Abstract:
A projection display apparatus including a lighting system, a projection lens and a display device. The lighting system has a light source, a lens set, and an Yttrium Aluminum Garnet filter (YAG filter) is provided. The light source is suitable for providing a light beam. The lens set is disposed on the transmission path of the light beam. The YAG filter is disposed between the light source and the lens set and on the transmission path of the light beam as well. Additionally, the projection lens is disposed on the transmission path of the light beam. The display device is disposed between the lighting system and the projection lens and on the transmission path of the light beam as well. The projection apparatus having the YAG filter is benefited in dispelling the heat of the light source and optical devices, thereby extending lifetime of the light source and optical devices.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     The present invention relates to a projection display apparatus and an optical filter. In particular, the present invention relates to an optical filter capable of absorbing the infrared rays, and heat dissipation of the projection display apparatus is improved by using the optical filter.  
         [0003]     2. Description of Related Art  
         [0004]     In general, the projection display apparatuses in the prior art are applied in the displaying apparatuses of the front-projection type or large-screen rear-projection type, so the light sources required must be able to supply higher total luminance to have the projection image with higher brightness. Therefore, halogen lamps or a variety of high-pressure mercury lamps are widely used as light sources in projection display apparatuses. Despite the merit of high brightness, there are still many drawbacks accompanied with those light sources, such as high power consumption, short lifetime, and immense heat generation and so forth. Among those drawbacks, in particular, the immense heat generated by light sources often leads to shortened lifetime of light sources and damages of optical devices in the projection display apparatus.  
         [0005]      FIG. 1  schematically illustrates a projection display apparatus in the prior art. Please refer to  FIG. 1 . The image display apparatus  100  comprises a lighting system  110 , a projection lens  130 , and a display unit  120 . Wherein, the lighting system  110  comprises a light source  112 , a lens set  116  and an ultraviolet/infrared ray filter  114  (UV/IR filter). The light source  112  is suitable for providing a light beam  140 . The lens set  116  is disposed on the transmission path of the light beam  140 , and the UV/IR filter  114  is disposed between the light source  112  and the lens set  116  and on the transmission path of the light beam  140  as well. Further, the projection lens  130  is disposed on the transmission path of light beam  140 , and the display unit  120  is disposed between the lighting system  110  and the projection lens  130  and on the transmission path of light beam  140  as well. The display unit  120  includes a color-combination prism  120   a  and a display device  120   b . After the modulating operation via the display device  120   b  and combining operation of color lights (R, G and B) via color-combination prism  120   a  in the display unit  120 , the light beam  140  from light source  112  is projected by the projection lens  130  for forming the image.  
         [0006]     In the projection displaying apparatus  100 , several optical devices (such as the lens set  116  shown in  FIG. 1 ) are made of organic materials. In addition to visual lights, the light beam  140  provided by the light source  112  also includes lights that cannot be visualized like the ultraviolet light  140   a  (UV) and infrared ray  140   b  (IR), etc. Once lights including the ultraviolet light  140   a  and the infrared ray  140   b  enter the lens set  116 , due to excessive absorption of the ultraviolet light  140   a  and infrared ray  140   b , damage of the lens set  116  occurs. To avoid the circumstances mentioned above, usually the UV light  140   a  and IR  140   b  are reflected back to the light source  112  for blocking the access to the optical devices located behind by placing an UV/IR filter  114  ahead of the light source  112 .  
         [0007]      FIG. 2  schematically shows for a projection display apparatus in the prior art, a spectrum diagram of light beams measured after being filtered by an UV/IR filter. Please refer to  FIGS. 1 and 2  simultaneously. Lights in the visual-light region  210  (wavelengths ranging from 400 nm to 700 nm) have an averaged transmittance rate 95%. Besides, the UV lights  140   a  and IR  140   b , in the local IR-region  220  (wavelengths ranging from 740 nm to 920 nm) and local UV-region  230  (wavelengths ranging from 200 nm to 380 nm), would hardly penetrate through the UV/IR filter  114 . Namely, after passing through UV/IR filter  114 , only visual lights of light beam  140  remain and IR  140   a  and UV lights  140   b  are reflected back to the light source  112 .  
