Abstract:
A light source device comprises a waveguide, an electrodeless lamp, a probe, and conversing means. The waveguide is formed to contain a medium enabling a microwave to resonate and has a surface and an aperture cavity with an aperture opened at a predetermined position of the surface. The electrodeless lamp is loaded in the aperture cavity in a state where part of the electrodeless lamp is protruded from the surface of the waveguide so that the part of the electrode lamp emits light in response to applying the microwave to the electrodeless lamp. The probe supplies a high-frequency signal to the waveguide so that the high-frequency signal is converted to the microwave in the waveguide. The converging means is disposed on the surface of the waveguide to face the aperture cavity and utilizes all the light emitted from the part of the electrodeless lamp to converge the light.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     Japanese Patent applications No. 2006-161481 filed on Jun. 9, 2006 and No. 2006-161486 filed on Jun. 9, 2006.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a light source device and an image displaying apparatus, and in particular, to a light source device comprising a waveguide and an electrodeless lamp loaded in an aperture cavity formed in the waveguide such that the electrodeless lamp emits light in response to microwaves generated in the waveguide, and to an image displaying apparatus that employs such a light source device.  
         [0004]     2. Description of the Related Art  
         [0005]     A light source device has been known which comprises a waveguide and an electrodeless lamp, in which the electrodeless lamp is arranged in the waveguide to emit light. Such light source devices are disclosed by U.S. Pat. No. 6,737,809, for example.  
         [0006]     Specifically, the above patent discloses a light source device that comprises a waveguide, a probe, and an electrodeless lamp. The waveguide has a cylindrical outer shape provided by a dielectric member and coated with a metal material. An aperture cavity with a bottom is formed in the waveguide so as to be located at the center in one end surface of the waveguide. The electrodeless lamp, which emits light in response to microwaves to be supplied, is made into a thin shape and loaded into the aperture cavity such that one end thereof faces the bottom and the other end thereof protrudes from the surface of the waveguide. The probe is linked with the other end of the waveguide at a position shifted outwardly from the center in the radial direction. This probe receives high-frequency power from a high-frequency power supply.  
         [0007]     When the high-frequency power is supplied to the prove  12 , the waveguide generates microwaves therein and is resonated with the use of the dielectric maternal as medium. The electric field caused by the microwaves becomes maximum at the radial center of the waveguide, that is, at the position of the aperture cavity. Plasma is generated in the wireless lamp due to the microwaves generated in the aperture cavity, whereby light is emitted from the end of the electrodeless lamp, the end of which is protruded from the surface of the waveguide.  
         [0008]     The electrodeless lamp has an inner wall providing a diffuse reflection surface (Irregular reflection surface). Thus the emitted light has a distribution which is similar to one obtained from the perfect diffuse surface, i.e., Lambertian diffuse surface.  
         [0009]     When such a light source device is applied, for example, to a projector, it is required that a light condensing system with various optical components such as an collimating lens or a convex lens system (such as condensing lenses) be arranged with the light source device. The light condensing system condenses the light emitted from the light source device.  
         [0010]     However, in the conventional light source device described above, the flux of light emitted from the electrodeless lamp has a projection angle which is considerably wide. Hence even if the light condensing system employs the convex lens system, a light condensing efficiency is low and unsatisfactory, because a flux of light passing a comparatively narrow angular range next to the light axis is utilized as light traveling toward the light condensing system, but a flux of light outside the range is not utilized.  
         [0011]     In addition, the above wider projection angle also brings about another difficulty that a light condensing system employed by a projector becomes large in its size.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention has been made in consideration of the foregoing difficulties, and an object of the present invention is to provide a light source device of which light condensing efficiency is made higher by reducing the “etendue” of the light source device.  
         [0013]     A further object of the present invention is to provide an image displaying apparatus which is compact in size and light in weight by employing a light source device allowing a light condensing system arranged with the device to be compact.  
         [0014]     In order to realize the object about the light source device, as one aspect, the present invention provides a light source device comprises a waveguide, electrodeless lamp, probe, and converging means. The waveguide is formed to contain a medium enabling a is microwave to resonate and formed to have a surface and an aperture cavity with an aperture opened at a predetermined position of the surface. The electrodeless lamp is loaded in the aperture cavity in a state where part of the electrodeless lamp is protruded from the surface of the waveguide so that the part of the electrode lamp emits light in response to applying the microwave to the electrodeless lamp. The probe supplies a high-frequency signal to the waveguide so that the high-frequency signal is converted to the microwave in the waveguide. The converging means is disposed on the surface of the waveguide to face the aperture cavity and formed to utilize all the light emitted from the part of the electrodeless lamp so as to converge the light.  
         [0015]     By way of example, the converging means comprises a spherical reflecting mirror formed into a quaquaversal shape having a top, disposed on the surface of the waveguide to enclose the aperture cavity, and formed to have a semi-spherical reflecting surface to be opposed to the aperture cavity and an aperture formed at the top of the mirror, the reflecting surface providing a focus located at the part of the electrodeless lamp and the aperture of the mirror allowing the light emitted from the part of the electrodeless lamp to pass therethrough.  
