through the first transmissive region of the phosphor wheel. In this case, the back-side conversion light travels back along the light path of the excitation radiation via the same optical elements of the optical device in the opposite direction. In this way, the back-side conversion light can be redirected by the optical device through the first transmissive region onto the front of the phosphor wheel and thus coupled into the front-side conversion light path, i.e., chronologically sequential to the front-side conversion light. As a result, the front-side conversion light path is used alternately by the front-side and back-side conversion light.

[0033] Alternatively, the optical device can comprise a dichroic mirror that diverts the conversion light emitted by a phosphor on the back of the carrier substrate of the phosphor wheel from the counter-propagating excitation radiation. For this purpose, the dichroic mirror is designed to reflect the excitation radiation and transmit the counter-propagating back-side conversion light. In this case, the back-side conversion light no longer needs to be redirected through the first transmissive region of the carrier substrate.

[0034] The optical device preferably comprises at least one optical element which acts as a deflecting mirror for the excitation radiation and the rear conversion light.

[0035] A filter element can be arranged in the beam path of the conversion light emitted from the back of the carrier substrate, i.e., in the back conversion light path. The filter element can be designed as a wavelength- and / or polarization-dependent filter.

[0036] To couple out the front-side conversion light, an optical element can be arranged in the beam path between the excitation radiation source and the front side of the carrier substrate of the phosphor wheel, i.e., in the front-side conversion light path. This optical element branches off the conversion light in a direction different from the opposite excitation radiation direction. For this purpose, the optical element can be designed as a dichroic mirror that transmits the excitation radiation and reflects the conversion light, or vice versa. The spectrum of the conversion light can also be modified as needed by this dichroic mirror.

[0037] In addition, an optical integrator can be provided for feeding and spatially homogenizing the conversion light and optionally also the excitation light.

[0038] The illumination device described above can be used, for example, in a projector. For this purpose, the sequentially generated light is typically directed into an optical integrator and from there onto an imaging unit. For the sequential generation of the color partial images, the imaging unit is synchronized with the phosphor wheel. The color partial images are projected onto a projection surface using projection optics.

[0039] A method for operating the lighting device according to the invention comprises the following method steps: • Front conversion phase: irradiating the at least one phosphor arranged on the front side of the carrier substrate of the rotating phosphor wheel with the excitation radiation, • Rear conversion phase: Illumination of the first transmissive segment from the front with the excitation radiation and deflection of the transmitted excitation radiation onto the at least one phosphor arranged on the rear side of the carrier substrate of the rotating phosphor wheel.

[0040] If blue light is used as excitation radiation, the following process step can be added: • Wrap-around phase: The excitation radiation passes through the second transparent segment from the front, the transmitted excitation radiation is deflected onto the third transparent segment, and the third transparent segment is passed through from the back with the deflected excitation radiation.

[0041] The front and back conversion light generated sequentially by the rotating phosphor wheel and optionally additionally the blue excitation light are combined in a common direction via optical elements, such as deflection and / or dichroic mirrors and lenses, and directed, for example, into an optical integrator.

[0042] Further advantages, features and details of the invention, both with regard to the device and the method aspects, emerge from the claims, the following description of preferred embodiments and from the drawings. Short description of the drawings

[0043] The invention will be explained in more detail below using exemplary embodiments. The figures show: Fig. 1 a lighting device with a double-sided fluorescent wheel according to a first embodiment, Fig. 2a the front of the fluorescent wheel according to Fig. 1, Fig. 2b the back of the fluorescent wheel according to Fig. 1, Fig. 3 the lighting device according to Fig. 1 with optical lenses, Fig. 4 a lighting device with a double-sided fluorescent wheel according to a second embodiment, Fig. 5 a lighting device with a double-sided fluorescent wheel in a variant adapted for 3D projection, Fig. 6a the front of the fluorescent wheel according to Fig. 5, Fig. 6b the back of the fluorescent wheel according to Fig. 5. Preferred embodiment of the invention

[0044] For the sake of simplicity, identical or similar features may be designated by the same reference symbols below.

