Illumination optical system including light guide on which blue light is incident at one end surface and green and red light are incident on a side surface, and projector including the same

An illumination optical system includes: a light source device including: a red light-emitting device that emits red light; a blue light-emitting device that emits blue light; and a fluorescence plate comprising a green fluorescence region and a light transmission region, wherein the green fluorescence region is excited by the blue light to emit green light, and the light transmission region transmits the blue light; a light guide including a dichroic layer therein, wherein the dichroic layer is arranged to intersect a center axis of the light guide at about 45 degree to transmit the blue light while reflecting the green light and the blue light; a mirror group and a lens group. The blue light transmitted through the light transmission region is incident on an end surface of the light guide, and the red light and the green light are incident on a side surface of the light guide.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2010-145483, filed on Jun. 25, 2010, the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

Embodiments described herein relate to relates to an illumination optical system, a light source device having the illumination optical system, and a projector having the light source device.

2. Related Art

Nowadays, data projectors are used frequently as image projecting devices for projecting, onto a screen, a displayed image of a personal computer, a video image, an image that is produced based on image data stored in a memory card or the like, and other images. Such projectors display a color image on a screen by condensing light emitted from a light source on a micro-mirror display device called DMD (digital micro-mirror device) or a liquid crystal plate.

With the spread of personal computers and video equipment such as DVD players/recorders, uses of projectors are expanding which include business presentation and home use. Whereas previously projectors mainly employed a high-luminance discharge lamp as a light source, in recent years many projectors that employ a semiconductor light-emitting device such as a laser diode as a light source have been developed or proposed. In this connection, illumination optical systems are known in which a fluorescence is excited by laser light and resulting fluorescent light emitted from the fluorescence is used as light-source light. JP-A-2003-295319 discloses a projector in which incoherent light that is emitted from a fluorescence when it is illuminated with condensed laser light is converted into parallel light by a reflector.

The present applicant proposed, in a prior patent application, a light source unit which is equipped with a blue laser diode, a fluorescence wheel in which a fluorescent light emitting region in which a green fluorescence layer is formed on a reflection surface and a diffuse transmission region in which an opening is provided with a diffuse transmission plate are arranged in the circumferential direction, and a red light-emitting diode. In this proposal, light emitted from the red light-emitting diode is used as light-source light in a red wavelength band, light emitted from the green fluorescence layer when it is illuminated with light emitted from the blue laser diode (excitation light) is used as light-source light in a green wavelength band, and light that originates from the blue laser diode and is diffuse-transmitted by the diffuse transmission plate is used as light-source light in a blue wavelength band.

In the projector disclosed in Patent document 1, the efficiency of utilization of emission light can be made high in the case where light emitted from the fluorescence when it is illuminated with excitation light emitted from a laser diode (excitation light source) is converted into parallel light by the reflector. However, this projector is associated with a problem that a projected image is prone to have unevenness in screen illuminance.

In the projector in which blue laser light is diffused by the diffusing plate is projected onto a screen, illuminance unevenness can be prevented by increasing the diffusion angle of the diffusing plate. However, the absolute value of illuminance may be reduced by loss that is caused by an increased diffusion angle. Therefore, an illumination optical system capable of capturing diffused light as efficiently as possible is necessary.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention address the above disadvantages and other disadvantages not described above. However, the present invention is not required to overcome the disadvantages described above, and thus, an exemplary embodiment of the present invention may not overcome any of the disadvantages described above.

Embodiments described herein provide an illumination optical system which includes a light guide etc. and in which laser light is diffused by a diffusing member provided in the light guide and resulting diffused laser light can be captured reliably and more efficiently by the light guide, as well as a light source device and a projector which are increased in efficiency of light utilization because of the use of such an illumination optical system.

According to one or more illustrative aspects of the present invention, there is provided an illumination optical system. The system comprises: a light source device comprising: a red light-emitting device that emits red light; a blue light-emitting device that emits blue light; and a fluorescence plate comprising a green fluorescence region and a light transmission region, wherein the green fluorescence region is excited by the blue light to emit green light, and the light transmission region transmits the blue light; a light guide comprising a dichroic layer therein, wherein the dichroic layer is arranged so as to intersect a center axis of the light guide at about 45 degree to transmit the blue light while reflecting the green light and the blue light; a mirror group and a lens group, which guide the red light, the blue light and the green light to the light guide, such that the blue light transmitted through the light transmission region is incident on an end surface of the light guide, and the red light and the green light are incident on a side surface of the light guide.