         [0008]     Nevertheless, since UV lights  140   a  and IR  140   b  are reflected back to the light source  112  by the UV/IR filter  114 , energy of UV lights  140   a  and IR  140   b  is accumulated on the light source  112  and that causes heavy heat-loading of the light source  112 . Also, being unable to eliminate heat effectively, lifetime of the light source  112  will be shortened. The optical devices (such as the lens set  116  shown in  FIG. 1 ) made of organic materials would probably get damaged as well.  
       SUMMARY OF THE INVENTION  
       [0009]     In view of this, one object of the present invention is to provide a projection display apparatus capable of extending lifetime of the light source and optical devices.  
         [0010]     One another object of the present invention is to provide an optical filter suitable for absorbing the infrared rays to dissipate heat.  
         [0011]     The present invention provides a projection display apparatus comprising a lighting system, a projection lens and a display unit. Wherein, the lighting system comprises a light source, a lens set and an Yttrium Aluminum Garnet filter (YAG filter). The light source is suitable for providing a light beam. The lens set is disposed on the transmission path of the light beam, and the YAG filter is disposed between the light source and the lens set and on the transmission path of the light beam as well. In addition, the projection lens is disposed on the transmission path of the light beam, and the display unit is disposed between the lighting system and the projection lens and on the transmission path of the light beam as well.  
         [0012]     In one preferred embodiment of the present invention, the YAG filter mentioned above, for example, further comprises at least a coating layer disposed on the surface of the YAG filter.  
         [0013]     In one preferred embodiment of the present invention, the coating layer mentioned above for example is an anti-reflective coating (AR coating), and the material of the anti-reflective coating includes MgF 2  or Na 3 AlF 6 .  
         [0014]     In one preferred embodiment of the present invention, the coating layer mentioned above, for example, is an ultraviolet-blocking coating (UV-blocking coating) and a material of the UV-blocking coating can be a blended material of TiO 2  and SiO 2  for example.  
         [0015]     In one preferred embodiment of the present invention, the coating layer mentioned above, for example, includes an AR coating and an UV-blocking coating.  
         [0016]     In one preferred embodiment of the present invention, the projection display apparatus, for example, further comprises a heat-sink apparatus disposed on the side of the YAG filter.  
         [0017]     In one preferred embodiment of the present invention, the light source mentioned above for example is an ultra high pressure lamp (UHP lamp).  
         [0018]     In one preferred embodiment of the present invention, the lens set mentioned above includes a polarization converter and a condenser lens, for example.  
         [0019]     In one preferred embodiment of the present invention, the display unit mentioned above, for example, includes a color-combination prism and at least a display device. And wherein, the display unit may be a liquid crystal on silicon (LCOS) display panel, a high temperature poly-silicon (HTPS) display panel, or the digital light processing (DLP) technique, for example.  
         [0020]     The present invention provides an optical filter comprising an YAG filter and at least a coating layer. Wherein, the coating layer is disposed on the surface of the YAG filter.  
         [0021]     In one preferred embodiment of the present invention, the coating layer mentioned above is an anti-reflective coating (AR coating) for example, and the material of the anti-reflective coating (AR coating) includes MgF 2  or Na 3 AlF 6 .  
         [0022]     In one preferred embodiment of the present invention, the coating layer mentioned above for example is an ultraviolet-blocking coating (UV-blocking coating), and the material of the UV-blocking coating can be a blended material of TiO 2  and SiO 2  for example.  
         [0023]     In one preferred embodiment of the present invention, the coating layer mentioned above includes an AR coating and an UV-blocking coating, for example.  
         [0024]     Based on the present invention, because of the adoption of the YAG filter owning merits, including the ability of absorbing the infrared rays and a high coefficient of thermal conductivity, heat dissipation of the projection display apparatus can be improved and the accumulated heat generated by the infrared rays that cause shortened lifetime of the light source can be prevented. Moreover, the coating layer disposed on the surface of the YAG filter is helpful in reflecting the UV lights and raising the transmittance rate of visual lights, so not only the damages of optical devices made of organic materials can be avoided but also utility efficiency of lights can be increased.  
