Abstract:
An illumination system is provided, which includes a first solid-state light source, a second solid-state light source, a third solid-state light source, a light combining element, a light homogenizing element, a first plate and a first band-stop filter. The first solid-state light source to the third solid-state light source respectively provide a first-wavelength light beam to a third-wavelength light beam. The first plate has a first surface opposite to an outputting surface of the light combining element and a first phosphor, while the first phosphor is excited by the third-wavelength light beam to produce a fourth-wavelength light beam. The first band-stop filter allows the first-wavelength light beam to the third-wavelength light beam to pass therethrough and reflects the fourth-wavelength light beam. With these arrangements, the illumination system can strengthen the light of a specific color and the volume of the illumination system can be reduced.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority to Taiwan Patent Application No. 101117936 filed on May 21, 2012, which is hereby incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an illumination system, and more particularly, to an illumination system for a projection apparatus. 
     2. Descriptions of the Related Art 
     Due to advantages such as a short startup time and a long service life, light emitting diodes (LEDs) have been widely used as light sources of common projection apparatuses in place of conventional high-pressure mercury lamps (HPLs). 
     Generally, a projection system uses LEDs to provide light beams of the three primary colors (i.e., red, green and blue) that are projected in different directions, and then, the light beams of the three primary colors are combined by a light combining element into a full-color (i.e., white color) light beam for projection to a light valve (e.g., a DMD, an LCD or an LCoS) of a projection apparatus. However, as compared to the intensities of the red light beam provided by the red LED or the blue light beam provided by the blue LED, the intensity of the green light beam provided by the green LED is weaker. As a consequence, the brightness of the green color of the image projected by the projection apparatus is relatively low, which makes the image look unnatural. 
     Therefore, an illumination system capable of enhancing the intensity of the green light has been developed in the art.  FIG. 1  illustrates an illumination system  1  that comprises a red LED  11 , two blue LEDs  13 ,  15 , and an ultraviolet (UV) LED  17 . The red LED  11  and the blue LED  13  are adapted to provide a red light beam and a blue light beam respectively for the illumination system  1 . The blue LED  15  and the UV LED  17  are adapted to excite a green phosphor  12  via two light splitters  19   a ,  19   b  respectively to provide a green light beam of an adequate intensity for the illumination system  1 . 
     Because the illumination system  1  needs to use more than one light splitters and each of the LEDs must be provided with a lens, the size of the projection apparatus is increased. If the volume of the projection apparatus needs to be reduced, the structure of the illumination system must be reduced, which would cause a decrease in the brightness thereof. Furthermore, the green light beam provided by the illumination system  1  does not have an adequate intensity that matches the intensities of the red light beam and the blue light beam. 
     Accordingly, it is important to provide an illumination system that can enhance the intensity of a light beam of a specific color (e.g., the green light) and that has a reduced volume. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to reduce the space occupied by an illumination system. By reducing the number of solid-state light sources, the size of conventional illumination systems can be avoided (i.e. the problem that conventional illumination systems occupy a large space can be avoided). The illumination system of the present invention can reduce the space occupied without compromising the intensity of a light beam of a specific color (e.g., a green light beam). 
     To achieve the aforesaid objective, the present invention provides an illumination system, which comprises a first solid-state light source, a second solid-state light source, a third solid-state light source, a light combining element, a light homogenizing element, a first plate and a first band-stop filter. The first solid-state light source is adapted to provide a first-wavelength light beam; the second solid-state light source is adapted to provide a second-wavelength light beam; and the third solid-state light source is adapted to provide a third-wavelength light beam. The light combining element has three inputting surfaces: an outputting surface, a second-wavelength-light-beam reflecting surface and a gap layer. The second-wavelength-light-beam reflecting surface and the gap layer intersect with each other. The second-wavelength-light-beam reflecting surface and the gap layer are located among the three inputting surfaces and the outputting surface. The second-wavelength-light-beam reflecting surface is used to allow the first-wavelength light beam and the third-wavelength light beam to pass therethrough and reflect the second-wavelength light beam. The first, the second and the third solid-state light sources are disposed in front of the three inputting surfaces respectively. The light homogenizing element is disposed apart from the outputting surface. The first plate is disposed apart from the outputting surface, and has a first phosphor and a first surface opposite the outputting surface. The first phosphor is disposed on the first surface to be excited by the third-wavelength light beam to produce a fourth-wavelength light beam. The first band-stop filter is disposed between the outputting surface and the light homogenizing element, and is used to allow the first-wavelength light beam to the third-wavelength light beam to pass therethrough and reflect the fourth-wavelength light beam. 