According to one or more illustrative aspects of the present invention, there is provided a light source device comprising: a red light-emitting device that emits red light; a blue light-emitting device that emits blue light; and a fluorescence plate comprising a green fluorescence region and a light transmission region, wherein the green fluorescence region is excited by the blue light to emit green light, and the light transmission region transmits the blue light; a motor that rotates the fluorescence plate; and a light source controller that controls lighting of the blue light-emitting device and the red light-emitting device and rotation of the motor.

According to one or more illustrative aspects of the present invention, there is provided a projector. The projector comprises: a light source device comprising: a red light-emitting device that emits red light; a blue light-emitting device that emits blue light; and a fluorescence plate comprising a green fluorescence region and a light transmission region, wherein the green fluorescence region is excited by the blue light to emit green light, and the light transmission region transmits the blue light; a motor that rotates the fluorescence plate; and a light source controller that controls lighting of the blue light-emitting device and the red light-emitting device and rotation of the motor; a light guide comprising a dichroic layer therein, wherein the dichroic layer is arranged so as to intersect a center axis of the light guide at about 45 degree to transmit the blue light while reflecting the green light and the blue light; a mirror group and a lens group, which guide the red light, the blue light and the green light to the light guide, such that the blue light transmitted through the light transmission region is incident on an end surface of the light guide, and the red light and the green light are incident on a side surface of the light guide; a display device that generates a projection image using the red light, the blue light and the green light output from the light guide; a optical system that projects the projection image onto a screen; and a projector controller that controls the light source device, the display device, and the optical system.

Other aspects and advantages of the present invention will be apparent from the following description, the drawings and the claims.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will be now described with reference to the drawings. It should be noted that the scope of the invention is not limited to the illustrated example.

As shown inFIGS. 1-4, a projector10is equipped with a light source device, a display device51which generates a projection image using illumination light coming from the light source device, a projection-side optical system220which projects, onto a screen, the projection image generated by the display device51, and a projector controller which controls the light source device, the display device51, and the projection-side optical system220.

The light source device is equipped with a fluorescence wheel101which is a fluorescence plate having a green fluorescence region and a light transmission region, a wheel motor110which rotates the fluorescence wheel101, a blue light-emitting device70, a red light-emitting device120, and a light source control circuit41(light source controller) which controls the lighting of the blue light-emitting device70and the red light-emitting device120and the rotation of the wheel motor110. The light source device is also equipped with an illumination optical system consisting of a guiding optical system170and a light-source-side optical system140which guides, to a light guide175, by means of plural mirrors, a lens group, etc., fluorescent light generated by a green fluorescence region of the fluorescence wheel101when it is illuminated with light emitted from the blue light-emitting device70, transmission light that has passed through the light transmission region of the fluorescence wheel101, and light emitted from the red light-emitting device120. In the fluorescence wheel101, the green fluorescence region and the light transmission region are arranged in the circumferential direction.

The illumination optical system includes the light-source-side optical system140which causes light that has passed through the light transmission region of the fluorescence wheel101to shine on an end surface of the light guide175and causes light emitted from the red light-emitting device120and light emitted from the green fluorescence region of the fluorescence wheel101to shine on a side surface of the light guide175, and the light guide175having a dichroic mirror175c. The end surface, on which light that has passed through the light transmission region shines, of the light guide175is provided with a diffusing plate175a(diffusing member). The dichroic mirror175c(dichroic layer) is provided inside the light guide175. The main body of the light guide175is shaped like a rectangular prism. The dichroic mirror175ctransmits blue light while reflecting green light and red light, and is disposed so as to intersect the center axis of the light guide175at 45°.

The light guide175is tapered into a truncated rectangular pyramid shape near the diffusing plate175a, and hence the area of the diffusing plate175ais smaller than the lateral cross section of the rectangular-prism-shaped main body of the light guide175.

The light guide175may be configured such that its tapered portion is a tapered glass rod175bor slant walls that are four flat-plate mirrors and its main body includes two glass rods175dwhose slant surfaces which intersect the center axis at 45° are in contact with each other.

The side walls of the main body of the light guide175may be four flat-plate mirrors. One flat-plate mirror has an opening at a position that is located on a line that intersects the center axis of the main body perpendicularly and intersects the dichroic mirror175cat 45° at its center.

