Abstract:
A light-emitting device and a projection system, comprising: a laser array light source which comprises a non-light-emitting region and a light-emitting region consisting of a plurality of laser elements; a reflective light-condensing system which comprises a light-condensing region and a non-light-condensing region, wherein the light-condensing region is used for focusing and reflecting emergent light of the laser array light source; and a light-collecting system used for collecting and emitting the emergent light from the reflective light-condensing system. The light-collecting system, the non-light-emitting region and the non-light-condensing region are located in the same straight line parallel to a light axis of the emergent light of the laser array light source, and the light-collecting system passes through the non-light-emitting region and/or the non-light-condensing region. The light-emitting device and the projection system have small volumes and can emit high-brightness and uniform faculae.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to illumination and display fields, and in particular, it relates to a light emitting device and a projection system. 
         [0003]    2. Description of Related Art 
         [0004]    As television and other display apparatus are adopting high resolutions and large sizes, their requirements for brightness of the light source increase. In particular, for special applications such as cinema projection systems, light sources up to ten thousand lumens are often required. 
         [0005]    To achieve high brightness light sources, conventional technologies use array light sources formed by arrayed light emitting elements, and compress the output light of the array light source to increase brightness. For example,  FIG. 1  illustrates a light emitting device according to a conventional technology. As shown in  FIG. 1 , the light emitting device includes a laser array light source  110 , a collimating lens array  120 , a focusing lens  130 , a light homogenizing rod  140 , a lens  150 , and a phosphor wheel  160 .  FIG. 2  is a right side view of the laser array light source of  FIG. 1 . As shown in  FIG. 2 , the laser array light source is formed by multiple laser diodes forming an array. The laser array light source has a high power and can emit high brightness laser light. The collimating lens array  120  includes multiple collimating lens units, each collimating lens unit corresponding to a laser diode, to collimate the light emitted by the laser diode. To reduce the cross section of the light beam, the focusing lens  130  focuses the output light of the collimating lens array  120 . The focused light is homogenized by the light homogenizing rod  140 , and is them focused by the lens  150  onto the phosphor wheel  160  to generate a desired converted light. 
         [0006]    However, because the focal length of the focusing lens  130  is relatively long, the length of the entire light emitting device is long, and its size is large. 
       SUMMARY 
       [0007]    An object of the present invention is to provide a light emitting device that has a small size and can output high brightness and uniform light spot, and related projection system. 
         [0008]    An embodiment of the present invention provides a light emitting device, which includes: 
         [0009]    A laser array light source, including a non-emitting region and an emitting region formed by multiple laser elements; 
         [0010]    A reflective light focusing system, including a focusing region and a non-focusing region, the focusing region focusing and reflecting an output light of the laser array light source; 
         [0011]    A light collecting system, for collecting an output light of the reflective light focusing system and outputting it; 
         [0012]    The light collecting system, the non-emitting region and the non-focusing region are located on a common straight line which is parallel to an optical axis of the output light of the laser array light source, and the light collecting system penetrates through the non-emitting region and/or the non-focusing region. 
         [0013]    Preferably, the reflective light focusing system is a reflector cup, wherein a center region of the reflector cup is the non-focusing region, and a region other than the center region is the focusing region, wherein the light collecting system penetrates through the non-emitting region. 
         [0014]    Preferably, the reflective light focusing system includes a reflector cup and a reflecting element, wherein the reflector cup includes a hollow region, the hollow region being the non-focusing region, and the region other than the hollow region and the reflecting element are the focusing region, and wherein the light collecting system penetrates through the hollow region of the reflector cup. 
         [0015]    Preferably, the reflecting element is mounted on the non-emitting region of the laser array light source. 
         [0016]    Preferably, the reflective light focusing system includes a reflecting element and a focusing lens having a hollow region, wherein the hollow region of the focusing lens is the non-focusing region, and the region of the focusing lens other than the hollow region and the reflecting element are the focusing region, wherein the region other than the hollow region of the focusing lens focuses the output light of the laser array light source, wherein the reflecting element reflects the output light of the focusing lens, and wherein the light collecting system penetrates through the hollow region of the focusing lens and the non-emitting region of the laser array light source. 
         [0017]    Preferably, the reflecting element includes a convex reflecting surface or a concave reflecting surface, wherein the convex reflecting surface or concave reflecting surface reflects the output light of the reflective focusing system and focuses it. 
         [0018]    Preferably, the light emitting device further includes a supplemental light source, wherein the supplemental light source is located on the same straight line as the non-emitting region and the non-focusing region, and is not located on the optical path of the output light of the laser array light source, and wherein the output light of the supplemental light source is incident on the light collecting system. 
         [0019]    Preferably, the light collecting system includes a light homogenizing rod. 
         [0020]    Preferably, the output port of the light homogenizing rod is located between the laser array light source and the reflective focusing system. 
