EP2526700A1

EP2526700A1 - Light emitting device and method for creating a multi-colored light beam

Info

Publication number: EP2526700A1
Application number: EP10732935A
Authority: EP
Inventors: Jan Oliver Drumm
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2010-07-12
Filing date: 2010-07-12
Publication date: 2012-11-28
Also published as: WO2012007027A1

Abstract

The light emitting device (1) comprises a radiation source (6) and at least one switch (8, 11), wherein the at least one switch (8, 11) is adapted to direct an incoming radiation beam (b) from the radiation source (6) towards at least two light channels (9, 12, 13); and wherein at least one of the light channels (9, 12; 22) comprises at least one phosphor for at least partially converting a wavelength of the incoming radiation beam (b; uv). The method is provided for creating a multi-colored light beam (r, g, b) from a radiation beam (b) from the radiation source (6), wherein the method at least comprises directing the radiation beam (b) from the radiation source (6) towards at least two light channels (9, 12, 13) wherein at least one of the light channels (9, 12) at least partially converts a wavelength of the radiation beam (b) from the radiation source (6) by means of at least one phosphor.

Description

Light emitting device and method for creating a multi-colored light beam.

The invention relates to a light emitting device, in particular a laser pumped light emitting device. The invention further relates to a method for creating a multicolored light beam, in particular from a laser light beam.

There are known light emitting devices that create a sequentially multi-colored light beam from a laser light beam by illuminating a rotating disc by means of a laser. The rotating disc comprises several light-transmissive sectors that are sequentially illuminated by the laser. The sectors may comprise a wave-length converting substance ('phosphor') so that a laser beam illuminating such a sector creates a light beam with a different wave length or color. When the rotating disc rotates, it creates a sequence of light beams with different colors. If the rotation is fast enough, the sequence is perceived by an observer as a mixed light that is composed of a sequence of light beams within a certain time period or cycle. In other words, the light beams of different colors are integrated by an observer over a time period that corresponds to a resolution of the human eye. By choosing the kind of phosphors, the color of the different light beams over a revolution of the rotating disc can be determined. A desired chromaticity coordinate of the mixed light (as defined by a position within a CIE diagram, for example) is preset by choosing corresponding lengths or relative lengths of the sectors. This results in a fixed 'on time' color ratio. A variation of the chromaticity coordinate can (apart from changing the rotating disc which is often not practically possible) only be achieved by reducing the intensity of the laser light ('dimming'), e.g. by reducing the laser power, while illuminating certain sectors of the rotating disc. But as a consequence, a maximum brightness of the mixed light can only be achieved for the pre-determined chromaticity coordinate that does not need the dimming.

It is the object of the present invention to at least partially overcome the disadvantages of the prior art and to particularly provide a multi-colored light beam with a chromaticity coordinate that may be varied without a significant loss of brightness.

The object is achieved according to the features of the independent claims. Preferred embodiments can be derived, inter alia, from the dependent claims.

The object is achieved by a light emitting device, comprising a radiation source and at least one switch; wherein the at least one switch is adapted to (alternately or simultaneously) direct an incoming radiation beam from the radiation source towards at least two light channels; and wherein at least one of the light channels comprises at least one phosphor for at least partially converting a wavelength of the incoming radiation beam from the radiation source.

Thus, the radiation source can create individual light beams having an individual wavelength or wavelength spectrum by sending the original radiation beam through the individual light channels. The resulting group of the individual light beams can create a light beam that is or is perceived as a mixed light having a certain chromaticity coordinate. Since the activating or illuminating the light channels is not structurally fixed but can be varied over a wide range by simply switching the at least one switch accordingly, the incoming radiation beam from the radiation source does not need to be dimmed to change the chromaticity coordinate. Rather, the radiation source may be operated at a substantially constant (in particular maximum) power or brightness for all light channels and thus for all available color components. This light emitting device also allows for a robust design.

In the context of the present invention, a 'phosphor' may be any substance that converts a wavelength of an impinging radiation beam by means of luminescence, in particular photo- luminescence and/or radio-luminescence. The photo- luminescence may in particular comprise phosphorescence and/or fluorescence.

The at least one phosphor may generally comprise a wavelength-downconverting and/or a wavelength-upconverting phosphor . The phosphor or phosphors may be arranged in a light transmissive configuration or in a light reflective configuration .

The kind of the radiation source is not limited. The radiation source may emit electromagnetic (e.g. light) or corpuscular radiation (e.g. ions or electrons). If the radiation source emits light, the light may comprise ultra^¬ violet (UV) light, visible light and/or infrared (IR) light. The radiation source may be a lamp (e.g. a vacuum-UV lamp, another UV lamp, a lamp emitting visible light and/or an IR lamp) , a light emitting diode (LED), including a superluminescent LED, a laser diode, a gas laser, a non- solid state solid laser, or a solid state laser (SSL) . The use of a solid state laser and/or a laser diode is particularly preferred.

The radiation source may be a small-banded light source (comprising a bandwidth of only several nm) or a broad-banded radiation source with an appropriate filter. The radiation source may generally comprise a single solid state emitter or multiple solid state emitters that can combine their individual output light beams to form a single output beam of the radiation source. This combination of the individual output light beams of the multiple solid state emitters can be achieved spatially, spectrally, by polarization, or by any combination thereof. In case of multiple solid state emitters, the solid state emitters are advantageously driven by the same control signal or control pulse.

