Abstract:
An illumination device includes an image element configured to convert light incident thereon to image light and to output the image light, a first light path extending to pass through the image element, and a second light path extending without passing through the image element. The first light path and the second light path are configured to project lights passing therethrough, respectively, on an object existing outside the illumination device.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to Japanese Patent Application No. 2013-229825 filed on November 5, the entire contents of which are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to an illumination device and, more particularly, to an illumination device capable of irradiating light for illumination and light for image. 
       BACKGROUND ART 
       [0003]    A projector as an image display device that enlarges and projects various images onto a screen becomes widespread (see, e.g., Japanese Unexamined Patent Application Publication No 2009-199854). More specifically, there are known a projector of the type that projects an image by allowing the light emitted from a light source to transmit through a transmission type image element and a projector of the type that projects an image by allowing the light emitted from a light source to be reflected by a reflection type image element. 
         [0004]    If an illumination device is capable of emitting not only light for illumination but also light for image, the illumination device can be used in a wide variety of applications. 
       SUMMARY OF THE INVENTION 
       [0005]    In view of the above, the present disclosure provides an illumination device capable of simultaneously emitting light for illumination and light for image. 
         [0006]    In accordance with an aspect of the present invention, there is provided an illumination device, including: an image element configured to convert light incident thereon to image light and to output the image light; a first light path extending to pass through the image element; and a second light path extending without passing through the image element, wherein the first light path and the second light path are configured to project lights passing therethrough, respectively, on an object existing outside the illumination device. 
         [0007]    The illumination device may further include a projection lens configured to project the lights passing through the first light path and the second light path, respectively, on the object, wherein the first light path includes a light path extending toward the projection lens via the image element, the second light path includes a light path extending toward the projection lens without passing through the image element, and the first light path and the second light path are two split light paths, extending directions of which are substantially identical with each other. 
         [0008]    The image element may be a substantially planar element, and the first light path and the second light path may respectively extend through two separate regions on a plane including the image element. 
         [0009]    When viewed in the extending direction of the first light path, the first light path may be surrounded by the second light path in at least a portion thereof along the extending direction. 
         [0010]    The illumination device may further include a light shielding member configured to isolate at least a portion of the first light path from the second light path. 
         [0011]    At least a portion of the first light path may be provided adjacent to the second light path without being isolated from the second light path. 
         [0012]    The image element may include a light-transmission-type image element configured to convert the light transmitting therethrough to the image light. 
         [0013]    The first light path and the second light path may be two light paths split on a plane including two separate regions one of which is an image forming region where the image element is provided and the other of which is a light transmitting region, the first light path is for light passing through the image forming region to be incident on the projection lens, and the second light path is for light passing through the light transmitting region to be incident on the projection lens. 
         [0014]    The illumination device may further include a substrate, and wherein the image forming region and the light transmitting region are provided in the substrate. An opening may be formed in the light transmitting region. 
         [0015]    The image element may include a transmission-type liquid crystal panel. 
         [0016]    The illumination device may further include a polarizing element that includes a light transmitting region and a polarization control region where a polarization control element for polarizing light moving toward the image element or light emitted from the image element is provided. 
         [0017]    The polarizing element may further include a substrate in which the polarization control region and the light transmitting region are provided. 
         [0018]    The image element may include a light-reflection-type image element configured to reflect the light incident on the image element as the image light. 
         [0019]    The first light path and the second light path may be two light paths split on a plane including two separate regions one of which is an image forming region where the image element is provided and the other of which is a light reflecting region, the first light path is for light that is reflected in the image forming region to be incident on the projection lens, and the second light path is for light that is reflected in the light reflecting region to be incident on the projection lens. 
         [0020]    The illumination device may further include a substrate, and wherein the image forming region and the light reflecting region are provided in the substrate. 
         [0021]    The image element may include a reflection-type liquid crystal panel. 
         [0022]    The image element may be a micro mirror array. 
         [0023]    The illumination device according to the present invention can simultaneously emit light for illumination but also light for image. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The figures depict one or more implementations in accordance with the present teaching, by way of example only, not by way of limitations. In the figures, like reference numerals refer to the same or similar elements. 