         [0021]    Preferably, the light collecting system further includes a lens or a transparent glass plate, the lens or transparent glass plate being mounted on the non-emitting region or the non-focusing region, wherein the output light from the light homogenizing rod penetrates through the non-emitting region or the non-focusing region and transmits through the lens or transparent glass plate. 
         [0022]    Preferably, the light collecting system further includes a collimating lens, the collimating lens being confocal with the reflective light focusing system, wherein the collimating lens collimates the output light from the reflective light focusing system and outputs it to the light homogenizing rod. 
         [0023]    Preferably, the light emitting device includes a collimating lens array, the collimating lens array including collimating lens units that correspond one to one with the laser elements of the laser array light source, wherein each of the laser elements of the laser array light source is located at a predetermined position on an optical axis of its corresponding collimating lens unit but off from a focal point of the collimating lens unit, so that an output light from the collimating lens unit has a predetermined divergence angle. 
         [0024]    Another embodiment of the present invention provides a projection system, which includes the above light emitting device. 
         [0025]    Compared to conventional technologies, embodiments of the present invention have the following advantages: 
         [0026]    In embodiments of the present invention, the output light emitted from the emitting region of the laser array light source is reflected by the reflective light focusing system and focused to the light collecting system. Because of the reflection in the optical path, and because the light collection system, the non-emitting region and the non-focusing region are located on the same straight light parallel to the optical axis of the output light of the laser array light source, the light output from the light emitting device has to pass through the non-emitting region and/or the non-focusing region. Both the laser array light source and the reflective light focusing system have a finite size, but because the reflective light focusing system penetrates through the non-emitting region of the laser array light source and/or the non-focusing region of the reflective light focusing system, the laser array light source and/or the reflective light focusing system does not take up extra length, so the size of the light emitting device is reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  illustrates a light emitting device according to a conventional technology. 
           [0028]      FIG. 2  is a right side view of the laser array light source of  FIG. 1 . 
           [0029]      FIG. 3   a  schematically illustrates the structure of a light emitting device according to an embodiment of the present invention. 
           [0030]      FIG. 3   b  schematically illustrates the light emitting device of  FIG. 3   a  with a supplemental light source. 
           [0031]      FIG. 4  is a right side view of the laser array light source of  FIG. 3   a.    
           [0032]      FIG. 5   a  schematically illustrates the structure of a light emitting device according to another embodiment of the present invention. 
           [0033]      FIG. 5   b  schematically illustrates the light emitting device of  FIG. 5   a  with a supplemental light source. 
           [0034]      FIG. 6  is a right side view of the laser array light source of  FIG. 5   a.    
           [0035]      FIG. 7   a  schematically illustrates the structure of a light emitting device according to another embodiment of the present invention. 
           [0036]      FIG. 7   b  schematically illustrates the light emitting device of  FIG. 7   a  with a supplemental light source. 
           [0037]      FIG. 8  is a right side view of the focusing lens  431  of  FIG. 7   a.    
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0038]    Embodiments of the present invention are described below in detail with reference to the drawings. 
         [0039]      FIG. 3   a  schematically illustrates the structure of a light emitting device according to an embodiment of the present invention. As shown in  FIG. 3   a , the light emitting device includes a laser array light source  210 , a collimating lens array  220 , a reflective light focusing system  230 , and a light collecting system  240 . 
         [0040]    The laser array light source  210  includes multiple laser elements. The laser elements may be laser diodes. Laser diodes can emit light having high energy density and very low divergence angles, i.e. a near parallel light. Because they can provide high brightness output light, they are preferred light sources for high brightness light emitting devices.  FIG. 4  is a right side view of the laser array light source of  FIG. 3   a . As shown in  FIG. 4 , the laser array light source  210  includes a round shaped hollow region at its center, where the hollow region is a non-emitting region  212  and the region other than the hollow region is an emitting region  211 . The laser elements are disposed in the emitting region  211 . 
         [0041]    Although a laser light has relatively good collimation, it still has a certain divergence angle, so through its propagation the cross-section of the light beam will increase and its brightness will decrease. Therefore, the light emitted by the laser array light source  210  is collimated by the collimating lens array  220  and then output. Corresponding to the laser array light source  210 , the collimating lens array  220  also includes a hollow region; this hollow region and the non-emitting region  212  of the laser array light source are located on the same straight line that is parallel to the optical axis. The non-hollow region of the collimating lens array  220  covers the emitting region  211  of the laser array light source, to collimate the light emitted by the laser array light source  210 . However, with the divergence angle of the laser light is small and negligible, or when the requirement for the divergence angle of the laser light is not very high, the collimating lens array  220  may be omitted. 
