Abstract:
A light source apparatus for illuminating an image formation element, includes: a substrate; a driving source that rotates the substrate; a groove formed on a surface of the substrate so as to surround a rotational axis of the substrate; a phosphor layer formed in the groove; a laser light source that emits laser light delivered to the phosphor layer; and an optical system that guides first light emitted from the phosphor layer excited by the laser light, to the image formation element.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a light source, and in particular, to a light source suitable for a projection display apparatus. 
       BACKGROUND ART 
       [0002]    As light sources for projection display devices, discharge lamps have been used such as extra high pressure mercury lamps, metal halide lamps, and xenon lamps. However, in recent years, solid light sources such as light-emitting diodes (LED) and laser diodes (LD) have been receiving attention as next-generation light sources. 
         [0003]    When a laser diode is used as a light source for a projection display apparatus, the direct use of laser light is not preferable for safety reasons, and laser light is preferably converted into incoherent light before use. Preferably, for example, a phosphor is excited by laser light emitted from the laser diode so that light released from the excited phosphor is utilized. Thus, a light source has been proposed which includes a laser diode and a substrate with a phosphor layer formed thereon and irradiated with laser light emitted from the laser diode. 
         [0004]    However, laser light that is delivered to the phosphor layer has the power of several watts to several tens of watts. Furthermore, the spot size of the laser light that is delivered to the phosphor layer is very small (about 1.0 mm 2 ). Thus, when one point on the phosphor layer is continuously irradiated with laser light, the phosphor or a binder that is contained in the phosphor may be damaged by heat. 
         [0005]    Thus, a light source device has been proposed which includes color wheel  1  as shown in  FIG. 1  or  FIG. 2 . Color wheel  1  shown in  FIG. 1  or  FIG. 2  includes circular substrate  2  and motor  3  for rotating circular substrate  2 . Furthermore, a surface of illustrated circular substrate  2  is divided into a first segment area and a second segment area. 
         [0006]    In the first segment area of circular substrate  2  shown in  FIG. 1 , green phosphor layer  4  is formed which emits green light by being excited by laser light. In the second segment area, red phosphor layer  5  is formed which emits red light by being excited by laser light. 
         [0007]    In the first segment area of circular substrate  2  shown in  FIG. 2 , green phosphor layer  4  is formed which emits green light by being excited by laser light. In the second segment area, diffusion layer  6  is formed. 
         [0008]    In color wheel  1  shown in  FIG. 1  or  FIG. 2 , the phosphor layer is formed on circular substrate  2  that is continuously rotated. This prevents a single point on the phosphor layer from being continuously irradiated with laser light, and avoids a thermal loss in the phosphor or the binder that is contained in the phosphor. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: JP2009-277516A 
         Patent Literature 2: JP2011-013313A 
       
     
       SUMMARY OF INVENTION 
     Technical Program 
       [0011]    The efficiency of light utilization in a projection display device as a whole depends significantly on matching between the etendue of an illumination optical system and the etendue of a projection optical system. 
         [0012]    When a DMD (Digital Micro-mirror Device) is used as an image formation element for the projection display device, a polarizing direction of light illuminating the DMD need not be aligned. In such a case, the etendue (E Light ) of the illumination optical system matches the etendue (E MD ) of the projection optical system when the following formula holds true. 
         [0000]      E Light ≦E MD  
 
         [0013]    Furthermore, when a liquid crystal panel is used as an image formation element for the projection display device, the polarizing direction of light illuminating the liquid crystal panel needs to be aligned. In such a case, the etendue (E Light ) of the illumination optical system is effectively doubled. Hence, the etendue (E Light ) of the illumination optical system matches the etendue (E LCD ) of the projection optical system when the following formula holds true. 
         [0000]      2E Light ≦E LCD  
 
         [0014]    Thus, in order to match the etendue of the illumination optical system with the etendue of the projection optical system, the etendue of the illumination optical system is desirably reduced. 
         [0015]    However, light that is released from the phosphor that is excited by laser light scatters. Thus, as shown in  FIG. 3 , diameter (D 1 ) of light  12  that is emitted from phosphor layer  11  that is formed on substrate  10  is larger than spot size (D 2 ) of laser light  13 . In other words, light emission area of phosphor layer  11  is larger than the irradiated area of the phosphor layer irradiated with the laser light. Thus, when an illumination optical system is configured using a light source device with color wheel  1  shown in  FIG. 1  or  FIG. 2 , it is difficult to match the etendue of the illumination optical system with the etendue of the projection optical system. 
