Patent Publication Number: US-9407886-B2

Title: Illumination optical system and projector including fluorophore

Description:
The present application is a Continuation Application of U.S. patent application Ser. No. 14/635,364, filed on Mar. 2, 2015, which is a Continuation Application of U.S. patent application Ser. No. 14/004,131, filed on Sep. 9, 2013, now U.S. Pat. No. 8,985,775, issued on Mar. 24, 2015, which is based on International Application No. PCT/JP2011/056525, filed on Mar. 18, 2011, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an illumination optical system including a fluorophore unit that emits fluorescent light due to excitation light from a light source and relates to a projector including the illumination optical system. 
     BACKGROUND 
     Various illumination optical systems are currently proposed as the illumination optical system used in a projector such as an LED (Liquid Crystal Display) projector or a DLP (Digital Light Processing) projector. 
     Japanese Unexamined Patent Application Publication No. 2010-237443 (hereinbelow referred to as Patent Document 1) and Japanese Unexamined Patent Application Publication No. 2010-256457 (hereinbelow referred to as Patent Document 2) disclose illumination optical systems and projectors in which a fluorophore is irradiated by an excitation light to obtain light emission of a predetermined wavelength band from a fluorophore. 
     The illumination optical system (light source device) disclosed in each of these patent documents is equipped with a light source that irradiates laser light of the blue wavelength band and a light-emitting wheel on which is provided a light-emitting substance that emits light with light irradiated from the light source as excitation light. The light-emitting wheel is provided with: a red region in which a light-emitting substance is provided that emits light of the red wavelength band when excited by light from the light source, a green region in which a light-emitting substance is provided that emits light of the green wavelength band, and a blue region that transmits light of the blue wavelength band. The light-emitting substances of the light-emitting wheel are formed on a reflection layer. 
     The light-emitting wheel is configured so as to be rotatable. Due to the rotation of the fluorophore wheel, blue light that is emitted from the light source successively irradiates the red region, the green region, and the transmission region of the light-emitting wheel. The red light and green light generated from the fluorophores are reflected by the reflection layer. 
     Red light and green light that are reflected by the reflection layer and blue light that is transmitted by the transmission region are combined by a dichroic mirror or relay optical system. The combined light is irradiated upon a digital mirror device (DMD). Light of each color that is emitted in time divisions by the light-emitting wheel is spatially modulated according to input images by the DMD and projected by way of a projection lens onto a screen. 
     LITERATURE OF THE PRIOR ART 
     Patent Documents 
     Patent Document 1: Japanese Unexamined Patent Application Publication No. 2010-237443 
     Patent Document 2: Japanese Unexamined Patent Application Publication No. 2010-256457 
     SUMMARY 
     Technical Problem 
     In the case of the illumination optical systems described in Patent Document 1 and Patent Document 2, the light path of blue light differs from the light path of red light and green light. This difference occurs because the blue light is transmitted through the fluorophore wheel while the red light and green light are reflected by the fluorophore wheel. As a result, the optical system through which the blue light passes differs from the optical system through which the red light and green light pass. 
     In order for the blue light and red and green light that pass over different light paths to be emitted from the illumination optical system in the same direction, an optical system is absolutely necessary that combines the light paths of the light of each color. The problem therefore arises in which the size of the illumination optical system increases or in which the number of optical parts that make up the illumination optical system increases. 
     A compact illumination optical system having few optical parts is therefore desired in the illumination optical system that includes a fluorophore that produces fluorescent light by the irradiation of excitation light. 
     Solution to Problem 
     The illumination optical system of one aspect of the present invention comprises: a light source emitting light of a first wavelength; a fluorophore unit; an optical element; and a quarter-wave plate that is provided on the light path between the optical element and the fluorophore unit. The fluorophore unit includes: a fluorophore region in which a fluorophore that, by the irradiation of light of the first wavelength, emits fluorescent light of a wavelength that differs from the first wavelength, and a reflection region that reflects light of the first wavelength. The fluorophore unit can move such that light from the light source is successively irradiated on the fluorophore region and the reflection region. The optical element separates light of the first wavelength into a first linearly polarized light component and a second linearly polarized light component that is orthogonal to the first linearly polarized light component and guides the first linearly polarized light component that is emitted from the light source to the fluorophore unit. Light that is reflected by the reflection region and light emitted by the fluorophore region are again irradiated into the optical element. The optical element emits light of the first wavelength that was reflected by the reflection region and fluorescent light that was emitted by the fluorophore region in the same direction. 
     The projector of the present invention includes the above-described illumination optical system. 
     According to the above-described configuration, light of the first wavelength that is reflected in the fluorophore unit and fluorescent light that is emitted from a fluorophore both pass by way of the same light path and optical system. Accordingly, the number of constituent parts of the illumination optical system is decreased and the size of the illumination optical system is reduced. 
     The above and other objects, characteristics, and merits of the present invention will become clear from the following explanation that refers to the accompanying drawings that present examples of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing the configuration of a projector that includes the illumination optical system according to the first exemplary embodiment of the present invention. 
         FIG. 2  is a plan view showing one surface upon which light from a light source is irradiated in the fluorophore unit shown in  FIG. 1 . 
         FIG. 3  is a graph showing the transmission property of light of the optical element belonging to the illumination optical system according to the first exemplary embodiment. 
         FIG. 4  is a schematic view showing the configuration of a projector that includes the illumination optical system according to the second exemplary embodiment of the present invention. 
         FIG. 5  is a graph showing the transmission property of light of the optical element belonging to the illumination optical system according to the second exemplary embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Exemplary embodiments of the present invention are next described with reference to the accompanying drawings. 
       FIG. 1  shows the configuration of a projector that includes the illumination optical system according to the first exemplary embodiment of the present invention. The projector includes: illumination optical system  10 , image formation element  22  that spatially modulates light from illumination optical system  10 , and projection lens  24  that projects light that was spatially modulated by image formation element  22 . 
     Illumination optical system  10  includes: light source  11  that emits light of a first wavelength, optical element  13 , quarter-wave plate  14 , and fluorophore unit  16 . Fluorophore unit  16  includes fluorophore that emits fluorescent light by the irradiation of light of the first wavelength. Light source  11  functions as a light source that not only emits light of the first wavelength that is emitted from illumination optical system  10  but also irradiates excitation light onto the fluorophore. 
     Quarter-wave plate  14  is provided between optical element  13  and fluorophore unit  16 . As needed, illumination optical system  10  may also include, for example, collimators  12  and  15 . 
       FIG. 2  is a plan view of fluorophore unit  16  as seen from the direction of the incidence of excitation light. Fluorophore unit  16  includes reflection region  16   a  and fluorophore regions  16   b  and  16   c . Reflection region  16   a  is a region having a reflection film or mirror that reflects at least light of the first wavelength. 
     In the example shown in  FIG. 2 , the fluorophore regions include: first fluorophore region  16   b  in which a fluorophore is provided that, by the irradiation of light of the first wavelength, emits light of a second wavelength that is longer than the first wavelength; and second fluorophore region  16   c  in which a fluorophore is provided that, by the irradiation of light of the first wavelength, emits light of a third wavelength that is even longer than the second wavelength. In fluorophore regions  16   b  and  16   c , the fluorophores are provided on a reflection surface that reflects light. 
     In order to realize a projector capable of displaying full-color images in the present exemplary embodiment, the light of the first wavelength is blue light, the light of the second wavelength is green light, and the light of the third wavelength is red light. 
     Fluorophore unit  16  is able to move such that the irradiation spot S of light from light source  11  irradiates reflection region  16   a  and fluorophore regions  16   b  and  16   c  in time divisions. More specifically, fluorophore unit  16  is configured to freely rotate around rotation axis  28  that is orthogonal to the surface on which the reflection region and the fluorophore regions are provided. Fluorophore unit  16  is caused to rotate by motor  17 . The light from light source  11  successively irradiates reflection region  16   a  and fluorophore regions  16   b  and  16   c  due to the rotation of fluorophore unit  16 . 