           [0025]      FIGS. 1A and 1B  are views for explaining the use of an illumination device according to an embodiment. 
           [0026]      FIG. 2  is a view conceptually showing the configuration of the illumination device according to the embodiment. 
           [0027]      FIG. 3  is a view schematically showing an optical system of the illumination device according to the embodiment. 
           [0028]      FIG. 4  is a sectional view of light paths taken along line IV-IV in  FIG. 3 . 
           [0029]      FIG. 5  is a view showing a configuration of the light splitting member according to the embodiment. 
           [0030]      FIGS. 6A and 6B  are first diagrams illustrating other configuration examples of the light splitting member. 
           [0031]      FIGS. 7A and 7B  are second diagrams illustrating other configuration examples of the light splitting member. 
           [0032]      FIG. 8  is a plan view showing a light splitting member provided with a light shielding member. 
           [0033]      FIG. 9  is a view showing an optical system of a single-plate-type illumination device according to the embodiment. 
           [0034]      FIG. 10  is a view showing an optical system of a three-plate-type illumination device according to the embodiment. 
           [0035]      FIG. 11  is a view showing an optical system of an illumination device using a reflection-type image element according to another embodiment. 
           [0036]      FIG. 12  is a first diagram conceptually illustrating an illumination device in which a first light path and a second light path are provided by another method. 
           [0037]      FIG. 13  is a second diagram conceptually illustrating an illumination device in which a first light path and a second light path are provided by a further method. 
           [0038]      FIG. 14  is a view showing an application example of the illumination device. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Hereinafter, embodiments of an illumination device (or lighting projector) will be described in detail with reference to the accompanying drawings. Each of the embodiments described below shows one preferred specific example of the present invention. Accordingly, the numerical values, the shapes, the materials, the components, the arrangement positions of the components and the connection form of the components set forth in the following embodiments are nothing more than one example and are not intended to limit the present invention. Among the components of the following embodiments, the components not recited in an independent claim that defines a top concept of the present invention will be described as arbitrary components. 
         [0040]    The drawings are schematic views and are not strictly depicting the present invention. In the drawings, like reference numerals will be used for like or corresponding parts and will not be repeatedly described or will be described in a simplified manner. 
       First Embodiment 
       [0041]    First, description will be made on the use of an illumination device according to a first embodiment.  FIGS. 1A and 1B  are views for explaining the use of the illumination device according to the first embodiment. 
         [0042]    As shown in  FIG. 1A , the illumination device  100  according to the first embodiment can simultaneously irradiate image light  10  (light for image) and an illumination light  20  (light for illumination). For example, the illumination device  100  can irradiate the image light  10  onto a surface (irradiation surface) of a structure and can illuminate the surroundings of the image light  10  with the illumination light  20 . 
         [0043]    More specifically, for example, if the illumination device  100  is installed above a desk, the illumination device  100  can illuminate the desk and display an image on the desk. Furthermore, as shown in  FIG. 1B , the illumination device  100  can also turn on and off only the irradiation of the image light  10 . 
         [0044]    As set forth above, the illumination device  100  has not only an illumination function but also a function of presenting an image to a user. 
         [0045]    Next, description will be made on the configuration of the illumination device  100 .  FIG. 2  is a view conceptually showing the configuration of the illumination device  100  according to the first embodiment.  FIG. 3  is a view schematically showing an optical system of the illumination device  100  according to the first embodiment. 
         [0046]    As shown in  FIGS. 2 and 3 , the illumination device  100  includes an image element  110 , a projection lens  120  and a substrate  130 . The optical system of the illumination device  100  shown in  FIG. 3  is a simplified optical system and is different in configuration from the detailed optical system to be described later. 
         [0047]    The image element  110  is a substantially planar element that converts incident light to image light and outputs the image light (that generates light for image). In the first embodiment, the image element  110  is a transmission type liquid crystal panel. The image element  110  is provided in the central portion of the substrate  130  which is made of a light transmitting material. The projection lens  120  is a lens for projecting light onto an object. The projection lens  120  is a lens that has been conventionally used to focus the image light  10  on an object. 