         [0042]    As shown in  FIG. 4 , to realize a high power light emitting device, tens or even hundreds of laser elements may be arrayed in the emitting region  211  of the laser array light source  210 , so the size of the emitting area of the laser array light source may be large. To compress the cross section of the light beam for the benefit of downstream optical process, the light emitting device is provided with the reflective light focusing system  230 . In this embodiment, the reflective light focusing system  230  is a reflector cup. A center region of the reflector cup covers, in the direction of the optical axis, the non-emitting region of the laser array light source  210 , so it will not receive any incident light, and therefore constitutes a non-focusing region. The region other than the center region is a focusing region, which covers, in the direction of the optical axis, the emitting region of the laser array light source  210 , and focuses and reflects the light incident onto this region. The reflector cup  331  may be made of an aluminum reflector, or a concave mirror coated with a reflective film. 
         [0043]    To collect the light output from the reflective light focusing system  230 , the light emitting device further includes the light collecting system  240 . The light collecting system  240  includes a light homogenizing rod  241 , which collects the light output from the reflective light focusing system  230  and homogenizes it. The light homogenizing rod  241  penetrates through the non-emitting region  212  of the laser array light source, and the light output plane of the light homogenizing rod  241  protrudes out of the laser array light source  210 , and constitutes the output port of the light emitting device. 
         [0044]    Further, the light homogenizing rod  241  can perform de-coherence function for the laser light. This is because, although the light emitted by the laser diodes has fixed polarization, when multiple laser beams with different polarizations are mixed, the polarization can be partially eliminated. Here, the structure of the light homogenizing rod may be a solid rod or a hollow rod, and its shape may be a square rod or a cone shaped rod. The aspect ratio of the light homogenizing rod may be designed based on need; preferably, the aspect ratio is 16:9 or 4:3, to meet the requires of various light modulators of projection systems. 
         [0045]    Moreover, in other embodiments of the present invention, the light collecting system  240  may alternatively use a fly-eye lens pair to replace the light homogenizing rod, which also has the effect of light collection and light homogenization. 
         [0046]    To ensure proper light output, the light collecting system  240 , the non-emitting region  212  of the laser array light source  210  and the non-focusing region of the reflective light focusing system  230  are located on a common straight line which is parallel to the optical axis of the output light of the laser array light source  210 , and the output light of the reflective light focusing system  230  is collected by the light collecting system  240  and travels in the direction toward the non-emitting region of the laser array light source  210 . In this embodiment, because the light homogenizing rod  241  penetrates through the non-emitting region  212  of the laser array light source  210 , the laser array light source  210  and the collimating lens array  220  do not take up extra length, which reduces the size of the light emitting device. 
         [0047]    Therefore, the light emitting device according to this embodiment can output high power, uniform light and has a relatively small size. The light emitting device can be used in ultra-high brightness laser projection systems. For example, the laser array light source in this embodiment may be a red laser light source, a green laser light source, or a blue laser light source, which can be used as light sources of projection systems. 
         [0048]    It should be noted that the non-emitting region  212  of the laser array light source and the hollow region of the collimating lens array  220  do not have to have a round shape; their shapes can be designed according to practical needs, as long as they allow the light homogenizing rod  241  to penetrate through. Also, the non-emitting region  212  of the laser array light source, the hollow region of the collimating lens array  220 , and the non-focusing region of the reflective light focusing system  230  do not have to be located in the center region of the respective devices; the reflective light focusing system  230  can be designed to change the location of the focal point it forms after reflecting and focusing the incident light, so that the focal point is not located in the center region. In this situation, it is only required that the non-emitting region  212  of the laser array light source, the hollow region of the collimating lens array  220 , the non-focusing region of the reflective light focusing system  230  and the point that the light is focused to are located on the same straight line which is parallel to the optical axis of the output light of the laser array light source. 
         [0000]    1 Because the light emitted by the laser is well collimated, the output light of the laser array light source  210  is formed by multiple small light beams, each small light beam corresponding to a laser element. After being focused by the reflective light focusing system  230 , the multiple small light beams are focused toward one point, but the internal divergence angle of each small light beam is still small; it is equivalent to a proportional reduction of the light distribution on the output surface of the laser array light source  210 . In this situation, the light homogenizing rod  241  cannot effectively homogenize the light. Therefore, the light collecting system  240  is provided with a scattering element  242 , which may be a scattering plate. The scattering plate  242  is disposed between the light homogenizing rod  241  and the reflective light focusing system  230 , and coincides with the focal point of the reflective light focusing system  230 . It scatters the incident light to increase the internal divergence angle of each small light beam, which improves the light homogenizing effect of the light homogenizing rod  241 , and also has a de-coherence effect for the laser. 