     In the example shown in  FIG. 2 , reflection region  16   a  and fluorophore regions  16   b  and  16   c  are generally fan-shaped regions having a central angle of a predetermined size. The proportions of each of the central angles of reflection region  16   a  and fluorophore regions  16   b  and  16   c  match the proportions of time when light is irradiated from light source  11  to each of the corresponding regions. Accordingly, the sizes of reflection region  16   a  and fluorophore regions  16   b  and  16   c , which are the central angles in this case, are set according to, for example, the use of the illumination optical system. 
     In the present exemplary embodiment, the sizes of reflection region  16   a  and each of fluorophore regions  16   b  and  16   c  can be determined based on the intensity and chromaticity coordinates of light that is projected on a screen by way of projection lens  24  of the projector. In particular, the proportions of the central angles of reflection region  16   a  and fluorophore regions  16   b  and  16   c  are preferably determined by giving consideration to the intensity and chromaticity of white light that is formed by combining the light of each color. 
     Optical element  13  guides the first linearly polarized light component of light that is emitted from light source  11  to fluorophore unit  16 . The light that is reflected and the light that is emitted by the fluorophores in fluorophore unit  16  are again irradiated into optical element  13 . Optical element  13  emits the light of the first wavelength that is reflected in fluorophore unit  16  and light of the second wavelength that is emitted in fluorophore unit  16  in the same direction. 
     A dichroic mirror having a predetermined spectral transmittance characteristic can be used as this optical element  13 . 
     In the above-described exemplary embodiment, the first linearly polarized light component is an S-polarized light component that is orthogonal to the incidence plane on dichroic mirror  13 . The second linearly polarized light component is a P-polarized light component that is parallel to the incidence plane on dichroic mirror  13 . 
       FIG. 3  shows the spectral transmittance characteristic of dichroic mirror  13  and the spectrum of light that is transmitted from light source  11 . Dichroic mirror  13  has a characteristic such that the S-polarized light component of blue light of a wavelength on the order of 450 nm is reflected and the P-polarized light component of blue light is transmitted, whereby dichroic mirror  13  is able to separate light that is emitted from light source  11  into an S-polarized light component and a P-polarized light component that is orthogonal to the S-polarized light component. Dichroic mirror  13  guides substantially only light of the S-polarized light component to fluorophore unit  16 . 
     More specifically, relating to the S-polarized light component, dichroic mirror  13  reflects light of wavelengths no greater than the wavelength of blue light and transmits light of wavelengths sufficiently longer than the wavelength of blue light. Further, relating to the P-polarized light component, dichroic mirror  13  reflects light of sufficiently shorter wavelengths than the wavelength of blue light and transmits light of wavelengths equal to or greater than the wavelength of blue light. As a result, dichroic mirror  13  reflects the S-polarized light component and transmits the P-polarized light component in the wavelength band of blue light. The spectrum of light that is emitted from light source  11  belongs to the wavelength band of this blue light. 
     Dichroic mirror  13  can be constituted by a multilayer film of dielectrics each having different refractive indices. The dichroic mirror having the spectral reflectance characteristic shown in  FIG. 3  is easily fabricated by appropriately adjusting the refractive indices of each of the dielectric films, the film thicknesses, and the number of laminated layers of dielectrics to determine the desired cutoff wavelength. 
     In the present exemplary embodiment, light source  11  is preferably a component that emits light having substantially only the S-polarized light component. Most of the light from light source  11  is guided through dichroic mirror  13  to fluorophore unit  16 , whereby the efficiency of the utilization of light of illumination optical system  10  is improved. A blue laser that emits light of a blue wavelength, for example, a wavelength in the vicinity of 450 nm, can be used as this light source  11 . 
     When the light source of the blue excitation light that excites the fluorophores is a laser, irradiation spot S of the excitation light can be made an extremely small surface area. As a result, the irradiation surface area upon fluorophore unit  16  can be reduced, the etendue can be decreased, and a high-efficiency illumination optical system can be realized. 