         [0048]    In the illumination device  100 , there are provided a first light path  111  passing through the image element  110  and extending toward the projection lens  120  and a second light path  112  extending toward the projection lens  120  without passing through the image element  110 . That is to say, the illumination device  100  includes an optical system that constitutes the first light path  111  and the second light path  112 . The first light path  111  is a light path through which the light emitted as the image light  10  passes. The second light path  112  is a light path through which the light emitted as the illumination light  20  passes. 
         [0049]    In this regard, the first light path  111  and the second light path  112  are two split light paths and the directions of the split light paths are substantially identical with each other. 
         [0050]    More specifically, the first light path  111  and the second light path  112  are two light paths spatially split in a plane (split-emission plane) that intersects the light advancing direction. The first light path  111  and the second light path  112  are light paths (cross-sectionally split light paths) that are directed toward the substantially identical direction near the split-emission plane. In other words, in the vicinity of the split-emission plane, the advancing direction of the light passing through the first light path  111  and the advancing direction of the light passing through the second light path  112  are substantially identical with each other. In this regard, the term “substantially identical” means that the advancing directions of the light are substantially identical with each other in view of the deviation in the arrangement of parts of the optical system, the tolerance in the dimension of the respective parts, and the like. 
         [0051]    The light passing through the first light path  111  transmits through the image element  110  to be incident on the projection lens  120 . Thus, the image light  10  is projected onto a first region of an object. On the other hand, the light passing through the second light path  112  is incident on the projection lens  120  without transmitting through the image element  110 . Thus, the illumination light  20  is projected onto a second region of the object. The first region of the object onto which the image light  10  is projected does not essentially overlap with the second region of the object onto which the illumination light  20  is projected. In the object, the second region is essentially positioned around the first region. 
         [0052]    When seen in an optical axis direction (in an advancing direction of light), the second light path  112  is provided to surround at least a portion of the first light path  111 .  FIG. 4  is a sectional view of the light paths taken along line IV-IV in  FIG. 3  (a sectional view showing a cross section perpendicular to the optical axis). As shown in  FIG. 4 , when seen in the advancing direction of the light passing through the first light path  111 , the first light path  111  is surrounded by the second light path  112  in at least a portion thereof along the advancing direction. 
         [0053]    The light paths of the light moving toward a light splitting member  140  are not split. In other words, the first light path  111  of the light moving toward the light splitting member  140  is not shielded from, but is formed adjacent to (integrated with), the second light path  112  of the light moving toward the light splitting member  140 . 
         [0054]    In the first embodiment, the first light path  111  and the second light path  112  are two light paths split by the substrate  130  (hereinafter referred to as a light splitting member  140 ) provided with the image element  110 . 
         [0055]    Next, the light splitting member  140  which is a feature of the illumination device  100  will be described in detail with reference to  FIG. 5 . 
         [0056]      FIG. 5  is a view showing a configuration of the light splitting member  140  according to the first embodiment. The light splitting member  140  includes a first substrate  131 , a second substrate  132 , and the image element  110  (a first image element member  110   a  and a second image element member  110   b ). 
         [0057]    The first substrate  131  and the second substrate  132  are circular glass substrates having a light transmitting property. The first image element member  110   a  is provided in a central portion of a major surface of the first substrate  131 . Similarly, the second image element member  110   b  is provided in a central portion of a major surface of the second substrate  132 . 
         [0058]    The light splitting member  140  is formed by bonding the first substrate  131  and the second substrate  132  together. That is to say, the first image element member  110   a  and the second image element member  110   b  are overlapped with each other to form the image element  110 . 
         [0059]    The light transmitting through the region (image forming region) of the light splitting member  140  in which the image element  110  is provided, is converted to the light corresponding to the image of the image element  110  and is incident on the projection lens  120 . That is to say, the light transmitting through the image element  110  (the image forming region) passes through the first light path  111 . In other words, the image region (the image element  110 ) of the light splitting member  140  is included in the optical system that constitutes the first light path  111 . 