         [0016]    An object of the present invention is to reduce, as much as possible, the etendue of the light source apparatus using a laser light source, thus improving the efficiency of light utilization in a projection display apparatus. 
       Solution to Problem 
       [0017]    A light source apparatus for illuminating an image formation element, includes: a substrate; a driving source that rotates the substrate; a groove formed on a surface of the substrate so as to surround a rotational axis of the substrate; a phosphor layer formed in the groove; a laser diode that emits laser light delivered to the phosphor layer; and an optical system that guides first light emitted from the phosphor layer excited by the laser light, to the image formation element. 
         [0018]    The projection display apparatus according to the present invention includes an illumination optical system including the light source apparatus according to the present invention. 
       Advantageous Effects of Invention 
       [0019]    The present invention can reduce the etendue of a light source apparatus using a laser light source. The present invention facilitates matching of the etendue of the illumination optical system with the etendue of the projection optical system. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1  is a plan view and a side view showing an example of a color wheel relative to the present invention, 
           [0021]      FIG. 2  is a plan view and a side view showing another example of a color wheel relative to the present invention, 
           [0022]      FIG. 3  is a schematic cross-sectional view of the color wheel shown in  FIG. 1  and  FIG. 2 , 
           [0023]      FIG. 4  is a diagram showing a first exemplary embodiment according to the present invention, 
           [0024]      FIG. 5  is a plan view and a side view of the color wheel shown in  FIG. 4 , 
           [0025]      FIG. 6  is a schematic cross-sectional view of the color wheel shown in  FIG. 4 , 
           [0026]      FIG. 7  is a schematic cross-sectional view of a variation of the color wheel, 
           [0027]      FIG. 8  is a perspective view of the appearance of a projection display apparatus with the light source apparatus shown in  FIG. 4 , 
           [0028]      FIG. 9  is a schematic diagram showing the internal structure of the projection display apparatus shown in  FIG. 8 , and 
           [0029]      FIG. 10  is a diagram showing a second exemplary embodiment according to the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Exemplary Embodiment 
       [0030]    A first exemplary embodiment according to the present invention will be described below. As shown in  FIG. 4 , light source apparatus  20  according to the first exemplary embodiment includes laser light source (laser diode)  30  that emits blue laser light, first solid light source (blue light-emitting diode)  40 , dichroic mirror  50 , color wheel  60 , and a plurality of optical elements. Laser diode  30  is hereinafter referred to as “LD  30 ”. Blue light-emitting diode  40  is hereinafter referred to as “blue LED  40 ”. 
         [0031]    Laser light that is emitted from LD  30  is reflected by dichroic mirror  50 , and then enters color wheel  60 . The laser light having entered color wheel  60  is converted into red light or green light by a phosphor on color wheel  60 . The converted red light or green light is delivered to the illumination target (not shown) via a plurality of optical elements including dichroic mirror  50 . On the other hand, blue light that is emitted from blue LED  40  is reflected by dichroic mirror  50 , and is delivered to the illumination target via the plurality of optical elements. In short, light source apparatus  20  according to the first exemplary embodiment illuminates the illumination target with the red light and green light obtained by carrying out wavelength conversion on the laser light and the blue light emitted by blue LED  40 . The components will be specifically described below. 
         [0032]    Dichroic mirror  50  has wavelength selectivity with which dichroic mirror  50  reflects blue light, while allowing red light and green light to transmit through. As shown in  FIG. 4 , LD  30  and blue LED  40  are arranged opposite each other with dichroic mirror  50  interposed therebetween. Furthermore, a first lens group is arranged between dichroic mirror  50  and color wheel  60 , and a second lens group is arranged between dichroic mirror  50  and blue LED  40 . The first lens group and the second lens group are collimator lens groups that make light beams parallel to one another. 
         [0033]    As shown in  FIG. 4 , focusing lens  70 , rod lens  71 , relay lens group  72 , and reflection mirror  73  are arranged in this order on an optical path of red light and green light, which are transmitted through dichroic mirror  50 . An optical path of blue light that is emitted from blue LED  40  and that is reflected by dichroic mirror  50  is the same as the optical path of the red light and green light, which are transmitted through dichroic mirror  50 . 