[0045] Fig. Figure 1 shows a schematic representation of a lighting device 100 according to a first embodiment of the invention. For the sake of clarity, the optical lenses for beam shaping that are common in such devices are shown in Fig. 1 not shown (but see Fig. 3). Furthermore, the optical beam paths are only indicated schematically.

[0046] The illumination device 100 has a laser device 101 as the excitation radiation source. The laser device 101 is designed to emit laser light in the blue spectral range, since, on the one hand, this represents a suitable excitation wavelength for most phosphors. On the other hand, this enables the use of the unconverted blue laser light (wrap-around light path) as a blue light channel (B), for example, for an RGB projection unit. The emission wavelength of the blue laser radiation 1 is preferably in the range of, for example, approximately 400-470 nm. The excitation radiation source 101 can be designed, for example, as a laser diode matrix having a plurality of laser diodes.

[0047] The blue laser light 1 (=excitation light) is - after passing through a dichroic mirror 10 - by means of an optical lens system (in Fig. 1) is focused onto a phosphor wheel 102. The phosphor wheel 102 has a circular disk-shaped carrier substrate 7 with a rotational axis 8 arranged perpendicularly and centrally thereto. The carrier substrate 7 is made of metal, for example, in order to effectively dissipate the heat loss from the phosphor conversion.

[0048] In the following, reference will also be made to the Fig. 2a, Fig. 2b, which show the phosphor wheel 102 in a schematic representation, namely the front side 5 and the back side 6. The flat front side 5 of the carrier substrate 7 of the phosphor wheel 102, which is irradiated by the incident laser light 1 during the front-side conversion phase, has an annular region divided into six annular segments 5a-5e and 5a'. The three segments 5a, 5a', and 5b are transparent to the blue laser light 1, specifically in the form of through-openings in the metallic carrier substrate. The segments 5c-5e are coated with phosphor, for example, for the sequential wavelength conversion of the blue laser light 1 into yellow (using yellow phosphor), green (using green phosphor), or cyan light (using cyan phosphor). Depending on the desired color light sequence, the phosphor segments 5c to 5e can have the same phosphor or different ones.The flat rear side 6 of the carrier substrate 7 of the phosphor wheel 102, which is irradiated by the laser light 1 during the rear conversion phase, also has an annular region divided into six annular segments 6a-6e and 6a'. The three segments 6a, 6a', and 6b (=rear side of the through-openings) are the counterparts to the three segments 5a, 5a', and 5b of the front side and are therefore necessarily also transparent to the blue laser light 1. Segment 6c, for example, is coated with a yellow phosphor. Depending on the desired color light sequence, the phosphor segments 6d and 6e can have the same phosphor or different ones.

[0049] During operation, the blue laser light 1 strikes a phosphor segment 5c, 5d, 5e on the front side 5 of the phosphor wheel 102 during a corresponding rotation phase of the rotating phosphor wheel 102. The converted light 2, wavelength-converted backscattered by the currently irradiated phosphor segment of the front side, is reflected by the dichroic mirror 10 out of the laser light path 1 toward the light output L for further application-specific use. The spectrum of the converted light 2 can be specifically influenced by designing the spectral properties of the dichroic mirror 10, thus changing the light color as needed.

[0050] Alternatively, the dichroic mirror 10 can be designed to reflect the blue laser light 1 and transmit the converted light 2. In this case, the laser light source 101 and the light output L must be swapped, and the tilt angle of the dichroic mirror 10 must be adjusted (not shown).

[0051] If the blue laser light 1 strikes the transparent segment 5b (or 6b) during a corresponding rotation phase of the rotating phosphor wheel 102, it is deflected onto the back of the phosphor wheel via two mirrors 11, 12. During this back conversion phase, the deflected blue laser light 1 strikes the rotating back phosphor segments 6c-6e. The converted light 3 (back conversion light) scattered back by the back phosphor segments 6c-6e travels the same light path back to the dichroic mirror 10, where it is reflected out of the laser light path 1 toward the light output L.