     The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a conventional illumination system; 
         FIG. 2  is a schematic view of an illumination system according to the first embodiment of the present invention; 
         FIG. 3  is a schematic view illustrating a light combining element of the illumination system according to the first embodiment of the present invention; 
         FIG. 4  is a schematic view illustrating the first plate of the illumination system according to the first embodiment of the present invention; 
         FIG. 5  is a schematic view illustrating light paths of the illumination system according to the first embodiment of the present invention; 
         FIG. 6  is a schematic view of an illumination system according to the second embodiment of the present invention; 
         FIG. 7A  is a schematic view illustrating an implementation of the first plate and second plate of the illumination system according to the second embodiment of the present invention; 
         FIG. 7B  is a schematic view illustrating another implementation of the first plate and the second plate of the illumination system according to the second embodiment of the present invention; and 
         FIG. 8  is a schematic view illustrating the light paths of the illumination system according to the second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 2  illustrates a schematic view of an illumination system according to the first embodiment of the present invention. The illumination system  2  has a first solid-state light source  21 , a second solid-state light source  22 , a third solid-state light source  23 , a light combining element  24 , a light homogenizing element  25 , a first plate  26  and a first band-stop filter  27 . 
     The first solid-state light source  21  is adapted to (i.e. used to) provide a first-wavelength light beam  211 ; the second solid-state light source  22  is adapted to provide a second-wavelength light beam  221 ; and the third solid-state light source  23  is adapted to provide a third-wavelength light beam  231 . The first-wavelength light beam  211 , the second-wavelength light beam  221  and the third-wavelength light beam  231  have a specific waveband (or wavelength) respectively; and any two of the wavebands of the first-wavelength light beam  211 , the second-wavelength light beam  221  and the third-wavelength light beam  231  may be completely overlapping, partially overlapping or not overlapping at all. 
     In this embodiment, the first solid-state light source  21  and the second solid-state light source  22  may be a blue LED and a red LED respectively, while the third solid-state light source  23  may be a blue laser light source. Furthermore, the first-wavelength light beam  211  and the second-wavelength light beam  221  may be a blue light beam and a red light beam respectively, while the third-wavelength light beam  231  may be a blue laser light beam. 
       FIG. 3  illustrates a schematic view of the light combining element of the illumination system according to the first embodiment of the present invention. The light combining element  24  has three inputting surfaces, an outputting surface, a second-wavelength-light-beam reflecting surface  241  and a gap layer  243 . The second-wavelength-light-beam reflecting surface  241  and the gap layer  243  intersect with each other, and are located between the three inputting surfaces and the outputting surface to form an X-shaped structure to divide the light combining element  24  into four light-path regions. In this embodiment, the light combining element  24  is an X-cube; however, in other embodiments, the light combining element  24  may also be an X-plate. 
     With reference back to  FIG. 2 , the three inputting surfaces and the outputting surface correspond to the four light-path regions of the light combining element  24  respectively, and the first solid-state light source  21 , the second solid-state light source  22  and the third solid-state light source  23  are disposed in front of the three inputting surfaces respectively. The light combining element  24  is adapted to provide (or define) a light travelling route for each of the first-wavelength light beam  211 , the second-wavelength light beam  221  and the third-wavelength light beam  231 . 
     The second-wavelength-light-beam reflecting surface  241 , which may be an optical coating, has the property of reflecting the second-wavelength light beam  221  but can allow the first-wavelength light beam  211  and the third-wavelength light beam  231  to pass therethrough. 
     The gap layer  243  has a specific refractive index. Specifically, when a light beam is emitted to the gap layer  243  at an incident angle larger than or equal to a critical angle of total internal reflection, the light beam will be totally reflected by the gap layer  243 ; and when a light beam is emitted to the gap layer  243  at an incident angle smaller than the critical angle of total internal reflection, the light beam will be partially reflected or pass through the gap layer  243 . In this embodiment, the gap layer  243  is an air layer. The first solid-state light source  21  and the second solid-state light source  22  are disposed in such a way that the incident angles of the first-wavelength light beam  211  and the second-wavelength light beam  221  are smaller than the angle of total reflection, so the first-wavelength light beam  211  and the second-wavelength light beam  221  can pass through the gap layer  243 . The third solid-state light source  23  is disposed in such a way that the incident angle of the third-wavelength light beam  231  is larger than the angle of total reflection, so the third-wavelength light beam  231  will be reflected by the gap layer  243 . 
     Still, with reference to  FIG. 2 , the light homogenizing element  25  is disposed apart from the outputting surface to homogenize the light beams. In the first embodiment, the light homogenizing element  25  is an integration rod; however, in other embodiments, people skilled in the art can also readily devise other forms of the light homogenizing element such as a lens array, a fly lens or a light tunnel. 