         [0049]    Because the output power of the laser array light source  210  is relatively high, the light emitting device may further include a drive device (not shown in the drawings), to drive the scattering plate  242  to move, such as to rotate, so that the laser light spot formed on the scattering plate  242  moves on the scattering plate  242  along a predetermined path. Thus, the heat generated by the light spot is spread over an area of the scattering  242 , preventing the scattering element  242  from being burned. Moreover, a stationary scattering plate  242  has relatively poor de-coherence effect. This is because the scattering materials are not ideal, and cannot scatter 100% of the incident light; moreover, it also needs to ensure a certain light transmission rate. As a result, the projected light spot formed by the light emitting device will still have interference spots. When the drive device is provided, the scattering plate  242  motes, so the position of the light spot on the scattering plate  242  changes with time; in turn, the locations of the interference spots in the projected light spot change with time. When this change occurs at a sufficiently fast rate, the human eyes cannot detect the interference spots, and therefore a better de-coherence effect is achieved. 
         [0050]    Further, the scattering plate  242  may be replaced by a fly-eye lens pair, where each lens unit in the fly-eye lens pair can de-collimate the incident light by a certain degree. Similarly, a drive device can be provided to drive the fly-eye lens pair to mode, to improve heat dissipation. Also, to further improve high temperature resistance, the scattering plate or the fly-eye lens pair is preferably formed of a glass material. 
         [0051]    The transmission rate of the scattering plate is not high; to increase the transmission rate, the scattering plate  242  may be replaced by a concave lens, disposed between the reflective light focusing system  230  and the focal point of the reflective light focusing system  230 , where the concave lens and the reflective light focusing system  230  are confocal. Even after the laser light is collimation by the collimating lens array  220 , the small light beam corresponding to each laser diode still has a small divergence angle. The light output from the reflective light focusing system  230  is collimated by the concave lens; here, collimation means the different small light beams become parallel to each other, while the internal divergence angle of the small light beams are actually increased. This is because the light spot formed by the concave lens is much smaller than the light output surface of the laser array light source  210 ; because of the conservation of etendue, the divergence angle will increase. For example, if the size of the light beam is compressed by the concave lens to one tenth of the size of the light output surface of the laser array light source  210 , then the divergence angle of the small light beams will be ten times their original value. Therefore, the concave lens has the effect of diverging the small light beams within the incident laser light. It should be noted that, if the scattering plate  242  is replaced by a convex lens, then the convex lens is located between the light homogenizing rod  241  and the focal point of the reflective light focusing system  230 , and the convex lens and the reflective light focusing system  230  are confocal. Such a convex lens can also collimate the incident laser light and increase the diverge angle of the small light beams inside the laser. 
         [0052]    To further improve the light homogenization effect, the laser elements of the laser array light source  210  may be positioned to be off focus from the lenses of the collimating lens array  220 , i.e., each laser element of the laser array light source  210  is located on the optical axis of the corresponding collimating lens unit of the collimating lens array but at a predetermined point which is spaced away from the focal point of the collimating lens unit. This gives the small light beams a predetermined divergence angle. This way, without significantly changing the overall size of the output light beam, the light homogenizing effect of the light homogenizing rod  241  is improved. In practical applications, the predetermined divergence angle is within 4 degrees; such a value does not cause the overall light beam to have an overly large divergence angle, but can improve the light homogenizing effect of the light homogenizing rod  241 . 
         [0053]    Compared to the scattering plate and the fly-eye lens, concave and convex lenses are easier to make using glass materials; they have low cost and better temperature resistance, so they are preferred designs. 
         [0054]    It should be noted that in other implementations of this embodiment, a supplemental light source may be added to the light emitting device shown in  FIG. 3   a .  FIG. 3   b  schematically illustrates the light emitting device of  FIG. 3   a  with a supplemental light source. As shown in  FIG. 3   b , the light emitting device additionally includes a supplemental light source  250 , which is located on the same straight line as the non-emitting region of the laser array light source  210  and the non-focusing region of the reflective light focusing system  230 ; it and the laser array light source  110  are located on two different sides of the reflective light focusing system  230 , and it is not located on the output light path of the laser array light source  210 , so the supplemental light source  250  will not block the output light of the laser array light source  110 . 
         [0055]    To ensure that the output light from the supplemental light source  250  enters the light collecting system  240 , the non-focusing region of the reflective light focusing system  230  is a hollow region. This way, the output light of the supplemental light source  250  transmits through the non-focusing region of the reflective light focusing system  230  to be incident on the scattering plate  242  of the light collecting system  240 . Of course, the non-focusing region of the reflective light focusing system  230  can be other than a hollow region; in this case, the supplemental light source  250  can be mounted on the non-focusing region, as long as it does not block the output light from the laser array light source  110 . In such a situation, preferably, the non-emitting region is a plane, which is convenient for mounting the supplemental light source. 
         [0056]    Here, the supplemental light source  250  is a laser light sources, but of course it may also be a LED light source or other types of light source. Also, the supplemental light source  250  and the laser array light source  210  may emit light of the same wavelength, to increase the brightness of the light emitting device. Or, they can emit light of different wavelengths; for example, the supplemental light source  250  may emit a 462 nm blue light and the laser array light source  210  may emit a 445 nm blue light, or the supplemental light source  250  may emit a red light while the laser array light source  210  may emit a blue light. 
