Patent Publication Number: US-2010110389-A1

Title: Laser projection system

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a projection system, and more particularly, to a projection system using a laser as a light source. 
     (2) Description of the Prior Art 
     A projector is constituted of a light source, an illuminating module, an image generating module and so on. The illuminating module has an integration rod and a focusing lens, etc. The image generating module has a light engine and a projection lens, etc. The light beam is emitted from the light source and passes through the integration rod, the focusing lens, and the light engine to form an image beam, and then the image beam is projected on a screen through the projection lens to form an image. Generally, the light source may be a lamp, a light emitting diode (LED) or a laser light source. The projectors may be classified into liquid crystal panels, liquid crystal on silicon panels (LCOS panel), and digital micro-mirror devices (DMD). 
     In recent years, the development of the projector becomes very quickly, and the micro projector has become a new trend in the projector market. Luminous efficiency of the light source is the key factor in the development of the projector. Conventional projectors use light emitting diodes (LEDs) as light sources but the photoelectric converting efficiency is limited. Accordingly, it is promoted that manufacturers of projectors seek a better light source. 
     Comparing a laser light source with LED and an incandescent bulb, the laser light source has higher photoelectric converting efficiency and color saturation degree. Thus, some manufacturers have already replaced the LED with the laser light source. 
     Refer to  FIG. 1  for a conventional laser projection system  100 . The laser projection system  100  includes red, green, and blue (RGB) laser light sources  120   r ,  120   g , and  120   b , a light combining module  140 , a light engine  160 , and a projection lens  180 . The laser light beams from the laser light source  120   r ,  120   g , and  120   b  are mixed into a white light by the light combining module  140 . The white light passes through the light engine  160  to form an image beam, and the image beam is projected on a screen  200  via the projection lens  180 . 
     Laser light is coherence and it is a high energy and preferred orientation light beam with the same wavelength, identical phase, and a single frequency. However, when the laser is used as the light source of a projector, laser speckles appear. 
     When the laser is projected on a screen, it is reflected by the rough surface of the screen to form a lot of reflected waves. After these reflected waves are received by an image receiver (human eyes), interference phenomenon and light spots come out. The laser speckles interrupt the normal appearance of the image. Thus, how to decrease the laser speckles is a main subject in the popularization of the laser projection technology. 
     The traditional way of eliminating the laser speckles is adding an actuating mechanism  220 , for example, a motor, for the screen  200 , which keeps the screen  220  moving or rotating to corrupt the coherence of the laser light for further decreasing interference. 
     The conventional screen  200  is very large, and the actuating mechanism  220  may be large enough to drive the screen  200 , which is inconvenient in application and also has problems about noise and shock resistance in the product reliability test. 
     SUMMARY OF THE INVENTION 
     The present invention is to provide a laser projection system capable of improving the phenomenon of the laser speckles on the image. 
     For achieving one, some or all of the above mentioned object, a laser projection system is provided as an embodiment of the present invention. The laser projection system includes a plurality of laser light sources, a light combining module, an image generating module, a lens, a diffusion module, and a projection lens. 
     These laser light sources provide a plurality of laser light beams with different colors. The light combining module is disposed in the light path of the laser light beams for mixing the laser beams to form a mixing light beam. The image generating module is disposed in the light path of the mixing light beam for receiving the mixing light beam to generate a first image. The lens is disposed in the transmitting path of the first image for providing an imaging position. The first image is capable of passing through the lens to form a second image at the imaging position. The diffusion module includes a diffuser and an actuator. The diffuser is disposed at the imaging position of the lens, and the actuator is connected to the diffuser. The projection lens is disposed in the transmitting path of the second image for projecting the second image on a screen. 
     In one embodiment, the image generating module includes a transparent liquid crystal panel. The lens is a relay lens. An illuminating module is disposed in the light path of the mixing light beam and between the light combining module and the transparent liquid crystal panel. The illuminating module includes a focus lens, an integration rod, and a plurality of relay lenses, and the focus lens is disposed between the light combining module and the integration rod, and the integration rod is disposed between the focus lens and the relay lenses. 