         [0025]     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     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.  
         [0027]      FIG. 1  schematically shows a projection display apparatus in the prior art.  
         [0028]      FIG. 2  schematically shows the measured spectrum of light beams after being filtered by an UV/IR filter in a projection display apparatus of the prior art.  
         [0029]      FIG. 3  schematically shows a projection display apparatus according to one preferred embodiment of the present invention.  
         [0030]      FIG. 4  schematically shows the measured spectrum of light beams after being filtered by the YAG filter in the projection apparatus of the present invention.  
         [0031]      FIG. 5  schematically shows temperature measurements on the light source of the projection display apparatus of the present invention by using thermal couples.  
         [0032]      FIG. 6  schematically shows the temperature measurements on the light source of the projection display apparatus of the present invention by using thermal couples.  
         [0033]      FIG. 7  schematically shows an optical filter according to one preferred embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     The First Embodiment  
       [0034]      FIG. 3  schematically shows a projection display apparatus according to one preferred embodiment of the present invention. Referring to  FIG. 3 , the projection display apparatus  300  may comprise a lighting system  310 , a projection lens  330  and a display unit  320 , for example.  
         [0035]     The lighting system  310  may comprise a light source  312 , a lens set  316  and an Yttrium Aluminum Garnet filter (YAG filter)  314 , for example. The light source  312  is suitable for supplying a light beam  340 , and in one preferred embodiment the light source  312  can be an ultra high pressure (UHP) lamp which is filled with high-pressure mercury-vapor. The lens set  316  is disposed on the transmission path of the light beam  340 , and in one preferred embodiment it may comprise a PS converter  316   a  for converting the P-direction and S-direction polarized lights of the light beam  340  and a condenser lens  316   b  for focusing the light beam  340  to enhance the intensity of the light beam  340 .  
         [0036]     Please continue to refer to  FIG. 3 . The YAG filter  314  in the lighting system  310  is disposed between the light source  312  and the lens set  316  and also disposed on the transmission path of the light beam  340 . The YAG filter  314  made of Yttrium Aluminum Garnet features a high coefficient of thermal conductivity, a high melting point, a high transmittance rate, robust mechanical strength and high insulation capability, etc. It&#39;s worthy to note that the Yttrium Aluminum Garnet (YAG) is of mono-crystalline structure with thermal conductivity 0.12 W/cm.K that is twelve times of thermal conductivity of the glass (0.01 W/cm.K at room temperature). Thus, the YAG owns better ability of conduction heat transfer than that of the glass.  
         [0037]     In addition, the YAG has the characteristic of absorbing infrared rays (IR), and therefore, the YAG filter  314  shown in  FIG. 3  is capable of absorbing infrared rays  340   a  from the light source  312 . In comparison with the traditional method that is to reflect the infrared rays  140   a  back to the light source  112  by using an UV/IR filter  114  shown in  FIG. 1 , the present invention is to utilize the YAG filter  314  to absorb the energy of IR  340   a . Also, the YAG filter  314  with high capability of conduction heat transfer is used to effectively absorb and conduct away the heat generated by IR  340   a , but not to reflect the IR  340   a  back otherwise. Thus, no heat loading applied on the light source  312  appears. In one preferred embodiment, the projection display apparatus, for example, further comprises a heat-sink apparatus  350  disposed on the side of the YAG filter  314 . This heat-sink apparatus  350  can be a heat-sink fan that is suitable for dissipating the heat accumulated in the YAG filter  314  or the heat around the light source  312 .  
         [0038]     Refer to  FIG. 3  again. It is worthy to note, in one embodiment of the present invention, at least one coating layer  314   a / 314   b  disposed on the surface of the YAG filter  314  is further comprised, for increasing the transmittance efficiency of visual lights transferring through the YAG filter  314 , or for enabling the YAG filter  314  to reflect the UV lights. By doing so, not only the transmittance rate of visual lights is increased but also UV lights are prevented from entering into the optical module located behind and damaging the optical devices made of organic materials.  