Generally, the radiation source may comprise, inter alia, a stack design, a bar design, or a combination thereof, in particular a laser stack design and/or a laser bar design. The light guidance can be effected using a fiber, a fiber bundle, a waveguide structure and/or one or more optical elements, like lenses etc. The output power of the radiation source is preferably in the range of watts, in particular 1 to 20 watts. The radiation source may for example comprise: - Multi-watt optical output laser bars from 'broad area' or 'tapered' structures, as e.g. available from OSRAM, Germany, as SPL BX81-2S laser diodes;

- Near-IR (NIR) Laser systems built from stacked laser bars with spatial interleaving, polarization beam combining and wavelength combining, as described in: Kohler et. al . ,

Dilas GmbH, High-brightness high-power kW-system with tapered diode bars, Photonics West 2005;

- Coupling a laser stack as described in: Kohler et. al . , Dilas GmbH, 11 kW direct diode laser system with homogenized 55x20mm² Top-Hat intensity distribution,

Photonics West 2007;

- Coupling a laser stack into 50 μιτι, 100 μιτι, 200 μιτι, 400 μιτι, 600 μιη or 800 μιη multi-mode fibers, as described in: Kohler et. al . , Dilas GmbH, High-brightness high-power kW- system with tapered diode bars, Photonics West 2005;

- A laser bar with 415 nm emitters, as described in: Kohler et . al., Dilas GmbH, High-power diode laser modules from 410nm-2200nm, Photonics West 2010, Proc. of SPIE, Vol. 7583;

- Laser bars in fiber bundles, as described in: Niu et. al . , Fiber optic coupling of high power laser diode array, Chinese Optics Letters, Vol. 5, S148-S150 (2007);

- A 400 nm to 405 nm laser diode having an output power of 600 mW, as disclosed in a datasheet for a violet laser diode NDV7112 of Nichia Corp., Japan;

- A 440 nm to 455 nm laser diode having an output power of 500 mW, as disclosed in a datasheet for a blue laser diode

NDB7112E of Nichia Corp., Japan; and/or

- A 450 nm single-mode single emitter having an output power of 50mW, as disclosed in a datasheet for a blue laser PL T4 NSB of Osram, Germany.

The kind of switch is not limited and may for example comprise :

- A waveguide coupler for single mode waveguides which allows for very short switching times (> 10 MHz) ;

- A Pockels cell which also allows for very short switching times (< 1 μ3) ;

- An electro-optical modulator which as well allows for very short switching times (< 1 μ3) ;

- An acusto-optical modulator which allows for very short switching times (< 1 μ3) and a spatial channel switching;

- A piezo fiber switch which in particular allows for switching with multi-mode fibers;

- A p i e z o-mechanical tilting switch which allows large mirrors with high reflectivities;

- An analog MEMS (MicroElectroMechanical System) mirror, e.g. a dual-axis pointing mirror TALP1000B from Texas Instruments, USA, which allows for a spatial channel separation and a large mirror area, and has low requirements regarding a beam divergence and a beam spectrum; and/or

- a digital MEMS (Microelectromechanical system) tilting switch, e.g. arranged in a DMD mirror (e.g. DLP1700 from Texas Instruments) which allows for short switching times (-10 ]is) , a spatial channel separation, and a large mirror area) . At the same time it has low requirements regarding a beam divergence and a beam spectrum.

One switch may direct the incoming radiation beam towards two or more directions.

It is one embodiment that the at least one switch is adapted to alternately or sequentially direct an incoming radiation beam from the radiation source towards the at least two light channels. The resulting sequence of the individual light beams can create a (sequentially multi-colored) light beam that is perceived as a mixed light having a certain chromaticity coordinate. Since the time and time ratio for alternately or sequentially activating or illuminating the light channels is not fixed but can be varied over a wide range by simply switching the at least one switch accordingly, the incoming radiation beam from the laser source does not need to be dimmed to change the chromaticity coordinate .

It is another embodiment that the at least one switch is adapted to switch between light channels in an adjustable time pattern. In other words, the time period the incoming radiation beam (incoming from the radiation source) is directed towards one certain light channel can be varied or adjusted freely such that a time pattern (e.g. a sequence of time periods for sequentially activated light channels) can be set. For example, the same time pattern may be used for a prolonged period of operation compassing several repetitions of a sequence of activations of all light channels (several ' cycles ' ) . It is yet another embodiment that the at least one switch is adapted to simultaneously divide and direct an incoming radiation beam from the radiation source towards the at least two light channels. In other words the at least two light channels are each activated simultaneously by a corresponding fraction [0 ... 1] of the original incoming radiation beam. The resulting group of the individual light beams can create a mixed light that at all times has a certain chromaticity coordinate. Since a fraction ratio of the different light channels is not fixed but can be varied over a wide range by simply switching the at least one switch accordingly, the incoming radiation beam from the laser source does not need to be dimmed to change the chromaticity coordinate. Rather, the radiation source may be operated at a substantially constant (in particular maximum) power or brightness for all light channels and thus for all available color components. And there is the advantage that a switching operation of the switches is limited to a shift or variation of the chromaticity co-ordinate, thus improving an efficiency of the light emitting device.

It is a special embodiment that the at least one switch is adapted to adjust the fractions of the incoming radiation beam directed towards the light channels. Thus, the at least one switch is adapted to change a fraction ratio (regarding brightness, intensity and/or luminous flux etc.) of the re^¬ directed at least two outgoing light beams.

It is also an embodiment that the radiation source is dimmable (i.e. can be operated with a reduced output power) . At least for one cycle, the different light channels should preferably all be illuminated or activated by an incoming laser beam of the same power (dimmed or not) to facilitate control of the light emitting device, and its chromaticity coordinate in particular. However, it may be possible to dim the radiation beam of and/or at the radiation source for one or more particular light channels.

It is another embodiment that one of the light channels is adapted to retain a wavelength of the incoming radiation beam unchanged. Thus, a color of the original radiation beam (e.g. a blue laser light beam) can directly be used to define the chromaticity coordinate. In other words, the original (in particular solid state) radiation beam is used as one light component of the mixed light. This gives the advantage that the light emitting device can be implemented in a particular cost-effective manner.

It is yet another embodiment that all light channels are adapted to at least partially convert a wavelength of the incoming radiation beam. This is particularly advantageous if the original radiation beam created by the radiation source does not constitute a desired light component for the mixed light, e.g. if using an ultraviolet (UV) or an infrared (IR) laser.

It is a particularly advantageous embodiment that the light channels and/or the at least one phosphor which are adapted to at least partially convert a wavelength of the incoming radiation beam are adapted to substantially completely (with a conversion rate of at least about 80%, in particular at least about 90%, in particular at least 95%) convert a wavelength of the incoming radiation beam. This facilitates a determination of the chromaticity coordinate for a certain time pattern. Furthermore, the group or area of obtainable chromaticity coordinates (color gamut) is enlarged.

The light emitting device may, after the phosphor(s) , comprise a filter filtering out the wavelength of the incoming radiation beam so as to achieve a pure wave-length converted light beam. This enlarges the obtainable chromaticity coordinates (gamut) of the light emitting device . It is even another embodiment that the light emitting device comprises at least two light channels that are adapted to at least partially convert a wavelength of the incoming radiation beam, and wherein each light channel is adapted to at least partially convert the incoming radiation beam to a different wavelength. This also enlarges the group of obtainable chromaticity coordinates.

It is still another embodiment that

- the light emitting device comprises a first switch and a second switch, wherein

- the first switch is adapted to (alternatingly or simultaneously) direct the incoming radiation beam towards a first light channel and the second switch, and wherein

- the second switch is adapted to (alternatingly or simultaneously) direct the incoming beam towards a second light channel and a third light channel.

Thus, for the alternating or sequential mode of operation, there may be three switching states of the at least one switch and light emitting device (if the switches each are able to direct the incoming radiation beam (incoming towards them) into two distinct channels) :

(i) in a first switching state, the first switch directs the incoming radiation beam from the radiation source towards the first light channel (as a consequence, the first light channel is activated while the other light channels are 'dark');

(ii) in a second switching state, the first switch directs the incoming radiation beam from the radiation source towards the second switch, and the second switch redirects this radiation beam towards the second light channel (as a consequence, the second light channel is activated while the other light channels are dark) ;

(iii) in a third switching state, the first switch directs the incoming radiation beam from the radiation source towards the second switch, and the second switch redirects this radiation beam towards the third light channel (as a consequence, the third light channel is activated while the other light channels are dark) . This tree-like structure can be expanded to incorporate four or more light channels, or be reduced to e.g. comprise only two light channels and one switch. The use of three light channels has the advantage that corresponding three different colors (e.g. red, green, and blue) are often sufficient to set a wide range of chromaticity coordinates.

Alternatively, the three light channels may be activated by a single switch that itself has three switching directions or states, etc.

To enhance an efficiency of the light emitting device, a color portion of the color having the highest dominating wavelength is directed via only one switch. Color portions of a color with a smaller dominant wavelength may be directed via more than one switch. This is equivalent to the embodiment that the first light channel (that is illuminated by the first switch behind the radiation source) emits light having a higher dominant wavelength than light emitted from the second light channel and the third light channel. This embodiment has the advantage that a maximum loss for any of the light beams emitted from the light channels can be limited since for down-converting phosphors (e.g. from blue or UV down to green and red; and blue, green or red, respectively) the Stokes losses are greatest for the greatest difference in the wavelength (e.g. from UV or blue to red), and the switches also cause a certain loss. It is even another embodiment that

- the radiation source comprises at least one blue solid state emitter, that

- one of the light channels (in particular the first channel) is adapted to at least partially convert blue light into red light, and that

- one of the light channels is adapted to at least partially convert blue light into green light. Another one of the light channels retains the wavelength of the incoming blue light beam unchanged. This embodiment allows the composition of the mixed light with RGB light components .

It is still another embodiment that

- the radiation source comprises at least one UV solid state emitter, and wherein

- the light channels are adapted to at least partially convert UV light into red, green, and blue light, respectively .

Therefore, none of the channels is adapted to retain the wavelength of the incoming UV light beam unchanged. This embodiment also allows the composition of the mixed light with RGB light components.

Alternatively, the three light channels may be activated by a single switch that itself has three switching directions or states .

It is another embodiment that the at least one switch comprises at least one digital MEMS switch. In particular, the digital MEMS switch is rather inexpensive and allows switching light from of a high power radiation source with a relatively low loss and a fast switching (switch time for one switching event of less than 200 με, e.g. of about 10 ]is) while allowing for an overall switch time or switch duration of less than about 400 \is (which amounts to less than 5% of a cycle time of 8.33 ms allowing 3D-RGB projection with a image repetition rate of 120 Hz. During the switching time, no following light channel is activated. The radiation source may be switched off or deactivated during the switching time of the at least one switch. It is another embodiment that the radiation beam or beam from the radiation source is directed towards each of the light channels with a image repetition rate of at least 120 Hz. It is yet another embodiment that the radiation source comprises at least one continuous wave (CW) laser emitter or laser light source. This allows a particular high output power. The CW laser may be switched off or 'set dark' for certain time intervals, e.g. during a switching time of the at least one switch to save energy, avoid undefined lighting states, and avoid damage to the light emitting device. It is even another embodiment that the light emitting device comprises a combination optics to spatially combine or merge the light beams of the different light channels. Thus, the light beams of the different light channels may exit the light emitting device at at least approximately the same area or spot and in the same direction.

The combination optics may comprise one or more optical elements, like a lens and/or a mirror. The combination optics may combine the light beams of the different light channels in any possible combination.

It is yet another embodiment that the light emitting device comprises one or more optical elements to form the light beam(s) (single light beams and/or combined light beams), e.g. to focus, deflect, and/or parallelize the light beams.