     The first plate  26  is also disposed apart from the outputting surface. With reference to  FIG. 4  in combination with  FIG. 2 ,  FIG. 4  is a schematic view of the first plate  26  of the first embodiment. The first plate  26  has a first phosphor  263  and a first surface  261  that is opposite to the outputting surface of the light combining element  24 . The first phosphor  263  is disposed on the first surface  261 . Thereby, after being reflected by the gap layer  243 , the third-wavelength light beam  231  provided by the third solid-state light source  23  can excite the first phosphor  263  disposed on the first surface  261  of the first plate  26  to generate a fourth-wavelength light beam  233 . The first surface  261  may be a mirror surface adapted to reflect the fourth-wavelength light beam  233 . In this embodiment, the first phosphor  263  may be a green phosphor. 
     Still, with reference to  FIG. 2 , the first band-stop filter  27  is disposed between the outputting surface of the light combining element  24  and the light homogenizing element  25 , and is used to allow the first-wavelength light beam  211  to the third-wavelength light beam  231  to pass therethrough and reflect the fourth-wavelength light beam  233 . The first band-stop filter  27  may also be a coating containing a filtering component, and can be directly coated and disposed on the outputting surface to achieve the filtering effect. 
     A first lens set  245 , a second lens set  247  and a third lens set  249  may be further provided for two inputting surfaces and the outputting surface of the light combining element  24  respectively. The first lens set  245  is disposed between the first solid-state light source  21  and the light combining element  24  to control a light path of the first-wavelength light beam  211 . The second lens set  247  is disposed between the second solid-state light source  22  and the light combining element  24  to control a light path of the second-wavelength light beam  221 . The third lens set  249  is disposed between the light homogenizing element  25  and the first band-stop filter  27  to control the light paths of the first-wavelength light beam  211  to the fourth-wavelength light beam  233 . 
     In detail, the first-wavelength light beam  211  can be refracted by the first lens set  245  and then propagate into the light combining element  24  at a specific angle. The second-wavelength light beam  221  can be refracted by the second lens set  247  and then propagate into the light combining element  24  at a specific angle. After exiting from the light combining element  24 , the first-wavelength light beam  211  and the second-wavelength light beam  221  can be refracted by the third lens set  249  and then propagate into the light homogenizing element  25  at a specific angle. After exiting from the light combining element  24 , the third-wavelength light beam  231  can be refracted by the third lens set  249  and then propagates to the first plate  26  at a specific angle. Furthermore, the fourth-wavelength light beam  233  can also be refracted by the third lens set  249  and then propagates to the first band-stop filter  27  and the light homogenizing element  25  at a specific angle. 
     With reference to  FIGS. 2 and 5 , the light paths of the light beams will be detailed.  FIG. 5  is a schematic view illustrating light paths of the illumination system according to the first embodiment of the present invention. The first-wavelength light beam  211  (the blue light beam) provided by the first solid-state light source  21  propagates through the light combining element  24  into the light homogenizing element  25  along a first light path  201 . The second-wavelength light beam  221  (the red light beam) provided by the second solid-state light source  22  is reflected by the second-wavelength-light-beam reflecting surface  241  to propagate into the light homogenizing element  25  along a second light path  202 . The third-wavelength light beam  231  (the blue laser light beam) provided by the third solid-state light source  23  is reflected by the gap layer  243  out of the light combining element  24  along a third light path  203 . 
     When being projected to the first phosphor  263  on the first plate  26 , the third-wavelength light beam  231  can be converted by the first phosphor  263  into the fourth-wavelength light beam  233 . Because the first phosphor  263  is a green phosphor, the fourth-wavelength light beam  233  generated through the excitation of the first phosphor  263  by the third-wavelength light beam  231  is a green light beam. The fourth-wavelength light beam  233  is reflected to the first band-stop filter  27  and then reflected by the first band-stop filter  27  into the light homogenizing element  25  along a fourth light path  204 . 
     As can be known from the above descriptions, the light beams entering into the light homogenizing element  25  include the first-wavelength light beam  211  (the blue light beam), the second-wavelength light beam  221  (the red light beam) and the fourth-wavelength light beam  233  (the green light beam). Both the first-wavelength light beam  211  and the second-wavelength light beam  221  are provided by LEDs and thus, have adequate intensities. Because the fourth-wavelength light beam  233  is generated through the excitation of the first phosphor  263 , the intensity thereof is also adequate. In other words, the light beams of various colors outputted from the light homogenizing element  25  all have an adequate intensity, so an image projected by the projection apparatus finally will not suffer from an inadequate intensity of a specific color (e.g., the green color). 
     Thus, the illumination system according to the first embodiment of the present invention has been described above. Next, an illumination system according to another embodiment of the present invention will be described. 