       Second Embodiment 
       [0057]      FIG. 5   a  schematically illustrates the structure of a light emitting device according to another embodiment of the present invention. As shown in  FIG. 5   a , the light emitting device includes a laser array light source  310 , a collimating lens array  320 , a reflective light focusing system  330 , and a light collecting system  340 . The light collecting system  340  includes a concave lens  342  and a light homogenizing rod  341 .  FIG. 6  is a right side view of the laser array light source of  FIG. 5   a . As shown in  FIG. 6 , the laser array light source  310  includes an emitting region  311  and a non-emitting region  312 . 
         [0058]    Differences between the light emitting device of this embodiment and that of  FIG. 3  include: 
         [0059]    In the embodiment of  FIG. 3 , because the light output surface of the laser array light source  210  is large, the size of the reflector cup  230  also needs to be sufficiently large in order to completely collect the output light of the laser array light source  210 , which makes the focal length of the reflector cup  230  long and thus the size of the light emitting device large. To further reduce the size of the light emitting device, in this embodiment, the reflective light focusing system  330  includes a reflector cup  331  and a reflecting element  332 . The reflector cup  331  includes a hollow region  331   b , which is the non-focusing region, and the region other than the hollow region  331   b  is the focusing region  331   a . The focusing region  331   a  reflects the light output from the collimating lens array  320  and focuses it. 
         [0060]    In this embodiment, the reflecting element  332  is a reflecting mirror. The reflecting mirror  332  is located between the reflector cup  331  and the focal point of the reflector cup  331 , and is perpendicular to the optical axis of the output light of the reflector cup  331 . The reflecting mirror  332  reflects the light output from the reflector cup  331 , while maintaining the focusing of the reflected light. This way, by the cooperation of the reflector cup  331  and the reflecting mirror  332 , the focusing of the light occurs in two optical path segments, and the two optical path segments overlap each other in space, which shortens the optical path required to focus the output light from the laser array light source  110 , and reduces the size of the light emitting device. Advantages of the reflecting mirror is its simple structure and low cost. 
         [0061]    After twice reflected by the reflector cup  331  and the reflecting mirror  332 , the light reflected by the reflecting mirror  332  travels toward the reflector cup  331 . To ensure that the light reflected by the reflecting mirror  332  can be output, the light homogenizing rod  341  of the light collecting system  340  penetrates through the hollow region  331   b  of the reflector cup (i.e. the non-focusing region of the reflective light focusing system  330 ). 
         [0062]    Further, because the reflecting mirror  332  is relatively close to the laser array light source  310 , as shown in  FIG. 6 , the reflecting mirror  332  can be mounted on the non-emitting region of the laser array light source  310 , to solve the problem caused by mounting a suspended reflecting mirror  332 . 
         [0063]    However, in this embodiment, when the position of the reflecting mirror  332  is maintained unchanged, its focal point for the reflected light is also fixed. In other embodiments, the reflecting element  332  may use a concave lens or a convex lens, where the concave lens or convex lens has a reflecting surface (e.g., by coating its surface with a reflective film). As compared to a reflecting mirror, light reflected by a convex lens can be focused at a closer location, and light reflected by a concave lens can be focused at a farther away location, and the curved surface of the concave lens or convex lens can be designed based on need to control the distance of the focal point of the reflected light. This way, by selecting a reflecting mirror, a concave lens or a convex lens, the location of the focal point of the reflected light can be controlled. 
         [0064]    Further, because the size of the reflector cup  331  is large, its reflected light may have significant aberration, which cannot be eliminated by designing the curved surface of the reflector cup  331  alone; but the reflector cup  331  and the reflecting surface of the concave lens or convex lens can cooperate with each other to eliminate aberration. Therefore, when cost is not a great concern, the concave lens having a concave reflecting surface or the convex lens having a convex reflecting surface is a preferred solution. It should be noted that the concave lens having a concave reflecting surface can be replaced by a reflective aluminum plate having a concave reflecting surface, which can achieve the same effect; similarly, the convex lens having a convex reflecting surface can be replaced by a reflective aluminum plate having a convex reflecting surface. 
         [0065]    It should also be noted that in this embodiment, the output plane of the light homogenizing rod  341  protrudes out from the hollow region of the reflector cup  331 , which is beneficial for clamping and mounting the light homogenizing rod  341 . In other implementations of the embodiment, the reflective light focusing system  330  and the light collecting system  340  can be adjusted so that the output plane of the light homogenizing rod  341  is located right at the hollow region of the reflector cup  331 , which can make the overall structure of the light emitting device more compact. In this situation, the output plane of the light homogenizing rod  341  can be covered with a transparent glass plate, so as to form a closed space to prevent dust from entering. Of course, the reflective light focusing system  330  and the light collecting system  340  can also be adjusted such that the output plane of the light homogenizing rod  341  is located between the reflector cup  331  and the laser array light source  310 . In this situation, the light collecting system  340  can further includes a lens, which or focuses the output light from the light homogenizing rod  341  and provide it to downstream optical elements. This lens can be mounted at the hollow region  331   b  of the reflector cup  331 , so that the overall structure of the light emitting device is compact. 