         [0060]    On the other hand, the region (light transmitting region) of the light splitting member  140  in which the image element  110  is not provided, is formed of light transmitting glass as mentioned above. Thus, the light transmitting through the light transmitting region is incident on the projection lens  120 . That is to say, the light transmitting through the light transmitting region passes through the second light path  112 . In other words, the light transmitting region of the light splitting member  140  is included in the optical system that constitutes the second light path  112 . The advancing direction of the light coming out from the light splitting member  140  and passing through the first light path  111  and the advancing direction of the light coming out from the light splitting member  140  and passing through the second light path  112  are substantially identical with each other. 
         [0061]    In the illumination device  100 , the first light path  111  and the second light path  112  are formed by the light splitting member  140 . Thus, for example, the illumination device  100  can project the image light  10  on a surface (irradiation surface) of a structure and can illuminate the surrounding of the image light  10  with the illumination light  20 . 
         [0062]    The configuration of the light splitting member  140  is not limited to the configuration shown in  FIG. 5 .  FIGS. 6A and 6B  are views illustrating other configuration examples of the light splitting member. 
         [0063]    A light splitting member  140   a  shown in  FIG. 6A  is formed by inserting an image element  110  into an opening (or hole)  30   a  defined at the center of a disc-shaped light transmitting member  130   a . The light transmitting member  130   a  may be made of any material such as a resin or the like as long as the material has a light transmitting property. 
         [0064]    A light splitting member  140   b  shown in  FIG. 6B  has a configuration in which an image element  110  is held by a frame-shaped holding member  130   b  instead of a substrate. More specifically, the holding member  130   b  holds the image element  110  using an opening (holding portion)  30   b  corresponding in shape to the image element  110 . 
         [0065]    The holding member  130   b  is a frame-shaped member made of a light transmitting material. In addition to the opening  30   b , four additional openings  30  are formed inside a circular main frame  135  that defines the contour of the holding member  130   b . In case of the holding member  130   b , a light transmitting region is defined by the holding member  130   b  and the openings  30 . 
         [0066]    While examples of the light splitting member have been described above, the shape (external form) of the light splitting member and the arrangement of the image element  110  within the light splitting member are not limited to the aforementioned configurations. The light splitting member may have any configuration as long as the light splitting member includes an image forming region in which the image element  110  is provided and a light transmitting region. 
         [0067]    The shape (plan-view contour) of the light splitting member may be, e.g., a race track shape.  FIG. 7A  is a schematic diagram showing a light splitting member  140   c  having a race track shape. In the light splitting member  140   c , an image element  110  is provided at the center of the light splitting member  140   c  in such a way that the image element  110  is interposed between two light transmitting regions  150 . 
         [0068]    As shown in  FIG. 7B , the shape of the light splitting member may be rectangular.  FIG. 7B  is a schematic diagram showing a rectangular light splitting member  140   d . The light splitting member  140   d  is split into two rectangular regions, one of which is an image forming region where the image element  110  is provided and the other of which is a light transmitting region  150 . 
         [0069]    A light shielding member may be provided in a border between the image forming region and the light transmitting region.  FIG. 8  is a plan view illustrating a light splitting member  140   e  provided with a light shielding member  115 . The light splitting member  140   e  shown in  FIG. 8  has the same configuration as the light splitting member  140  except that the light splitting member  140   e  is provided with the light shielding member  115 . 
         [0070]    As shown in  FIG. 8 , when seen in a plan view, a mask (light shielding member)  115  that does not transmit light is provided in a border between the image element  110  (the image forming region) and the substrate  130  (the light transmitting region) of the light splitting member  140   e . That is to say, the first light path  111  and the second light path  112  are isolated by the mask  115 . In other words, the first light path  111  and the second light path  112  are isolated by the mask  115  in a portion along the light paths. The mask  115  is one example of the light shielding member. The light shielding member may be other members. 
         [0071]    Next, description will be made on an optical system of the illumination device  100 . The illumination device  100  is realized by, e.g., a single-plate-type illumination device  100 . 