         [0034]    Now, color wheel  60  will be described. As shown in  FIG. 5  and  FIG. 6 , color wheel  60  includes circular glass substrate  61  and driving source (motor  62 ) configured to rotate glass substrate  61 . Illustration of motor  62  is omitted from  FIG. 6 . 
         [0035]    Ring-like recess portion (groove  63 ) concentric with substrate  61  is formed on a surface of glass substrate  61 . A chain line in  FIG. 5  shows a trajectory of laser light that is reflected by dichroic mirror  50  ( FIG. 4 ) and that enters glass substrate  61 . That is, groove  63  is formed along the trajectory of laser light. In other words, the laser light traces groove  63 . 
         [0036]    A reflection film (not shown) that is reflects visible light is formed on the inner surfaces of groove  63  (opposite side surfaces  63   a  and  63   b  and bottom surface  63   c ). Moreover, groove  63  is divided into two areas (a first area and a second area) along the circumferential direction of groove  63 , and includes first phosphor layer  64  formed on the reflection film in the first area and second phosphor layer  65  formed on the reflection film in the second area. A phosphor that forms first phosphor layer  64  releases green light by being excited by laser light. On the other hand, a phosphor that forms second phosphor layer  65  releases red light by being excited by laser light. 
         [0037]    Light that is released from the phosphor that is excited by laser light scatters. Phosphor layers  64  and  65  are provided inside groove  63 , and thus, light that is emitted from phosphor layers  64  and  65  is repeatedly reflected inside groove  63 . Moreover, as shown in  FIG. 6 , width (W) of groove  63  is smaller than spot size (D 3 ) of laser light  31 . Thus, the diameter of light  32  that is emitted from phosphor layers  64  and  65  is smaller than spot size (D 3 ) of laser light  31 . Therefore, when an illumination optical system of a projection display apparatus is configured using light source apparatus  20  shown in  FIG. 4 , the etendue of the illumination optical system can be easily matched with the etendue of the projection optical system. This advantageously allows the brightness of the projection display apparatus as a whole to be improved. 
         [0038]    Additionally, in the first exemplary embodiment, phosphor layers  64  and  65  are stacked on the reflection film formed on inner surfaces  63   a ,  63   b , and  63   c  of groove  63 . Thus, since light that is emitted from phosphor layers  64  and  64  is prevented from being absorbed by glass substrate  61 , this leads to a reduced loss. 
         [0039]    On the other hand, since width (W) of groove  63  is smaller than spot size (D 3 ) of laser light  31 , an edge of laser light  31  sticks out from groove  63  as shown in  FIG. 6 . In other words, the edge of laser light  31  is prevented from being delivered to phosphor layers  64  and  65 . However, the intensity distribution of laser light  31  is a Gaussian distribution, and thus, the edge does not have a very high intensity. Thus, the possibility that optical loss will occur is low, and at least the above-described advantages exceed the possible optical loss. The above-described advantages may be obtained even when width (W) of groove  63  is the same as or larger than spot size (D 3 ) of laser light  31 . For example, when width (W) of groove  63  is smaller than diameter (D 1 ) of light  12  shown in  FIG. 3 , the etendue diminishes. 
         [0040]    When phosphor layers  64  and  65  are excessively thin, a larger amount of laser light (exciting light) exits color wheel  60  without being subjected to wavelength conversion. On the other hand, when phosphor layers  64  and  65  are excessively thick, a larger amount of light is subjected to wavelength conversion two or more times or is absorbed by the phosphor. The phosphor has a particle size of several tens of micrometer, and thus, the thickness of each of the phosphor layers  64  and  65  is preferably 50 μm or more and 300 μm or less. In other words, the depth of groove  63  is preferably 50 μm or more and 300 μm or less. Indeed, the preferred thickness of each of phosphor layers  64  and  65  varies depending on the particle size of the phosphor. 
         [0041]    The operation of light source apparatus  20  will be described with reference to  FIG. 4  and  FIG. 5 . Laser light (blue light) that is emitted from LD  30  is reflected by dichroic mirror  50 , and then enters the first lens group. The laser beams having entered the first lens group are made parallel to one another by the first lens group. The laser light that is emitted from the first lens group enters rotating glass substrate  61 . Specifically, the light enters the first area or second area of groove  63  shown in  FIG. 5 . In other words, the laser light enters first phosphor layer  64  or second phosphor layer  65  on glass substrate  61 . When the laser light enters first phosphor layer  64 , first phosphor layer  64  emits green light. On the other hand, when the laser light enters second phosphor layer  65 , second phosphor layer  65  emits red light. The light beams that are emitted from phosphor layer  64  or  65  (green light or red light) are transmitted through the first lens group again and made parallel to one another, and the parallel light beams are transmitted through dichroic mirror  50 . The light having been transmitted through dichroic mirror  50  is transmitted through focusing lens  70 , rod lens  71 , and relay lens group  72  in this order and then enters reflection mirror  73 . The light having entered reflection mirror  73  is reflected toward the predetermined illumination target by reflection mirror  73 . 