         [0066]    The above structure can also be applied to the light emitting device of the embodiment of  FIGS. 3   a  and  3   b  and later embodiments. Take the embodiment of  FIG. 3   a  as an example, in the light emitting device, the reflective light focusing system  230  and the light collecting system  240  can be adjusted such that the output plane of the light homogenizing rod  241  is located at the non-emitting region of the laser array light source  210 , and a glass plate is provided at the output plane of the light homogenizing rod  241 ; or such that the output plane of the light homogenizing rod  241  is located between the laser array light source  210  and the reflector cup  230 , and a lens is mounted in the non-emitting region of the laser array light source  210 . Both designs can achieve a compact structure of the light emitting device. However, because the back side of the substrate of the laser array light source  210  often has a heat dissipating device, it may be difficult to implement it on this side; on the other hand, if the a liquid cooling is used for heat dissipation, then the substrate of the  210  does not need a heat dissipation device, and can be simply provided with a heat dissipation plate, so the above structure can be more easily implemented. 
         [0067]    Similar to the embodiment of  FIG. 3   a , the light emitting device in  FIG. 5   a  can also be provided with a supplemental light source.  FIG. 5   b  schematically illustrates the light emitting device of  FIG. 5   a  with a supplemental light source. As shown in  FIG. 5   b , the light emitting device additionally includes a supplemental light source  350 , which is located on the same straight line as the non-emitting region of the laser array light source  310  and the non-focusing region of the reflective light focusing system  330 . Specifically, the supplemental light source  350  is mounted on the non-emitting region of the laser array light source  310 . In such a case, the reflecting mirror  332  of the reflective light focusing system  330  cannot be mounted on the non-emitting region of the laser array light source  310 , but should be located on the output light path of the supplemental light source  350 . Preferably, the reflecting mirror  332  is mounted on the hollow region of the collimating lens array  320 . 
         [0068]    To ensure that the output lights from the laser array light source  310  and the supplemental light source  350 , after the reflecting mirror  332 , both enter the light collecting system  330 , in  FIG. 5   b , the reflecting mirror  332  is not an ordinary reflecting mirror, but rather a wavelength selective filter plate. Correspondingly, the laser array light source  310  and the supplemental light source  350  output lights of different wavelengths, which are respectively reflected and transmitted by the wavelength selective filter plate  332  to enter the light collecting system  330 . Alternatively, the reflecting mirror  332  may also be a polarizing filter plate, and correspondingly, the laser array light source  310  and the supplemental light source  350  output lights of different polarizations, which are respectively reflected and transmitted by the polarizing filter plate  332  to enter the light collecting system  330 . As another alternative, the reflecting mirror  332  may also be an angle selective filter plate, and because the light from the laser array light source  310  and light from the supplemental light source  350  are incident on the reflecting mirror  332  at different angles, they are respectively reflected and transmitted by the reflecting mirror. In short, the lights output by the laser array light source  310  and the supplemental light source  350  have certain different optical properties, and the reflecting mirror  332  can respectively reflect and transmit these lights based on these different optical properties. 
       Third Embodiment 
       [0069]      FIG. 7   a  schematically illustrates the structure of a light emitting device according to another embodiment of the present invention. As shown in  FIG. 7   a , the light emitting device includes a laser array light source  410 , a collimating lens array  420 , a reflective light focusing system  430 , and a light collecting system  440 . The light collecting system  440  includes a light homogenizing rod  441  and a concave lens  442 . 
         [0070]    Compared to the light emitting device in the embodiment of  FIG. 5   a , the differences of this embodiment include: 
         [0071]    (1) The reflective light focusing system  430  in this embodiment includes a focusing lens  431  and a reflecting element  432 .  FIG. 8  is a right side view of the focusing lens  431  of  FIG. 7   a . As shown in  FIG. 8 , the focusing lens  431  is a convex lens having a hollow region  431   b , which is the non-focusing region. The region other than the hollow region  431   b  and the reflecting element  432  constitute the focusing region. The focusing region focuses the output light form the laser array light source  410 , to reduce the cross section of the laser light. 
         [0072]    Similar to the reflecting cup in the embodiment of  FIG. 5   a , the size of the focusing lens  431  also needs to be sufficiently large in order to completely collect the output light of the laser array light source  410 . The focal length of a convex lens depends on its size; the larger the size, the longer the focal length. Thus, the focal length of the focusing lens  431  is long. 
