Patent Publication Number: US-7905631-B2

Title: Illumination system having coherent light source and integrator rotatable transverse the illumination axis

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 96125388, filed on Jul. 12, 2007 The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an illumination system, and more particularly to an illumination system adapted to be used on a projection apparatus. 
     2. Description of Related Art 
     Referring to  FIG. 1 , a conventional projection apparatus  200  includes an illumination system  100 , a light valve  210  and a projection lens  220 . The illumination system  100  includes a laser light source  110 , a beam expander  120 , an integration rod.  130  and two focusing lenses  142  and  144 . The laser light source  110  is used to provide an illumination beam  112 , and the beam expander  120  is used to expand the illumination beam  112 . The focusing lens  142  is used for focusing the illumination beam  112  on the integration rod  130 . The integration rod  130  is used for uniforming the illumination beam  112 , and the focusing lens  144  is used for focusing the illumination beam  112  from the integration rod  130  on the light valve  210 . In addition, the focusing lens  144  also forms an image of a light exit end  132  of the integration rod  130  on the light valve  210 . Furthermore, the light valve  210  converts the illumination beam  112  into an image beam  112 ′, and the projection lens  220  projects the image beam  112 ′ on a screen  50 , so that an image is formed on the screen  50 . 
     Because the illumination beam  112  provided by the laser light source  110  is a highly coherent illumination beam, diffraction and interference of the illumination beam may easily occur. This often leads to a speckle phenomenon in the image on the screen  50 , thereby affecting the imaging quality. In the prior art, a number of methods for lowering the coherence of the illumination beam  112  are used to reduce the degree of the speckle phenomenon. For example, in U.S. Pat. No. 7,030,383, the coherence of the illumination beam  112  is lowered to reduce the degree of the speckle phenomenon by rotating the focusing lens  144  in the direction of the arrow  42  or moving the focusing lens  144  in the direction of the arrow  44 . 
     However, the focusing lens  144  forms the image of the exit end  132  of the integration rod  130  on the light valve  210 , such that moving or rotating the focusing lens  144  makes the image of the exit end  132  of the integration rod  130  not formed on the light valve  210  accurately, which adversely affects the imaging quality of the projection apparatus  200 . 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides an illumination system capable of reducing the degree of the speckle phenomenon. 
     An embodiment of the present invention provides an illumination system including a coherent light source, a light integrator and a first actuator. The coherent light source is capable of providing an illumination beam. The light integrator is disposed on a transmission path of the illumination beam, and the first actuator is connected to the light integrator. The light integrator has a light entering end and a light exit end opposite to the light entering end, and the light entering end faces the coherent light source. The first actuator is capable of driving the light integrator to move and/or rotate, so as to change a position at the light entering end entered by the illumination beam. 
     By using the first actuator to drive the light integrator to move or rotate, coherence of the illumination beam is lowered, so that the degree of the speckle phenomenon is reduced. 
     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 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic diagram of a conventional projection apparatus. 
         FIG. 2  is a schematic diagram of a projection apparatus using an illumination system according to an embodiment of the present invention. 
         FIG. 3  is a perspective diagram of the first actuator and the light integrator in  FIG. 2 . 
         FIG. 4  is a schematic diagram of an illumination system according to another embodiment of the present invention. 
         FIG. 5  is a schematic diagram of an illumination system according to another embodiment of the present invention. 
         FIG. 6  is a schematic diagram of an illumination system according to another embodiment of the present invention. 
         FIG. 7  is a schematic diagram of an illumination system according to another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     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 can be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no 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. 
     As shown in  FIGS. 2 and 3 , a projection apparatus  400  according to an embodiment of the present invention includes an illumination system  300 , a light valve  410  and a projection lens  420 . The light valve  410  is disposed between the illumination system  300  and the projection lens  420 . The light valve  410  is used for converting an illumination beam  312  provided by the illumination system  300  into an image beam  312 ′. The projection lens  420  is used for projecting the image beam  312 ′ to a screen  50 , so that an image is formed on the screen  50 . 
     The illumination system  300  includes a coherent light source  310 , a light integrator  320  and a first actuator  330 . The coherent light source  310  is, for example, a laser light source capable of providing the above illumination beam  312 . The light integrator  320  is disposed on a transmission path of the illumination beam  312 , and the first actuator  330  is connected to the light integrator  320 . The light integrator  320  has a light entering end  322  and a light exit end  324  opposite to the light entering end  322 , and the light entering end  322  faces the coherent light source  310 . 
     In addition, the illumination system  300  further includes a beam expander  340  and a focusing lens  352  disposed between the coherent light source  310  and the light integrator  320  and on the transmission path of the illumination beam  312 . The beam expander  340  is used for expanding the illumination beam  312 , and the focusing lens  352  is used for focusing the illumination beam  312  on the light integrator  320 . Furthermore, the illumination system  300  may further include a focusing lens  354  disposed between the light integrator  320  and the light valve  410  and on the transmission path of the illumination beam  312 . The focusing lens  354  is used for focusing the illumination beam  312  on the light valve  410 . Moreover, the focusing lens  354  is disposed in a location such that the image of the light exit end  324  of the light integrator  320  is formed accurately on the light valve  410 . 
     The coherent light source  310  provides the illumination beam  312  which is a highly coherent illumination beam, the coherence of the illumination beam  312  must be lowered to reduce the degree of the speckle phenomenon appearing in the image on the screen  50 . The present embodiment uses a first actuator  330  to drive the light integrator  320  to move and/or rotate, so as to change the position at the light entering end  322  entered by the illumination beam  312 , so that the coherence of the illumination beam  312  is lowered. 