The dichroic mirror175cmay be formed on one surface of a glass prism which is disposed in a mirror tunnel whose side walls are four flat-plate mirrors.

Blue light sources71of the blue light-emitting device70are laser diodes, and the red light-emitting element121of the red light-emitting device120is a light-emitting diode.

An embodiment of the invention will be hereinafter described in detail with reference to the drawings.FIG. 1is a perspective view showing an appearance of the projector10. In the embodiment, the right side and the left side of the projector10are defined with respect to the projection direction, and its front side is defined as the screen side, that is, the light traveling destination side (the rear side is opposite to the front side).

As shown inFIG. 1, the projector10is generally shaped like a rectangular parallelepiped. The projector10has a lens cover19for covering a projection hole on the left of a front panel12which is a front side plate of a projector cabinet. Plural air inlets18are formed through the front panel12. The projector10is equipped with an Ir receiver (not shown inFIG. 1) for receiving a control signal from a remote controller.

A top panel11of the cabinet is provided with a key/indicator unit37, which includes a power switch key, a power indicator which indicates power-on or off, a projection switch key for switching between projection on and off states, an overheat indicator which indicates overheat of a light source unit, a display device, a control circuit, or the like, and other keys and indicators.

A rear panel of the cabinet is provided with an input/output connector having a D-SUB terminal, an S terminal, an RCA terminal, etc. for input of an image signal, a USB terminal, and various terminals20such as a power adaptor plug. Plural air inlets18are formed through the rear panel. Plural air outlets17are formed through a right-hand panel (not shown) and a left-hand panel15(side plate; seeFIG. 1) of the cabinet. Air inlets18are formed through a corner portion, close to the rear panel, of the left-hand panel15.

Next, the projector controller of the projector10will be described with reference to a block diagram ofFIG. 2. The projector controller includes a controller38, an input/output interface22, an image converter23, a display encoder24, a display driver26, etc. An image signal of any of various standards that is input from an input/output connector21is supplied via the input/output interface22and a system bus (SB) to the image converter23, where it is converted into an image signal having a prescribed, unified format that is suitable for display. A resulting image signal is output to the display encoder24.

The display encoder24develops and stores the received image signal in a video RAM25, generates a video signal based on the information stored in the video RAM25, and outputs the generated video signal to the display driver26.

The display driver26, which is functions as a display device controller, drives the display device51(spatial optical modulator (SOM)) at a proper frame rate according to a video signal that is output from the display encoder24. A light beam emitted from a light source unit60, that is, a light beam that is condensed on a prescribed surface by the light-source-side optical system140of the light source unit60, is applied to the display device51via the guiding optical system170, whereby an optical image is formed by reflection light of the display device51. The optical image is projected onto a screen (not shown) via the projection-side optical system220(described later). A movable lens group235of the projection-side optical system220is driven by a lens motor45for zoom adjustment and focus adjustment.

An image compander31performs recording processing of compressing a luminance signal and a color difference signal of an image signal by ADCT, Huffman coding, etc. and writing resulting data to a memory card32(removable recording medium) sequentially. In a reproduction mode, the image compander31also performs processing of reading image data from the memory card32, expanding individual image data constituting a moving image, for example, on a frame-by-frame basis, and outputting resulting image data to the display encoder24via the image converter23so that the moving image can be displayed based on the image data stored in the memory card32.

The controller38, which controls operations of the individual circuits of the projector10, includes a CPU, a ROM which is stored with operation programs including various settings in a fixed manner, a RAM which is used as a work memory, and other components.

An operation signal generated by the key/indicator unit37which is provided on the top panel11of the cabinet and consists of main keys, indicators, etc. is directly sent to the controller38. A key operation signal generated by the remote controller is received by an Ir receiver35and demodulated by an Ir processor36, and a resulting code signal is output to the controller38.

An audio processor47is connected to the controller38via the system bus (SB). Equipped with a sound source circuit such as a PCM sound source, the audio processor47converts audio data into an analog signal and drives a speaker48to cause output of an amplified sound in a projection mode and a reproduction mode.

The controller38controls the light source control circuit41(light source controller). The light source control circuit41individually controls the light emission of the light sources71of the blue light-emitting device70and the light emission of the light-emitting element121of the red light-emitting device120so that light-source light in a prescribed wavelength band that is required during image generation is emitted from the light source60. The light source control circuit41controls the wheel motor110to rotationally drive the fluorescence wheel101of a fluorescent light emitting device.