[0052] Preferably, a wavelength filter 9 is arranged in the rear light path in order to modify the spectrum of the back-converted light 3 as desired, i.e., to obtain light 4 with a changed light color after passing through the wavelength filter 9. In particular, in this way, for example, the broadband conversion light converted by the yellow phosphor segment 6c can be filtered to red light with the aid of the wavelength filter 9 (although the conversion light spectrum of the yellow phosphor has its focus in the yellow spectral range, it has wing-like edge regions on both sides into the green and red spectral ranges, respectively). As already mentioned for the light path for the front-converted light 2, the spectrum of the back-converted and optionally filtered light 4 can additionally be further modified as desired by the suitably designed spectral properties of the dichroic mirror 10.

[0053] If the blue laser light 1 strikes the transparent segment 5a on the front side during a corresponding rotation phase of the rotating phosphor wheel 102 or the transparent segment 5a' after a 180° rotation of the phosphor wheel 102, it shines through there, is deflected via the two mirrors 11, 12 onto the other transparent segment 6a' (or 6a) on the back side and shines through this again onto the front side of the phosphor wheel 102. The blue laser light 1, which once again shines through the phosphor wheel 102, is deflected back via a further mirror 13 onto the dichroic mirror 10 and passes through this to the light output L ("wrap-around" light path for the blue laser light 1).

[0054] Fig. 3 shows the already in Fig. 1 shows a simplified device 100, here with optical lenses for beam shaping. The laser device 101 is designed, for example, as an 8 by 4 matrix of blue laser diodes 103 including primary lenses. Each of the 8 rows of 4 laser diodes is assigned a step mirror element 104, which deflects the blue laser light by 90° toward the phosphor wheel 102. Furthermore, the cross-sectional area of ​​the laser beam is compressed in this way. A downstream first optical lens group 201 further compresses and collimates the laser beam.

[0055] Immediately after the first lens group 201, a homogenizer 202 is arranged in order to achieve the most uniform possible power density distribution of the blue laser light 1 on the phosphor segments of the phosphor wheel 102.

[0056] The collimated and homogenized laser light is focused onto the front side of the phosphor wheel 102 using a focusing lens group 203 (the laser focus does not necessarily have to be exactly on the front side). This focusing lens group 203 also collects and collimates the backscattered light converted by the phosphor segments 5c-5e on the front side of the phosphor wheel 102 (front-side conversion light), which is coupled out by the dichroic mirror 10 to the light output L. A focusing lens 204 finally focuses the coupled-out light into a rod-shaped optical integrator 205.

[0057] The laser light focused from the front side of the phosphor wheel 102 through a translucent segment is collimated by another lens group 206. This lens group 206 also serves to focus the converted light (back-conversion light) backscattered from a phosphor segment on the back side of the phosphor wheel 102 through a translucent segment. The further light path of the back-converted light then corresponds to that of the front-converted light.

[0058] Another focusing lens group 207 focuses the laser light collimated by the other lens group 206 onto the back of the phosphor wheel 102. This other focusing lens group 207 also serves—similar to the focusing lens group 203 on the front side—to collect and collimate the returning light converted by the phosphor segments on the back of the phosphor wheel 102. Finally, the other focusing lens group 207 also serves to focus the blue laser light from the back through a translucent segment of the phosphor wheel 102. This transmitted blue laser light is collimated by another lens system 208 and returned to the dichroic mirror 10 via a deflection mirror 13 (a "wrap-around" light path).

[0059] The wrap-around light path can alternatively be guided around the “upper” end of the phosphor wheel (not shown; therefore the following explanation with reference to Fig. 1). Polarized laser light is provided to split the laser light path into one for irradiating the back and one for irradiating the phosphor wheel. Furthermore, the deflection mirror 12 for the laser light is designed to be polarization-dependent, for example, reflective for S-polarized light and transmissive for P-polarized light. For the temporally sequential change of polarization, a translucent segment in the phosphor wheel is provided with a λ / 2 filter. S-polarized blue laser light is then first converted into P-polarized light in the λ / 2 filter segment and then transmitted by the mirror 12. The P-polarized blue light is guided around the phosphor wheel 102 by an additional deflection mirror and directed onto the dichroic mirror 10 via an offset deflection mirror 13.