     In one embodiment, the image generation module includes a reflective liquid crystal panel and a polarization beam splitter. An illuminating module is disposed in the light path of the mixing light beam, and between the light combining module and the reflective liquid crystal panel. The illuminating module includes a fly eye lens and a plurality of relay lenses, and the fly eye lens is disposed between the light combining module and the relay lenses. 
     In one embodiment, the image generating module includes a plurality of one-dimensional scanning lenses. The lens is an f-theta lens. 
     In above embodiments, the laser light sources includes a red laser light source, a blue laser light source, and a green laser light source. The light combing module includes two parallel dichroic mirrors. The actuator of the diffusion module is capable of driving the diffuser selectively moving in two different directions at a predetermined frequency. In addition, the diffuser of the diffusion module may be a disc. A motor is used as the actuator for rotating the diffuser. 
     The embodiments of the present invention uses the lens to focus the image formed by the image generating module on the moveable or rotatable diffuser, so as to corrupt the coherence of the laser light for further decreasing the laser speckle of the image. 
     Other objectives, features and advantages of the present invention will be further understood from the further technological features disclosed by the embodiments of the present invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a conventional laser projection system. 
         FIG. 2 . is a schematic view of a laser projection system in accordance to with an embodiment of the present invention. 
         FIG. 3  is a schematic view of a laser projection system with a transparent liquid crystal panel in accordance with an embodiment of the present invention. 
         FIG. 4  is a schematic view of a laser projection system with a reflective liquid crystal panel in accordance with an embodiment of the present invention. 
         FIG. 5  is a schematic view of a laser scanning projection system in accordance with an embodiment of the present invention. 
         FIG. 6  is a schematic view of a diffusion module of a laser projection system in accordance with an embodiment of the present invention. 
         FIG. 7A  and  FIG. 7B  are schematic views of a diffusion module of a laser projection system in accordance with an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” etc., is used with reference to the orientation of the Figure(s) being described. The components of the present invention may be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no to way limiting. On the other hand, the drawings are only schematic and the sizes of components may be exaggerated for clarity. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. Similarly, the terms “facing,” “faces” and variations thereof herein are used broadly and encompass direct and indirect facing, and “adjacent to” and variations thereof herein are used broadly and encompass directly and indirectly “adjacent to”. Therefore, the description of “A” component facing “B” component herein may contain the situations that “A” component facing “B” component directly or one or more additional components is between “A” component and “B” component. Also, the description of “A” component “adjacent to” “B” component herein may contain the situations that “A” component is directly “adjacent to” “B” component or one or more additional components is between “A” component and “B” component. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. 
     Referring to  FIG. 2 , a laser projection system  300  includes a plurality of laser light sources R, G, and B, a light combining module  320 , an image generating module  340 , a lens  360 , a diffusion module  380 , and a projection lens  390 . 
     The laser light sources R, G, and B are used to provide laser light beams with different colors respectively. For example, the laser light source R provides a red laser light beam L 1 , the laser light source G provides a green laser light beam L 2 , and the laser light source B provides a blue laser light beam L 3 . The light combining module  320  is disposed in the light path of the laser light beams L 1 , L 2 , and L 3  for mixing the laser light beams L 1 , L 2 , and L 3  into a mixing light beam L 4 . 
     The image generating module  340  is disposed in the light path of the mixing light beam L 4  for receiving the mixing light beam L 4  to generate a first image I 1 . Noticeably, the lens  360  is disposed in the transmitting path of the first image I 1  and provides an imaging position. The first image I 1  passes through the lens  360  for forming a second image I 2  at the imaging position. The diffusion module  380  includes a diffuser  382  and an actuator  384 . The diffuser  382  is disposed at the imaging position of the lens  360  and is connected to the actuator  384  for controlling the movement and rotation of the diffuser  382 . The projection lens  390  is disposed in the transmitting path of the second image I 2  for projecting the second image I 2  on a screen  400  to form a colorful projection image I 3 . 