         [0072]      FIG. 9  is a view showing an optical system of the single-plate-type illumination device  100 . As shown in  FIG. 9 , the illumination device  100  includes a white light source  160 , a collimator lens  165 , an integrator lens  170 , a polarizing beam splitter  175 , a condensing lens  180  and a collimator lens  185 . The illumination device  100  further includes an incidence-side polarizing element  190 , a light splitting member  140 , an emission-side polarizing element  195  and a projection lens  120 . 
         [0073]    The white light source  160  is a light source that generates white light. Specifically, the white light source  160  is a light source that makes use of a discharge lamp or a solid light emitting element such as a light emitting diode (LED), a semiconductor laser, an organic EL (Electroluminescence) element, an inorganic EL element or the like. 
         [0074]    The light generated by the white light source  160  is made parallel in the collimator lens  165 . The illuminance distribution of the light is made uniform by the integrator lens  170 . Then, the light whose illuminance distribution is made uniform is converted to linearly polarized light by the polarizing beam splitter  175 . It is assumed that the light whose illuminance distribution is made uniform is converted to, e.g., P-polarized light. 
         [0075]    The P-polarized light is incident on the condensing lens  180  and is made parallel by the collimator lens  185 . Then, the light is incident on the incidence-side polarizing element  190 . 
         [0076]    The incidence-side polarizing element  190  is a substrate provided with a polarizing plate (polarization control element) that polarizes the light incident toward the image element  110 . The emission-side polarizing element  195  is a substrate provided with a polarizing plate that polarizes the light emitted from the image element  110 . 
         [0077]    In this regard, the incidence-side polarizing element  190  and the emission-side polarizing element  195  have a structure corresponding to the light splitting member  140 . More specifically, the incidence-side polarizing element  190  (or the emission-side polarizing element  195 ) is configured such that a polarizing plate is provided only in the portion corresponding to the image forming region of the light splitting member  140  (i.e., the portion overlapping with (corresponding to) the image forming region of the light splitting member  140  when seen in a direction perpendicular to an optical axis), with the remaining portion configured to transmit light. That is to say, the incidence-side polarizing element  190  (or the emission-side polarizing element  195 ) includes a polarization control region where the polarizing plate is provided and a light transmitting region around the polarization control region. 
         [0078]    Since the polarization control region is configured to transmit P-polarized light, the light incident on the polarization control region of the incidence-side polarizing element  190  is incident on the image element  110  and is emitted from the image element  110  after being optically modulated pursuant to the image of the image element  110 . 
         [0079]    Unlike the polarization control region of the incidence-side polarizing element  190 , the polarization control region of the emission-side polarizing element  195  is configured to transmit only S-polarized light. Thus, only an S-polarized light component of the optically modulated light is incident on the projection lens  120  after passing through the polarization control region of the emission-side polarizing element  195 . As a result, the image light  10  is projected on a screen or the like through the projection lens  120 . 
         [0080]    On the other hand, the light incident on the light transmitting region of the incidence-side polarizing element  190  passes through (transmits) the light transmitting region of the light splitting member  140  and the light transmitting region of the emission-side polarizing element  195  sequentially. Then, the light is incident on the projection lens  120 . As a result, the illumination light  20  is projected on a screen or the like through the projection lens  120 . 
         [0081]    As described above, the illumination device  100 , which is a single-plate-type illumination device, can simultaneously project the image light  10  and the illumination light  20 . 
         [0082]    The present invention may be realized by a three-plate-type illumination device.  FIG. 10  is a view showing an optical system of a three-plate-type illumination device  100   a  according to the first embodiment. In the following description, components substantially identical with those shown in  FIG. 9  will not be described. 
         [0083]    The illumination device  100   a  includes a phosphor wheel  200 , an excitation light source  203 , a red light source  204 , a blue light source  205 , a collimator lens array  206 , and condensing lenses  207 ,  208  and  218 . The illumination device  100   a  further includes collimator lenses  209 ,  210 ,  211  and  212 , dichroic mirrors  213 ,  214 ,  219  and  223 , and integrator lens arrays  215  and  216 . The illumination device  100   a  further includes a polarizing beam splitter  217 , reflection mirrors  221 ,  225  and  227 , relay lenses  220 ,  222 ,  224  and  226 , and field lenses  228 ,  229  and  230 . 