         [0016]     Furthermore, in order to realize the object concerning the image displaying apparatus, the present invention provides an image displaying apparatus comprising a light source device. This light source device comprises a waveguide formed to contain a medium enabling a microwave to resonate and formed to have a surface and an aperture cavity with an aperture opened at a predetermined position of the surface; an electrodeless lamp loaded in the aperture cavity in a state where part of the electrodeless lamp is protruded from the surface of the waveguide so that the part of the electrode lamp emits light in response to applying the microwave to the electrodeless lamp; a probe supplying a high-frequency signal to the waveguide so that the high-frequency signal is converted to the microwave in the waveguide; and converging means disposed on the surface of the waveguide to face the aperture cavity and formed to utilize all the light emitted from the part of the electrodeless lamp so as to converge the light. The image displaying apparatus further comprises a separator separating the light emitted from the light source device into fluxes of light of three primary colors consisting of red, green and blue; a modulator modulating each of the separated fluxes of light of the three primary colors depending on image signals; and a dichroic prism optically combining the modulated fluxes of light to emit the combined fluxes of light as image light. 
     
    
     BRIEF DESCRIPTIONS OF THE DRAWINGS  
       [0017]     In the accompanying drawings:  
         [0018]      FIG. 1  is a side view, which is partly sectioned and accompanied by a light distribution, showing the configuration of a light source device according to a first embodiment of the present invention;  
         [0019]      FIGS. 2-7  are side views, which are partly sectioned, showing the configuration of light source devices according to second to seventh embodiments of the present invention, respectively;  
         [0020]      FIGS. 8-10  are outlined schematic diagrams showing image displaying apparatuses according to eight to tenth embodiments of the present invention, respectively;  
         [0021]      FIG. 11  is a side view, which is partly sectioned, showing the configuration of a light source device according to an eleventh embodiment of the present invention;  
         [0022]      FIG. 12  is a view for illustrating how to decide a radius of a complex paraboloidal light-condensing mirror according to the eleventh embodiment;  
         [0023]      FIG. 13  is a graph showing the relationship the etendue and the coupling efficiency concerning light-condensing optical systems according to the conventional and the present invention;  
         [0024]      FIG. 14  is a side view, which is partly sectioned, showing the configuration of a light source device according to a twelfth embodiment of the present invention;  
         [0025]      FIG. 15  is a side view, which is accompanied by a light distribution, showing the configuration of a light source device according to a thirteenth embodiment of the present invention;  
         [0026]      FIGS. 16A-16C  show practical outer contours of light pipes used in the thirteenth embodiment;  
         [0027]      FIG. 17  is a side view, which is partly sectioned, showing the configuration of a light source device according to a fourteenth embodiment of the present invention; and  
         [0028]      FIGS. 18-20  are outlined schematic diagrams showing image displaying apparatuses according to fifteenth to seventeenth embodiments of the present invention, respectively. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0029]     Referring to accompanying drawings, various embodiments of a light source device and an image displaying apparatus according to the present invention will now be described.  
       First Embodiment  
       [0030]     Referring to  FIG. 1 , a first embodiment of the light source device according to the present invention will now be described.  
         [0031]     As shown in  FIG. 1 , a light source device  1 A of the present embodiment is provided with a waveguide  11 , a probe  12 , an electrodeless lamp  14 , and a spherical reflecting mirror  15 . Of these, the waveguide  11  is a cylindrical member made of a dielectric material with an outer surface coated with a metal material. The waveguide  11  has a central axis along an axial direction and both circular end surfaces in the axial direction. At a part of one of both axial end surfaces, which part is located at the center or near the center thereof, an aperture cavity  13  is formed to open outside.  
         [0032]     The electrodeless lamp  14  is a lamp emitting light in response to applying microwaves thereto and is formed to have a thin and long shape having a longitudinal direction. This electrodeless lamp  14  is loaded in the aperture cavity  13  such that one end of this electrodeless lamp  14  in the longitudinal direction is placed in the electrodeless lamp  14  and the other end  14   a  is partly protruded from the circular end surface of the waveguide  11 . The other end  14   a  serving as a light emitting part.  
         [0033]     The probe  12  has both ends, one of which is electrically connected with a not-shown high-frequency power supply and the other end of which is linked to the other end surface of the waveguide at a position radially shifted from the center of this end surface. The spherical reflecting mirror  15  is formed into a dome-like member with an inner reflecting surface  16  formed to have an approximately semi-spherical shape. Thus the reflecting surface  16  has a radially central top portion in which an aperture  17  is formed, and the mirror  16  is formed to have a focus located at the light emitting part  14   a  of the electrodeless lamp  14 , which light emitting part  14   a  is protruded from the end surface of the wave guide  11 . With this geometry maintained, the spherical reflecting mirror  15  is mounted to the end surface of the waveguide  11 .  
         [0034]     When high-frequency power is supplied to the waveguide  11  via the probe  12  from the not-shown high-frequency power supply, microwaves are generated in the waveguide  11  which is resonant with the dielectric material used as a medium. As this dielectric material, a ceramic material is used because of its higher relative permittivity. In addition, the probe  12  is positioned at a radial central position of the waveguide  11 , which radial central position is in the aperture cavity  13  and subject to appearance of a maximum electric field generated in the waveguide  11 . The microwaves generated in the aperture cavity  13  enables the generation of plasma at the electrodeless lamp  14 , whereby light is emitted from the light-emitting part  14   a  protruded from the end surface of the waveguide  11 .  
         [0035]     A flux of light emitted from the light-emitting part  14   a  of the electrodeless lamp  14  is reflected by the semicircular spherical reflecting surface  16  of the mirror  15  such that the flux of light is returned to the light-emitting part  14   a . The returned light is reflected by a diffused reflection surface of an inner wall of the electrodeless lamp  14  to overlap with the light emitted from the light-emitting part  14   a . Thus the luminance of the lamp  14  is enhanced. This results in emission of a large amount of flux of light from the aperture  17  of the spherical reflecting mirror  15 . Hence an emitted light distribution Ad becomes as shown in  FIG. 1 , in which the distribution is longer in its light axis direction. Compared to an emitted light distribution of the conventional apparatus, which distribution is nearly a Lambertian-diffuse surface, the emitted light distribution according to the present embodiment is improved largely.  