[0060] The mirrors 11 and 12 on the back of the phosphor wheel 102 and the wavelength filter 9 can alternatively be replaced by a dichroic coated elliptical reflector and / or a suitable dichroic coated freeform reflector (not shown).

[0061] The segments transparent to the blue laser light can also be partially equipped with color or polarization filters or polarization-rotating optical elements. This allows both the blue laser light and the converted light to be further manipulated.

[0062] Fig. Figure 4 shows a schematic representation of a lighting device 110 according to a second embodiment of the invention. Here, the light path for the back-converted light 3, 4 is different from that shown in Fig. 1. The mirror 11' is now designed as a (second) dichroic mirror (high reflection (HR) 445-470 nm and anti-reflection (AR) 480-750 nm), which reflects the blue laser light but transmits the converted light 4 (filtered by the wavelength filter 9). The back-converted light 4 does not pass through the phosphor wheel 102 in this variant. Rather, the back-converted light 4 is deflected away from the laser light path 1 via the second dichroic mirror 11'. A deflecting mirror 14 and a further (third) dichroic mirror 15 are provided for the spatial combination of the converted light originating from the front and back. The deflection mirror 14 deflects the front-converted light 2 and the blue laser light 1 from the wrap-around light path to the reflection side of the third dichroic mirror 15.The back-converted light 4 is combined with the blue laser light 1 and the front-converted light 2 via the transmission side of the third dichroic mirror 15. Within the spectral ranges defined by the third dichroic mirror 15, the front-converted light 2 and the back-converted light 4 can be spectrally filtered independently of one another. The spectral filtering of the back-converted light 4 can be achieved by the wavelength filter 9 and / or the spectral properties of the second dichroic mirror 11'.

[0063] The illumination device 110 is suitable, for example, for generating a temporal sequence of red and green converted light using a phosphor wheel. For this purpose, a green phosphor can be provided on the front side of the phosphor wheel and a yellow phosphor on the back side. The green light converted on the front side can be spectrally modified as needed by the first dichroic mirror 10. The converted yellow light originating from the back side is filtered into red light by the second dichroic mirror 11'.

[0064] Furthermore, the illumination device 110 can be used in particular for 3D projection displays. For this purpose, the user requires glasses that are matched to the spectral properties or polarization properties of the exciting laser light and the filters or dichroic mirrors.

[0065] When utilizing special properties of light (wavelength, polarization), complementary filters are inserted into the 3D glasses for the left and right partial images, i.e., for the left and right eyes. Complementary here means that the image content emitted by the 3D projector can be decoded for the right and left eyes by the respective glasses filters, creating a 3D effect for the viewer. Different methods can be used for this, such as interference filtering (e.g., Dolby® 3D), shutter glasses (e.g., XPAND 3D), or polarizing filters (e.g., RealD 3D).

[0066] Fig. 5 shows a schematic representation of a lighting device 120, which essentially corresponds to the one shown in Fig. 4, but is specifically adapted to the previously mentioned interference filter method for 3D projection.

[0067] Among other things, two different wavelengths are used for the blue laser light. For this purpose, the excitation radiation source 121 comprises two laser types that emit laser radiation at two different wavelengths, e.g., 450 nm and 465 nm. The two laser types are electronically switched sequentially. Since the laser light is narrow-band enough, no wavelength filters are required. The first dichroic mirror 10 is designed to be transparent to the laser light (AR 445 nm - 470 nm). The filters of the 3D glasses only transmit the wavelength intended for the left and right eyes, respectively.

