Abstract:
This invention realizes an illumination optical system with a small etendue that has a longer lifetime and a high degree of brightness. The invention includes: a laser light source that generates excitation light having a first wavelength; a phosphor wheel including a blue fluorescent light generation region that generates fluorescent light having a second wavelength by means of the excitation light, and a green fluorescent light generation region that generates fluorescent light having a third wavelength by means of the excitation light; an LED light source that generates light having a fourth wavelength; and a dichroic mirror that reflects fluorescent light having the second wavelength and fluorescent light having the third wavelength and allows light having the fourth wavelength to pass therethrough, to thereby emit each of the lights in the same direction.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an illumination optical system that generates illumination lights of a plurality of colors for forming image lights of a plurality of colors, and a projector that projects the image lights produced by the illumination optical system. 
       BACKGROUND ART 
       [0002]    Technology that uses an LED (Light Emitting Diode) as a light source of a projector that projects an image onto a screen such as a liquid crystal projector or a DMD (Digital Micromirror Device) projector has been receiving attention (see Patent Literature 1). 
         [0003]    Because an LED has a long lifetime and offers high reliability, projectors that employ an LED as a light source have the advantages of long lifetime and high reliability. 
         [0004]    However, because the brightness of the light of an LED is low for use as a projector, it is not easy to obtain a projected image that has sufficient brightness with a projector employing an LED as a light source. The extent to which a display panel can utilize light from a light source as projection light is limited by the etendue. More specifically, unless the value of the product of a light-emission area of a light source and the angle of radiation is made less than or equal to the value of the product of the area of the plane of incidence of the display panel and the capturing angle that is determined by an f-number of the illumination optical system, the light from the light source can not be effectively utilized as projection light. 
         [0005]    Although the light quantity of a light source that employs an LED can be increased by increasing the light-emission area, if the light-emission area increases, the etendue of the light source will also increase. As a light source for a projector, it is desirable in terms of the limitation produced by the etendue to increase the light quantity without increasing the light-emission area. However, it is difficult for a light source that employs an LED to increase the light quantity without increasing the light-emission area. 
       CITATION LIST 
     Patent Literature 
       [0006]    Patent Literature 1: JP2003-186110A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    The etendue of a light source that using only a LED is increases. The present invention realizes an illumination optical system with a small etendue, a longer lifetime, and a high level of brightness. 
       Solution to Problem 
       [0008]    An illumination optical system of the present invention comprises: 
         [0009]    a laser light source that generates an excitation light having a first wavelength; 
         [0010]    a phosphor wheel that includes a blue fluorescent light generation region that generates fluorescent light having a second wavelength by means of the excitation light, and a green fluorescent light generation region that generates fluorescent light having a third wavelength by means of the excitation light; 
         [0011]    an LED light source that generates light having a fourth wavelength; and 
         [0012]    a dichroic mirror that reflects fluorescent light having the second wavelength and fluorescent light having the third wavelength, and allows light having the fourth wavelength to pass therethrough to thereby emit each of the lights in the same direction. 
         [0013]    Further, a projector according to the present invention comprises the above described illumination optical system. 
       Advantageous Effects of Invention 
       [0014]    According to the present invention, since a laser with a high energy density converges on a phosphor as excitation light, and since fluorescent light is emitted from the place at which the laser converges is used, an illumination optical system can be realized that has a small etendue, a longer lifetime and a higher level of brightness. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a block diagram that illustrates the configuration of an exemplary embodiment of an illumination optical system according to the present invention. 
           [0016]      FIG. 2  is a plan view of phosphor wheel  105  as viewed from laser light source  101  side (from the left side towards the right side in  FIG. 1 ). 
           [0017]      FIG. 3  is a sectional view illustrating the structure of blue phosphor region  105   1  in  FIG. 2 . 
           [0018]      FIG. 4  is a sectional view illustrating the structure of green phosphor regions  105   2  and  105   4  in  FIG. 2 . 
           [0019]      FIG. 5  is a block diagram illustrating the circuit configuration of a projector that uses an illumination optical system according to the present invention. 
           [0020]      FIGS. 6(   a ) to ( c ) are plan views that illustrate the structure of principal parts of a second exemplary embodiment of the illumination optical system according to the present invention, and  FIGS. 6(   d ) to ( f ) are plan views that illustrate the structure of principal parts of a third exemplary embodiment of the illumination optical system according to the present invention. 
           [0021]      FIG. 7  is a timing chart that illustrates light emission times of a second exemplary embodiment. 
           [0022]      FIG. 8  is a timing chart that illustrates light emission times of a third exemplary embodiment. 
           [0023]      FIG. 9  is a block diagram that illustrates the structure of principal parts of a fourth exemplary embodiment of the illumination optical system according to the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0024]    Next, exemplary embodiments are described with reference to the drawings. 
         [0025]      FIG. 1  is a block diagram that illustrates the configuration of one exemplary embodiment of an illumination optical system according to the present invention. 
         [0026]    The present exemplary embodiment includes laser light source  101 , LED light source  102 , dichroic mirrors  103  and  104 , phosphor wheel  105 , light tunnel  106 , lens groups  107  to  109 , and reflection mirrors  110   1  and  110   2 . 
         [0027]      FIG. 2  is a plan view of phosphor wheel  105  as viewed from the left side towards the right side of  FIG. 1 . 
         [0028]    Laser light source  101  generates an excitation laser light of wavelength □ 1 . Phosphor wheel  105  includes blue phosphor region  105   1  and green phosphor regions  105   2  and  105   4  that generate blue fluorescent light and green fluorescent light, respectively, of wavelengths □ 2  and □ 3  (□ 2 &lt;□ 3 ) that are longer than wavelength □ 1  when an excitation laser light is incident thereon. Phosphor wheel  105  also includes transparent region  105   3  that allows light to pass through. 
         [0029]    First, the properties of each optical element of the present exemplary embodiment are described. 
         [0030]    LED light source  102  generates red light having wavelength □ 4  that is longer than wavelength □ 3 . Thus, according to the present exemplary embodiment, lights having four wavelengths, □ 1  to □ 4 , are used, and the relationship between the wavelengths is □ 1 &lt;□ 2 &lt;□ 3 &lt;□ 4 . The reflecting surfaces of dichroic mirrors  103  and  104  are parallelly arranged. Dichroic mirror  103  reflects only light of □ 3 , and allows light of □ 1 , □ 2  and □ 4  to pass. Dichroic mirror  104  reflects only light of □ 2 , and allows light of □ 1 , □ 3  and □ 4  to pass. In this connection, dichroic mirror  104  may also be provided so as to reflect light of □ 1  and □ 2 , and to allow light of □ 3  and □ 4  to pass. 
         [0031]      FIG. 3  and  FIG. 4  are sectional views that illustrate the structure of blue phosphor region  105   1  and green phosphor regions  105   2  and  105   4 . 
         [0032]    As shown in  FIG. 3 , in blue phosphor region  105   1 , reflective layer  304  and blue phosphor layer  305  are formed on substrate  303  that is transparent with respect to wavelengths □ 1  to □ 4 . When excitation laser light having wavelength □ 1  is incident on blue phosphor layer  305 , blue phosphor layer  305  generates blue fluorescent light having wavelength □ 2 . Reflective layer  304  allows the excitation laser light having wavelength □ 1  to pass therethrough, and reflects blue fluorescent light having wavelength □ 2  generated at blue phosphor layer  305 . Therefore, as shown in  FIG. 3 , when excitation laser light  301  having wavelength □ 1  is incident from the side of substrate  303 , blue fluorescent light  302  having wavelength □ 2  is emitted from blue phosphor layer  305  side. 
         [0033]    As shown in  FIG. 4 , in green phosphor regions  105   2  and  105   4 , reflective layer  402  and green phosphor layer  403  are formed on substrate  303  that is transparent with respect to wavelengths □ 1  to □ 4 . When excitation laser light  301  having wavelength □ 1  is incident on green phosphor layer  403 , green phosphor layer  403  generates green fluorescent light having wavelength □ 3 . Reflective layer  402  reflects green fluorescent light having wavelength □ 3  generated at green phosphor layer  403 . Therefore, as shown in  FIG. 4 , when excitation laser light  301  having wavelength □ 1  is incident from the side of green phosphor layer  403 , green fluorescent light  403  having wavelength □ 3  is generated at green phosphor layer  305 , and the thus generated light is reflected by reflective layer  402  and emitted from the side of green phosphor layer  305 . 
         [0034]    Next, the arrangement of an optical system according to the present exemplary embodiment is described. 
         [0035]    When a case is assumed in which there is no phosphor wheel  105 , each member is arranged so that outgoing light of laser light source  1  passes through dichroic mirror  103  and lens group  109 , is returned by reflection mirrors  110   1  and  110   2 , and is incident on dichroic mirror  103  through lens group  108 . The optical axes of lens group  107  and lens group  108  and the rotational axis of phosphor wheel  105  are parallel, and the center of rotation of phosphor wheel  105  is midway between the optical axes of lens group  107  and lens group  108 . 
         [0036]    The optical axis of laser light source  101  is perpendicular to the optical axis of LED light source  102 . The outgoing light of laser light source  101  is incident on phosphor wheel  105  via dichroic mirror  103  and lens group  109 . As described above, phosphor wheel  105  includes three kinds of regions, and the action after light is incident on phosphor wheel  105  differs depending on the region that light is incident on. 
         [0037]    As shown in  FIG. 2 , circular phosphor wheel  105  is divided into four regions, of which blue phosphor region  105   1  and transparent region  105   3 , and green phosphor region  105   2  and green phosphor region  105   4  are arranged so as to be symmetrical about a point. 
         [0038]    Outgoing light of laser light source  101  is incident on phosphor wheel  105  via dichroic mirror  103  and lens group  107 . The point of incidence thereof (hereunder, referred to as “primary focal point”) is in any one of the above described three kinds of regions. When the primary focal point is in transparent region  105   3 , incident light passes through transparent region  105   3 , is returned by reflection mirrors  110   1  and  110   2 , and is incident at a secondary focal point in blue phosphor region  105   1  at a position that is symmetrical about a point with respect to the primary focal point of phosphor wheel  105 . 
         [0039]    Hereunder, the action after light is incident is described with respect to cases where the primary focal point is green phosphor region  105   2  and green phosphor region  105   4 , transparent region  105   3 , and blue phosphor region  105   1 , respectively. 
         [0040]    When the primary focal point is in green phosphor region  105   2  and green phosphor region  105   4 , the configuration is as shown in  FIG. 4 . Green fluorescent light having wavelength □ 3  that is generated at green phosphor layer  403  is diffused light, and is collimated by lens group  107 . Thereafter, the green fluorescent light is reflected towards light tunnel  106  by dichroic mirror  103 . Subsequently, the green fluorescent light passes through dichroic mirror  104 , is condensed by lens group  109 , and is incident on light tunnel  106 . 
         [0041]    When the primary focal point is transparent region  105   3 , outgoing light of laser light source  101  is incident at the secondary focal point in blue phosphor region  105   1  from the rear surface of phosphor wheel  105  (from the left side of the figure towards the right side in  FIG. 1 ), and a configuration is entered as shown in  FIG. 3 . Blue fluorescent light having wavelength □ 2  generated at blue phosphor layer  305  is diffused light, and is collimated by lens group  108 . Thereafter, the blue fluorescent light is reflected towards light tunnel  106  by dichroic mirror  104 , is condensed by lens group  109 , and is incident on light tunnel  106 . 
         [0042]    When the primary focal point is blue phosphor region  105   1 , blue fluorescent light having wavelength □ 2  generated at blue phosphor layer  305  is collimated by lens group  107 , passes through dichroic mirror  103 , and is returned to laser light source  101 . Thus, blue fluorescent light generated when the primary focal point is in blue phosphor region  105   1  is not utilized as illumination light. According to the present exemplary embodiment, when the primary focal point is in blue phosphor region  105   1 , laser light source  101  is extinguished, LED light source  102  is lit, and red outgoing light having wavelength □ 4  of LED light source  102  is incident on light tunnel  106  through dichroic mirrors  103  and  104  and lens group  109 . 
         [0043]    As described above, according to an illumination optical system of the present exemplary embodiment, when the primary focal point is in green phosphor region  105   2  and green phosphor region  105   4 , green fluorescent light is incident on light tunnel  106 . When the primary focal point is in transparent region  105   3 , blue fluorescent light is incident on light tunnel  106 . When the primary focal point is in blue phosphor region  105   1 , red light of LED light source  102  is incident on light tunnel  106 . The illumination distribution of each of these incident lights inside light tunnel  106  is uniformized, so that uniformized red light, green light, blue light, and green light appear in that order on the outgoing light side of light tunnel  106  to be used as illumination light. In this connection, yellow or magenta may be used as illumination light by using a yellow phosphor or a magenta phosphor instead of one of the green phosphors. 
         [0044]      FIG. 5  is a block diagram that illustrates a circuit configuration of a projector that uses an illumination optical system of the present exemplary embodiment. 
         [0045]    A projector illustrated in  FIG. 5  includes user interface  501 , controller  502 , storage portion  503 , video signal processor  504 , synchronization signal processor  505 , LD driver  506 , LED driver  507 , phosphor wheel driver  508 , display element driver  509 , rotational state detector  510 , and display element  511 , as well as laser light source  101 , LED light source  102 , and phosphor wheel  105  shown in  FIG. 1 . 
         [0046]    User interface  501  accepts instructions input from a user, and outputs the instructions to controller  502 . User interface  501  also displays the current operating state of the projector on a display apparatus (not shown) such as an indicator or a display panel. 
         [0047]    Controller  502  controls each component comprising the projector in accordance with a program stored in storage portion  503 . 
         [0048]    Storage portion  503  stores a control program of controller  503 , or temporarily stores video data. 
         [0049]    Video signal processor  504  converts a video signal input from outside into a video signal to be used inside the projector. Since video signals of the present exemplary embodiment are formed by illumination lights of respective colors being output sequentially by an illumination optical system as described above, video signals according to each color are generated sequentially. 
         [0050]    Synchronization signal processor  505  converts synchronization signals that are synchronized with video signals input from outside into video signals to be used inside the projector. More specifically, synchronization signal processor  505  generates and outputs synchronization signals that show the output timing of video signals of each color. 
         [0051]    LD driver  506  controls the lighting state of laser light source  101  according to synchronization signals output from synchronization signal processor  505 . LED driver  507  controls the lighting state of LED light source  102  according to synchronization signals output from synchronization signal processor  505 . 
         [0052]    Rotational state detector  510  detects the rotational state of phosphor wheel  105 , and outputs the detected result to phosphor wheel driver  508 . 
         [0053]    Phosphor wheel driver  508  controls the rotational state of phosphor wheel  105  so that the color of a video signal indicated by a synchronization signal output by synchronization signal processor  505  and a color output by the illumination optical system that indicates the rotational state of phosphor wheel  105  detected by rotational state detector  510  match. 
         [0054]    Display element driver  509  drives display element  511  in accordance with video signals output by the video signal processor. In this case, a reflective image forming element in which a plurality of micromirrors are arranged in a matrix and which forms an image according to the reflection state of each micromirror, or a transmission-type liquid crystal display element or reflective liquid crystal display element is used as a display element. 
         [0055]    shuusei 
         [0056]    According to the projector configured as described above, display element  511  that displays images corresponding to each color by means of illumination light of each color sequentially output from the illumination optical system is illuminated, and reflection images or transmission images of display element  511  are sequentially projected through a projection optical system (not shown). 
         [0057]    Next, another exemplary embodiment is described. 
         [0058]      FIGS. 6(   a ) to ( c ) are plan views that illustrate the structure of principal parts of a second exemplary embodiment of the illumination optical system according to the present invention.  FIGS. 6(   d ) to ( f ) are plan views that illustrate the structure of principal parts of a third exemplary embodiment of the illumination optical system according to the present invention. 
         [0059]    Phosphor wheel  105  shown in  FIG. 2  is equally divided into four regions in which blue phosphor region  105   1  and transparent region  105   3 , and green phosphor region  105   2  and green phosphor region  105   4  are arranged so as to be symmetrical about a point. In contrast, in phosphor wheel  105 ′ shown in  FIG. 5(   a ) to ( c ), the areas of blue phosphor region  105   1 ′ and transparent region  105   3 ′ are different from the areas of green phosphor region  105   2 ′ and green phosphor region  1054 . Since the remaining configuration is the same as in the exemplary embodiment illustrated in  FIG. 1 , a description thereof is omitted here. 
         [0060]    The areas of green phosphor region  105   2 ′ and green phosphor region  105   4 ′ are made to be twice the areas of blue phosphor region  105   1 ′ and transparent region  105   3 ′. Since phosphor wheel  105  illustrated in  FIG. 2  is divided into equal regions, when phosphor wheel  105  is rotated once, red light, green light, blue light, and green light appear for the same period. In contrast, according to the present exemplary embodiment, each time period for which green light appears is twice the time period for which red light and blue light appear. 
         [0061]      FIG. 7  is a timing chart that shows light emission times of a second exemplary embodiment. 
         [0062]    As shown in  FIG. 6(   a ), when primary focal point  601  is on blue phosphor region  105   1 ′, laser light source  101  is placed in an extinguished state, and LED light source  102  is lit so that red LED light appears (lighting time is taken as period T). 
         [0063]    As shown in  FIG. 6(   b ), when primary focal point  601  is on green phosphor region  105   4 ′, green fluorescent light appears (period  2 T). 
         [0064]    As shown in  FIG. 6(   c ), when primary focal point  601  is on transparent region  105   3 ′, blue fluorescent light appears that is generated at secondary focal point  602  (period T). 
         [0065]    Thereafter, when primary focal point  601  is on green phosphor region  105   2 ′, green fluorescent light appears (period  2 T). 
         [0066]    Although the generated proportions of each color light, when the phosphor wheel is rotated once, are the same in the exemplary embodiment shown in  FIG. 6(   d ) to ( f ) as in the exemplary embodiment shown in  FIG. 6(   a ) to ( c ), the phosphor wheel in the exemplary embodiment shown in  FIG. 6(   d ) to ( f ) is arranged so that green fluorescent light appears consecutively. 
         [0067]    According to the present exemplary embodiment, the rotational axis of phosphor wheel  603  is placed in a different position to that of phosphor wheel  105  shown in  FIG. 1  and phosphor wheel  105 ′ shown in  FIG. 6(   a ) to ( c ), and the size thereof is also changed. Since the remaining configuration is the same as in the exemplary embodiment illustrated in  FIG. 1 , a description thereof is omitted here. 
         [0068]    In phosphor wheel  603 , blue phosphor region  604   1  and transparent region  604   3  of equal area and green fluorescent light region  604   2  of an area four times the size of the area of blue phosphor region  604   1  and transparent region  604   3  are formed in an arc shape. As described above, since the axis of the center of rotation of phosphor wheel  603  is midway between the optical axes of lens group  107  and lens group  108 , according to the present exemplary . embodiment, the relation between primary focal point  605  and secondary focal point  606  is not one in which primary focal point  605  and secondary focal point  606  are point symmetric with regard to phosphor wheel  603 . In the present exemplary embodiment, as shown in  FIGS. 6(   d ) to ( f ) primary focal point  605  and secondary focal point  606  have a positional relationship that maintains a predetermined interval that matches the interval of blue phosphor region  604   1  or transparent region  604   3 . 
         [0069]      FIG. 8  is a timing chart that shows light emission times of the second exemplary embodiment. 
         [0070]    As shown in  FIG. 6(   f ), when primary focal point  605  is on blue phosphor region  604   1 ′, laser light source  101  is placed in an extinguished state and LED light source  102  is lit so that red LED light appears (lighting time taken as period T). 
         [0071]    As shown in  FIG. 6(   d ), when primary focal point  605  is on green phosphor region  604   2 ′, green fluorescent light appears (period  4 T). 
         [0072]    As shown in  FIG. 6(   e ), when primary focal point  605  is on transparent region  105   3 ′, blue fluorescent light appears that is generated at secondary focal point  606  (period T). 
         [0073]      FIG. 9  is a block diagram that illustrates the structure of principal parts of a fourth exemplary embodiment of the illumination optical system according to the present invention. 
         [0074]    The present exemplary embodiment includes laser light source  901 , LED light source  902 , dichroic mirror  903 , lens groups  904  and  906 , and phosphor wheel  905 . 
         [0075]    Laser light source  901  generates excitation laser light having wavelength □ 1 . 
         [0076]    LED light source  902  generates red light having wavelength □ 4  that is longer than wavelength □ 3 . 
         [0077]    Dichroic mirror  903  allows light having wavelength □ 4  to pass therethrough, and reflects light of wavelengths  58   1  to □ 3 . 
         [0078]    Similarly to phosphor wheel  105  shown in  FIG. 1 , phosphor wheel  905  includes a blue phosphor region and a green phosphor region that generate blue fluorescent light and green fluorescent light, respectively, having wavelengths □ 2  and □ 3  (□ 2 &lt;□ 3 ) that are longer than wavelength □ 1  when an excitation laser light is incident thereon. Phosphor wheel  905  also includes a transparent region. 
         [0079]    When laser light from laser light source  901  is emitted towards phosphor wheel  905 , blue fluorescent light is generated when the incidence position of the laser light is in the blue phosphor region. The blue fluorescent light is collimated by lens group  906 , reflected by dichroic mirror  903 , and emitted as illumination light through lens group  904 . 
         [0080]    When the incidence position of the laser light is in a green phosphor region, green fluorescent light is generated. The green fluorescent light is collimated by lens group  906 , reflected by dichroic mirror  903 , and emitted as illumination light through lens group  904 . 
         [0081]    When the incidence position of laser light is in the transparent region, the laser light passes through phosphor wheel  905  without generating fluorescent light, and is reflected by dichroic mirror  903  and emitted. Thus, illumination light is not generated when the incidence position of laser light is in a transparent region. According to the present exemplary embodiment, when the primary focal point is in the transparent region, laser light source  901  is extinguished, LED light source  902  is lit, and red outgoing light having wavelength □ 4  of LED light source  902  is emitted as illumination light through dichroic mirror  903  and lens group  904 . 
         [0082]    As described above, in both the second and third exemplary embodiments, red light, green light, blue light, and green light, that are used as illumination light, appear in sequence, and by driving display element  511  by means of the arrangement illustrated in  FIG. 5 , a projector with a high level of brightness and a long lifetime can be realized. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           101  Laser light source 
           102  LED light source 
           103 ,  104  Dichroic mirror 
           105  Phosphor wheel 
           106  Light tunnel 
           107  to  109  Lens group 
           110   1 ,  110   2  Reflection mirror