         [0036]     In this way, the spherical reflecting mirror  15  is mounted to make it possible that a large amount of flux of light is radiated through the aperture  17  with a smaller solid angle. In comparison with the conventional, “etendue” can be made smaller, whereby the light source device with a higher coupling efficiency can be provided. In addition, by changing the bore of the aperture  17 , an amount of reduction in etendue can be adjusted freely.  
         [0037]     The term “etendue” will now be described. The “etendue” is an invariant indicating a spatial spread of a flux of light passing an optical system and a cross section through which the flux of light passes. The etendue can be expressed as a product of an area S and a solid angle θ. That is, a value ξ(sr·m 2 ) of the etendue can be defined as follows: 
 
ξ= n·S ·sin θ·sin θ  (1) 
 
 For example, for improving the etendue of a light source (i.e., a lamp) used for a projector, the etendue should be made smaller. Thus, in such a case, the etendue can be improved by making a light-emitting area smaller and/or making a light radiation angle smaller. 
 
       Second Embodiment  
       [0038]     Referring to  FIG. 2 , a second embodiment of the present invention will now be described. In the present embodiment and subsequent embodiments, for the sake of removing redundancy of the description, components identical or similar to those described in the previous embodiments will be given the same reference numerals and the explanations therefore will be omitted or simplified.  
         [0039]     In the present embodiment, the light source device is reduced Into practice in another form.  
         [0040]      FIG. 2  shows the structure of a light source device  1 B according to the present embodiment. As shown therein, the light source device  1 B is additionally provided with a convex lens  21  mounted on the spherical reflecting mirror  15  to cover the aperture  17  thereof. The remaining components of this device  1 B are identical to those in  FIG. 1  explaining the first embodiment.  
         [0041]     Accordingly, the flux of light radiated through the aperture  17  of the spherical reflecting mirror  15  is collimated into a collimated flux of light corresponding to the area of the aperture  17 . The collimated flux of light is then radiated from the convex lens  21 .  
         [0042]     In the present embodiment, the light source device can be provided, which is smaller in the etendue than the conventional device and higher in the coupling efficiency, thus being suitable for use in optical systems such as smaller-diameter light pipes. Besides, the bore of the aperture  17  can be changed freely to adjust an amount of reduction in the etendue, as in the first embodiment.  
       Third Embodiment  
       [0043]     Referring to  FIG. 3 , a second embodiment of the present invention will now be described. In the present embodiment, the light source device is reduced into practice in another form.  
         [0044]      FIG. 3  shows the structure of a light source device  1 C according to the present embodiment. As shown therein, the light source device  1 C is additionally provided with a lens system consisting of convex lenses  22  and  23 . Of these, the convex lens  22  is mounted on the spherical reflecting mirror  15  to cover the aperture  17  thereof, while the convex lens  23  is fixedly located apart from the convex lens  22  by a predetermined distance in front of the convex lens  22 . The remaining components of this device  1 C are identical to those in  FIG. 1  explaining the first embodiment.  
         [0045]     Hence the flux of light radiated through the aperture  17  of the spherical reflecting mirror  15  is narrowed in its radiation angle by the first convex lens  22 , and then collimated by the second convex lens  23 . Accordingly, as illustrated in  FIG. 3 , the collimated flux of light, of which collimated sectional area is larger than the area of the aperture  17 , is radiated.  
         [0046]     In the present embodiment, the light source device can be provided which is smaller in the etendue than the conventional device and higher in the coupling efficiency, thus being suitable for use in optical systems such as medium-sized-diameter light pipes. Besides, the bore of the aperture  17  can be changed freely to adjust an amount of reduction in the etendue, as in the first embodiment.  
       Fourth Embodiment  
       [0047]     Referring to  FIG. 4 , a fourth embodiment of the present invention will now be described. In the present embodiment, the light source device is reduced into practice in another form.  
         [0048]      FIG. 4  shows the structure of a light source device  1 D according to the present embodiment. As shown therein, the light source device  1 D is additionally provided with a convex lens  24  mounted on the spherical reflecting mirror  15  to cover the aperture  17 ′ thereof. This convex lens  24  has a focal distance shorter than that of the convex lens  21  adopted in the structure shown in  FIG. 2 . The remaining components of this device  1 D are identical to those in  FIG. 1  explaining the first embodiment.  
         [0049]     In this structure of the fourth embodiment, the flux of light radiated through the aperture of the spherical reflecting mirror  15  is converged to radiate the converged light.  
         [0050]     It is therefore possible to provide the light source device gaining advantages identical or similar to those in the second embodiment.  
       Fifth Embodiment  
       [0051]     Referring to  FIG. 5 , a fifth embodiment of the present invention will now be described. In the present embodiment, the light source device is reduced into practice in another form.  
         [0052]      FIG. 5  shows the structure of a light source device  1 E according to the present embodiment. As shown therein, the light source device  1 E is additionally provided with a lens system consisting of a concave lens  2 S and a convex lens  26 . Of these, the concave lens  25  is mounted on the spherical reflecting mirror  15  to cover the aperture  17  thereof, while the convex lens  26  is fixedly located apart from the concave lens  25  by a predetermined distance in front of the concave lens  25 . The remaining components of this device  1 E are identical to those in  FIG. 1  explaining the first embodiment.  