Furthermore, the controller38causes a cooling fan drive control circuit43to detect temperatures using plural temperature sensors provided in the light source unit60etc. and to control the rotation speeds of plural cooling fans individually according to temperature detection results. In addition, the controller38causes the cooling fan drive control circuit43to let the cooling fans continue rotating even after power-off of the projector main body using a timer or the like or to, for example, power off the projector main body depending on the temperature detection results of the temperature sensors.

Next, the internal configuration of the projector10will be now described.FIG. 3is a schematic plan view showing the internal configuration of the projector10. As shown inFIG. 3, in the projector10, a control circuit board241is disposed near the right-hand panel14. The control circuit board241is mounted with a power circuit block, a light source control block, etc. The light source unit60is disposed beside the control circuit board241, that is, approximately at the center of the projector cabinet. An optical system unit160is disposed between the light source unit60and the left-hand side plate15. The illumination optical system according to the embodiment is a light source device optical system which includes the red light-emitting device120, the blue light-emitting device70, the fluorescence wheel101having the green fluorescence region and the light transmission region, and the light guide175having the dichroic mirror175c. The illumination optical system also has mirrors and a lens group which guide, to the light guide175, three kinds of light, that is, light emitted from the red light-emitting device120, light that originates from the blue light-emitting device70and has passed through the light transmission region of the fluorescence wheel101, and light emitted from the green fluorescence region of the fluorescence wheel101when it is illuminated with excitation light emitted from the blue light-emitting device70. The illumination optical system causes light that has passed through the light transmission region of the fluorescence wheel101to be incident on the end surface of the light guide175and causes light emitted from the red light-emitting device120and light emitted from the green fluorescence region of the fluorescence wheel101to be incident on the side surface of the light guide175. The light guide175, which is generally shaped like a rectangular prism, has the diffusing plate175aat one end and the dichroic mirror175cinside. The dichroic mirror175ctransmits blue light while reflecting green light and red light, and is disposed so as to intersect the center axis of the light guide175at 45°.

The light source unit60is equipped with the blue light-emitting device70which is disposed approximately at the center of the projector cabinet in the right-left direction near the rear panel13, a fluorescent light emitting device100which is disposed on the optical axis of a light beam emitted from the blue light-emitting device70near the front panel12, the red light-emitting device120which is disposed between the blue light-emitting device70and the fluorescent light emitting device100, and the light-source-side optical system140which applies (condenses), to (on) the side surface of the light guide175, green fluorescent light emitted from the fluorescent light emitting device100and light emitted from the red light-emitting device120so that they share the same optical axis and applies light that originates from the blue light-emitting device70and has passed through the fluorescent light emitting device100to the end surface of the light guide175.

The blue light-emitting device70is equipped with the light source group consisting of the plural blue light sources71which are arranged in such a manner that their optical axes are parallel with the rear panel13, plural reflection mirrors75which changes, by 90°, the directions of the optical axes of light beams emitted from the respective blue light sources71to the directions toward the front panel12, a condenser lens78which condenses light beams emitted from the blue light sources71and reflected by the reflection mirrors75, respectively, a heat sink81which is disposed between the blue light sources71and the right-hand panel14, and other components.

In the light source group, the blue light sources71(blue laser diodes) are arranged in matrix form. A collimator lens73which converts light emitted from each blue light source71into parallel light to enhance its directivity is disposed on the optical axis of the blue light source71. The reflection mirrors75are arranged stepwise so as to reflect, toward the condenser lens78, light beams emitted from the blue light sources71while decreasing their intervals and thereby reducing the horizontal cross section of a combined light beam that is output from the light source group.

Cooling fans261are disposed between the heat sink81and the rear panel13. The blue light sources71are cooled by the cooling fans261and the heat sink81. Another cooling fan261is disposed between the reflection mirrors75and the rear panel13, and cools the reflection mirrors75and the condenser lens78.

The fluorescent light emitting device100is equipped with the fluorescence wheel101which is disposed parallel with the front panel12, that is, perpendicularly to the optical axis of light emitted from the blue light-emitting device70, the wheel motor110which rotationally drives the fluorescence wheel101, a condenser lens group111which condenses a light beam emitted from the blue light-emitting device70on the fluorescence wheel101and condenses a light beam that is emitted from the fluorescence wheel101toward the rear panel13, and a condenser lens115which condenses a light beam that is output from the fluorescence wheel101toward the front panel12.