         [0084]    The illumination device  100   a  further includes incidence-side polarizing elements  190   b ,  190   g  and  190   r , light splitting members  240   b ,  240   g  and  240   r , emission-side polarizing elements  195   b ,  195   g  and  195   r , a cross dichroic prism  240 , and a projection lens  241 . 
         [0085]    The incidence-side polarizing elements  190   b ,  190   g  and  190   r  are substantially identical in configuration with the incidence-side polarizing element  190  described above. The emission-side polarizing elements  195   b ,  95   g  and  195   r  are substantially identical in configuration with the emission-side polarizing element  195  described above. The light splitting members  240   b ,  240   g  and  240   r  are substantially identical in configuration with the light splitting member  140  except that they are provided with image elements  110  corresponding to blue, green and red colors, respectively. 
         [0086]    First, description will be made on a light source unit  250  shown in  FIG. 10 . 
         [0087]    The phosphor wheel  200  is provided with a glass substrate. A dichroic coat that efficiently reflects visible light is formed on the surface of the glass substrate. A phosphor  201  that generates green light is coated on the dichroic coat in the shape of a thin film. The method of forming the thin film of the phosphor  201  is not particularly limited and may be a precipitation method or a printing method. In case where x, y and z coordinate axes are set as shown in  FIG. 10 , the phosphor wheel  200  rotates about the z axis. 
         [0088]    The excitation light source  203  is a blue semiconductor laser that oscillates at or around a wavelength of about 445 nm. The excitation light source  203  is configured by a plurality of laser diodes. In  FIG. 10 , twenty five laser diodes are arranged in a 5×5 matrix pattern. The number of the laser diodes is not particularly limited and may be properly set depending on the intensity of light to be extracted. 
         [0089]    The laser light generated from the excitation light source  203  is collimated by the collimator lens array  206 . The laser diodes that constitute the excitation light source  203  are arranged in one-to-one correspondence to the respective lens cells of the collimator lens array  206 . 
         [0090]    The collimated laser light passes through a dichroic mirror  213 . Thereafter, the laser light is collected on the phosphor  201  by the condensing lenses  207  and  208 . As a result, green light is generated from the phosphor  201 . 
         [0091]    In this regard, the dichroic mirror  213  transmits the laser light generated from the excitation light source  203  and the red light generated from the red light source  204 . The dichroic mirror  213  reflects the green light generated from the phosphor  201 . 
         [0092]    Meanwhile, a dichroic mirror  214  reflects the green light generated from the phosphor  201  and the red light generated from the red light source  204 . The dichroic mirror  214  transmits the blue light generated from the blue light source  205 . 
         [0093]    Accordingly, the green light generated from the phosphor  201  is reflected by the dichroic mirrors  213  and  214  and is emitted from the light source unit  250 . 
         [0094]    The red light source  204  is an LED having a dominant wavelength of 623 nm. The red light generated from the red light source  204  is collimated by the collimator lenses  209  and  210 . The collimated red light passes through the dichroic mirror  213 . The red light is reflected by the dichroic mirror  214  and is emitted from the light source unit  250 . 
         [0095]    The blue light source  205  is an LED having a dominant wavelength of 462 nm. The blue light generated from the blue light source  205  is collimated by the collimator lenses  211  and  212 . The collimated blue light passes through the dichroic mirror  214 . Then, the blue light is emitted from the light source unit  250 . 
         [0096]    Next, description will be made on an optical system other than the light source unit  250 . 
         [0097]    The illuminance distribution of each of the green light, the red light and the blue light emitted from the light source unit  250  is made uniform by the integrator lens arrays  215  and  216 . Each of the green light, the red light and the blue light is converted to linearly polarized light by the polarizing beam splitter  217  and is incident on the condensing lens  218 . 
         [0098]    In this regard, the dichroic mirror  219  has a property of reflecting the red light and transmitting the green light and the blue light. Accordingly, the red light is reflected by the dichroic mirror  219  and is incident on the field lens  228  via the relay lens  220  and the reflection mirror  221 . 