         [0053]     Hence the flux of light radiated through the aperture  17  of the spherical reflecting mirror  15  is widened in its radiation angle by the concave lens  25 , and then collimated by the convex lens  26 . Accordingly, as illustrated in  FIG. 5 , the collimated flux of light, of which collimated sectional area is greatly larger than the area of the aperture  17 , is radiated.  
         [0054]     It is therefore possible to provide the light source device with advantages similar to those gained in the third embodiment. Especially, it is preferred that this device is applied to optical systems such as larger-diameter light pipes.  
       Sixth Embodiment  
       [0055]     Referring to  FIG. 6 , a sixth embodiment of the present invention will now be described. In the present embodiment, the light source device is reduced into practice in another form.  
         [0056]      FIG. 6  shows the structure of a light source device  1 F according to the present embodiment. As shown therein, the light source device  1 F is additionally provided with a convex lens  21  and a polarization/conversion unit  2   a  composed of a quarter wave plate  27  and a reflective polarization plate  28 .  
         [0057]     Of these additional components, the convex lens  21  is mounted on the spherical reflecting mirror  15  to cover the aperture  17  thereof. Meanwhile, the quarter wave plate  27  and the reflective polarization plate  28  are fixedly inserted in the optical path from the convex lens  21  in turns such that the components are positioned at intervals in front of the convex lens  21 . The remaining components of this device  1 E are identical to those in  FIG. 1  explaining the first embodiment.  
         [0058]     Thus the flux of light radiated through the aperture  17  of the spherical reflecting mirror  15  is once collimated by the convex lens  21 , and the collimated flux of light passes the polarization/conversion unit  2   a . In this situation, light of a polarized plane which is not allowed to pass the reflective polarization plate  28  is returned to the light emitting part  14   a  of the electrodeless lamp  14  via the quarter wave plate  27  and the convex lens  21 , thus enabling the light emitting part  14   a  to use the returned light as emitted light again.  
         [0059]     Even in a case where the quarter wave plate  27  is not provided, the light which is not allowed to pass the reflective polarization plate  28  can be returned to the light emitting part  14   a.    
         [0060]     Therefore, the light source device according to the present embodiment is able to gain advantages identical to those in the second embodiment. An additional advantage in the present embodiment is that, compared to the optical system shown in  FIG. 2 , where only the convex lens  21  is mounted to the aperture  17 , the coupling efficiency can be enhanced more.  
       Seventh Embodiment  
       [0061]     Referring to  FIG. 7 , a seventh embodiment of the present invention will now be described. In the present embodiment, the light source device is reduced into practice in another form.  
         [0062]      FIG. 7  shows the structure of a light source device  1 G according to the present embodiment. As shown therein, the light source device  1 G is based on the structure of the light source device  1 A shown in  FIG. 1 , but the spherical reflecting mirror  15  is replaced by a reflecting mirror  30 . This reflecting mirror  30  is mounted on the surface of the waveguide  11  such that the mirror  30  contains the light emitting part  14   a.    
         [0063]     The reflecting mirror  30  is composed of a spherical reflecting mirror part  31  and an ellipsoidal reflecting mirror part  32 , which are linked with each other but positionally divided by a plane P hypothetically set perpendicularly to the surface of the waveguide  11  at the position of the electrodeless lamp  14 . This hypothetical plane P is able to divide the flux of light from the light emitting part  14   a  into approximately two fluxes in a hypothetical manner.  
         [0064]     The spherical reflecting mirror part  31  is positioned to receive and reflect one flux of light hypothetically divided by the plane P, in which an amount of light reflected by this mirror part  31  is nearly half of the amount of light from the light emitting part  14   a . In addition, this mirror part  31  is given a focal point positioned at the light emitting part  14   a . Hence the flux of light reflected by this mirror part  31  is returned to the light emitting part  14   a  for re-emission therefrom.  
         [0065]     In contrast, the ellipsoidal reflecting mirror part  32  is positioned to receive and reflect the other flux of light hypothetically divided by the plane P and laterally opened to the outside as shown in  FIG. 7 . An amount of light reflected by this mirror part  32  is nearly half of the amount of light from the light emitting part  14   a . Thus the flux of light received by the mirror part  32  is reflected through the opening between the mirror part  32  and the waveguide  11 , and then converges at a point outside the waveguide  11 .  
         [0066]     A modification is to replace the ellipsoidal reflecting mirror part  32  by a reflecting mirror provided with a paraboloidal reflecting mirror part. A paraboloid of this mirror part also reflects the light in the similar way as the ellipsoidal reflecting mirror part  32 , so that the collimated light can also be obtained outside the waveguide  11 .  
         [0067]     The light source device according to the present embodiment is able to reduce the etendue down to approximately ¼ of the etendue of the conventional device. Hence the coupling efficiency can be made higher than the conventional. In addition, the light source device can preferably be applied to optical systems such as smaller-diameter light pipes.  
       Eighth Embodiment  
       [0068]     Referring to  FIG. 8 , an eighth embodiment of the present invention will now be described. In the present embodiment, the light source device  1 A according to the first embodiment is reduced into practice as a light source of an image displaying apparatus of the present invention.  