         [0073]    In this embodiment, the reflecting element  432  is a convex lens having a convex reflecting surface (e.g., by coating the surface of the convex lens). The convex lens  432  is located between the focusing lens  431  and the focal point O of the focusing lens  431 , and the convex reflecting surface reflects the output light from the focusing lens  431 , while maintaining the focusing of the reflected light. This way, by the cooperation of the focusing lens  431  and the convex lens  432 , the focusing of the light occurs in two optical path segments, and the two optical path segments overlap each other in space. Thus, the reflective light focusing system of this embodiment shortens the optical path required to focus the output light from the laser array light source, and reduces the size of the light emitting device. 
         [0074]    Moreover, to ensure that the light reflected from the convex lens  432  can be output, the optical axis of the reflected light faces the hollow region of the focusing lens  431 . The light homogenizing rod  441  of the light collecting system  440  penetrates through the hollow region  431   b  of the focusing lens  431  (the non-focusing region of the reflective light focusing system), the non-emitting region of the laser array light source  410 , and the hollow region of the collimating lens array  420 . This way, the light output from the focusing lens  431  is reflected by the convex lens  432 , and sequentially passes through the hollow region  431   b  of the focusing lens  431 , the hollow region of the collimating lens array  420 , and the non-emitting region of the laser array light source  410 , to be ultimately output. 
         [0075]    (2) In this embodiment, the light emitting device further includes a wavelength conversion device  480 . When the wavelength conversion material is directly excited by a high power excitation light, high heat is generated. In particular, the laser light has a Gauss distribution, and the light spot it forms on the surface of the wavelength conversion material is not uniform, which may cause a drop in the light emitting efficiency of the wavelength conversion materials. In this embodiment, the laser light emitted from the light homogenizing rod  441  is more uniform, which helps to improve the light emitting efficiency of the wavelength conversion materials. 
         [0076]    Specifically, the light from the light homogenizing rod  441  is incident on the lens  450 , is collimated by it and then incident onto the filter plate  460 . The filter plate  460  transmits the laser light and reflects the converted light output from the wavelength conversion device  480 . For example, a blue laser excitation light may excite a yellow phosphor to generate a yellow converted light, and the filter plate transmits blue light but reflects yellow light. The laser light transmits through the filter plate  460 , and is focused by the lens  470  onto the wavelength conversion device  480 , to excite the wavelength conversion material to generate the converted light. The converted light is collimated by the lens  470  and then incident on the filter plate  460  and is reflected by it, so that the light emitting device outputs a high brightness converted light. 
         [0077]    In other embodiments of the present invention, the light emitted by the wavelength conversion device can be mixed with light from another light source. For example, the yellow converted light can be mixed with the output light of another blue light source to obtain a white light. 
         [0078]    Similarly, the light emitting device in  FIG. 7   a  can also be provided with a supplemental light source.  FIG. 7   b  schematically illustrates the light emitting device of  FIG. 7   a  with a supplemental light source. As shown in  FIG. 7   b , the light emitting device additionally includes a supplemental light source  410   a , which is located on the same straight line as the non-emitting region of the laser array light source  410  and the non-focusing region of the reflective light focusing system  430 . Specifically, the supplemental light source  410   a  and the laser array light source  410  are located on two different sides of the reflective light focusing system  430 . 
         [0079]    Here, the convex lens  432  of the reflective light focusing system  430  is coated on its surface with a filter film. The thin film may be a wavelength selective filter plate, and correspondingly, the laser array light source  410  and the supplemental light source  410   a  output lights of different wavelengths, which are respectively reflected and transmitted by the convex lens  432 . Alternatively, the filter film on the surface of the convex lens  432  may be a polarizing filter film, and correspondingly, the laser array light source  410  and the supplemental light source  410   a  output lights of different polarizations, which are respectively reflected and transmitted by the convex lens  432 . As another alternative, the filter film on the surface of the convex lens  432  may also be an angle selective filter film, and because the light from the laser array light source  310  and from the supplemental light source  350  are incident on the coated surface of the convex lens  432  at different angles, they are respectively reflected and transmitted by the convex lens. In short, the lights output by the laser array light source  410  and the supplemental light source  410   a  have certain different optical properties, and the convex lens  432  can respectively reflect and transmit these lights based on these different optical properties. This way, the light output from the supplemental light source  410   a  will transmit through the convex lens  432 , and enters the light collecting system  440  together with the output light of the laser array light source  410  that has been reflected by the convex lens  432 . 
         [0080]    Specifically, the laser array light source  410  and the supplemental light source  410   a  are both laser light sources, and the output light of each of them is formed of multiple small light beams, each small light beam being emitted by one laser element. The small light beams are parallel to each other, and each small light beam has an internal divergence angle. 