     That is to say, the projection lens  390  has a physical object surface and a physical image surface. The diffuser  382  is disposed on the object surface, and the screen  400  is disposed on the image surface. Thus, the projection lens  390  treats the second image I 2  on the diffuser  382  as a physical object and projects the second image I 2  on the screen  400  for forming the colorful projection image I 3 . 
     The diffuser  382  of the present embodiment has an irregular rough surface, which disperses the laser light beam of the second image I 2  to decrease the orientation of the laser light beam. The diffuser  382  may move or rotate to disrupt the coherence of the laser light to further avoid the laser speckles forming on the projection image I 3 . Moreover, the diffuser  382  is disposed at the imaging position of the lens  360  that is the imaging position of the second image I 2 . The projection image I 3  received by human eyes is an image formed by the lens  390  projecting the second image I 2  on the screen  400 . Therefore, it is useful to decrease the laser speckles on the projection image I 3  by disposing the diffuser  382  at the imaging position of the second image I 2  and moving or rotating the diffuser  382  to disrupt the coherence of the laser light beam of the second image I 2 . 
     Referring to  FIG. 3  to  FIG. 5 , laser projection systems  500 ,  600  and  700  in following three embodiments have the same basic structure as the laser projection system  300  in  FIG. 2 . The image generating modules of the laser projection systems  500 ,  600  and  700  adopt a transparent liquid crystal panel  540 , a reflective liquid crystal panel  641  cooperating with a polarization beam splitter (PBS)  642 , and scanning lenses  741  and  742  respectively. 
     Referring to  FIG. 3 , the light combining module  520  of the laser projection system  500  has two parallel dichroric mirrors (DM)  521  and  522 . An illuminating module  530  is disposed in the light path of the mixing light beam L 4  and between the light combining module  520  and the transparent liquid crystal panel  540  for homogenizing the mixing light beam L 4 . The illuminating module  530  has a focus lens  531 , an integration rod  532 , and a plurality of relay lenses  533  and  534 . The focus lens  531  is disposed between the light combining module  520  and the integration rod  532 , and the integration rod  532  is disposed between the focus lens  531  and the relay lenses  533  and  534 . In the present embodiment, a relay lens  560  is disposed behind the transparent liquid crystal panel  540  and has the same function as the lens  360  in  FIG. 2 . 
     The red, green and blue laser light beams R, G, and B are mixed into a white light beam by the light combining module  520 . After passing through the focus lens  531 , the white light beam is focused at the integration rod  532  and homogenized by the integration rod  532 . The light beam from the integration rod  532  passes through the relay lenses  533  and  534  to concentrate on the transparent liquid crystal panel  540 . After processing an image process of the transparent liquid crystal panel  540 , the first image I 1  is formed. The second image I 2  is formed on the diffuser  582  by the first image I 1  through the relay lens  560 . 
     The diffuser  582  is controlled by the actuator  584  to move up and down, left and right (biaxial direction) or rotate as well as to adjust the movement frequency or the rotation speed. Then, the second image I 2  on the diffuser  582  is projected on the screen  400  through the projection lens  590 . 
     Referring to  FIG. 4 , a light combining module  620  of a laser projection system  600  has two parallel dichroric mirrors  621  and  622  and has the same structure and function as the light combining module  520  in  FIG. 3 . In the present embodiment, the illuminating module  630  includes a fly eye  631  and a plurality of relay lenses  633  and  634 . The fly eye  631  is disposed between the light combining module  620  and the relay lenses  633  and  634  and has functions of collimation, focusing, homogenizing, and beam splitting. The image generating module  640  includes a reflective liquid crystal panel  641  and a polarization beam splitter  642 . 