     The light paths of the light in the illumination optical system of the configuration shown in  FIG. 1  are next described. Light generated from light source  11  is converted to parallel light by collimator  12 . The S-polarized light component of this parallel light is reflected by dichroic mirror  13  and guided in the direction of fluorophore unit  16 . 
     In  FIG. 1 , collimator  12  is made up of one lens, but collimator  12  may be a lens system made up of a plurality of lenses. 
     S-polarized light that is reflected by dichroic mirror  13  passes by way of quarter-wave plate  14  and collimator  15  and is then incident to fluorophore unit  16 . The S-polarized light is converted to circularly polarized light by quarter-wave plate  14 , and this circularly polarized light is condensed on reflection region  16   a  or fluorophore regions  16   b  and  16   c  of fluorophore unit  16 . 
     In  FIG. 1 , collimator  15  is a lens system made up of two lenses, but collimator  15  may be one lens or may be a lens system made up of three or more lenses. 
     When light of the first wavelength is irradiated upon first fluorophore region  16   b  of fluorophore unit  16 , green light is emitted from the fluorophore. This green light advances in the opposite direction on the light path of blue light that is incident to fluorophore unit  16  and is converted to parallel light by collimator  15 . 
     Green light that has been converted to parallel light is transmitted through quarter-wave plate  14  and again irradiated into dichroic mirror  13 . The Lambert diffused light that is emitted from the fluorophore is unpolarized light, i.e., randomly polarized light, and despite passage through quarter-wave plate  14 , the polarized state of the light does not change. 
     The green light passes through dichroic mirror  13  as shown in  FIG. 3 . Accordingly, the green light is emitted in a direction that differs from the position of arrangement of light source  11 . 
     When light of the first wavelength is incident to second fluorophore region  16   c  of fluorophore unit  16 , red light is emitted from the fluorophore. This red light passes by way of the same light path as the green light that is emitted from the first fluorophore region  16   b  and is again incident to dichroic mirror  13 . The red light passes through dichroic mirror  13  as shown in  FIG. 3 . Accordingly, the red light is emitted in the same direction as the green light. 
     When blue light that is guided from light source  11  to fluorophore unit  16  is incident to reflection region  16   a  of fluorophore unit  16 , the blue light is reflected. The reflected blue light passes along a light path similar to that of the red light and green light that were emitted by fluorophore regions  16   b  and  16   c  and passes through collimator lens  15  and quarter-wave plate  14 . 
     The blue light that is reflected by reflection region  16   a  is converted from circularly polarized light to P-polarized light by quarter-wave plate  14  and then incident to dichroic mirror  13 . The P-polarized blue light passes through the dichroic mirror as shown in  FIG. 3 . 
     Accordingly, the blue light that is reflected by reflection region  16   a  is emitted from illumination optical system  10  by way of a light path similar to that of the green light and red light. 
     As described hereinabove, dichroic mirror  13  functions as a polarization beam splitter with respect to light of the blue wavelength band, whereby blue light that is reflected by reflection region  16   a  of the fluorophore unit is emitted in a direction that differs from light source  11 , i.e., in the same direction as green light and red light. 
     According to the above-described configuration, blue light that is reflected at reflection region  16   a  of fluorophore unit  16  and red light and green light that are emitted from fluorophore regions  16   b  and  16   c  all pass through the same optical system. Accordingly, a separate optical system need not be used for each wavelength of light, whereby the number of constituent parts of illumination optical system  10  can be decreased and the size of the illumination optical system can be reduced. 
     Light that has passed by way of dichroic mirror  13  of illumination optical system  10  is irradiated upon image formation element  22  by way of integrator  18 , field lens  19 , mirror  20 , condenser lens  21 , and TIR prism  23 . Integrator  18 , field lens  19 , and condenser lens  21  are provided to irradiate light both uniformly and as a rectangle on image formation element  22 . Integrator  18 , field lens  19 , mirror  20 , and condenser lens  21  may be constituent elements of the illumination optical system. 