         [0099]    The red light incident on the field lens  228  is split by the incidence-side polarizing element  190   r , the light splitting member  240   r  and the emission-side polarizing element  195   r . The split red light is moved through the cross dichroic prism  240  and is separated into a red component of the image light  10  and a red component of the illumination light  20 , which are projected through the projection lens  241 . 
         [0100]    The dichroic mirror  223  has a property of reflecting the green light and transmitting the blue light. Accordingly, the green light passes through the dichroic mirror  219  and then the relay lens  222 . Then, the green light is reflected by the dichroic mirror  223  and is incident on the field lens  229 . 
         [0101]    The green light incident on the field lens  229  is split by the incidence-side polarizing element  190   g , the light splitting member  240   g  and the emission-side polarizing element  195   g . The split green light is moved through the cross dichroic prism  240  and is separated into a green component of the image light  10  and a green component of the illumination light  20 , which are projected through the projection lens  241 . 
         [0102]    The blue light passes through the dichroic mirror  219 , the relay lens  222  and the dichroic mirror  223  in the named order. Then, the blue light is moved through the relay lens  224 , the reflection mirror  225 , the relay lens  226  and the reflection mirror  227  in that order and is incident on the field lens  230 . 
         [0103]    The blue light incident on the field lens  230  is split by the incidence-side polarizing element  190   b , the light splitting member  240   b  and the emission-side polarizing element  195   b . The split blue light is moved through the cross dichroic prism  240  and is separated into a blue component of the image light  10  and a blue component of the illumination light  20 , which are projected through the projection lens  241 . 
         [0104]    As described above, the illumination device  100   a , which is a three-plate-type illumination device, can simultaneously project the image light  10  and the illumination light  20 . 
         [0105]    Described above are the illumination device  100  and the illumination device  100   a  according to the first embodiment. In the illumination device  100  and the illumination device  100   a , there are provided the first light path  111  which extends toward the projection lens  120  via the image element  110  and the second light path  112  which extends toward the projection lens  120  without passing through the image element  110 . The first light path  111  and the second light path  112  are two split light paths which extend in the substantially identical direction. 
         [0106]    With this configuration, the illumination device  100  and the illumination device  100   a  can simultaneously project the image light  10  and the illumination light  20 . 
       Second Embodiment 
       [0107]    In the first embodiment, description has been made on the illumination device  100  (the illumination device  100   a ) that makes use of the transmission-type image element  110 . However, the present invention may be realized using a reflection-type image element. 
         [0108]    In the second embodiment, description will be made on an illumination device which makes use of a reflection-type image element.  FIG. 11  is a view showing an optical system of an illumination device using a reflection-type image element according to the second embodiment. 
         [0109]    As shown in  FIG. 11 , the illumination device  300  according to the second embodiment includes a white light source  360 , a light splitting member  340  provided with a reflection-type image element  310 , a condensing lens  365 , a rod integrator  370 , a relay lens  380 , and a field lens  385 . 
         [0110]    First, description will be made on the light splitting member  340  according to the second embodiment. 
         [0111]    The light splitting member  340  according to the second embodiment makes use of, e.g., a disc-shaped mirror member (light reflecting member) in place of the disc-shaped light transmitting member  130   a  employed in the light splitting member  140   a  shown in  FIG. 6A . The light splitting member  340  is formed by inserting a reflection-type image element  310 , instead of the image element  110 , into an opening defined at the center of the mirror member. 
         [0112]    The mirror member may be formed of any material as long as the material can reflect light. The light splitting member using the reflection-type image element  310  may have a configuration in which the image element  310  is provided in a substrate capable of reflecting light. 
         [0113]    In the second embodiment, a micro mirror array is used as the reflection-type image element  310 . The micro mirror array is an element in which micro mirrors are arranged in a matrix pattern. The respective micro mirrors correspond to pixels of an image. The slope of each of the micro mirrors is changed pursuant to an image signal. The amount of the light incident on the projection lens  120  (the brightness and darkness of an image) is changed depending on the slopes of the micro mirrors. Thus, the image light  10  is projected through the projection lens. 