In the fluorescence wheel101, the green fluorescent light emitting region which emits fluorescent light in a green wavelength band when illuminated with excitation light emitted from the blue light-emitting device70and the light transmission region which transmits light emitted from the blue light-emitting device70are arranged in the circumferential direction. A base member used in the green fluorescent light emitting region is made of a metal such as copper or aluminum, and the rear-panel-13-side surface of the base member is mirror-coated by silver evaporation or the like. A green fluorescence layer is formed on the mirror-coated surface.

Light emitted from the blue light-emitting device70and shining on the green fluorescence layer of the fluorescence wheel101excites the green fluorescence of the green fluorescence layer. Fluorescent light emitted from the green fluorescence to all directions enters the condenser lens group111after traveling toward the rear panel13directly or being reflected by the surface of the fluorescence wheel101and output to toward the rear panel13. Light emitted from the blue light-emitting device70and shining on the light transmission region of the fluorescence wheel101enters the condenser lens115as transmission light. A cooling fan261is disposed between the wheel motor110and the front panel12, and cools the fluorescent light emitting device100etc.

The red light-emitting device120is a monochrome light-emitting device which is equipped with the red light-emitting element121disposed in such a manner that its optical axis is perpendicular to the optical axis of the blue light-emitting device70and a condenser lens group125which condenses light emitted from the red light-emitting element121. The red light-emitting element121is a red light-emitting diode. The red light-emitting device120is disposed in such a manner that its optical axis crosses the optical axes of light emitted from the blue light-emitting device70and green-wavelength-band light emitted from the fluorescence wheel101. The red light-emitting device120is equipped with a heat sink130which is disposed on the right-hand panel14side of the red light-emitting element121. A cooling fan261is disposed between the heat sink130and the front panel12, and cools the red light-emitting element121.

The light-source-side optical system140includes condenser lenses which condense light beams in red, green, and blue wavelength bands and reflection mirrors and a dichroic mirror which change the directions of the optical axes of light beams in the red, green, and blue wavelength bands to, for example, equalize part of those optical axes, and other components. More specifically, a first dichroic mirror141is disposed at a position where blue-wavelength-band light emitted from the blue light-emitting device70, green-wavelength-band light emitted from the fluorescence wheel101, and red-wavelength-band light emitted from the red light-emitting device120cross each other. The first dichroic mirror141transmits the blue-wavelength-band light and the red-wavelength-band light, and reflects the green-wavelength-band light to change the direction of its optical axis by 90° toward the left-hand panel15.

The first dichroic mirror141can thus equalize the optical axes of red-wavelength-band light and green-wavelength-band light, and input them to the light guide175through its side surface while they are condensed by lenses.

A first reflection mirror143is disposed on the optical axis of blue laser light that has passed through the fluorescence wheel101, that is, between the condenser lens115and the front panel12. The first reflection mirror143changes the direction of the optical axis of the blue laser light by 90° toward the left-hand panel15by reflecting it. A second reflection mirror145is disposed near the optical system unit160on the optical axis of blue laser light reflected by the first reflection mirror143. The second reflection mirror145changes the direction of the optical axis of the blue laser light by 90° toward the rear panel13. Blue laser light reflected by the second reflection mirror145shines on the diffusing plate175awhich serves as an incidence surface of the light guide175. Since blue laser light that has passed through the fluorescence wheel101enters the condenser lens115without being diffused, the condenser lens115, the first reflection mirror143, and the second reflection mirror145can be made smaller in area and more compact than in the conventional case in which blue laser light is diffuse-transmitted by a fluorescence wheel.

The dichroic mirror175cis disposed inside the light guide175at a position where the optical axes of red-wavelength-band light that has passed through the first dichroic mirror141, green-wavelength-band light reflected by the first dichroic mirror141, and blue laser light reflected by the second reflection mirror145cross each other. The dichroic mirror175ctransmits the blue-wavelength-band light, and reflects the red-wavelength-band light and the green-wavelength-band light to change the directions of their optical axes by 90° toward the rear panel13. The condenser lenses are disposed between the above dichroic mirrors and the reflection mirrors.

The light source unit160, which is generally shaped like a bracket, includes three blocks, that is, an illumination-side block161which is located on the left side of the blue light-emitting device70, an image forming block165which is located near the position where the rear panel13and left-hand panel15intersect each other, and a projection-side block168which is located between the light-source-side optical system140and the left-hand panel15.