[0068] In addition, the front-converted light is adapted to a first filter characteristic of 3D glasses (e.g., for the right eye). For this purpose, the first dichroic mirror 10 is designed to be reflective with the first filter characteristic, i.e., to match the first filter of the 3D glasses. The light 2a converted on the front side 5 of the filter wheel 102 is thus reflected by the first dichroic mirror 10 according to the first filter characteristic. The light 2b thus filtered and converted on the front side passes via the deflection mirror 14 to the third dichroic mirror 15, which is also designed to be reflective according to the first filter characteristic and reflects the filtered, front-converted light 2b without any further spectral change.

[0069] The back-converted light is finally adapted to a second filter characteristic of a pair of 3D glasses (e.g., for the left eye). This second filter characteristic is therefore complementary to the first filter characteristic in the sense explained above. For this purpose, the wavelength filter 9 is provided with the same coating as the first and third dichroic mirrors 10 and 15, respectively, and is arranged at an angle of 45° in the light path of the back-converted light 3. As a result, the wavelength filter 9 reflects a portion of the back-converted light 3 according to the first filter characteristic, which is absorbed by an absorber 16. The portion of the back-converted light 4 corresponding to the inverted spectrum, however, is transmitted by the wavelength filter 9, matching the second filter of the 3D glasses.The back-converted light 4 thus filtered according to the second filter characteristic passes the second dichroic mirror 11 (HR 445 - 470 nm and AR 480 - 750 nm) and is spatially combined via the third dichroic mirror 15 (transmitting for inverted spectrum, according to the second filter characteristic) with the blue laser light path (with two laser wavelengths) and the front-converted light 2b filtered according to the first filter characteristic.

[0070] Alternatively, it is also possible to omit the wavelength filter 9, to design the first dichroic mirror 10 as highly reflective (HR) for 470 nm–700 nm, and to use only the third dichroic mirror 15 as an element that imposes the filter characteristics. All the intended light colors then appear sequentially on both sides of the dichroic mirror 15, filtered with the corresponding filter characteristics. With the help of two projection devices (two DMDs, LCD, and optics), one on each output side of the dichroic mirror 15, it is possible to ensure that all the light is used for projection.

[0071] Polarization filters can also be used to distinguish between the two channels required for a 3D projection.

[0072] The Fig. 6a, b show a for the lighting device 120 of Fig.5 and the double filtering provided there (both the front and rear converted light is spectrally filtered) suitable phosphor wheel 5 in schematic front and rear view.

[0073] The front and back sides are each divided into six circular segments 5a-5e and 5a', and 6a-6e and 6a', respectively. The three segments 5a, 5a' and 5b, and 6a, 6a' and 6b, are transparent to the blue laser light 1. Segments 5c-5e and 6c-6e are coated with green, yellow, and red phosphors. Preferably, the phosphor distributions on the front and back sides are the same or, at most, slightly different to compensate for any differences in losses.

[0074] In the embodiments explained above, the angular positions of the mirrors are shown only as an example at 45° to the incident light beam and can also be selected differently.

[0075] The invention proposes an illumination device (100) with an excitation radiation source (101) and a double-sided phosphor wheel (102). At least one phosphor is provided on each side of the double-sided phosphor wheel (102), i.e., on both the front side (5) and the opposite rear side (6). The phosphors on both sides are excited sequentially in time. For this purpose, at least one transmissive region is provided in the rotating phosphor wheel, through which the excitation radiation can shine and be directed onto the phosphor on the rear side (6) by means of an optical system (11, 12).