For example, an optics (comprising one or more optical elements) may be used to focus the original radiation beam from the radiation source and to collimate the wavelength converted light of the light channels. Also, the wavelength converted light of the light channels may be combined using at least one prism and/or at least one dichromic or dichroic mirror (or another dichroic optical element) . The original light from the radiation source and wavelength converted light may be separated using at least one prism and/or at least one dichroic mirror (or another dichroic optical element) . To reduce a color shift caused by a temperature shift of the phosphor (s), the phosphors ( s ) may be arranged on or associated with a heat sink. The phosphors of at least two different light channels may be arranged on different heat sinks or on a common heat sink.

The object is also achieved by a method for creating a multi^¬ colored light beam from a (radiation beam from the radiation source, wherein the method at least comprises directing the radiation beam towards at least two light channels wherein at least one of the light channels at least partially converts a wavelength of the radiation beam by means of at least one phosphor. This achieves the same advantages as the light emitting device.

It is an embodiment that the method is provided for creating a sequentially multi-colored light beam wherein the method at least comprises alternatingly directing the radiation beam from the radiation source towards at least two light channels .

It is an alternative embodiment that the method is provided for creating a multi-colored light beam wherein the method at least comprises simultaneously directing the radiation beam towards at least two light channels.

It is one embodiment for the method at least comprising alternatingly directing the radiation beam from the radiation source towards the at least two light channels that a duration of the directing of the radiation beam from the radiation source towards a particular of the light channels can be adjusted. By this, a chromaticity coordinate can be set without dimming the power of the original radiation beam.

It is another embodiment of the method at least comprising alternatingly directing the radiation beam from the radiation source towards the at least two light channels that a cycle of a 11 ernatingly directing the radiation beam towards (potentially all) the light channels (with directing the radiation beam towards each of the light channels not more than once) has a image repetition rate of at least 120 Hz. That means that the incoming radiation beam may be directed towards each of the light channels at least 120 times a second. If not all light channels are activated at every cycle, the image repetition rate for a particular light channel may be lower. In other words, each light channel may at the maximum be activated with a frequency of at least 120 Hz (and a variable time period, as discussed above) . This enables an illumination with a mixed light that is integrally composed of the sequentially multi-colored light beam wherein single color components of the mixed light cannot be resolved by a human eye even for challenging light applications like 3D object generation, in particular 3D moving object (video/film) generation.

The sequential activation of the three different (RGB) light channels 9, 12, 13 and beams r. g. b, corresponding to the three different switching states, may be called a cycle .

In the following drawings certain embodiments of the invention are schematically described in greater detail. Same numerals may be used for same elements or for functionally same or similar elements throughout the different embodiments .

Fig.l shows a block diagram of a light emitting device according to a first embodiment;

Fig.2 shows a block diagram of a light emitting device according to a second embodiment;

Fig.3 shows a diagram of some elements of the light emitting device according to the first embodiment or according to the second embodiment including one switch; Fig.4 shows a diagram concerning a beam combination of the light emitting device according to the first embodiment ;

Fig.5 shows a diagram concerning a beam combination of the light emitting device according to the second embodiment ;

Fig.6 shows a data projector using the light emitting device according to the first or the second embodiment .

Fig.l shows a block diagram of a light emitting device 1 according to a first embodiment. The light emitting device 1 comprises a control electronics 2 that controls or drives a laser driver 3, a first switch driver 4, and a second switch driver 5.

The laser driver 3 is adapted to control or drive a radiation source implemented as a laser light source 6 that emits blue laser light (blue laser light source 6) . The (original) blue laser light beam b (the radiation beam) emitted from the laser light source 6 impinges onto an optics 7.

The optics 7 forms the impinging laser light beam b such that it is directed towards a first switch 8 in a suitable manner (fitting angle of incidence, fitting beam width etc.) . The first switch 8 is driven by the first switch driver 4 and is adapted to direct the incoming laser light beam b either towards a first (red) light channel 9 or, via a second optics 10, towards a second switch 11. The second optics 10 is adapted to form the laser light beam b coming from the first switch 8 such that it is suitably directed onto the second switch 11.

The second switch 11 is driven by the second switch driver 5 and is adapted to direct the incoming (blue) laser light beam b either towards a second (green) light channel 12 or towards a third (blue) light channel 13. The first (red) light channel 9 and the second (green) light channel 12 each comprise (in this order for an original (blue) laser light beam b) a third optics 14, a wavelength converting element 15 and 16, respectively, and a fourth optics 17. The third optics 14 is adapted to form the incoming (original) laser light beam such that it is suitably directed towards the wavelength converting element 15 and 16, respectively, in particular towards an associated wavelength converting substance or phosphor. In each case, the fourth optics 17 is adapted to form the wavelength converted light beam r or g emitted from the wavelength converting element 15 and 16, respectively, such that it is suitably directed towards a combination optics 18.

The third (blue) light channel 13 only comprises the forth optics 17 such that the original blue laser light beam b, which remains unchanged in its wavelength, is suitably directed towards the combination optics 18.

The combination optics 18 spatially combines the light beams r, g, b coming from the light channels 9, 12, and 13 such that they cannot be spatially resolved and are directed into the same direction. The output light from the combination optics 18 is again formed by a fifth optics 19 before leaving the light emitting device 1.

In a first switching state, the control electronics 2 instructs the laser driver 3 to operate the blue laser light source 6 on a certain power level. The control electronics 2 also instructs the first switch driver 4 to switch the first switch 8 in the direction of or towards the first light channel 9. Thus, the laser light source 6 emits a blue laser light beam b onto the first optics 7, which forms (redirects and/or shapes) the blue laser light beam b to fall onto the first switch 8. The first switch 8 directs the blue laser light beam b towards the first light channel 9. At the first light channel 9, the blue laser light beam b firstly impinges upon the third optics 14 that forms the blue laser light beam b to hit a blue-red wavelength converting element 15 where the blue laser light beam b is at least partially (preferably substantially completely) converted into a red light. The fourth optics 17 forms the red light to exit the first light channel 9 as a red light beam b that is directed towards the combination optics 18. From the combination optics 18, the red light beam b is emitted from the light emitting device 1 via the fifth optics 19.

In a second switching state, the control electronics 2 instructs the laser driver 3 to operate the blue laser light source 6 on the same power level as for the first switching state. The control electronics 2 also instructs the first switch 8 driver to now switch the first switch 8 towards the second switch 11. The control electronics 2 further instructs the second switch 11 driver to switch the second switch 11 towards the second light channel 12. Thus, the laser light source 6 emits a blue laser light beam b onto the first optics 7, which forms (redirects and/or shapes) the blue laser light beam b to fall onto the first switch 8. The first switch 8 directs the blue laser light beam b towards the second optics 10. The second optics 10 forms the blue laser light beam b to fall onto the second switch 11. The second switch 11 directs the blue laser light beam b towards the second light channel 12. At the second light channel 12, the blue laser light beam b firstly impinges upon another third optics 14 that forms the blue laser light beam b to hit a blue-green wavelength converting element 16 where the blue laser light beam b is at least partially (preferably substantially completely) converted into a green light. Another fourth optics 17 forms the green light to exit the first light channel 9 as a green light beam g that is directed towards the combination optics 18. From the combination optics 18, the green light beam g is emitted from the light emitting device 1 via the fifth optics 19. In a third switching state, the control electronics 2 instructs the laser driver 3 to operate the blue laser light source 6 on the same power level as for the first switching state and the second switching state. The control electronics 2 also instructs the first switch 8 driver to switch the first switch 8 towards the second switch 11 or maintain its switching position. The control electronics 2 further instructs the 1 driver to switch the second switch 11 towards the third light channel 13. Thus, the laser light source 6 emits a blue laser light beam b onto the first optics, which forms (redirects and/or shapes) the blue laser light beam b to fall onto the first switch 8. The first switch 8 directs the blue laser light beam b towards the second optics 10. The second optics 10 forms the blue laser light to fall onto the second switch 11. The second switch 11 directs the blue laser light beam b towards the third light channel 13. At the third light channel 13, the blue laser light beam b passes a corresponding fourth optics 17 to exit the first light channel 9 as a blue light beam b that is directed towards the combination optics 18. From the combination optics 18, the blue laser light beam b is emitted from the light emitting device 1 via the fifth optics 19. Thus, in the third light channel 13, the (original) blue laser light beam b is only formed (shaped and/or re-directed) but not wavelength converted .

The three switching states are activated in a sequential order. The red, green and blue light beams r, g, b exiting the fifth optics 19 are aligned to point into the same direction and preferably ride at least substantially on the same straight line. The sequential activation of the three different (RGB) light channels 9, 12, 13 and beams r. g. b, corresponding to the three different switching states, may be called a cycle. During operation of the light emitting device 1, the cycle may be repeated with a certain, preferably fixed, image repetition rate, in particular with a image repetition rate of about 120 Hz or more. This image repetition rate and corresponding short cycle time of about 8.33 ms or less makes it impossible for a human observer to resolve the different light beams or colors. Consequently, the light emitted from the light emitting device 1 is perceived to be a mixed light composed of the (RGB) color components of the different light beams r, g, and b. The chromaticity coordinate of the mixed light is therefore determined by the color portions of the different (single) light beams r , g, and b, which corresponds to the ratio of the time or time periods for activating the different light channels 9, 12, 13. Thus, a chromaticity coordinate can easily be varied by varying the time ratio of the differently colored light beams or activation of the different light channel. The chromaticity coordinate may, for example, correspond to a white mixed light. This can be achieved without a need to dim the laser light source 6.

However, the laser light source 6 may be dimmed for different cycles but preferably does not show a different power level during the same cycle. By dimming the laser light source 6 for different cycles, the laser light source 6 may take grey level information into account, in particular the RGB grey level data RGB-gld. This grey level information may have been input into the control electronics 2 using a picture or video signal. In general, all suitable data to control the light emitting device 1 may be input into the control electronics 2. Theses input data may be sent from an SPI (Serial Peripheral Interface Bus), a computer, a hand-held device etc.

In particular, the control electronics 2 may synchronize a switching off of the laser light source 6 during switching operation of the switches 8 and/or 11, e.g. to avoid damage to the light emitting device 1. The switching times or phases may, for example, be initiated if levels of the RGB grey level data RGB-gld are changed. For the sequential mode of operation, levels are chosen in relation to each other such that a level for a certain light channel is set to 'high' while the levels for the other light channels are set to 'low'. Only if a level is set to 'high', the corresponding light channel is activated or illuminated. If, for example, the level for the second (green) light channel is set to 'high', the switches 8 and 11 are set such that a green light beam is generated / the green light channel 12 is activated. The switching operation may be initiated when a level set to 'high' is re-set to 'low' and one of the other levels is re^¬ set from 'low' to 'high'. In the example shown, only one level is set to 'high' at the same time.

Thus, if the light channels 9, 12, and 13 emit a substantially pure red, green, and blue light, the laser light source 6 may about cover the whole RGB color spectrum, and for each cycle, an RGB dimming level (power output level) may be set. Generally, corner positions of the area of the obtainable color coordinates within a color diagram (color gamut) are defined by the color of the light exiting the respective light channels.

The light emitting device 1 may also comprise an optical feedback means 20 that is adapted and arranged to analyze the combined light beams and that is positioned after the combination optics 18. The optical feedback means 20 may comprise one or more light sensors. The light beam(s) passing the combination optics 18 can, at least partially, be directed towards the optical feedback means 20 by the fifth optics 19. The directing of the combined light beams towards the optical feedback means 20 may particular be used during a non-sequential mode of operation.

During the non-sequential mode of operation, the laser light source 6 may be operated in a non-sequential manner such that some or all of the light channels are activated at the same time. This can be achieved by the switches not only being able to switch the impinging light towards one direction or another direction but also being able to switch the impinging light into all, in particular both, directions. For example, using a micromirror (DMD) as the digital MEMS switch, some of the micromirrors may be tilted into one direction and the other micromirrors may be tilted into the other direction. By defining the number of micromirrors tilting in the one or the other direction, pre-determined light fractions or ratios may be sent through the light channels and, subsequently, pre- determined ratios of the differently colored light beams or colors are created simultaneously.

In practice, the fractions or ratios of the light beams (their intensity or brightness etc.) may be different from what has been pre-determined, for example because of an area of the light beam impinging on a switch deviating from the ideal area. Thus, the chromaticity coordinate may vary from the correct chromaticity coordinate. If the light emitting device 1 is operated in the non-sequential mode of operation, the color temperature of the mixed light may be sensed by the optical feedback means 20, and a corresponding feedback signal may be sent to the control electronics 2. The control electronics 2 may then compare the pre-determined (pre- calculated or pre-set) chromaticity coordinate with the sensed chromaticity coordinate, and, on the grounds of this comparison, may correct the number of micromirrors to switch towards the respective directions to gain the correct (pre^¬ determined) chromaticity coordinate. The light emitting device 1 may be operated in its non^¬ sequential mode of operation on a constant power level or brightness level (in particular on a maximum level or alternatively on a dimmed level) a for all chromaticity coordinates. The number of switching states (micromirror groupings or divisions) may in particular be sufficient to achieve a color depth of 24 bits, e.g. by using a DMD micromirror device DLP 1700 from Texas Instruments. Fig.2 shows a block diagram of a light emitting device 21 according to a second embodiment. The light emitting device 21 differs from the light emitting device 1 in that the laser light source 6 is now an ultraviolet (UV) light source 6. Further, the third light channel 22 is composed of a third optics 14, followed by at least one wavelength converting element 23 that comprises a phosphor to convert the UV laser light beam uv into blue light. Accordingly, the first light channel 9, the second light channel 12, and the third light channel 22 each comprise at least one wavelength converting element 15, 16, and 23, respectively, that in turn comprises a phosphor to convert the UV laser light beam uv into red, green, and blue light, respectively.

This embodiment has the advantage that in case of an efficient suppression of the emission of UV radiation from the light emitting device 21, the light emitting device 21 may be classified into eye safety class 1 according to DIN EN 60825-1 for all realizable luminous fluxes.

Fig.3 shows a diagram of some elements of the light emitting device 1 according to the first embodiment or the light emitting device 21 according to the second embodiment including one switch. As an example only, the switch is now described to be the first switch 8 of the light emitting device 1 according to the first embodiment.

The blue laser light source 6 emits the blue laser light beam b onto the first optics 7 that is embodied in form of a lens that broadens the laser light beam b such that it impinges onto a large area of the first switch 8. The first switch 8 is implemented as a micromirror device, and the blue broadened laser light beam b is illuminating most or all of these micromirrors . In the sequential mode of operation, depending on the tilting direction of all the micromirrors (all micromirrors are pointing in the same direction / have the same setting) , the blue laser light is either directed towards the third optics 14 of the first light channel 9 or towards the second optics 10. The third optics and the second optics 10 each comprise a lens 24 and 25, respectively, (to shape the light beams, e.g. with respect to its beam width), and a tilted mirror 26, and 27, respectively, to re-direct the incoming laser light beam b the first wavelength converting element 15 and the second switch 11, respectively.

To keep a light loss small during a sequential mode of operation, it may be desired to keep the switching time (the time needed to switch the switches 8, 11 from one setting to the other setting) below 5% of the cycle time. If the image repetition rate is set at 120 MHz, the cycle time is about 8.33 ms . Thus, it may be desired that the necessary switching time of the at least one switch 8, 11 is limited to not more than about 400 ]is . Since for the light emitting devices 1 or 21 with their RGB color components two switching operations are typically used in one cycle for each switch 8, 11, at least the first switch 8 should be able to complete switching operation within 200 \is or less. This is achievable by a digital MEMS switch, as e.g. the DMD device.

The switch 8 may preferably be operated in the shown configuration, wherein the incoming light beam substantially vertically or perpendicularly impinges upon the plane comprising the micromirrors of the switch 8, 11 (while normally a DMD device is operated such that the incoming light beam impinges under an angle of less than 90° upon the plane containing the micromirrors) . This has the advantage that a beam quality and efficiency is identical for both sides (light channels) . In the non-sequential (parallel) mode of operation, at the same time, the switch 8 directs a certain ratio or portion of the incoming blue laser light onto the third optics 14, and a complementary ratio or portion onto the second optics 10. This may be achieved by tilting a certain fraction of the micromirrors into one direction and a complementary fraction of the micromirrors into the other direction. The micromirrors may also take on more than two tilting directions .

While this embodiment is described with the help of the first switch, it is also applicable to other switches, e.g. the second switch 11. In that case, the blue light beam is directed to the green light channel 12 and the blue light channel 13 or 22.

The tilting switch, in particular DMD device, may be optimized in a number of ways to improve its optical efficiency :

Since the DMD device, e.g. a DLP micromirror device of Texas Instruments, is illuminated by a narrow-band light source 6, an anti-reflection effect of a window of the DMD device (that acts as a protection to the micromirrors) and a reflectivity of the micromirrors may be improved. For example, an anti- reflection coefficient or transmission coefficient of the window may be raised from T = 0.97 to T = 0.99.