         [0114]    Instead of the micro mirror array, a reflection-type liquid crystal panel (LCOS: Liquid Crystal on Silicon) may be used as the reflection-type image element. 
         [0115]    Thus, the light splitting member  340  includes an image forming region where the image element  310  is provided and a light reflecting region (a region of the mirror member other than the image forming region). 
         [0116]    In the second embodiment, the first light path  111  and the second light path  112  are two light paths split by the light splitting member  340  (an element which includes a plane having an image forming region and a light reflecting region). More specifically, the first light path  111  is a light path of the light reflected in the image forming region and incident on the projection lens  120 . The second light path  112  is a light path of the light reflected in the light reflecting region and incident on the projection lens  120 . 
         [0117]    Next, description will be made on an optical system shown in  FIG. 11 . 
         [0118]    The light generated from the white light source  360  is collected onto the rod integrator  370  by the condensing lens  365 . The light whose illuminance is made uniform is emitted from the rod integrator  370 . 
         [0119]    Then, the light emitted from the rod integrator  370  passes through the relay lens  380  and the filed lens  385 . The light is reflected by the reflection mirror  390  and is incident on the light splitting member  340  provided with the reflection-type image element  310 . 
         [0120]    As mentioned above, the light incident on the image forming region of the light splitting member  340  is converted to the image light depending on the slopes of the micro mirrors and is incident on the projection lens  320 . As a result, the image light  10  is projected on a screen or the like through the projection lens  320 . 
         [0121]    On the other hand, the light incident on the light reflecting region of the image element  310  is reflected by the light reflecting region and is incident on the projection lens  320 . As a result, the illumination light  20  is projected on a screen or the like through the projection lens  320 . 
         [0122]    Described above is the illumination device  300  according to the second embodiment. In the illumination device  300 , there are provided the first light path  111  which extends toward the projection lens  320  via the reflection-type image element  310  and the second light path  112  which extends toward the projection lens  320  without passing through the reflection-type image element  310 . The first light path  111  and the second light path  112  are two light paths split on the plane which intersects the optical axis (the plane which includes the image element  310 ). 
         [0123]    With this configuration, the illumination device  300  can simultaneously project the image light  10  and the illumination light  20 . 
         [0124]    The present invention may be realized by a three-plate-type illumination device that makes use of the reflection-type image element  310 . No description will be made on an optical system available in this case. 
       OTHER EMBODIMENTS 
       [0125]    While the illumination devices according to the first and second embodiments have been described above, the present invention is not limited to these embodiments. 
         [0126]    In the aforementioned embodiments, description has been made on an example in which the light emitted from one light source is split to pass through the first light path  111  and the second light path  112 . Alternatively, a light source for generating the light that passes through the first light path  111  and a light source for generating the light that passes through the second light path  112  may be provided independently of each other. 
         [0127]    If the first light path  111  passing through the image element and the second light path  112  not passing through the image element are provided in the illumination device, it is possible for the illumination device to project the image light  10  and the illumination light  20 . Therefore, the first light path  111  and the second light path  112  may be light paths split by a method other than the methods described in the aforementioned embodiments. 
         [0128]    For example, as shown in a conceptual diagram of  FIG. 12 , the first light path  111  and the second light path  112  are directionally split light paths. The second light path  112  may be a light path which does not pass through the vicinity of the image element  110 . More specifically, the first light path  111  and the second light path  112  may be light paths which are split by a half mirror or the like, at a location where the light is not yet incident on the image element, so as to extend in different directions. 
         [0129]    For example, as shown in a conceptual diagram of  FIG. 13 , the second light path  112  may be a light path that does not pass through both the image element  110  and the projection lens  120 . 
         [0130]    The illumination devices according to the aforementioned embodiments can be realized into, e.g., a projector  1  shown in  FIG. 14 . 
         [0131]    The present invention may be realized not only into the illumination device but also into the light splitting member or the polarizing element (the incidence-side polarizing element and the emission-side polarizing element) described in the aforementioned embodiments. 
         [0132]    While the illumination device according to one or more embodiments have been described above, the present invention is not limited to these embodiments. 
         [0133]    While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that they may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all modifications and variations that fall within the true scope of the present teachings.