         [0039]     In one aforementioned embodiment of the present invention, the coating layer mentioned above, for example, is an anti-reflective coating (AR coating)  314   a  used for raising the transmittance rate of visual lights, and the material of this AR coating  314   a  can be MgF 2  or Na 3 AlF 6 , for example.  
         [0040]     In another embodiment of the present invention, the coating layer mentioned above, for example, is an UV- blocking coating  314   b  used for reflecting UV lights. And the material of the UV-blocking coating can be a blended material of TiO 2  and SiO 2 , for example.  
         [0041]     Without a doubt, in one another embodiment of the present invention, the coating layer mentioned above, for example, includes both one AR coating  314   a  and one UV-blocking coating  314   b  used for further improving the performance of the YAG filter  314 . For the sequence of the coating layers to be formed on the surface of the YAG filter  314 , either the AR coating  314   a  or the UV-blocking coating  314   b  is fabricated first.  
         [0042]     In a word, by using the YAG filter  314  and the coating layers  314   a ,  314   b  coated on the surface of the YAG filter  314 , the projection display apparatus  300  is enabled to absorb IR  340   a  and dissipate the heat generated, to raise the transmittance rate of visual lights of light beam  340 , and to reflect the UV lights  340   b  so as to prevent the UV lights  340   b  from damaging the optical devices made of organic materials.  
         [0043]     Still referring to  FIG. 3 , the projection lens  330  in the projection display apparatus  300  is disposed on the transmission path of the light beam  340  for projecting the image data onto a screen (not shown) and displaying the image. The display unit  320  is disposed between the lighting system  310  and the projection lens  330  and disposed on the transmission path of light beam  340  as well. In one preferred embodiment of the present invention, the display unit  320  may comprise a color-combination prism  320   a  and at least a display device  320   b , for example. Wherein, the display device  320   b  may be a liquid crystal on silicon (LCOS) display panel, a high temperature poly-silicon (HTPS) display panel, or the digital micro-mirror device (DMD) for the digital light processing (DLP) technique. The display unit  320  can also be the digital micro-mirror device (DMD) of the digital light processing (DLP) technique. In one embodiment, if the display unit  320  is composed of LCOS panels, then the display unit  320  can be a projection system composed of the three-panel reflective-type LCD panels, of the single-panel reflective-type LCD panels, or of the dual-panel type LCD panels. To form the images, sequential operations including modulating of light beams from the light source  312  via the display unit  320  and combining of color lights R, G and B via the color-combination prism  320   b  (not shown), are performed in the display unit  320 . And finally the images are displayed via the projecting operation by the projection lens  330 . After the modulating operation via the display device  320   b  and combining operation of color lights (R, G and B) via color-combination prism  320   a  in the display unit  320 , the light beam from light source  312  is projected by the projection lens  330  for forming the image.  
         [0044]     Please refer to the spectrum diagram shown in  FIG. 4  for further illustrations of the capability of absorbing IR by the YAG filter.  
         [0045]      FIG. 4  schematically shows the measured spectrum of light beams after being filtered by the YAG filter  314  in the projection display apparatus of the present invention. Referring to  FIG. 4 , the averaged transmittance rate of visual lights is above 95% in the visual-light region  410  (wavelengths ranging from 400 nm to 700 nm), indicating the transmission effect of visual lights wouldn&#39;t be affected by the YAG filter  314  and an excellent brightness is maintained. In addition, the transmittance rate of UV lights  340   b  in the UV-region  430  (wavelengths ranging from 200 nm to 380 nm) is almost zero, namely, UV lights  340   b  can hardly penetrate through the YAG filter  314  and get reflected otherwise. Furthermore, the wave peaks for lights in the local IR-region  420  (wavelengths between 740 nm and 920 nm) still posses portion of the transmittance rate which tends to descend, and it means that only few of infrared rays  340   a  is reflected by the YAG filter  314 , in comparison with the IR-region  220  shown in  FIG. 2 . And the results of  FIG. 4  reveal that, most of infrared rays  340   a  can pass through the YAG filter  314  and they do not get reflected back to the locations where the light source and optical devices are. Therefore, the heat accumulation on the light source and optical devices can be avoided by using the YAG filter  314 .  