         [0069]      FIG. 8  shows the configuration of a projector serving as the above image displaying apparatus. This projector is provided with, in addition to the light source device  1 A shown in  FIG. 1 , a condensing device  2 , an integrator  3 , and a first field lens  4  placed in the course of a light output path from the light source device  1 A in this order. On the output side of this lens system, dichroic mirrors  5 B,  5 Y and  5 G and mirrors  6 B and  6 Y are placed as color separation means for separating the light into three primary colors of light. On the output side of these mirrors, spatial light modulation devices  8 R,  8 G and  8 B each composed of a reflective liquid crystal display panel are placed for modulation of each flux of color light separated.  
         [0070]     Second field lenses  7 R,  7 G and  7 B are placed after the mirrors  6 B and  6 Y and dichroic mirror  5 G. Between each of the second field lenses  7 R,  7 G and  7 B and each of the spatial light modulation devices  8 R,  8 G and  8 B, polarizing beam splitters  9 R,  9 G and  9 B is placed, respectively. These polarizing beam splitters  9 R,  9 G and  9 B are placed to guide, to a cross dichroic prism  10 , each flux of color light modulated by each of the spatial light modulation devices  8 R,  8 G and  8 B. The cross dichroic prism  10  is placed for synthesizing all the fluxes of color modulated light. In the output optical path from this prism  10 , there is placed a projection lens  20 .  
         [0071]     The operations of this projector shown in  FIG. 8  will now be detailed.  
         [0072]     Light emitted from the light source device  1 A is converted to a parallel flux of light by the condensing device  2 . In order to gain an even Illuminating light, the integrator  3  receives the converted parallel flux of light and separates it into a plurality of segments of light, and makes an image formation relationship for illuminating display elements, segment by segment. The first field lens  4  corresponds in size to the aperture of the integrator  3  and makes the flux of light enter the dichroic mirrors  5 B and  5 Y in compliance with the apertures of the dichroic mirrors  5 B and  5 Y. The dichroic mirror  5 Y reflects each of the fluxes of red and green light, while the dichroic mirror  5 B reflects the flux of blue light. Each of the fluxes of red and green light reflected by the dichroic mirror  5 Y is bent by the mirror  6 Y and then makes Incidence onto the dichroic mirror  5 G. This dichroic mirror  5 G reflects the flux of green light and allows the flux of red light to pass therethrough.  
         [0073]     The flux of green light, which reflected from the dichroic mirror  5 G, makes incidence onto the spatial light modulation device  8 G via the second field lens  7 G and the polarizing beam splitter  9 G. The flux of green light, which have entered this device  8 G, is subjected to modulation on image signals, and the modulated light is reflected by the polarizing beam splitter  9 G to enter the cross dichroic prism  10 .  
         [0074]     Further, the flux of red light, which have transmitted the dichroic mirror  5 G, makes incidence onto the spatial light modulation device  8 R via the second field lens  7 R and the polarizing beam splitter  9 R. The flux of red light, which have entered the modulation device  8 R, is then subjected to modulation on image signals, and then the modulated light is reflected by the polarizing beam splitter  9 R to make incidence onto the cross dichroic prism  10 .  
         [0075]     Moreover, the flux of blue light, which has been reflected by the dichroic mirror  5 B, is bent by the mirror  6 B to make incidence onto the spatial light modulation device  8 B after passing the second field lens  7 B and the polarizing beam splitter  9 B in turns in this order. The flux of blue light, which have entered this modulation device  8 B, is subjected to modulation on image signals, and the modulated light is reflected by the polarizing beam splitter  9 R to make incidence onto the cross dichroic prism  10 .  
         [0076]     The fluxes of green, red and blue light modulated on the image signals respectively are synthesized with each other so that full-color image light enters the projection lens  20 . The incident full-color image light is enlarged by the projection lens  20  and projected on a not-shown screen.  
         [0077]     In the present eighth embodiment, the light source device  1 A with a smaller etendue, which has been explained in the first embodiment, is used. Hence the optical system for condensing light can be made compact, so that the image displaying apparatus can be formed as a compact and less-weight one. Additionally, the reflective liquid crystal display panel is used as each of the spatial light modulation devices  8 R,  8 G and  8 B, it is possible to provide an appropriate illuminating system to the smaller-etendue optical system on the polarizing conversion. This provides the image displaying apparatus with higher luminance, higher contrast, and longer operation life.  
       Ninth Embodiment  
       [0078]     Referring to  FIG. 9 , a ninth embodiment of the present invention will now be described. In the present embodiment, the light source device  1 B according to the second embodiment is reduced into practice as a light source of another image displaying apparatus of the present invention.  
         [0079]      FIG. 9  shows the configuration of a projector serving as the above image displaying apparatus. This projector is provided with, in addition to the light source device  1 B shown in  FIG. 2 , a polarizing conversion device  2   a  composed of a quarter wave plate  27  and a reflective polarizing plate  28 , which the device  2   a  is disposed in the light output path from the light source device  1 B. The remaining components other than the light source device  1 B and the polarizing conversion device  2   a  are the same as those shown in  FIG. 8 .  
         [0080]     From the light source device  1 B, as explained in the second embodiment (refer to  FIG. 2 ), a collimated flux of light is radiated. This collimated flux of light is made to enter the polarizing conversion device  2   a , where a flux of light with a polarized plane which is not allowed to pass the reflective polarizing plate  26  is returned to the light-emitting part  4   a  of the electrodeless lamp  4  via the quarter waver plate  27  and the convex lens  21  for re-emitting the light. Hence it is possible to provide the image displaying apparatus with a higher coupling efficient, compared to the image displaying apparatus shown in  FIG. 8 .  
         [0081]     As a modification, the light source device  1 F with the light source device  1 B and the reflective polarizing plate  2   a  integrated as shown in  FIG. 6  can also be applied to the present image displaying apparatus.  