The illumination-side block161has part of the guiding optical system170which guides, to the display device51of the image forming block165, light-source light emitted from the light source unit60. The part of the guiding optical system170which belongs to the illumination-side block161includes the light guide175which converts a light beam emitted from the light source unit60into a light beam having a uniform intensity profile, an optical axis conversion mirror181which changes the direction of the optical axis of a light beam emitted from the light guide175toward the image forming block165, and other components.

The image forming block165includes the other part of the guiding optical system170, that is, a condenser lens183which condenses light-source light reflected by the optical axis conversion mirror181on the display device51and an illumination mirror185which causes a light beam that has passed through the condenser lens183to shine on the display device51at a prescribed angle. The image forming block165also has the display device51which is a DMD. A heat sink190is disposed between the display device51and the rear panel13, and cools the display device51. A condenser lens195, which is a component of the projection-side optical system220, is disposed in front of the display device51in its vicinity.

The projection-side block168has a lens group of the projection-side optical system220which project light reflected by the display device51. The lens group of the projection-side optical system220includes a fixed lens group225which is housed in a fixed lens barrel and the movable lens group235which is housed in a movable lens barrel, and thereby serves as a variable focal length lens having a zoom function. Zoom adjustment and focus adjustment are enabled by moving the movable lens group235by the lens motor45.

In the projector10having the above configuration, the blue light-emitting device70and the red light-emitting device120are caused to emit light beams at different time points while the fluorescence wheel101is rotated. As a result, red-wavelength-band light, green-wavelength-band light, and blue-wavelength-band light are provided to the light guide175via the light-source-side optical system140and shine on the display device51via the guiding optical system170sequentially. The display device51(DMD) displays images of the respective colors in a time-divisional manner according to data, whereby color image is generated on a screen.

The illumination optical system will be described in detail below with reference toFIG. 4. The main body of the light guide175of the illumination optical system is formed by two glass rods175d. The light guide175has an incidence surface175eat one end and an exit surface175gat the other end, and also has a side incidence portion175f. A diffusing plate175ais placed at the end, to serve as the incidence surface175e, of the light guide plate175. Blue-wavelength-band light is diffused by the diffusing plate175and output from the exit surface175g. Red-wavelength-band light and green-wavelength-band light are input through the side incidence portion175f, reflected by the dichroic mirror175cwhich is provided inside the light guide175, and output from the exit surface175g.

Since blue laser light that has passed through the light transmission region of the fluorescence wheel101is not diffused until shining on the diffusing plate175aof the light guide175, the area of the incidence surface175eof the light guide175can be made small. The portion, adjacent to the incidence surface175e, of the light guide175is a tapered portion which is shaped like a truncated triangular pyramid, that is, a tapered glass rod175b. The portion, including the side incidence portion175f, is a main body which is shaped like a rectangular prism. The tapered portion may be formed by slant walls that are four flat-plate mirrors instead of the tapered glass rod175b.

Since blue laser light is not diffused until shining on the diffusing plate175aof the light guide175, the areas of the first reflection mirror143and the second reflection mirror145on which the blue laser light shines after passing through the light transmission region of the fluorescence wheel101can be made small.

The dichroic mirror175cwhich is provided inside the light guide175is formed by coating one of the slant bonding surfaces of the two glass rods175dwhich are bonded together. As such, the light guide175is formed by the tapered glass rod175bwhich is provided with the diffusing plate175aand the two glass rods175dbetween which the dichroic mirror175cis formed.

As described above, since the diffusing plate175aserves as the incidence surface175eof the light guide175, it is not necessary to condense blue laser light around the light transmission region of the fluorescence wheel101. Therefore, all blue light that has passed through the fluorescence wheel101is input to the light guide175, and hence the efficiency of utilization of blue-wavelength-band light can be increased. The light guide175has the tapered glass rod175badjacent to the incidence surface175eto narrow the diffusion angle of diffused blue-wavelength-band light, which also contributes to the increase of the efficiency of light utilization. Furthermore, since the optical path length of blue-wavelength-band light in the light guide175is longer than that of red-wavelength-band light and green-wavelength-band light, the unevenness in screen illuminance can be suppressed.

The main body of the light guide175includes the two glass rods175deach of which is shaped like a rectangular prism, and green light and red light are applied to the side surface of the one glass rod175dso as to shine on the dichroic mirror175c. Each of the green light and the red light is reflected by the dichroic mirror175c, travels through the one glass rod175dwhile being reflected totally, and is output from the exit surface175g.