       FIGS. 6 and 8  illustrate an illumination system according to the second embodiment of the present invention. The illumination system  2 ′ of the second embodiment differs from the illumination system  2  of the first embodiment in that the illumination system  2 ′ further comprises a second plate  28  and a second band-stop filter  29  while the third solid-state light source  23  is further adapted to provide a fifth-wavelength light beam  235 . A fifth light path  205  of the fifth-wavelength light beam  235  is different from the third light path  203  of the third-wavelength light beam  231 . The fifth-wavelength light beam  235  may also be a blue laser light beam. 
     The second plate  28  is disposed apart from the outputting surface of the light combining element  24 .  FIG. 7A  illustrates a schematic view illustrating an implementation of the first plate  26  and the second plate  28  of the illumination system of the second embodiment. The second plate  28  has a second phosphor  283  and a second surface  281  opposite the outputting surface. The second phosphor  283  is disposed on the second surface  281 . 
       FIG. 7B  illustrates a schematic view of a different implementation of the first plate  26  and the second plate  28  of the illumination system according to the second embodiment of the present invention. The first plate  26  and the second plate  28  may be combined into a plate  26 ′ with a relatively large area, and the first phosphor  263  and the second phosphor  283  are disposed on a surface  261 ′ of the plate  26 ′ respectively. 
     With reference back to  FIG. 6  and  FIG. 8 , the third-wavelength light beam  231  can excite the first phosphor  263  located on the first plate  26  to generate the fourth-wavelength light beam  233 ; and the fifth-wavelength light beam  235  can excite the second phosphor  283  located on the second plate  28  to generate a sixth-wavelength light beam  237 . 
     In the second embodiment, the second phosphor  283  may be a red phosphor, which would indicate that the sixth-wavelength light beam  237  is a red light beam. Furthermore, the second-wavelength light beam  221  and the sixth-wavelength light beam  237  are red light beams of different wavebands, and the waveband of the second-wavelength light beam  221  is contained within the waveband of the sixth-wavelength light beam  237 . 
     The second band-stop filter  29  is disposed between the outputting surface and the light homogenizing element  25 . In this case, the first band-stop filter  27  may be disposed on the outputting surface, the second band-stop filter  29  may be disposed in front of the first band-stop filter  27 , and an included angle is formed between the second band-stop filter  29  and the first band-stop filter  27 . The second band-stop filter  29  is adapted to allow the first-wavelength light beam  211  to the fifth-wavelength light beam  235  to pass therethrough and reflect the sixth-wavelength light beam  237 . 
     Next, the light paths of the light beams in the illumination system  2 ′ will be further described. The first light path  201  to the fourth light path  204  are just the same as the light paths of the light combining element  24  in the first embodiment, and thus, will not be further described herein. The fifth-wavelength light beam  235  (the blue laser light beam) from the third solid-state light source  23  propagates into the light combining element  24  along the fifth light path  205 , and is then reflected by the gap layer  243  out of the light combining element  24  along the fifth light path  205 . 
     Then, the fifth-wavelength light beam  235  projected out of the light combining element  24  propagates to the second phosphor  283  on the second plate  28  to generate the sixth-wavelength light beam  237  (the red light beam). The sixth-wavelength light beam  237  then advances to the second band-stop filter  29  along the sixth light path  206 . 
     After the sixth-wavelength light beam  237  reaches the second band-stop filter  29 , some light rays (i.e., light rays with the same waveband as the second-wavelength light beam  221 ) of the sixth-wavelength light beam  237  pass through the second band-stop filter  29  while the other light rays (i.e., the light rays having different wavebands from the second-wavelength light beam  221 ) are reflected by the second band-stop filter  29  into the light homogenizing element  25 . 
     It shall be appreciated that the included angle between the first band-stop filter  27  and the second band-stop filter  29  must be set in coordination with the first plate  26 , the second plate  28  and the light homogenizing element  25  so that the fourth-wavelength light beam  233  and the sixth-wavelength light beam  237  can be reflected by the first band-stop filter  27  and the second band-stop filter  29  into the light homogenizing element  25 . 
     Because the sixth-wavelength light beam  237  (the red light beam) is generated by the second phosphor  283 , the sixth-wavelength light beam  237  has an adequate intensity and can be mixed with the second-wavelength light beam  221  (the other red light beam) to enhance the intensity of the red light beam outputted by the light homogenizing element  25 . 
     According to the above descriptions, the illumination system of the present invention can reduce the space occupied by the illumination system and reduce the number of solid-state light sources to avoid the occupation of a large space as with conventional illumination systems. Furthermore, the illumination system of the present invention can not only reduce the space occupied but also enhance the intensity of a light beam of a specific color (e.g., a green light beam or a red light beam). 
     The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.