     More particularly, a light axis  312   a  of the illumination beam  312  travels along an X-axis to the light entering end  322  of the light integrator  320 . The first actuator  330  is capable of driving the light integrator  320  to move substantially within a predetermined range in a plane formed by a Y-axis and a Z-axis. Moreover, the X-axis, the Y-axis and the Z-axis are perpendicular to one another. In other words, the first actuator  330  is capable of driving the light integrator  320  move in a direction indicated by the arrow  62  and/or the arrow  64 , so as to change the position at the light entering end  322  entered by the illumination beam  312 . 
     In another embodiment, the first actuator  330  is capable of driving the light integrator  320  to swing substantially within a predetermined range in a plane formed by the X-axis and the Y-axis, or the X-axis and the Z-axis. In other words, the first actuator  330  is capable of driving the light integrator  320  to swing substantially in a direction indicated by the arrow  66  and/or the arrow  68 , so as to change the position at the light entering end  322  entered by the illumination beam  312 . 
     The illumination system  300  in the present embodiment uses the first actuator  330  to drive the light integrator  320  to move and/or rotate, so as to change the position at the light entering end  322  entered by the illumination beam  312 , so that the coherence of the illumination beam  312  is lowered. Consequently, the degree of the speckle phenomenon is reduced. In addition, there is no need to move or rotate the focusing lens  354 , such that the focusing lens  354  forms an image of the light exit end  324  of the light integrator  320  accurately on the light valve  410 . Therefore, adverse effects on the imaging quality of the projection apparatus  400  may be avoided. 
     As shown in  FIG. 4 , an illumination system  300   a  according to another embodiment of the present invention is similar to the illumination system  300  in  FIG. 2  except for the following differences. The illumination system  300   a  further includes a diffuser  360 , a micro lens array, a reticular lens or a diffraction optical element. In the present embodiment, a diffuser  360  disposed at the light entering end  322  of the light integrator  320  is used as an example. Because the diffuser  360  may follow the motion of the light integrator  320 , it is able to lower the coherence of the illumination beam  312 . Hence, the degree of the speckle phenomenon is further reduced. 
     As shown in  FIG. 5 , an illumination system  300   b  according to another embodiment of the present invention is similar to the illumination system  300  in  FIG. 2  except for the following differences. The illumination system  300   b  further includes a diffuser  360  and a second actuator  370 . Furthermore, the beam expander  340  in  FIG. 2  is not used in the illumination system  300   b . The diffuser  360  is disposed between the coherent light source  310  and the light integrator  320 . More specifically, the diffuser  360  is disposed between the coherent light source  310  and the focusing lens  352  and on the transmission path of the illumination beam  312 . In addition, the second actuator  370  is connected to the diffuser  360 , and the second actuator  370  is capable of driving the diffuser  360  to move and/or rotate, so as to change a position on the diffuser  360  struck by the illumination beam  312 . For example, the second actuator  370  is capable of driving the diffuser  360  to move in a direction indicated by the arrow  72  and/or to swing in a direction indicated by the arrow  74 , so as to change the position on the diffuser  360  struck by the illumination beam  312 . Consequently, the coherence of the illumination beam  312  may be lowered and the degree of the speckle phenomenon can be further reduced. 
     As shown in  FIG. 6 , an illumination system  300   c  according to another embodiment of the present invention is similar to the illumination system  300  in  FIG. 2  except for the differences described below. The illumination system  300   c  further includes a second actuator  370  and a wedge prism  380 , and the beam expander  340  in  FIG. 2  is not used in the illumination system  300   c . The wedge prism  380  is disposed between the coherent light source  310  and the light integrator  320 . More specifically, the wedge prism  380  is disposed between the coherent light source  310  and the focusing lens  352  and on the transmission path of the illumination beam  312 . In addition, the wedge prism  380  has a light incident surface  382  and a light emitting surface  384  on the opposite side of the light incident surface  382 . The light emitting surface  384  is substantially parallel to the light entering end  322  of the light integrator  320 , and the light incident surface  382  has an inclined angle with respect to the light emitting surface  384 . 
     Furthermore, the second actuator  370  is connected to the wedge prism  380 , and the second actuator  370  is capable of driving the wedge prism  380  to move and/or rotate, so as to change a position on the light incident surface  382  struck by the illumination beam  312 . For example, the second actuator  380  is capable of driving the wedge prism  380  to move in a direction indicated by the arrow  72  and/or to swing in a direction indicated by the arrow  74 , so as to change the position on the light incident surface  382  struck by the illumination beam  312 . Consequently, the coherence of the illumination beam  312  may be lowered, and the degree of the speckle phenomenon can be further reduced. 
     It should be noted that a diffuser  360  (as shown in  FIG. 7 ) may be disposed on the light emitting surface  384  of the wedge prism  380 . The diffuser  360  is located on the transmission path of the illumination beam  312 . The diffuser  360  may lower the coherence of the illumination beam  312 , so as to reduce the degree of the speckle phenomenon. 
     In summary, the illumination system of the present invention has at least the following advantages: 
     1. The present invention uses the first actuator to drive the light integrator to move and/or rotate, so as to change the position at the light entering end entered by the illumination beam. Therefore, the coherence of the illumination beam is lowered, so as to reduce the degree of the speckle phenomenon. 
     2. There is no need to move or rotate the focusing lens disposed between the light integrator and the light valve, such that the focusing lens forms an image of the light exit end of the light integrator accurately on the light valve, which prevents adverse effects on the imaging quality of the projection apparatus. 
     3. A movable diffuser or a movable wedge prism may be additionally set up between the coherent light source and the light integrator to lower the coherence of the illumination beam, so as to reduce the degree of the speckle phenomenon. 
     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 practitioners 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.