     Light that is incident to TIR prism  23  is reflected at air gap surface  23   a  in the prism to undergo a change of direction of advance and is then emitted toward image formation element  22 . The angle of the light beam that is emitted to image formation element  22  is appropriately adjusted by mirror  20  and TIR prism  23 . 
     In the projector of the present exemplary embodiment, reflective-type image formation element  22  is used. In this case, a DMD is used as reflective image formation element  22 . 
     Instead of a DMD, a liquid crystal panel (LCD), which is a transmissive-type image formation element, can also be used as image formation element  22 . 
     A DMD has as many micro-mirror elements as the number of picture elements. Each micro mirror element is configured to allow movement by a predetermined angle around an axis of rotation. In this example, the mirror elements rotate ±12 degrees. 
     Light that is incident to mirror elements that are tilted +12 degrees is reflected in the direction in which projection lens  24  is arranged. Light that is incident to projection lens  24  is projected to outside the projector. Light that is incident to a mirror element tilted −12 degrees is reflected in a direction in which projection lens  24  is not arranged. In this way, each mirror element selects whether light corresponding to a picture element is projected to outside the projector. By the DMD carrying out control for the light of each color, the projector is able to display color images on a screen. 
     Projection lens  24  can be composed of an optical system for enlarged projection. Light of each color from illumination optical system  10  is irradiated to image formation element  22  in time divisions. Light of each color that is incident to image formation element  22  is subjected to spatial modulation according to image information that is received as input to convert to image light. The spatially modulated image light is projected onto a screen by projection lens  24 . 
       FIG. 4  is a schematic view showing the configuration of a projector that includes illumination optical system  40  according to the second exemplary embodiment of the present invention. The projector includes: illumination optical system  40 , image formation element  22  that spatially modulates the light from illumination optical system  40 , and projection lens  24  that projects light that has been spatially modulated by image formation element  22 . 
     Illumination optical system  40  includes: light source  41  that emits light of the first wavelength, optical element  43 , quarter-wave plate  14 , and fluorophore unit  16 . Quarter-wave plate  14  is provided between optical element  43  and fluorophore unit  16 . Illumination optical system  40  may also have collimators  12  and  15  according to necessity. 
     Light source  41  in the second exemplary embodiment is preferably a blue laser that emits P-polarized excitation light. Light from light source  41  is converted to parallel light by collimator  12  and irradiated into dichroic mirror  43  that serves as the optical element. 
       FIG. 5  shows the spectral transmittance characteristic of dichroic mirror  43  and the spectrum of light that is generated from light source  41 . Dichroic mirror  43  has a characteristic by which the P-polarized light component of blue light is transmitted and the S-polarized light component of blue light is reflected. Dichroic mirror  43  is thus able to separate light that is emitted from light source  41  into a P-polarized light component as the first linearly polarized light component and an S-polarized light component as the second linearly polarized light component. In the present exemplary embodiment, dichroic mirror  43  guides substantially only the P-polarized light component as the first linearly polarized light component to fluorophore unit  16 . 
     As a more specific example, with relation to the P-polarized light component, dichroic mirror  43  transmits light of wavelengths equal to or less than the wavelength of blue light and reflects light of wavelengths sufficiently longer than the wavelength of blue light. Further, relating to the S-polarized light component, the dichroic mirror transmits light of wavelengths sufficiently shorter than the wavelength of blue light and reflects light of wavelengths equal to or greater than the wavelength of blue light. Dichroic mirror  43  thus reflects the S-polarized light component and transmits the P-polarized light component in the wavelength band of blue light. The spectrum of light emitted from light source  41  belongs to the wavelength band of this blue light. 
     Dichroic mirror  43  can be configured from a multilayer film of dielectrics each having different refractive indices. Dichroic mirror  43  having the spectral reflectance characteristic shown in  FIG. 5  is easily fabricated by appropriately adjusting, for example, the refractive indices and the film thicknesses of dielectric film or the number of laminations of dielectrics to determine a predetermined cutoff wavelength. 