         [0042]    On the other hand, light that is emitted from blue LED  40  enters the second lens group. The light beams having entered the second lens group are made parallel to one another by the second lens group. The light that is emitted from the second lens group is reflected by dichroic mirror  50 , and then enters focusing lens  70 . The light that is emitted from focusing lens  70  is transmitted through rod lens  71  and relay lens group  72  in this order and then enters reflection mirror  73 . The light having entered reflection mirror  73  is reflected toward the predetermined illumination target by reflection mirror  73 . 
         [0043]    The luminance distribution of the light (red light, green light, and blue light) is made even while the light is passing through rod lens  71 . Furthermore, the cross section of the light (luminous flux) that is emitted from rod lens  71  is shaped into a substantial rectangle. Moreover, the cross section of the light that is delivered to the illumination target by reflection mirror  73  is slightly larger than the illumination area on the illumination target. 
         [0044]      FIG. 7  shows a variation of the color wheel. Color wheel  60  shown in  FIG. 6  is different from color wheel  60  shown in  FIG. 7  in the cross section of groove  63 . The width of groove  63  on color wheel  60  shown in  FIG. 6  is constant. On the other hand, the width of groove  63  on color wheel  60  shown in  FIG. 7  is not constant. Specifically, the width of groove  63  increases from back surface side  61   a  toward front surface side  61   b  of glass substrate  61 . In other words, the distance between opposite side surfaces  63   a  and  63   b  gradually increases. In other words more, opposite side surfaces  63   a  and  63   b  are inclined so as to separate from each other. As a result, the angles between bottom surface  63   c  and each side surface  63   a  and  63   b  of groove  63  are larger than 90 degrees. Indeed, the maximum width of groove  63  is smaller than spot size (D 3 ) of laser light  31 . 
         [0045]    The light that is emitted from the phosphor is reflected by the reflection film formed on side surfaces  63   a  and  63   b  inclined as described above. As a result, the angle distribution of light  32  that is emitted from phosphor layers  64  and  65  is reduced, further decreasing the diameter of light  32 . 
         [0046]    Glass substrate  61  may be changed to a metal substrate (for example, an aluminum substrate). The reflection film may be formed of an optical multilayer film or a metal film. Dichroic mirror  50  may be changed to a cross dichroic prism. Rod lens  71  may be changed to a lens array. 
         [0047]    Groove  63  may be divided into three or more areas along the circumferential direction of groove  63 , and different phosphor layers may be formed in the respective areas. For example, a phosphor layer that is configured to emit green light is formed in a first area, a phosphor layer that is configured to emit red light is formed in a second area, and a phosphor layer that is configured to emit blue light is formed in a third area. In this case, blue LED  40  shown in  FIG. 4  may be omitted. Furthermore, when groove  63  is partitioned into three or more areas, the same phosphor layer may be formed in two or more areas. 
         [0048]      FIG. 8  is a perspective view of the appearance of projection display apparatus  80  with light source apparatus  20  shown in  FIG. 4 . Projection display apparatus  80  includes housing  81  formed of a synthetic resin. Projection lens  82  is provided on a front surface of housing  81 , and various connectors  83 , power supply switch  84 , and the like are provided on a rear surface of housing  81 . Furthermore, operation panel  86  including a plurality of operation buttons  85  is provided on an upper surface of housing  81 . 
         [0049]      FIG. 9  is a schematic diagram showing the internal structure of projection display apparatus  80  shown in  FIG. 8 . Projection display apparatus  80  includes DMD  87  as an image formation element. DMD  87  is illuminated by light source apparatus  20 . Specifically, light that is reflected by reflection mirror  73  in light source apparatus  20  is delivered to DMD  87 . DMD  87  modulates the delivered light in accordance with a video signal to form image light. The formed image light is projected on a screen (not shown) via projection lens  82 . 
         [0050]    DMD  87  and light source apparatus  20  are synchronized with each other. Specifically, the rotation angle and rotation speed of glass substrate  61  and light emission timings for LD  30  are set so as to irradiate second phosphor layer  65  ( FIG. 5 ) with laser light when DMD  87  is to display a red color. Furthermore, the rotation angle and rotation speed of glass substrate  61  and light emission timings for LD  30  are set so as to irradiate first phosphor layer  64  ( FIG. 5 ) with laser light when DMD  87  is to display a green color. Moreover, the rotation angle and rotation speed of glass substrate  61  and light emission timings for blue LED  40  and LD  30  are set so as to allow blue LED  40  to emit light while avoiding irradiation of glass substrate  61  with laser light when DMD  87  is to display a blue color. 
         [0051]    Instead of DMD  87 , a liquid crystal panel may be used as an image formation element. 
       Second Exemplary Embodiment 
       [0052]    A second exemplary embodiment of the light source apparatus will be described below.  FIG. 10  is a schematic diagram showing a configuration of light source apparatus  90  according to this exemplary embodiment. A basic configuration of light source apparatus  90  according to this exemplary embodiment is the same as the basic configuration of light source apparatus  20  according to the first exemplary embodiment. Thus, only differences from light source apparatus  20  will be described below, and aspects common to light source apparatus  90  and  20  will not be described. 
         [0053]    Light source apparatus  90  includes second solid light source (red light-emitting diode)  41  in addition to LD  30  and blue LED  40 . Furthermore, light source apparatus  90  uses cross dichroic prism  51  instead of dichroic mirror  50  shown in  FIG. 4  and uses lens array  75  instead of rod lens  71 . Moreover, only a first phosphor layer (not shown) is provided inside a groove (not shown) in glass substrate  61 . Red light-emitting diode  40  is hereinafter referred to as “red LED  41 ”. 
         [0054]    The operation of light source apparatus  90  will be described. Laser light (blue light) that is emitted from LD  30  is reflected by reflection mirror  100 , and then enters cross dichroic prism  51 . The light having entered the cross dichroic prism  51  is reflected by a refection film in the prism, and then enters rotating glass substrate  61 . Specifically, the laser light enters the first phosphor layer on glass substrate  61 , and the first phosphor layer emits green light. The green light that is emitted from the first phosphor layer enters cross dichroic prism  51  again. The green light having entered cross dichroic prism  51  is transmitted through the reflection film in the prism and enters lens array  75 . 
         [0055]    Light (red light) that is emitted from red LED  41  is reflected by reflection mirror  101 , and then enters cross dichroic prism  51 . The red light having entered cross dichroic prism  51  is reflected by the refection film in the prism, and them enters lens array  75 . 
         [0056]    Light (blue light) that is emitted by blue LED  40  enters cross dichroic prism  51 . The blue light having entered cross dichroic prism  51  is reflected by the refection film in the prism, and them enters lens array  75 . 
         [0057]    The light in the respective colors having entered lens array  75  as described above is split into a plurality of rectangular light sources by lens array  75 . The resultant rectangular light sources illuminate the predetermined illumination target via condenser lens  76  and reflection mirror  73 . At this time, condenser lens  76  superimposes the plurality of rectangular light sources on one another on the illumination target. As a result, the illumination target is illuminated with light having a necessary and sufficient magnitude and a uniform luminance distribution. 
         [0058]    A collimator lens group may be provided as necessary on an optical path shown in  FIG. 10 . Furthermore, of course, light source apparatus  20  shown in  FIG. 9  can be substituted with light source apparatus  90 . 
         [0059]    As well, the laser light source is not limited to the laser diode (semiconductor laser) but may be a solid laser, a liquid laser, a gas laser, or the like. In addition, the solid light source is not limited to the LED but may be a laser light source. In this case, laser light that is emitted by the laser light source is utilized without change, and thus, a low-power laser light source is preferably used. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               20 ,  90  Light source apparatus 
               30  Laser diode (LD) 
               40  Blue light-emitting diode (blue LED) 
               41  Red light-emitting diode (red LED) 
               50  Dichroic mirror 
               51  Dichroic prism 
               60  Color wheel 
               61  Glass substrate 
               62  Motor 
               63  Groove 
               64  First phosphor layer (green phosphor layer) 
               65  Second phosphor layer (red phosphor layer) 
               70  Focusing lens 
               71  Rod lens 
               72  Relay lens group 
               73  Reflection mirror 
               75  Lens array