Also, a reflectivity coefficient of the micromirrors may be raised from 0.88 to 0.95, e.g. by using a Enhanced Silver Coating, in particular for a wave length of 450 nm. Additionally using a dielectric coating, the reflectivity coefficient may be further improved to 0.99 since the reflectivity may be optimized for a pre-defined angle of incidence. Furthermore, a filling factor or space factor of the micromirrors may be increased from 92% to 95%, and a diffraction loss may be improved from 86% to 95% by tripling a pixel pitch which leads to an increase of the mirror area of a factor of about 10. By increasing the pixel pitch, the switching time becomes longer. For a pixel pitch of about 7.6 μιη of the current DLP1700 device of Texas Instruments, the switching time is less than 10 ]is . For the increased pixel pitch, the switching time would still be less than 200 μιη.

Fig.4 shows a diagram concerning a beam combination of the light emitting device 1 according to the first embodiment.

A blue laser light beam b that is directed to the first light channel 9 passes through the lens 24 (and mirror 26) of the third optics 14 of the first light channel 9 to impinge upon a dichroic mirror 28 of the first light channel 9 that is also part of the third optics 14. The dichroic mirror 28 reflects blue light and lets red light pass / does not reflect red light. The dichroic mirror 28 re-directs the blue laser light beam to a second lens 29 of the third optics 14 of the first light channel 9. The second lens 29 focuses the blue laser light towards the first wavelength conversion element 15 comprising the first wavelength conversion material. The first wavelength conversion material (at least mostly) converts the blue light into red light that is re- emitted through the second lens 29. The red light beam r then passes the dichroic mirror 28 without being re-directed. The red light beam r then impinges upon a first dichroic mirror 31 of the combination optics 18. The first dichroic mirror 31 reflects red light, but neither blue light nor green light. The red light beam r is subsequently re-directed onto a lens 32 that may be part of the fifth optics 19. By operating the switches 8 and 11, the blue laser light beam b may then be directed towards the second (green) light channel 12 and thus passes through a first lens 33 of the third optics 14 of the second light channel 12 to impinge upon a dichroic mirror 34 of the second light channel 12 that is part of the third optics 14 of the second light channel 12. The dichroic mirror 34 reflects blue light and lets green light pass / does not reflect green light. The dichroic mirror 34 re-directs the blue laser light beam to a second lens 35 of the second light channel 12 that is also part of the third optics 14 of the second light channel 12 and that focuses the blue laser light towards the second wavelength conversion element 16 comprising the second wavelength conversion material (the wavelength conversion material of the second light channel 12). The second wavelength conversion material (at least mostly) converts the blue light into green light that is re-emitted through the second lens 35. The green light beam g also passes the dichroic mirror 34 without being re-directed. The green light beam g then impinges upon a second dichroic mirror 36 of the combination optics 18. The second dichroic mirror 36 reflects green light, but not blue light. The green light beam g is thus reflected by the second dichroic mirror 36 onto the first dichroic mirror 31 of the combination optics 18, which it can pass, and further towards the lens 32.

By operating the switch 11, the blue laser light beam b may then be directed towards the third (blue) light channel and thus passes through a lens 37 of the fourth optics 17 of the third light channel 13 to pass through the second dichroic mirror 36, then through the first dichroic mirror 31, and further towards the lens 32.

Thus all differently colored light beams r, g, b pass through the fifth optics 19 and are directed in the same direction. Subsequently, a human eye cannot spatially resolve the differently colored light beams.

To improve a wavelength conversion efficiency, the wavelength conversion elements 15 and 16 are thermally connected to a heat sink 38. Alternatively, the wavelength conversion elements 15 and 16 may be thermally connected to a respective heat sink. The shown arrangement also works for the non-sequential mode of operation.

Fig.5 shows a diagram concerning a beam combination of the light emitting device 21 according to the second embodiment. This beam combination differs from the beam combination of the first embodiment in that the incoming laser light beam is an UV light beam instead of a blue laser light beam. The UV laser light beam passes a lens 39 of the first optics 14 of the third light channel 22 to impinge onto a dichroic mirror 40 of the first optics 14 of the third light channel 22 that re-directs the UV light beam onto the wavelength conversion element 23 via a second lens 41 of the first optics 14 of the third light channel 22. The wavelength conversion element 23 converts the UV laser light beam into blue light. In analogy, the wavelength conversion elements 15 and 16 now convert the UV light beam into red light and green light respectively etc .

The blue light is collected by the second lens 41 to form a blue light beam that passes the dichroic mirror 40 without being re-directed. The blue light beam then impinges upon a mirror 42 that may be part of the combination optics 18. The mirror 42 directs the blue light beam towards the second dichroic mirror 36, which it can pass, and further onto the first dichroic mirror 31, which it can also pass, and on towards the lens 32 of the fifth optics 19.

Fig.6 shows a data projector 43 using the light emitting device 1 according to the first embodiment or the light emitting device 21 according to the second embodiment. The light projector 43 comprises an image controller 44 into which video data are input. The image controller 44 outputs RGB grey level data RGB-gld to the control electronics of the light emitting device 1 or 21 and pixel grey level data p-gld to an imager 45 that modulates an optical signal with the corresponding grey level on a pixel level (a digital picture or a digital video image being composed of several pixels) . The imager 45 is optically coupled to the light emitting device 1 or 21 to receive the output light beam of the light emitting device 1 or 21 via an intermediary optics 46. The intermediary optics 46 forms the output light beam of the light emitting device 1 or 21 to be adapted for use with the imager. The pixel modulated optical signal emitted from the imager 45 is then passed through a final optics 47 of the light projector 43 to be projected onto a screen 48, for example .

Alternatively, the light projector may do without the imager. The pixel grey level data p-gld may then be sent to the light emitting device 1 or 21. The light emitting device 1 or 21 may than modulate its output light with the pixel grey level data p-gld by a suitable dimming of the radiation source.