     The reflective liquid crystal panel  641  may be a liquid crystal on silicon (LCOS) panel. The polarization beam splitter  642  is constituted of two isosceles right angle prisms whose bottoms are stuck together and able to reflect S polarized light (polarization direction is vertical to the incident direction) and allow P polarized light (polarization direction is parallel to the incident direction) to pass through. 
     The working principle of the image generating module  640  in  FIG. 4  is described as follows. The mixing light beam (white light) from the illuminating module  630  is incident to the polarization beam splitter  642  which reflects the S polarized light of the mixing light beam to the reflective liquid crystal panel  641  and allows the P polarized light of the mixing light beam to pass through. If the first image I 1  from the image generating module  640  has dark pixels, the liquid crystal units corresponding to the dark pixels in the reflective liquid crystal panel  641  are closed. The closed liquid crystal units reflect the S polarized light back to the polarization beam splitter  642 , but the S polarized light cannot pass through the polarization beam splitter  642 . The liquid crystal units corresponding to the bright pixels in the first image I 1  convert the incident S polarized light into the P polarized light, so as to pass through the polarization beam splitter  642 . 
     The first image I 1  outputted from the polarization beam splitter  642  passes through the relay lens  660  to form the second image I 2  on the diffuser  682  controlled by the actuator  684 , and then the second image I 2  is projected on the screen  400  by the projection lens  690 . 
     Referring to  FIG. 5  for an embodiment of a laser scanning projection system  700 . A light combining module  720  in the present embodiment has the same structure and functions as above embodiments. The white light from the light combining module  720  passes through an image generating module  740  including two one-dimensional scanning lenses  741  and  742  to form the first image I 1 . Noticeably in the present embodiment, a light homogenizing mechanism such as an illuminating module may not be disposed between the light combining module  720  and the image generation module  740 . 
     The above two one-dimensional scanning lenses  741  and  742  are two uniaxial rotating mirrors, which can make the light beam scan left and right, up and down on the mirror and be reflected out with a particular angle. In another embodiment, it may be a biaxial rotating mirror called two-dimensional scanning lens for achieving the same efficacy as the two one-dimensional scanning lenses  741  and  742 . 
     After the first image I 1  is generated by the image generating module  740 , the first image I 1  passes through an f-theta lens  760  to focus on the diffuser  782  controlled by the actuator  784  and forms a second image I 2  which and then the second image I 2  is projected on the screen  400  by the projection lens  790 . 
       FIG. 6  and  FIG. 7  ( FIG. 7A  and  FIG. 7B ) illustrate two types of the diffusion module. However, the diffusion module of the present invention is not limited to the two types. 
     Referring to  FIG. 6 , the actuator  384  of the diffusion module drives the diffuser  382  to move up and down, left and right (as arrows shown) at a predetermined frequency. The actuator  384  and the diffuser  382  are connected by a connecting mechanism  383  which includes an electric circuit and a mechanical structure. 
     Referring to  FIG. 7A  and  FIG. 7B , in another embodiment, the diffuser  382   a  of the diffusion module is a disc and the actuator is a motor  384   a  that drives the diffuser  382   a  to rotate. 
     The above embodiments use a lens, such as a relay lens or an f-theta lens, to focus the image generated by the image generating module on a movable or rotatable diffuser to solve the problem of laser speckles. 
     The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiments disclosed. Accordingly, the foregoing description should be regarded as illustrative rather than restrictive. Obviously, many modifications and variations will be apparent to manufacturers skilled in this art. The embodiments are chosen and described in order to best explain the principles of the invention and its best mode practical application, thereby to enable persons skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents in which all terms are meant in their broadest reasonable sense unless otherwise indicated. Therefore, the term “the invention”, “the present invention” or the like is not necessary limited the claim scope to a specific embodiment, and the reference to particularly preferred exemplary embodiments of the invention does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is limited only by the spirit and scope of the appended claims. The abstract of the disclosure is provided to comply with the rules requiring an abstract, which will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Any advantages and benefits described may not apply to all embodiments of the invention. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention as defined by the following claims. Moreover, no element and component in the present disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims.