Patent Publication Number: US-2023139540-A1

Title: Light source device and projector

Description:
TECHNICAL FIELD 
     The present invention relates to a light source device including a phosphor and a projector. 
     BACKGROUND ART 
     Patent Document 1 discloses a light source device that emits white light in which yellow fluorescent light and blue light are mixed. In this light source device, an excitation light source having a plurality of blue LDs (Laser Diodes) emits excitation light (blue LD light). The excitation light is incident on one surface of a dichroic mirror. The dichroic mirror reflects the excitation light toward a phosphor wheel. The phosphor wheel receives the excitation light to emit yellow fluorescent light in the direction of the dichroic mirror. The yellow fluorescent light is transmitted through the dichroic mirror. 
     A blue light source comprising a plurality of blue LDs emits blue LD light. The blue LD light is incident on the other surface of the dichroic mirror. In the dichroic mirror, the blue LD light is reflected and combined with the yellow fluorescent light that is transmitted through the dichroic mirror. 
     Incidentally, for the purpose of reducing the device cost, a laser module in which a plurality of LD chips is contained in one package may be applied to the excitation light source and the blue light source. There are several types of laser modules depending on the number of LD chips. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: JP-A-2019-158914 
       
    
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the light source device described in Patent Document 1, the following problems occur when a laser module is used. 
     In order to obtain white light having a desired color tone, it is necessary to design so that the ratio of the number of LD chips between the blue light source and the excitation light source is set to the value of a predetermined ratio. However, when using laser modules, the number of LD chips can be set only in module units. Therefore, the degree of freedom of the design was low, and the optimization of the number of LD chips was difficult. 
     Further, when the number of LD chips required for the light source is different from the accommodation number of LD chips of the laser module, a laser module is used whose accommodation number of LD chips is larger than the number of LD chips required. In this case, since it is necessary to reduce the amount of light of the laser module so that a predetermined amount of light is obtained, the light utilization efficiency is reduced. In addition, the power consumption increases because LD chips are driven that were not originally required. 
     An object of the present invention is to solve the above problems and to provide both a light source device in which the number of LD chips can be easily optimized and that has a high light utilization efficiency, and a projector. 
     Means for Solving the Problems 
     To achieve the above object, the light source device of the present invention includes a first light source unit that emits a first monochromatic light, a second light source unit that emits a second monochromatic light of the same color as the first monochromatic light, an optical member that splits the first monochromatic light emitted by the first light source unit into a first split light and a second split light and that integrates the first split light and the second monochromatic light emitted by the second light source unit into one optical path, and a phosphor unit that receives the second split light or the light that has been integrated into the one optical path to emit fluorescent light. 
     The projector of the present invention includes the light source device, a light modulation unit that modulates light emitted by the light source device to form an image, and a projection lens that projects the image formed by the light modulation unit. 
     Effect of the Invention 
     According to the present invention, the number of LD chips can be easily optimized and the light utilization efficiency can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram showing a configuration of a light source device according to a first embodiment of the present invention. 
         FIG.  2    is a schematic diagram showing a configuration of a light source device according to a second embodiment of the present invention. 
         FIG.  3 A  is a side view schematically showing a configuration of a light source device according to a third embodiment of the present invention. 
         FIG.  3 B  is a top view schematically showing the configuration of the light source device according to the third embodiment of the present invention. 
         FIG.  4 A  is a side view schematically showing a configuration of a light source device according to a fourth embodiment of the present invention. 
         FIG.  4 B  is a top view schematically showing the configuration of the light source device according to the fourth embodiment of the present invention. 
         FIG.  5    is a top view schematically showing a configuration of a light source device according to a fifth embodiment of the present invention. 
         FIG.  6    is a schematic diagram showing a configuration of a light source device according to a sixth embodiment of the present invention. 
         FIG.  7    is a schematic diagram showing a configuration of a light source device according to a seventh embodiment of the present invention. 
         FIG.  8    is a schematic diagram showing a configuration of a projector according to an embodiment of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Next, embodiments of the present invention will be described with reference to the drawings. 
     First Embodiment 
       FIG.  1    is a block diagram showing the configuration of a light source device according to a first embodiment of the present invention. 
     Referring to  FIG.  1   , the light source device includes first light source unit  1 , second light source unit  2 , optical member  3 , and phosphor unit  4 . First light source unit  1  emits first monochromatic light  1   a . Second light source unit  2  emits second monochromatic light  2   a  of the same color as first monochromatic light  1   a . Optical member  3  splits first monochromatic light  1   a  emitted by first light source unit  1  into first split light  3   a  and second split light  3   b  and integrates first split light  3   a  and second monochromatic light  2   a  emitted by second light source unit  2  into one optical path. Phosphor unit  4  receives second split light  3   b  or integrated light  3   c  integrated into the one optical path (first split light  3   a +second monochromatic light  2   a ) to emit fluorescent light  4   a.    
     In the light source device of the present embodiment, for example, when integrated light  3   c  is used as excitation light, second split light  3   b  is blue light, and conversely, when second split light  3   b  is used as excitation light, integrated light  3   c  is blue light. In the light source device of the present embodiment, first split light  3   a , which is a part of first monochromatic light  1   a  emitted by first light source unit  1 , can be turned to the side of second light source unit  2 . According to this configuration, even when a laser module is used to constitute first light source unit  1  and second light source unit  2 , by adjusting the division ratio between first split light  3   a  and second split light  3   b , the light quantity ratio between excitation light and blue light can be set to the value of a desired ratio. Thus, by enabling the adjustment of the division ratio, it is possible to easily perform the optimization of the number of LD chips which was difficult to achieve only by adjustment in module units, and it is possible to improve the light utilization efficiency. Further, since it is not necessary to drive LD chips wastefully such as in a configuration in which LD chips which are not originally required are driven, it is possible to reduce the consumption of power. 
     Hereinafter, the operation and effect will be described in detail. 
     One of first light source unit  1  and second light source unit  2  is used as an excitation light source, and the other is used as a blue light source. For example, in the case of exciting phosphor unit  4  with integrated light  3   c , light obtained by color-synthesizing second split light  3   b  and fluorescent light  4   a  into one optical path is the light output from the light source device. On the other hand, when the phosphor unit is excited with second split light  3   b , light obtained by color-synthesizing integrated light  3   c  and fluorescent light  4   a  into one optical path is the light output from the light source device. 
     For example, in order to obtain output light of a desired color tone, the ratio of the numbers of LD chips between the excitation light source and the blue light source is set to 45:15. In this case, the number of LD chips required for the blue light source is 15, and the number of LD chips required for the excitation light source is 45. Under this condition, we will consider a case in which a laser module with  20  LD chips is used to construct the excitation light source and the blue light source, and in which a part of the light emitted by the blue light source is turned to the side of the excitation light source. The number of modules of the excitation light source is 2 and the number of modules of the blue light source is 1. In this case, the number of LD chips of the excitation light source is 40, which is five less than 45 that is the number of chips required to obtain the desired color tone. On the other hand, the number of LD chips of the blue light source is 20, which is five more than 15 that is the number of chips required to obtain the desired color tone. Therefore, by turning the amount of light corresponding to the five LD chips from the blue light source to the side of the excitation light source, it is possible to obtain an output light of the desired color tone. 
     In the configuration shown in  FIG.  1   , first light source unit  1  is used as the blue light source, second light source unit  2  is used as the excitation light source, and the amount of light corresponding to the five LD chips from first light source unit  1  is diverted to the side of second light source unit  2 . Specifically, the division ratio between first split light  3   a  and second split light  3   b  is adjusted so that the ratio between the amount of second split light  3   b  and the amount of integrated light  3   c  (first split light  3   a +second monochromatic light  2   a ) becomes 3:1 (=45:15). This makes it possible to obtain the output light of the desired color tone. Thus, according to the light source device of the present embodiment, since the output light of the desired color tone can be obtained by adjusting the division ratio between first split light  3   a  and second split light  3   b , the degree of freedom in design can be improved, and the optimization of the number of LD chips can be easily performed. 
     Further, according to the light source device of the present embodiment, rather than reducing the amount of light of first light source unit  1 , since first split light  3   a  which is a part of first monochromatic light  1   a  emitted by first light source unit  1  is turned to the side of second light source unit  2 , the light utilization efficiency is improved. In addition, since it is not necessary to drive LD chips wastefully, it is possible to reduce the consumption of power. 
     In the light source device of the present embodiment, the configuration shown in  FIG.  1    is an example and can be changed as appropriate. 
     For example, in a case where phosphor unit  4  is excited by integrated light  3   c  to emit fluorescent light  4   a , a color synthesizing unit may be provided for color-synthesizing second split light  3   b  and fluorescent light  4   a  emitted by phosphor unit  4  into one optical path. In this case, a part of the light emitted by the blue light source is turned to the excitation light source. 
     When phosphor unit  4  is excited by second split light  3   b  to emit fluorescent light  4   a , a color light synthesizing unit may be provided for color-synthesizing integrated light  3   c  and fluorescent light  4   a  emitted by phosphor unit  4  into one optical path. In this case, a part of the light emitted by the excitation light source is turned to the blue light source. 
     Further, optical member  3  may include a retardation plate and a first polarization beam splitter by which first polarized light is reflected and through which second polarized light that is different from the first polarized light is transmitted. In this case, first monochromatic light  1   a  emitted by first light source unit  1  is incident to one surface of the first polarization beam splitter via the retardation plate. The first polarization beam splitter splits first monochromatic light  1   a  into first split light  3   a  made of the first polarized light and second split light  3   b  made of the second polarized light. 
     In the above case, second light source unit  2  emits second monochromatic light  2   a  made of the second polarized light, and second monochromatic light  2   a  may be incident to the other surface of the first polarization beam splitter. In this case, second monochromatic light  2   a  exits from one surface of the first polarization beam splitter on the same optical path as first split light  3   a  made of the first polarized light. 
     Optical member  3  may further include a second polarization beam splitter by which first polarized light is reflected and through which second polarized light is transmitted. In this case, second light source unit  2  emits second monochromatic light  2   a  made of the second polarized light, and second monochromatic light  2   a  enters one surface of the second polarization beam splitter. Furthermore, first split light  3   a  made of the first polarized light enters the other surface of the second polarization beam splitter. In the second polarization beam splitter, the second monochromatic light  2   a  exits from the other surface on the same optical path as first split light  3   a  made of the first polarized light reflected by the other surface. 
     Second light source unit  2  may emit a plurality of light beams, which are second monochromatic light  2   a , in the same direction and in a state in which each light beam is spatially separated from the others. In this case, optical member  3  includes a reflecting member that is provided in a space that does not block each beam in the optical path that includes the plurality of light beams and in which first split light  3   a  made of the first polarized light is reflected in the same direction as the exit direction of the plurality of light beams. 
     First light source unit  1  may include at least one first laser module comprising a plurality of LD chips, and second light source unit  2  may include a plurality of second laser modules, each module comprising a plurality of LD chips. 
     Second Embodiment 
       FIG.  2    is a schematic diagram showing the configuration of a light source device according to the second embodiment of the present invention. Incidentally, in  FIG.  2   , the optical paths and the optical elements are shown schematically, and their sizes and shapes may be different from an actual example. For example, for convenience, the figure shows a state in which one optical path jumps over another optical path, but in practice, each optical path is straight and is arranged to intersect with each other in a spatially separated state. 
     Referring to  FIG.  2   , the light source device includes blue light source  11 , excitation light source  12 , optical member  13 , and phosphor unit  14 . Both blue light source  11  and excitation light source  12  are composed of laser modules each comprising a plurality of LD chips, each LD chip emitting blue LD light (linearly polarized light) that is monochromatic light. Each LD chip is provided with a collimator lens that converts the emitted light into a parallel light beam. 
     Phosphor unit  14  is excited by blue LD light and emits yellow fluorescent light. As phosphor unit  14 , for example, a phosphor wheel can be used. The phosphor wheel comprises a rotation substrate. On one surface of the rotation substrate, a phosphor layer including a phosphor that emits yellow fluorescent light is formed along the circumferential direction. Between the phosphor layer and the rotation substrate, a reflection member is provided that reflects the fluorescent light incident from the phosphor layer to the phosphor layer side. Incidentally, by constituting the rotation substrate by a metal material, it is possible to omit the reflection member. 
     Optical member  13  includes retardation plate  20 , polarization beam splitter  21 , mirrors  22  and  23 , light integrating unit  24 , reduction optical system  25 , fly-eye lenses  26   a  and  26   b , dichroic mirror  27 , diffusion plate  28 , and condenser lens  29 . 
     Blue LD light (linearly polarized light) emitted by blue light source  11  is incident on one surface of polarization beam splitter  21  via retardation plate  20 . Retardation plate  20  is an element that gives a phase difference between the two orthogonal polarization components to change the state of the incident polarization. As retardation plate  20 , for example, a crystal plate such as quartz, a half-wave plate, a quarter-wave plate, or the like can be used. Blue LD light that has passed through retardation plate  20  includes P-polarized light and S-polarized light. Polarization beam splitter  21  is disposed at an inclination of 45 degrees with respect to the optical axis of blue light source  11 . Polarization beam splitter  21  is configured to reflect the S-polarized light and transmit the P-polarized light. The reflection angle of the S-polarized light is 45 degrees. Here, the reflection angle is the angle formed between a normal line perpendicular to the incident surface and the traveling direction of the reflected light. Retardation plate  20  and polarization beam splitter  21  are formed so that the division ratio between the S-polarized light and the P-polarized light becomes the value of a desired division ratio. 
     S-polarized blue LD light reflected by polarization beam splitter  21  is incident to light integrating unit  24  via mirror  22  and mirror  23 . Light integrating unit  24  integrates S-polarized blue LD light and blue LD light emitted by excitation light source  12  into one optical path. 
     For example, excitation light source  12  may emit a plurality of light beams in the same direction in a state in which each beam is spatially separated from the other light beams, and the mirrors that constitute light integrating unit  24  may be provided in the optical path that includes the light beams in a space that does not block each light beam. In this case, the mirrors reflect the S-polarized blue LD light in the same direction as the exit direction of excitation light source  12 . 
     As another example, light integrating unit  24  may be constituted by a polarization beam splitter disposed at an inclination of 45 degrees with respect to the optical axis of excitation light source  12 . In this case, excitation light source  12  emits P-polarized blue LD light. The polarization beam splitter transmits the P-polarized blue LD light emitted by excitation light source  12  and reflects S-polarized blue LD light from mirror  23  in the same direction as the exit direction of the P-polarized blue LD light. 
     Integrated light integrated by light integrating unit  24  is used as excitation light for exciting phosphor unit  14 . The integrated light from light integrating unit  24  enters the first surface of dichroic mirror  27  through reduction optical system  25  and fly-eye lenses  26   a  and  26   b . Reduction optical system  25  reduces the light beam diameter of the integrated light from light integrating unit  24 . By reducing the light beam diameter, it is possible to reduce the size of the optical system that follows reduction optical system  25 . Fly-eye lenses  26   a  and  26   b  constitute a light equalizing element that realizes uniform illuminance distribution on the irradiation surface of phosphor unit  14 . 
     Dichroic mirror  27  has the characteristic of reflecting light in the blue wavelength range and transmitting light in other wavelength ranges within the visible wavelength range. Dichroic mirror  27  reflects integrated light at a reflection angle of 45 degrees. Integrated light reflected by the first surface of dichroic mirror  27  is irradiated to phosphor unit  14  via condenser lens  29 . Phosphor unit  14  receives the integrated light, which is excitation light, and emits yellow fluorescent light toward the condenser lens  29  side. The yellow fluorescent light emitted from phosphor unit  14  is incident on the first surface of dichroic mirror  27  via condenser lens  29 . Condenser lens  29  has a function of condensing integrated light, which is excitation light, on the irradiation surface of phosphor unit  14 , and a function of converting yellow fluorescent light from phosphor unit  14  into pseudo-parallel light. 
     P-polarized blue LD light transmitted through polarization beam splitter  21  is incident on the second surface (the surface opposite to the first surface) of dichroic mirror  27  through diffusion plate  28 . Dichroic mirror  27  transmits yellow fluorescent light incident on the first surface and reflects blue LD light incident on the second surface in the transmission direction of the yellow fluorescent light. That is, dichroic mirror  27  color-synthesizes the blue LD light and the yellow fluorescent light into one optical path. Light color-synthesized by dichroic mirror  27  is the output light (white) of the light source device of the present embodiment. 
     Incidentally, diffusion plate  28  is used to reduce speckle noise. Here, speckle noise is a speckle-like noise generated when forming a projected image using a laser beam. 
     In the light source device of the present embodiment as well, a portion of the emitted light of blue light source  11  can be turned to the side of excitation light source  12 , whereby the same effect can be obtained as in the first embodiment. 
     Further, by configuring retardation plate  20  and polarization beam splitter  21  so that the division ratio between S-polarized light and P-polarized light becomes the value of a desired division ratio, it is possible to obtain output light of a desired color tone. For example, by rotating retardation plate  20  with the optical axis of blue light source  11  as the rotation axis, it is possible to adjust the division ratio of the S-polarized light and P-polarized light. 
     Third Embodiment 
       FIG.  3    is a schematic diagram showing the configuration of a light source device according to a third embodiment of the present invention disclosure.  FIG.  3 A  is a side view and  FIG.  3 B  is a top view. 
     Referring to  FIG.  3 A  and  FIG.  3 B , the light source device includes laser module  31  that is a blue light source, excitation light source  32 , optical member  33 , and phosphor unit  34 . Excitation light source  32  includes two laser modules  32   a  and  32   b . Each of laser modules  31 ,  32   a , and  32   b  has the same configuration, and here, each module is one in which 24 blue LD chips are accommodated in one package. Incidentally, the number of blue LD chips of the laser modules can be changed as appropriate. 
     Phosphor unit  34  has a structure similar to that of phosphor unit  14  described in the second embodiment. Optical member  33  includes retardation plate  40 , polarization beam splitter  41 , mirrors  42 - 44 , reduction optical system  45 , fly-eye lenses  46   a  and  46   b , dichroic mirror  47 , diffusion member  48 , and condenser lens  49 . Optical member  33  also has basically the same configuration as optical member  13  described in the second embodiment but is different in that light integrating unit  24  is constituted by mirror  44 . 
     In the present embodiment, mirror  44  is provided in a space that does not block the respective light beams in the optical path that includes the parallel light beams emitted by each of laser modules  32   a  and  32   b . Specifically, as shown in  FIG.  3 A , laser modules  32   a  and  32   b  are arranged one over the other. Laser modules  32   a  and  32   b  include a light emitting portion that is made of a plurality of LD chips arranged in a matrix and a support portion for supporting the light emitting portion. Since the support portion is larger than the light emitting portion, when laser modules  32   a  and  32   b  are arranged on the same plane, a certain amount of space is provided between laser modules  32   a  and  32   b . Mirror  44  can be disposed in the space between laser modules  32   a  and  32   b  and is formed in a size capable of reflecting parallel light beams from laser module  31 . 
     Mirror  44  integrates S-polarized blue LD light from polarization beam splitter  41  and blue LD light emitted by laser modules  32   a  and  32   b  into one optical path. Integrated light integrated by mirror  44  enters the first surface of dichroic mirror  47  through reduction optical system  45  and fly-eye lenses  46   a  and  46   b . Reduction optical system  45  includes multiple lenses  45   a  and  45   b  for reducing the light beam diameter of the integrated light. Fly eye lenses  46   a  and  46   b  constitute a light equalizing element. Dichroic mirror  47  reflects the integrated light toward phosphor unit  34 . Integrated light reflected by dichroic mirror  47  is incident to phosphor unit  34  via condenser lens  49 . 
     Yellow fluorescent light emitted from phosphor unit  34  enters the first surface of dichroic mirror  47  via condenser lens  49 . On the other hand, P-polarized blue LD light transmitted through polarization beam splitter  41  is incident on the second surface of dichroic mirror  47  through diffusion member  48 . Dichroic mirror  47  transmits the yellow fluorescent light incident on the first surface and reflects the blue LD light incident on the second surface in the transmission direction of the yellow fluorescent light. That is, dichroic mirror  47  color-synthesizes the blue LD light and the yellow fluorescent light into one optical path. 
     In the light source device of the present embodiment as well, a portion of the emitted light of laser module  31  that is a blue light source can be turned to the side of excitation light source  32 , whereby the same effect can be obtained as in the first embodiment. 
     Further, by forming retardation plate  40  and polarization beam splitter  41  so that the division ratio between S-polarized light and P-polarized light becomes the value of a desired division ratio, output light of a desired color tone can be obtained. 
     Fourth Embodiment 
       FIG.  4    is a schematic diagram showing the configuration of a light source device according to a fourth embodiment of the present invention.  FIG.  4 A  is a side view and  FIG.  4 B  is a top view. 
     Referring to  FIG.  4 A  and  FIG.  4 B , the light source device includes laser module  51  that is a blue light source, excitation light source  52 , optical member  53 , and phosphor unit  54 . Excitation light source  52  includes two laser modules  52   a  and  52   b . Laser modules  51 ,  52   a , and  52   b  are the same as laser modules  31 ,  32   a , and  32   b  described in the third embodiment. However, laser module  52   a  and  52   b  are arranged side by side in the lateral direction rather than one over the other in a vertical direction. 
     Phosphor unit  54  has the same structure as that of phosphor unit  14  described in the second embodiment. Optical member  53  includes retardation plate  60 , polarization beam splitter  61 , mirrors  62 - 64 , reduction optical system  65 , fly-eye lenses  66   a  and  66   b , dichroic mirror  67 , diffusion member  68 , and condenser lens  69 . 
     The optical axis of laser module  51  is perpendicular to the optical axis of excitation light source  52 , and polarization beam splitter  61  is provided at the position at which the optical axes intersect. Blue LD light (linearly polarized light) emitted by laser module  51  is incident on the first surface of polarization beam splitter  61  via retardation plate  60 . Retardation plate  60  is the same as retardation plate  20  described in the second embodiment. Blue LD light (P-polarized light) emitted by laser modules  52   a  and  52   b  is incident on the second surface (the surface opposite to the first surface) of polarization beam splitter  61 . 
     Polarization beam splitter  61  transmits P-polarized light and reflects S-polarized light. Of blue LD light that has passed through retardation plate  60 , P-polarized light is transmitted through polarization beam splitter  61 , whereas S-polarized light is reflected by the first surface of polarization beam splitter  61 . Blue LD light (P-polarized light) emitted by laser modules  52   a  and  52   b  is transmitted through polarization beam splitter  61 . That is, polarization beam splitter  61  integrates S-polarized blue LD light from retardation plate  60  and P-polarized blue LD light from laser modules  52   a  and  52   b  into one optical path. 
     Integrated light integrated by polarization beam splitter  61  is incident on the first surface of dichroic mirror  67  through reduction optical system  65 , which is made up of multiple lenses  65   a  and  65 , and fly-eye lenses  66   a  and  66   b . Reduction optical system  65  and fly-eye lenses  66   a  and  66   b  have the same structure as reduction optical system  45  and fly-eye lenses  46   a  and  46   b  described in the third embodiment. Dichroic mirror  67  reflects integrated light toward phosphor unit  54 . Integrated light reflected by dichroic mirror  67  is incident to phosphor unit  54  via condenser lens  69 . Yellow fluorescent light emitted from phosphor unit  54  enters the first surface of dichroic mirror  67  through condenser lens  69 . 
     On the other hand, P-polarized blue LD light that has passed through retardation plate  60  and transmitted through polarization beam splitter  61  enters the second surface (the surface opposite to the first surface) of dichroic mirror  67  through mirrors  63  to  64  and diffusion member  68 . Dichroic mirror  67  has the same structure as dichroic mirror  47  described in the third embodiment. Dichroic mirror  67  transmits the yellow fluorescent light incident on the first surface and reflects the blue LD light incident on the second surface in the transmission direction of the yellow fluorescent light. That is, dichroic mirror  67  color-synthesizes the blue LD light and the yellow fluorescent light into one optical path. 
     In the light source device of the present embodiment as well, a portion of the emitted light of laser module  51 , which is a blue light source, can be turned to the side of excitation light source  52 , whereby the same effect can be obtained as in the first embodiment. 
     Further, by forming retardation plate  60  and polarization beam splitter  61  so that the division ratio between S-polarized light and P-polarized light becomes the value of a desired division ratio, it is possible to obtain output light of a desired color tone. 
     Fifth Embodiment 
       FIG.  5    is a top view schematically showing the configuration of a light source device according to a fifth embodiment of the present invention. 
     Referring to  FIG.  5   , the light source device includes laser module  71  that is a blue light source, laser module  72  that is an excitation light source, optical member  73 , and phosphor unit  74 . For convenience, only one laser module  72  is shown as an excitation light source, but in practice two laser modules  72  are provided. Laser modules  71  and  72  and phosphor unit  74  have the same structures as laser modules  31 ,  32   a , and  32   b  and phosphor unit  34 , respectively, described in the third embodiment. 
     Optical member  73  includes retardation plate  80 , polarization beam splitter  81 , mirror  82 , dichroic mirrors  83  and  84 , reduction optical system  85 , fly-eye lenses  86   a  and  86   b , diffusion member  88 , and condenser lens  89 . Retardation plate  80 , polarization beam splitter  81 , reduction optical system  85 , fly-eye lenses  86   a  and  86   b , diffusion member  88 , and condenser lens  89  are basically the same as those of optical member  53  described in the fourth embodiment. 
     Blue LD light (linearly polarized light) emitted by laser module  71  is incident on the first surface of polarization beam splitter  81  via retardation plate  80 . Blue LD light (P-polarized light) emitted by laser module  72  is incident on the second surface (the surface opposite to the first surface) of polarization beam splitter  81 . Polarization beam splitter  81  integrates S-polarized blue LD light from retardation plate  80  and P-polarized blue LD light from laser module  72  into one optical path. 
     Integrated light integrated by polarization beam splitter  81  enters the first surface of dichroic mirror  84  through reduction optical system  85 , which is made of multiple lenses  85   a  and  85   b , and fly-eye lenses  86   a  and  86   b . Reduction optical system  85 , fly-eye lenses  86   a  and  86   b , and dichroic mirror  84  have the same structure as reduction optical system  45 , fly-eye lenses  46   a  and  46   b , and dichroic mirror  47  described in the third embodiment. Dichroic mirror  84  reflects the integrated light toward phosphor unit  74 . The integrated light reflected by dichroic mirror  84  is incident to phosphor unit  74  via condenser lens  89 . Yellow fluorescent light emitted by phosphor unit  74  enters the first surface of dichroic mirror  84  through condenser lens  89 . 
     The yellow fluorescent light that is transmitted through dichroic mirror  84  enters the first surface of dichroic mirror  83 . On the other hand, the P-polarized blue LD light that has passed through retardation plate  80  and that is transmitted through polarization beam splitter  81  enters the second surface (the surface opposite to the first surface) of dichroic mirror  83  through mirror  82  and diffusion member  88 . Dichroic mirror  83  has the characteristic of reflecting light in the blue wavelength range and transmitting light of other wavelength ranges within the visible wavelength range. Dichroic mirror  83  transmits the yellow fluorescent light incident on the first surface and reflects the blue LD light incident on the second surface in the transmission direction of the yellow fluorescent light. That is, dichroic mirror  83  color-synthesizes the blue LD light and the yellow fluorescent light into one optical path. 
     In the light source device of the present embodiment as well, a portion of the emitted light of laser module  71 , which is a blue light source, can be turned to the side of the excitation light source, whereby the same effect can be obtained as in the first embodiment. 
     Further, forming retardation plate  80  and polarization beam splitter  81  so that the division ratio between S-polarized light and P-polarized light becomes the value of a desired division ratio allows output light of a desired color tone to be obtained. 
     Sixth Embodiment 
       FIG.  6    is a schematic diagram schematically showing the configuration of a light source device according to a sixth embodiment of the present invention. Incidentally, in  FIG.  6   , the optical paths and the optical elements are shown schematically, and their sizes and shapes may be different from an actual example. For example, for convenience, the figure shows a state in which one optical path jumps over another optical path, but in practice, each optical path is straight and is arranged to intersect with each other in a spatially separated state. 
     The light source device of the present embodiment is different from the second embodiment in that beam splitter  15  is provided in place of retardation plate  20  and polarization beam splitter  21 . The configuration is otherwise the same as that of the second embodiment. 
     In the light source device of the present embodiment, blue LD light emitted by blue light source  11  is incident on one surface of beam splitter  15 . Beam splitter  15  splits the blue LD light from the blue light source  11  into a first blue split light and a second blue split light. Beam splitter  15  is, for example, a prism-type or plate-type beam splitter that uses a dielectric multilayer film. The beam splitter is capable of distributing the amount of light at a predetermined branching ratio (transmission/reflection distribution ratio). A beam splitter having a branching ratio of 50:50 is called a half-mirror. It is also possible to prepare a beam splitter having a branching ratio of 70:30 or 60:40. Beam splitter  15  may comprise at least one beam splitter having a predetermined branching ratio with respect to blue LD light or may constructed from a combination of a plurality of beam splitters having different branching ratios. 
     The first blue split light is incident to light integrating unit  24  via mirrors  22  and  23 . Light integrating unit  24  integrates the first blue split light and blue LD light emitted by excitation light source  12  into one optical path. 
     On the other hand, the second blue split light is incident on the second surface of dichroic mirror  27  through diffusion plate  28 . Dichroic mirror  27  color-synthesizes the yellow fluorescent light incident on the first surface and the second blue split light incident on the second surface into one optical path. Light synthesized by dichroic mirror  27  is the output light of the light source device of the present embodiment. 
     In the light source device of the present embodiment as well, a portion of the emitted light of blue light source  11  can be turned to the side of the excitation light source  12 , whereby the same effect can be obtained as in the first embodiment. 
     In addition, forming beam splitter  15  so that the division ratio between the first blue split light and the second blue split light becomes a desired value allows output light of a desired color tone to be obtained. 
     The light source device of the present embodiment also exhibits the following effects: Due to deposits caused by optical dust collection of a laser light, the polarization characteristics of an optical member that includes a retardation plate or a polarization beam splitter may change. Therefore, in a light source device in which polarized light is used to split a beam, changes in the color tone of the output light and changes in illuminance are likely to occur due to changes in polarization characteristics. In contrast, since polarized light is not used to split a beam according to the light source device of the present embodiment, the color tone and illuminance of the output light can be stably maintained. 
     Incidentally, in a configuration that utilizes polarized light only on the blue light source side as in the second embodiment or the third embodiment and that does not utilize polarized light on the excitation light source side, changes in the color tone and illuminance hardly occur compared with a configuration in which polarized light is utilized on both the blue light source side and the excitation light source side. 
     Seventh Embodiment 
       FIG.  7    is a schematic diagram showing the configuration of a light source device according to a seventh embodiment of the present invention. Incidentally, in  FIG.  7   , the optical paths and the optical elements are shown schematically, and their sizes and shapes may be different from an actual example. For example, for convenience, the figure shows a state in which one optical path jumps over another optical path, but in practice, each optical path is straight and is arranged to intersect with the other in a spatially separated state. 
     The light source device of the present embodiment is different from the second embodiment in that optical member  13  is configured to return a part of the emitted light of the excitation light source to the side of the blue light source. The configuration is otherwise the same as that of the second embodiment. Specifically, in optical member  13 , polarization beam splitter  21 A is used in place of light integrating unit  24 , and retardation plate  20  is disposed between excitation light source  12  and polarization beam splitter  21 A. Blue LD light emitted by excitation light source  12  is incident on the first surface of polarization beam splitter  21 A through retardation plate  20 . Polarization beam-splitter  21 A has the property of reflecting S-polarized light and transmitting P-polarized light. 
     P-polarized blue LD light that is transmitted through polarization beam splitter  21 A is used as excitation light for exciting the phosphor of phosphor unit  14 . P-polarized blue LD light enters the first surface of dichroic mirror  27  through reduction optical system  25  and fly-eye lenses  26   a  and  26   b . P-polarized blue LD light reflected by the first surface of dichroic mirror  27  is incident to phosphor unit  14  via condenser lens  29 . Phosphor unit  14  emits yellow fluorescent light toward condenser lens  29 . The yellow fluorescent light emitted from phosphor unit  14  is incident on the first surface of dichroic mirror  27  via condenser lens  29 . 
     On the other hand, S-polarized blue LD light reflected by polarization beam splitter  21 A is incident on the first surface of polarization beam splitter  21  through mirror  23  and mirror  22 . Blue LD light (P-polarized light) emitted by blue light source  11  is incident on the second surface (the surface opposite to the first surface) of polarization beam splitter  21 . Polarization beam splitter  21  transmits P-polarized blue LD light from blue light source  11  and reflects S-polarized blue LD light from mirror  22  in the transmission direction of the P-polarized blue LD light. That is, polarization beam splitter  21  integrates the P-polarized blue LD light and the S-polarized blue LD light into one optical path. Integrated light (blue LD light) integrated by polarization beam splitter  21  is incident on the second surface of dichroic mirror  27  through diffusion plate  28 . 
     Dichroic mirror  27  transmits yellow fluorescent light and reflects the integrated light (blue LD light) in the transmission direction of the yellow fluorescent light. That is, dichroic mirror  27  color-combines the yellow fluorescent light and the integrated light (blue LD light) into one optical path. Light synthesized by dichroic mirror  27  is the output light of the light source device of the present embodiment. 
     In the light source device of the present embodiment as well, a portion of the emitted light of excitation light source  12  is turned to the side of blue light source  11  to achieve the action and effect described in the first embodiment. 
     Further, forming polarization beam splitter  21 A so that the division ratio between P-polarized light and S-polarized light becomes a desired value allows output light of a desired color tone to be obtained. 
     The configuration for turning a part of the emitted light of the excitation light source to the side of the blue light source is not limited to the configuration shown in  FIG.  7   . 
     For example, in the configuration shown in  FIG.  4   , retardation plate  60  may be disposed between excitation light source  52  and polarization beam splitter  61 , and laser module  51 , which is a blue light source, may emit P-polarized blue LD light. Polarization beam splitter  61  integrates the P-polarized blue LD light from laser module  51  and the S-polarized blue LD light from excitation light source  52  into one optical path. Output light is obtained by color-synthesizing the integrated light and the yellow fluorescent light. Incidentally, excitation light source  52  may be used as the blue light source, laser module  51  may be used as the excitation light source, and laser module  51  may emit S-polarized blue LD light. 
     Further, in the configuration shown in  FIG.  5   , retardation plate  80  may be disposed between laser module  72 , which is the excitation light source, and polarization beam splitter  81 , and laser module  71 , which is a blue light source, may emit P-polarized blue LD light. Polarization beam splitter  71  integrates P-polarized blue LD light from laser module  51  and S-polarized blue LD light from laser module  72  into one optical path. Output light is obtained by color-synthesizing the integrated light and the yellow fluorescent light. 
     In the second to seventh embodiments described above, for the purpose of increasing the speckle reduction effect, a rotational diffusion unit may be used instead of the diffusion plate or the diffusion member. The rotational diffusion unit includes a rotational diffusion plate for diffusing incident light, a first condenser lens provided on the incident-surface side of the rotational diffusion plate, and a second condenser lens provided on the exit-surface side of the rotational diffusion plate. The first condenser lens condenses the light incident to the rotation diffusion plate. The second condenser lens converts light that has passed through the rotational diffusion plate into a parallel light beam. 
     Any of the light source devices of the first to seventh embodiments described above can be used as the light source device of a projector. The projector includes a light modulation unit that modulates the emitted light of the light source device to form an image, and a projection lens that projects the image formed by the light modulation unit. 
       FIG.  8    schematically shows the configuration of a projector according to an embodiment of the present invention. The projector includes light source device  90 , illumination optical system  91 , three light modulators  92 R,  92 G, and  92 B, cross-dichroic prism  93 , and projection lens  94 . Light source device  90  is the light source device described in any one of the first to seventh embodiments and emits a parallel light beam which is white light that includes yellow fluorescent light and blue LD light. 
     Illumination optical system  91  separates the white light emitted by light source device  90  into red light for illuminating light modulator  92 R, green light for illuminating light modulator  92 G, and blue light for illuminating light modulator  92 B. Each of light modulators  92 R,  92 G, and  92 B includes a liquid crystal panel that modulates light to form an image. 
     Illumination optical system  91  includes fly-eye lenses  5   a  and  5   b , polarization conversion element  5   c , superimposing lens  5   d , dichroic mirrors  5   e  and  5   g , field lenses  5   f  and  51 , relay lenses  5   h  and  5   j , and mirrors  5   i ,  5   k , and  5   m . White light emitted by light source device  90  is incident to dichroic mirror  5   e  through fly-eye lenses  5   a  and  5   b , polarization conversion element  5   c , and superimposing lens  5   d.    
     Fly-eye lenses  5   a  and  5   b  are disposed so as to be opposed to each other. Fly-eye lenses  5   a  and  5   b  each include a plurality of microlenses. Each microlens of fly-eye lens  5   a  faces a respective microlens of fly-eye lens  5   b . In fly-eye lens  5   a , light emitted from light source section  90  is divided into a plurality of light beams corresponding to the number of micro lenses. Each microlens has a shape similar to the effective display area of the liquid crystal panel and condenses the light beam from light source unit  90  to the vicinity of fly-eye lens  5   b.    
     Superimposing lens  5   d  and field lens  51  direct a principal ray from each microlens of fly-eye lens  5   a  toward the center portion of the liquid crystal panel of light modulator  92 R and superimpose the image of each microlens on the liquid crystal panel. Similarly, superimposing lens  5   d  and field lens  5   f  direct a principal ray from each microlens of fly-eye lens  2   a  toward the center portion of the liquid crystal panel of each of light modulators  92 G and  92 B and superimpose the image of each microlens on the liquid crystal panel. 
     Polarization conversion element  5   c  aligns the polarization direction of light that has passed through fly-eye lenses  5   a  and  5   b  with P-polarized light or S-polarized light. Dichroic mirror  5   e  has a characteristic such that, of visible light, light in the red wavelength range is reflected and light in other wavelength ranges is transmitted. 
     Light (red) reflected by dichroic mirror  5   e  is irradiated to the liquid crystal panel of light modulator  92 R through field lens  51  and mirror  5   m . On the other hand, light (blue and green) transmitted through dichroic mirror  5   e  enters dichroic mirror  5   g  through field lens  5   f . Dichroic mirror  5   g  has a characteristic such that, of visible light, light in the green wavelength range is reflected and light in other wavelength ranges is transmitted. 
     Light (green) reflected by dichroic mirror  5   g  is irradiated to the liquid crystal panel of light modulator  92 G. On the other hand, light (blue) transmitted through dichroic mirror  5   g  is irradiated to the liquid crystal panel of light modulator  92 B through relay lens  5   h , mirror  5   i , relay lens  5   j , and mirror  5   k.    
     Light modulator  92 R forms a red image. Light modulator  92 G forms a green image. Light modulator  92 B forms a blue image. Cross-dichroic prism  93  has first to third incident surfaces and an exit surface. In cross-dichroic prism  93 , the red image light is incident on the first incident surface, the green image light is incident on the second incident surface, and the blue image light is incident on the third incident surface. The red image light, the green image light, and the blue image light exit from the exit surface in the same optical path. 
     The red image light, the green image light, and the blue image light that have exited from the exit surface of cross dichroic prism  93  enter projection lens  94 . Projection lens  94  projects the red image, the green image, and the blue image on a screen such that these images coincide with each other. 
     EXPLANATION OF REFERENCE NUMBERS 
     
         
           1  First light source unit 
           1   a  First monochromatic light 
           2  Second light source unit 
           2   a  Second monochromatic light 
           3  Optical member 
           3   a  First split light 
           3   b  Second split light 
           3   c  Integrated light 
           4  Phosphor unit 
           4   a  Fluorescent light