     The P-polarized light component of blue light that is transmitted by dichroic mirror  43  passes through quarter-wave plate  14  and collimator lens  15  and is irradiated into fluorophore unit  16 . The P-polarized light is converted to circularly polarized light by quarter-wave plate  14 , and this circularly polarized light is condensed in fluorophore unit  16 . 
     The configuration of fluorophore unit  16  is similar to that of the first exemplary embodiment. When blue light from light source  41  is irradiated into fluorophore regions  16   b  and  16   c  of fluorophore unit  16 , light of a wavelength longer than that of the wavelength of blue light is emitted from the fluorophores. In the present exemplary embodiment, the fluorophores applied to fluorophore regions  16   b  and  16   c  emit green light or red light. 
     The light that is emitted from the fluorophores is changed to parallel light by collimator lens  15 , passes through quarter-wave plate  14 , and is again irradiated into dichroic mirror  43 . As shown in  FIG. 5 , dichroic mirror  43  reflects red light and green light. The red light and green light that are emitted from fluorophore regions  16   b  and  16   c  are therefore reflected at dichroic mirror  42  and emitted in the same direction from illumination optical system  40 . 
     When blue light from light source  41  is irradiated into reflection region  16   a  of fluorophore unit  16 , the blue light is reflected, advances along the same light path as the red light and green light, and passes through collimator lens  15  and quarter-wave plate  14 . 
     This blue light is converted from circularly polarized light to S-polarized light by quarter-wave plate  14  and irradiated into dichroic mirror  43 . As shown in  FIG. 5 , dichroic mirror  43  reflects S-polarized excitation light, whereby the blue light that is reflected by reflection region  16   a  passes along the same light path as the red light and green light and is emitted from illumination optical system  40 . 
     According to the above-described configuration, different optical systems need not be used for each wavelength of light, whereby the number of constituent parts of illumination optical system  40  is decreased and the size of the illumination optical system is also reduced. 
     The light reflected by dichroic mirror  43  of illumination optical system  40  is irradiated into image formation element  22  by way of integrator  18 , mirror  20 , field lens  19 , condenser lens  21 , and TIR prism  23 . The light that is converted to image light by image formation element  22  is enlarged and projected onto a screen by projection lens  24 . As in the first exemplary embodiment, a DMD can be used as image formation element  22 . 
     Integrator  18 , field lens  19 , and condenser lens  21  are provided for illuminating light on image formation element  22  both uniformly and as a rectangle. Integrator  18 , mirror  20 , field lens  19 , and condenser lens  21  may be constituent elements of illumination optical system  40 . 
     Fluorophore units  10  and  40  in the above-described first and second exemplary embodiments have two types of fluorophore regions  16   b  and  16   c . The fluorophore unit is not limited to this form and may have one type or three or more types of fluorophore regions. The wavelength of light that is emitted from each fluorophore region is selected as appropriate according to the use of the illumination optical system. 
     In an illumination optical system that includes a fluorophore unit having a reflection region and only one type of fluorophore region, light generated by the light source and fluorescent light that is generated by the fluorophore can be emitted in the same direction along the same light path. Accordingly, in an illumination optical system that emits two types of light, the light generated by the light source and the fluorescent light from the fluorophore, the number of constituent parts can be decreased and the size can be reduced. When a projector that displays full color is configured using this type of illumination optical system, another separate light source should be used. 
     Although a detailed explanation has been presented regarding preferable exemplary embodiments of the present invention, the present invention is not limited to the above-described exemplary embodiments, and it should be understood that the present invention is open to various modifications and amendments that do not depart from the gist of the present invention. 
     REFERENCE SIGNS LIST 
     
         
           10 ,  40  projector 
           11 ,  41  light source 
           12  collimator 
           13 ,  43  dichroic mirror (optical element) 
           14  quarter-wave plate 
           15  collimator 
           16  fluorophore unit 
           16   a  reflection region 
           16   b  fluorescent region 
           16   c  fluorescent region 
           17  motor 
           18  integrator 
           19  field lens 
           20  mirror 
           21  condenser lens 
           22  image formation element 
           23  TIR prism 
           23   a  air gap surface 
           24  projection lens