         [0046]     For further illustrations that heat accumulated in the light source and optical devices can be effectively eliminated via the YAG filter  314 , please refer to results of temperature measurements sketched in  FIGS. 5, 6  and Tab. 1.  
         [0047]      FIG. 5  schematically shows temperature measurements of the light source of the projection display apparatus in the present invention by using thermal couples.  FIG. 6  schematically shows the temperature measurements of the P-S converter of the projection display apparatus in the present invention by using thermal couples. In  FIG. 5  and  FIG. 6 , the temperature differences between the projection display apparatus with YAG filter  314  and that without YAG filter  314  (i.e. to use UV/IR filter  114 ) are measured by using thermal couples mounted respectively on the positions of L1, L2, L3 of the light source and P1 to P5 of the P-S converter  316   a . The results are shown in Tab. 1 below.  
                                                                                                     Temperature ° C.   L1   L2   L3   P1   P2   P3   P4   P5                                Without YAG   649   274   339   45.2   34.1   38.6   32.6   47       filter       With YAG filter   594   238   307   40.7   32.6   36.1   31.1   44                    
         [0048]     Tab. 1 temperature differences measured with YAG filter and without YAG filter.  
         [0049]     As can be seen from Tab. 1, the temperatures of the projection display apparatus with the YAG filter  314  measured are all lower than that of the projection display apparatus without the YAG filter  314 . Accordingly, the YAG filter  314  based on the present invention can effectively eliminate the heat caused by the infrared rays and decrease temperature of the light source  312  and P-S converter  316   a  and thus extend their lifetime.  
       The Second Embodiment  
       [0050]      FIG. 7  schematically shows an optical filter according to one preferred embodiment of the present invention. Referring to  FIG. 7 , the optical filter  500  comprises an Yttrium Aluminum Garnet filter (YAG filter)  510  and at least one coating layer  520 . Wherein, the coating layer  520  is disposed on the surface of the YAG filter  510 . Except being able to absorb the infrared rays, the YAG filter  510  owns the characteristics including a high coefficient of thermal conductivity, a high melting point, a high transmittance rate, robust mechanical strength, and high insulation capability.  
         [0051]     In one preferred embodiment of the present invention, the coating layer  520 , for example, is an anti-reflective coating (AR coating)  522  used to raise the transmittance rate of visual lights, and a material of this AR coating, includes MgF 2  or Na 3 AlF 6  for example.  
         [0052]     In another embodiment of the present invention, the coating layer  520  mentioned above, for example, is an UV- blocking coating  524  for reflecting UV lights and a material of the UV-blocking coating  524 , for example, is a blended material of TiO 2  and SiO 2 .  
         [0053]     In one another embodiment of the present invention, the coating layer  520  mentioned above includes both one AR coating  522  and one UV-blocking coating  524  for further improving performance of the YAG filter  510 . For the sequence of the coating layers to be formed on the surface of the YAG filter  510 , either the AR coating or the UV-blocking coating  524  is fabricated first. The optical filter  500  according to the present invention can be applied to the optical apparatus requiring the elimination of the infrared rays and ultraviolet rays to extend lifetime of the optical apparatus, such as a CCD projector or projecting apparatuses for example.  
         [0054]     To sum up, the projection display apparatus and the optical filter according to the present invention have the merits as follows.  
         [0055]     1. Due to the adoption of the Yttrium Aluminum Garnet filter (YAG filter) with a high coefficient of thermal conductivity, heat dissipation of the projection display apparatus is improved, heat of the infrared rays accumulated on the light source is reduced, and lifetime of the light source is extended.  
         [0056]     2. The coating layer on the surface of the YAG filter is helpful in reflecting the UV lights, raising the transmittance rate of visual lights, preventing the UV lights from damaging the optical devices made of organic materials, and increasing utility efficiency of lights.  
         [0057]     3. The optical filter based on the present invention can be applied on the related optical apparatus to reduce the heat caused by the infrared rays, and extend lifetime of the optical apparatus.  
         [0058]     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing descriptions, it is intended that the present invention covers modifications and variations of this invention if they fall within the scope of the following claims and their equivalents.