The light projector, e.g. 43, may be used as a beamer or as a stage projector, for example.

Of course, the invention is not restricted to the shown embodiment . For example, the light exiting from the light channels is generally not restricted to the visible spectrum. In one embodiment, the light exiting at least one of the light channels may be an IR light, e.g. for illuminating object in darkness, e.g. for automotive applications. References

1 light emitting device

2 control electronics

3 laser driver

4 first switch driver

5 second switch driver

6 laser light source

7 first optics

8 first switch

9 first light channel

10 second optics

11 second switch

12 second light channel

13 third light channel

14 third optics

15 first wavelength conversion element

16 second wavelength conversion element

17 fourth optics

18 combination optics

19 fifth optics

20 feedback means

21 light emitting device

22 third light channel

23 wavelength converting element

24 lens

25 lens

26 tilted mirror

27 tilted mirror

28 dichroic mirror

29 second lens

31 first dichroic mirror

32 lens

33 first lens

34 dichroic mirror

35 second lens

36 second dichroic mirror 37 lens

38 heat sink

39 lens

40 dichroic mirror

41 second lens

42 mirror

43 light projector

44 image controller

45 imager

46 intermediary optics

47 final optics

48 screen

r red light beam

g green light beam

b blue light beam

uv ultraviolet light beam p-gld pixel grey level data

RGB-gld RGB grey level data

Claims

1. A light emitting device (1; 21), comprising

- a radiation source (6), in particular laser light source, and

- at least one switch (8, 11);

- wherein the at least one switch (8, 11) is adapted to direct an incoming radiation beam (b; uv) from the radiation source (6) towards at least two light channels (9, 12, 13; 22); and

- wherein at least one of the light channels (9, 12;

22) comprises at least one phosphor for at least partially converting a wavelength of the incoming radiation beam (b; uv) .

2. The light emitting device (1; 21) according to claim 1, wherein the at least one switch (8, 11) is adapted to alternately direct an incoming radiation beam (b; uv) from the radiation source (6) towards the at least two light channels (9, 12, 13; 22); and wherein the at least one switch (8, 11) is adapted to switch between the light channels (9, 12, 13; 22) in an adjustable time pattern .

3. The light emitting device (1; 21) according to claim 1, wherein the at least one switch (8, 11) is adapted to simultaneously divide and direct an incoming radiation beam (b; uv) from the radiation source (6) towards the at least two light channels (9, 12, 13; 22); wherein the at least one switch is adapted to adjust the fractions of the incoming radiation beam (b; uv) directed towards the light channels (9, 12, 13; 22) .

4. The light emitting device (1) according to any of the preceding claims, wherein one of the light channels (13) is adapted to retain a wavelength of the incoming radiation beam (b) unchanged.

The light emitting device (21) according to any of the claims 1 to 4, wherein all light channels (9, 12, 22) are adapted to at least partially convert a wavelength of the incoming radiation beam (uv) .

The light emitting device (1; 21) according to any of the preceding claims, wherein the light emitting device ( 1 ; 21) comprises at least two light channels (9, 12,; 22) that are adapted to at least partially convert a wavelength of the incoming radiation beam (b; uv) , and wherein each light channel is adapted to at least partially convert the incoming radiation beam (b; uv) to a different wavelength.

The light emitting device (1; 21) according to any of the preceding claims, wherein

- the light emitting device (1; 21) comprises a first switch (8) and a second switch (11), wherein

- the first switch (8) is adapted to direct the incoming radiation beam (b; uv) towards a first light channel (9) and the second switch (11), and wherein

- the second switch is adapted to direct the incoming radiation beam (b; uv) towards a second light channel (12) and a third light channel (13; 22) .

The light emitting device (1; 21) according to claim 7, wherein the first light channel (9) emits light (r) having a higher dominant wavelength than light (g, b) emitted from the second light channel (12) and the third light channel (13; 22) .

The light emitting device (1) according to a combination of claim 4, claim 6, and any of the claims 7 or 8, wherein

- the radiation source (6) comprises at least one blue solid state emitter, wherein - one of the light channels (9) is adapted to at least partially convert blue light (b) into red light (r) , and wherein

- one of the light channels (12) is adapted to at least partially convert blue light (b) into green light

(g) .

10. The light emitting device (21) according to a combination of claim 5, claim 6, and any of the claims 7 or 8, wherein

- the radiation source (6) comprises at least one UV solid state emitter, and wherein

- the light channels (9, 12, 22) are adapted to at least partially convert UV light (uv) into red (r) , green (g) , and blue (b) light, respectively.

11. The light emitting device (1; 21) according to any of the preceding claims, wherein the at least one switch (, 11) comprises at least one digital MEMS switch.

12. The light emitting device (1; 21) according to any of the preceding claims, wherein the radiation source (6) comprises at least one CW solid state emitter. 13. A method for creating a multi-colored light beam (r, g, b) , wherein the method at least comprises directing a radiation beam (b; uv) from the radiation source (6) towards at least two light channels (9, 12,

13; 22) wherein at least one of the light channels (9, 12; 22) at least partially converts a wavelength of the radiation beam (b; uv) from the radiation source (6) by means of at least one phosphor.

14. The method according to claim 13, wherein, for alternatingly directing the radiation beam (b; uv) from the radiation source, a duration of the directing of the light beam (b; uv ) towards a particular of the light channels (9, 12, 13; 22) can be adjusted.

The method according to any of the claims 13 or 14, wherein, for alternatingly directing the radiation beam (b; uv) from the radiation source (6), a cycle of alternatingly directing the radiation beam (b; uv) from the radiation source (6) towards the light channels (9, 12, 13; 22) has a image repetition rate of at least 120 Hz .