Claims

[1] Lighting device (100; 110; 120), comprising a. an excitation radiation source (101; 121) for the emission of excitation radiation (1), b. a phosphor wheel (102) comprising a carrier substrate (7) with a front side (5) and a back side (6), wherein the phosphor wheel (102) is arranged in a beam path of the excitation radiation (1) such that the excitation radiation (1) can reach the front side (5), and wherein the phosphor wheel (102) further comprises the following: i. at least one phosphor arranged on the front side (5) for irradiation with excitation radiation (1) and wavelength conversion of the excitation radiation into wavelength-converted radiation (2), ii. at least one phosphor arranged on the rear side (6) for irradiation with excitation radiation (1) and wavelength conversion of the excitation radiation into wavelength-converted radiation (3), iii. a first region (5b, 6b) which is permeable to the excitation radiation (1) and is designed to allow the excitation radiation to reach the rear side (6), c. and wherein the illumination device (100; 110; 120) further comprises an optical device (11, 12) which is designed to redirect the excitation radiation (1) irradiating the front side (5) of the carrier substrate (7) and radiating through its first transmissive region (5b, 6b) onto the rear side (6) of the carrier substrate (7); wherein the carrier substrate (7) comprises a second and a third region (5a, 6a; 5a', 6a') permeable to the excitation radiation, and the illumination device (100) is designed such that the excitation radiation (1) irradiating the front side (5) of the carrier substrate (7) can radiate through the second permeable region (5a, 6a), is deflected by means of the optical device (11, 12) to the rear side (6) of the carrier substrate (7), and radiates through the third permeable region (6a, 6a'); and wherein the first transmissive region (5b, 6b) and / or a further or each transmissive region (5a, 6a; 5a', 6a') is provided with a color or polarization filter or a polarization-rotating optical element. [2] Lighting device (100) according to claim 1, wherein the optical device (11, 12) is designed such that the wavelength-converted radiation (3) emitted by a phosphor on the back side (6) of the carrier substrate (7) radiates back through the first transmissive region (5b, 6b) of the phosphor wheel (102) against the excitation radiation (1). [3] Lighting device (110; 120) according to claim 1, wherein the optical device comprises a dichroic mirror (11') which transmits the wavelength-converted radiation (3) emitted by a phosphor on the back side (6) of the carrier substrate (7). [4] Lighting device (100; 110; 120) according to one of the preceding claims, wherein the optical device comprises at least one optical element which acts as a deflecting mirror (11; 12) for the excitation radiation (1) and the wavelength-converted radiation (3) emitted by a phosphor on the back side (6) of the carrier substrate (7). [5] Lighting device (100; 110; 120) according to one of the preceding claims, with a filter element (9) arranged in the beam path of the wavelength-converted radiation emitted from the rear side (6) of the carrier substrate (7). [6] Lighting device (100; 110; 120) according to claim 5, wherein the filter element (9) is designed as a wavelength- and / or polarization-dependent filter. [7] Lighting device (100; 110; 120) according to one of the preceding claims, with an optical element (10) arranged in the beam path between the excitation radiation source (101; 121) and the front side (5) of the carrier substrate (7) of the phosphor wheel (102), which is designed to transmit the excitation radiation (1) and to reflect the wavelength-converted radiation (2, 4) or vice versa. [8] Lighting device (100) according to one of the preceding claims, wherein the excitation radiation source (101) comprises a laser diode matrix (103). [9] Lighting device (100; 110; 120) according to one of the preceding claims, wherein the first or each transmissive region (5a, 6a; 5a', 6a', 5b, 6b) is formed by an opening in the carrier substrate (7). [10] Lighting device according to claim 9, wherein the opening is filled with transparent or translucent material. [11] Method for operating a lighting device (100; 110; 120) according to one of the preceding claims, comprising the following method steps: • Front-side conversion phase: irradiating the at least one phosphor arranged on the front side (5) of the carrier substrate (7) of the rotating phosphor wheel (102) with the excitation radiation (1), • Rear conversion phase: radiating the first transmissive segment (5b, 6b) from the front side (5) with the excitation radiation (1) and deflecting the transmitted excitation radiation (1) onto the at least one phosphor arranged on the rear side (6) of the carrier substrate (7) of the rotating phosphor wheel (102). [12] Method according to claim 11 with the following additional method step: • Wrap-around phase: radiating the second transmissive segment (5a, 6a) from the front side (5) with the excitation radiation (1), deflecting the transmitted excitation radiation (1) onto the third transmissive segment (5a', 6a') and radiating the third transmissive segment from the rear side (6) with the deflected excitation radiation. [13] Use of a lighting device according to one of claims 1 to 10 in a projector for data or video projection.

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