         [0082]     Hence, the ninth embodiment also provides the identical advantages to those in the eighth embodiment, thanks to employment of the light source device  1 B with a smaller etendue.  
       Tenth Embodiment  
       [0083]     Referring to  FIG. 10 , a tenth embodiment of the present invention will now be described. In the present embodiment, the light source device  1 G according to the seventh embodiment is reduced into practice as a light source of another image displaying apparatus of the present invention.  
         [0084]      FIG. 10  shows the configuration of a projector serving as the above image displaying apparatus. This projector is provided with, in addition to the light source device  1 G shown in  FIG. 7 , a light condensing device  2 , an integrator  3 , and a first field lens  4  in the light output path from the light source device  1 G. The remaining components other than the above components are the same as those shown in  FIG. 8 .  
         [0085]     In the light source device  1 G, nearly half the flux of light emitted from the light emitting part  4   a  is reflected to the light emitting part  4   a , while the remaining light is made to enter the light condensing device  2  as a converged light. Accordingly, the image displaying apparatus having a coupling efficiency compatible to that of the image displaying apparatus shown in  FIG. 8  can be provided.  
         [0086]     Hence, the tenth embodiment also provides the identical advantages to those in the eighth embodiment, thanks to employment of the light source device  1 G with a smaller etendue.  
         [0087]     There can also be provided several other forms of the image displaying apparatus. Although the image displaying apparatuses according to the eighth and tenth embodiments adopt an optical structure in which the radiated light from the light condensing device  2  is directly made to enter the integrator  3  and the image displaying apparatus according to the ninth embodiment adopts an optical structure in which the radiated light from the polarizing conversion device  2   a  is also directly made to enter the integrator  3 , this is not a definitive list. For example, in each optical structure, a polarizing conversion device may additionally be placed before the integrator  3  so that the light is converted into linearly polarized light and then made incidence onto the integrator  3 .  
         [0088]     Further, the image displaying apparatuses according to the eight to tenth embodiments employ the light source devices described in the first, second and seventh embodiments, respectively. Besides this employment, any one of the light source devices described in the third to sixth embodiments may be employed.  
       Eleventh Embodiment  
       [0089]     Referring to  FIGS. 11-13 , an eleventh embodiment of the present invention will now be described. In the present embodiment, the light source device is reduced into practice in another form.  
         [0090]      FIG. 11  shows the structure of a light source device  1 H according to the present embodiment. As shown therein, the light source device is provided with a complex paraboloidal light-condensing mirror  115  in addition to the waveguide  11 , probe  12 , and electrodeless lamp  14  described before.  
         [0091]     The complex paraboloidal light-condensing mirror  115  is formed into a cylinder having both ends in the axial directions thereof. The mirror has a reflection surface  116  formed inside the cylindrical wall body. One of both ends serves as a light-source side opening  117 , while the other serves as a light-radiating opening  118 . This mirror  115  is secured on the surface of the waveguide  11  such that the center of the light-source side opening  117  is positioned at the light-emitting part  14   a  of the electrodeless lamp  14 .  
         [0092]     In this structure with the mirror  115 , of the flux of light emitted from the light-emitting part  14   a , a flux of light that passes a relatively narrow angular range positioned next to the light axis is radiated directly, as it is, through the light-radiating opening  118 . In contrast, a flux of light that passes outside the angular range is first reflected by the reflection surface  116  of the complex paraboloidal light-condensing mirror  115 , and then radiated from the mirror  15 .  
         [0093]     The fluxes of light directly radiated through the light-radiating opening  118  and radiated through the light-radiating opening  118  after the reflection on the reflection surface  116  change depending on the same of the complex paraboloidal light-condensing mirror  115 . Accordingly, the etendue and coupling efficiency change in the same manner.  
         [0094]     Though detailed later, the dimensions as to the radius and axial length of the mirror  115  are decided as below. It is assumed that an approximate center position of the light-emitting part  14   a  gives an apex and a solid angle is expressed by a conic surface having a center at which a radially-central axis P of the mirror  115  passes. That is, the axis P passes a radial center of each of both openings  117  and  118 . Under such assumptions, the radius and the axial length of the mirror  115  are designed such that a flux of light passing an angular range of approx. 0-45 degrees measured from the axis P is directly radiated through the light-radiating opening  118  and a flux of light passing an angular range of approx. 45-90 degrees measured from the axis P is first reflected by the reflection surface  116 .  
         [0095]      FIG. 12  illustrates how to decide the radius from to be measured from the axis P of the complex paraboloidal light-condensing mirror  115 . In  FIG. 12 , the radius of the light-source side opening  117  of the mirror  115  is given as “a” (i.e., diameter is “2a”), the axial length extending between the openings  117  and  118  is given as L, and an angular range that allows the flux of light emitted from the part  14   a  to be radiated through the light-radiating opening  118  is represented by a cone of which half angle θ. In such a case, the following formula is realized. 
   L=a (1+sin θ)/tan θ·sin θ  (2)  
         [0096]     For instance, in cases where the radius a=2.5 mm and the angle θ=45 degrees, the axial length L is approximately 6 mm.  
         [0097]     Additionally, it is assumed that the positions Z are taken along the axial direction of the mirror  115 , the light-source side opening  117  located on the surface of the waveguide  115  provides a reference position (i.e., Z=0), and the radius “r” of the mirror  115 , which radius is given until the opening  18 , is expressed as a function of the positions Z in the axial direction of the mirror  115 . Under such an assumption, the following formula can be realized, which defines the radius r.  
                   r   =       ⁢     {       -     (       sin   ⁢           ⁢     θ   ·   cos     ⁢           ⁢     θ   ·   Z       +       a   ⁡     (     1   +     sin   ⁢           ⁢   θ       )       2       )       +     √     (     (       sin   ⁢           ⁢     θ   ·   cos     ⁢           ⁢     θ   ·   Z       +                                   ⁢       a   ⁡     (     1   +     sin   ⁢           ⁢   θ       )       2     )     2     -       cos   2     ⁢     θ   (         Z   2     ⁢     sin   2     ⁢   θ     -     2   ⁢           ⁢   a   ⁢           ⁢     Z   ·   cos     ⁢           ⁢     θ   ·     (     2   +     sin   ⁢           ⁢   θ       )         -                               ⁢         a   2     ⁡     (     1   +     sin   ⁢           ⁢   θ       )       ⁢     (     3   +     sin   ⁢           ⁢   θ       )       )     }     /     cos   2       ⁢   θ                 (   3   )             
 
         [0098]     Substituting θ=45 degrees into the formulae (2) and (3) respectively leads to the decision of the length L and the radius r. By employing such a technique, the flux of light emitted from the electrodeless lamp  14  can be distributed in such a manner that a flux of light passing the angular range of approx. 0-45 degrees expressed as a half angle of the cone is made to be radiated directly through the light-radiating opening  118 . And a flux of light passing an angular range of approx. 45-90 degrees is made to be reflected on the reflection surface  116  of the mirror  115 , before being radiated through the light-radiating opening  118 .  
         [0099]      FIG. 13  shows graphs each showing a relationship between the etendue and the coupling efficiency as to each of the conventional light condensing system already explained by U.S. Pat. No. 6,737,809 and the light condensing system according to the present invention. The graphs show that the coupling efficiency under the same etendue is upgraded as much as approximately twice.  
         [0100]     In this way, the light source device according to the present embodiment is able to raise the coupling efficiency largely, compared to the conventional.  
       Twelfth Embodiment  
       [0101]     Referring to  FIG. 14 , a twelfth embodiment of the present invention will now be described. In the present embodiment, the light source device is reduced into practice in another form.  
         [0102]     A light source device  1 I shown in  FIG. 14  is characterized in that a heat sink  121  is added to the device  1 I whose other structures are the same as that shown in the eleventh embodiment.  
         [0103]     It is required that the waveguide  11  is cooled, because the electrodeless lamp  14  generates heat when being activated. In order is to cool down the waveguide  11  (that is, the device  1 I), the heat sink  121  is secured to the surface of the waveguide  11 . In this case, a further improvement is made such that a paraboloidal through hole for accepting the complex paraboloidal light-condensing mirror  115  is formed through the heat sink  21  itself. The reflection surface  116  of the mirror  115  is formed with metal, whereby the mirror  115  can be cooled down by the heat sink  121  and the heat of the waveguide can be radiated effectively through the heat sink  121  as well. Further, a cooling system for the mirror  115  and a mechanism supporting the mirror  115  become unnecessary, simplifying the whole structure of the light source device  1 I.  
         [0104]     In this way, the light source device according to the present embodiment can enjoy the advantages of not only largely increasing the coupling efficiency compared to the conventional but also simplifying the structure of the device  1 I.  
       Thirteenth Embodiment  
       [0105]     Referring to  FIGS. 15 and 16 A to  16 C a thirteenth embodiment of the present invention will now be described. In the present embodiment, the light source device is reduced into practice in another form.  
         [0106]     A light source device  1  shown in  FIG. 15  is provided with a reflector  131  and a light pipe  132 , instead of using the complex paraboloidal light-condensing mirror  115  used in the  FIG. 11  in the eleventh embodiment. The reflector  131  is designed and arranged to reflect a flux of light passing an angular range, which is distant from the light axis, into a direction almost perpendicular to the surface of the waveguide  11 . The light pipe  132  is formed to accept both the flux of light reflected from the reflector  131  and a flux of light passing an angular range which is near from the light axis. It is therefore possible that the device  1 J has a spatial distribution of light Ad which is longer in the direction of the light axis, compared to the conventional light source device shown in U.S. Pat. No. 6,737,809. Thus the coupling efficiency is increased when the light of flux from the light pipe  132  is made incident into a light-condensing lens system to be optically coupled to the light pipe  132 .  
         [0107]     The reflector  131  can be produced as a cone-type divergent reflecting member with a conic inner surface which reflects the light. Meanwhile, by way of example, the light pipe  132  can be selected from a range of variations shown in  FIGS. 16A  to  16 C.  FIG. 16A  provides a light pipe  132   a  having a circular section,  FIG. 16B  provides a light pipe  132   b  having a rectangular section, and  FIG. 16C  provides a light pipe  132   c  having a rectangular section and gradually shortening a width between mutually opposed sides of two of all four paired sides in the length direction thereof.  
         [0108]     When the light source device  1 J shown in  FIG. 15  is applied to, for example, to a projector serving as the image displaying device according to the present invention, the light pipe  132   b  or  132   c  may be used which have a rectangular section that corresponds to an aspect ratio given to a spatial light modulation device.  
         [0109]     Therefore, the light source device according to the present embodiment can also increase the coupling efficiency in comparison with that of the conventional device.  
       Fourteenth Embodiment  
       [0110]     Referring to  FIG. 17 , a fourteenth embodiment of the present invention will now be described. In the present embodiment, the light source device is also reduced into practice in another form.  
         [0111]     A light source device  1 K shown in  FIG. 17  is provided with an ellipsoidal reflecting mirror  141  in place of the complex paraboloidal light-condensing mirror  115  used in the  FIG. 11  in the eleventh embodiment. The ellipsoidal reflecting mirror  141  is produced to as to reflect the flux of light emitted from the light emitting part  14   a  of the electrodeless lamp  14  such that the reflected light flux converges outside the device. In addition, this mirror  141  is located on the surface of the waveguide  11  such that the mirror  141  has a focus located at the light emitting part  14   a  of the electrodeless lamp  14 .  
         [0112]     Incidentally, the ellipsoidal reflecting mirror  141  may be replaced by a paraboloidal reflecting mirror with a paraboloidal surface reflecting the light. This enables the light flux to be radiated and collimated outside the device.  
         [0113]     In the light source device according to the present embodiment, all the flux of light emitted by the light-emitting part  14   a  of the electrodeless lamp  14  is radiated to generate a converged light or a collimated light outside the device by using the ellipsoidal reflecting mirror  141  or the paraboloidal reflecting mirror. Hence, compared to the conventional, the coupling efficiency can be enhanced greatly.  
         [0114]     The above construction allows the etendue to be decreased by approximately ½ in comparison with the conventional device. It is possible to provide the light source device which has a high coupling efficiency and is preferably directed to optical systems such as small-diameter light pipes.  
         [0115]     There are provided modifications concerning the positions of the probe  12  and aperture cavity  13 . In the foregoing various embodiments, the probe  12  is linked with the waveguide  11  at the position radially shifted from the radial center of the waveguide  11 . However, this is not a decisive positioning way. As long as the electric filed at the aperture cavity  13  of the waveguide  11  becomes its maximum or values regarded as the maximum, the probe  12  may be linked to the waveguide  11  at the radial center or positions regarded as the center of the waveguide  11 . The aperture cavity  13  is not always limited to being formed in a central part of the waveguide  11 , but being positioned differently from the central part. It is sufficient that the prove  12  can be positioned to generate the electric field which becomes its maximum or thereabouts at the aperture cavity.  
         [0116]     The outer shape of the waveguide  11  is not limited to the foregoing cylindrical form, but may be rectangular parallelepiped or other forms.  
       Fifteenth Embodiment  
       [0117]     Referring to  FIG. 18 , a fifteenth embodiment of the present invention will now be described. In the present embodiment, the image displaying device according to the present invention is reduced into practice in another form.  
         [0118]      FIG. 18  shows the optical diagram of an image displaying device called projector, in which the light source device  1 H shown in the eleventh embodiment (refer to  FIG. 11 ) is adopted as a light source. The components other than the light source device  1 H are the same as those already explained.  
         [0119]     Since the projector shown in the fifteenth embodiment utilizes the light source device  1 H with a higher coupling efficiency, the light condensing system of the projector can be made compact, whereby the projector is compact in size and less in weight. Of course, the other advantages of the projector, which are described before, can be obtained as well.  
       Sixteenth Embodiment  
       [0120]     Referring to  FIG. 19 , a sixteenth embodiment of the present invention will now be described. In the present embodiment, the image displaying device according to the present invention is also reduced into practice in another form.  
         [0121]      FIG. 19  shows the optical diagram of a projector, in which the light source device  13  shown in the thirteenth embodiment (refer to  FIG. 15 ) is adopted as a light source. The components other than the light source device  13  are the same as those already explained.  
         [0122]     In the projector according to the present embodiment, there is provided the light source device  1 J whose coupling efficiency is higher, whereby the light condensing system of the projector can be made compact. Hence the projector is compact in size and less in weight. Additionally, the reflective liquid crystal display panels are used as the spatial light modulation devices  8 R,  8 G and  8 B, so that it is possible to provide an illumining system appropriate for a lower-etendue optical system on polarizing conversion. Hence a projector with a higher brightness, higher contrast, and longer operation life is provided as the image displaying apparatus.  
       Seventeenth Embodiment  
       [0123]     Referring to  FIG. 20 , a seventeenth embodiment of the present invention will now be described. In the present embodiment, the image displaying device according to the present invention is also reduced into practice in another form.  
         [0124]      FIG. 20  shows the optical diagram of a projector, in which the light source device  1 K shown in the fourteenth embodiment (refer to  FIG. 17 ) is adopted as a light source. The components other than the light source device  1 K are the same as those already explained.  
         [0125]     In the projector according to the present embodiment, there is provided the light source device  1 K whose coupling efficiency is higher, whereby the light condensing system of the projector can be made compact. Therefore, the operations and advantages similar or identical to those in the foregoing the sixteenth embodiment can be obtained in the present projector.  
         [0126]     Incidentally, in the projectors according to the fifteenth to seventeenth embodiments, the light coming from the light condensing device  2  is directly made incident into the integrator  3 . However another form is possible such that a quarter wave plate and a reflective polarizing plate are positioned before the integrator to covert the light Into linearly polarized light entering the integrator  3 .  
         [0127]     Further, the projectors according to the fifteenth to seventeenth embodiments may adopt the light source device  1 I according to the twelfth embodiment, instead of adopting the light source devices explained in the eleventh, thirteenth, and fourteenth embodiments. Such replacements can also provide the similar advantages to the foregoing ones.  
         [0128]     The present invention may be embodied in several other forms without departing from the spirit thereof. The present embodiments as described are therefore intended to be only illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them. All changes that fall within the metes and bounds of the claims, or equivalents of such metes and bounds, are therefore intended to be embraced by the claims.