         [0081]    Because the light emitting surface area of the laser array light source  410  is much larger than that of the supplemental light source  410   a , while the divergence angles of their output light are similar, the etendue of the light output from the laser array light source  410  is much larger than that of the supplemental light source  410   a . After the output lights of the laser array light source  410  and the supplemental light source  410   a  are homogenized by the light homogenizing rod  441 , the sizes of the two light spots formed by them on the output plane of the light homogenizing rod  441  are the same; because of the conservation of etendue, the divergence angle of the light originating from the laser array light source  410  is much larger than that of the light originating from the supplemental light source  410   a . Thus, when the output lights of the light homogenizing rod  441  are collimated by the lens  450 , the cross section of the light beam originating from the laser array light source  410  is much larger than that of the light beam originating from the supplemental light source  410   a . Therefore, the output light originating from the laser array light source  410  and the output light originating from the supplemental light source  410   a  can be separated using their etendue difference and treated respectively. 
         [0082]    Specifically, the filter plate  460  in  FIG. 7   a  is replaced with a light separation element  460  in  FIG. 7   b , and a scattering device  490  is additionally provided. As shown in  FIG. 7   b , the light separation element  460  includes a filter plate  461  and a small reflecting mirror  462  disposed at the center of the filter plate  461 . The small reflecting mirror  462  may be a mirror reflector, a wavelength selective filter plate, or a polarization plate. As shown in  FIG. 7   b , the filter plate  461  transmits the output light of the laser array light source  410  and the output light of the supplemental light source  410   a , while reflect the converted light emitted by the wavelength conversion device  480 . 
         [0083]    The output light from the supplemental light source  410   a  is incident on the small reflecting mirror  462  and reflected to the scattering device  490 . The Gaussian distribution of the laser becomes a Lambertian distribution after scattering, with a larger etendue, so a majority of the output light from the scattering device  490  transmits through the filter plate  461  and a small portion is reflected by the small reflecting mirror  462  and become lost. A majority of the light originating form the laser array light source  410  transmits through the filter plate  461  and is incident on the wavelength conversion device  480 , where it is absorbed and converted to the converted light, while a small portion is reflected by the small reflecting mirror  462  to the scattering device  490 . The converted light emitted by the wavelength conversion device  480  is incident on the filter plate  461  and is reflected by it, so that the converted light and the output light of the scattering device  490  are combined into one light beam for output. 
         [0084]    In this embodiment, the light separation element  460  separates the light originating from the laser array light source  410  and the light originating from the supplemental light source  410   a  based on their etendue difference. In practice, the light emitting device can also separate the lights using a filter plate with an aperture. In such a case, the positions of the wavelength conversion device  480  and scattering device  490  should be swapped, and the filter plate should reflect the lights originating from the laser array light source  410  and the supplemental light source  410   a  and transmit the converted light emitted by the wavelength conversion device  480 . 
         [0085]    The light originating from the supplemental light source  410   a  will be incident on the aperture of the filter plate and will pass through it to reach the scattering device  490 . The Gaussian distribution of the laser becomes a Lambertian distribution after scattering, with a larger etendue, so a majority of the output light from the scattering device  490  is reflected by the filter plate, and a small portion passes through the aperture and become lost. A majority of the light originating form the laser array light source  410  is reflected by the filter plate  461  to the wavelength conversion device  480 , where it is absorbed and converted to the converted light, while a small portion passes through the aperture to the scattering device  490 . The converted light emitted by the wavelength conversion device  480  is incident on the filter plate and transmits through it, so that the converted light and the output light of the scattering device  490  are combined into one light beam for output. 
         [0086]    Further, it should be noted that the light homogenizing rod  441  can be replaced by a fly-eye lens pair. In this situation, the size of the light spot formed on the coated surface of the convex lens  432  by the light from the supplemental light source  410   a  should be made smaller than that of the light spot formed by the light from the laser array light source  410 . This way, of the light spots formed on the fly-eye lens pair by the collimated light beams from the concave lens  442 , the size of the light spot formed by the light originating from the supplemental light source  410   a  will be smaller than that formed by the light originating from the laser array light source  410 . The fly-sys lens pair does not change the size ratio of the above light spots formed by the light originating from the supplemental light source  410   a  and the light originating from the laser array light source  410 . Therefore, on the surface of the light separation element  460 , the size of the light spot formed by the light originating from the supplemental light source  410   a  is smaller than that of the light spot formed by the light originating from the laser array light source  410 , so the two lights can be separated based on their etendue difference. 
         [0087]    The various embodiments in this disclosure are described in a progressive manner, where each embodiment is described by emphasizing its differences from other embodiments. The common or similar features of the embodiments can be understood by referring to each other. 
         [0088]    Embodiments of the present invention also provide a projection system, including a light emitting device which has the structures and functions of the light emitting device of the above described embodiments. The projection system may employ various projection technologies, such as liquid crystal display (LCD) projection technology, digital light processor (DLP) projection technology, etc. 
         [0089]    The above descriptions disclose the embodiments of the present invention, but do not limit the scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents, as well as direct or indirect applications of the embodiments in other related technical fields.