Next, modifications of the light guide175in which a light tunnel175dis used instead of the glass rods175dwill be described with reference toFIGS. 5A-5D.FIG. 5Ais a sectional view of the light guide175according to the above embodiment which uses the glass rods175d.FIGS. 5B-5Dare sectional views of light guides175each using a light tunnel175h.

As shown inFIGS. 5B-5D, the glass rods175d(main body) of the light guide175(seeFIG. 5A) can be replaced by a light tunnel175hwhich includes four flat-plate mirrors (side walls). In this case, the light guide175includes the tapered glass rod175b, the dichroic mirror175c, and the light tunnel175h. In the modification ofFIG. 5B, an incidence portion175fis formed by forming an opening through the flat-plate mirror at the position that is located on the line that intersects the center line of the main body of the light guide175perpendicularly (intersects the dichroic mirror175cat 45°) at the center of the dichroic mirror175c. Each of green light and red light is applied to the opening of the light tunnel175h, enters the light tunnel175h, and shines on the dichroic mirror175c. After being reflected by the dichroic mirror175c, each of the green light and the red light travels through the light tunnel175hwhile being reflected by the flat-plate mirrors and is output from the exit hole175g.

As shown inFIGS. 5C and 5D, the light tunnel175hof the light guide175may incorporate a glass prism obtained by obliquely cutting an end portion of a rectangular-prism-shaped glass member so as to produce a slant surface. The slant surface is coated to form the dichroic mirror175c. In this case, the light guide175includes the tapered glass rod175b, the dichroic mirror175cformed on the glass prism, and the light tunnel175h. An incidence portion175fis formed by forming an opening through the flat-plate mirror at the position that is located on the line that intersects the center line of the main body of the light guide175perpendicularly (intersects the dichroic mirror175cat 45°) at the center of the dichroic mirror175c. Each of green light and red light is applied to the opening of the plate-like mirror and shines on the dichroic mirror175c. After being reflected by the dichroic mirror175c, each of the green light and the red light travels through the light tunnel175hwhile being reflected by the flat-plate mirrors and is output from the exit hole175g. The glass prism may be disposed either on the diffusing plate175aside (seeFIG. 5C) or on the exit hole175gside (seeFIG. 5D) in the light guide175.

In the light guides175shown inFIGS. 5A-5D, the tapered portion is the glass rod. Alternatively, the tapered portion may be a hollow, truncated rectangular pyramid structure formed by connecting the oblique sides of four mirrors which are trapezoidal flat plates.

Whichever of the glass rods175dand the light tunnel175his used to form the light guide175, since blue laser light is diffused by the diffusing plate175awhich serves as the incidence surface175eof the light guide175and the diffusion angle of resulting diffused blue laser light is narrowed by the tapered glass rod175b, whereby the efficiency of user of blue-wavelength-band light can be increased and the illuminance unevenness can be suppressed.

As described above, according to the invention, light beams emitted from the light-emitting devices and the fluorescence can efficiently be guided to the light guide175by the mirrors and the lens groups. And the efficiency of light utilization can be increased by the illumination optical system in which laser light is diffused by the diffusing plate175a(diffusing member) provided in the light guide175and resulting diffused laser light can be captured reliably and more efficiently by the light guide175.

In the illumination optical system according to the invention, the blue light-emitting device70has laser diodes and the red light-emitting device120has a light-emitting diode. Light that has passed through the light transmission region of the fluorescence wheel101is caused to shine on the diffusing plate175aof the light guide175along the center axis of the light guide175. Light emitted from the red light-emitting device120and light emitted from the green fluorescence region are caused to shine on the side surface of the light guide175along the common optical axis and then shine on the dichroic mirror175c. The efficiency of utilization of blue-wavelength-band light can thus be increased.

In the illumination optical system according to the invention, the portion, adjacent to the diffusing plate175a, of the light guide175is the tapered portion having a truncated rectangular pyramid shape, whereby the area of the diffusing plate175ais smaller than the lateral cross section of the rectangular-prism-shaped main body of the light guide175. As a result, the optical path length of blue-wavelength-band light can be made long and hence the illuminance unevenness can be suppressed.

In the illumination optical system according to the invention, the main body of the light guide175is the two glass rods whose slant surfaces which intersect the center axis of the light guide175at 45° are in contact with each other. A dichroic mirror surface can be formed on one of the slant surfaces by coating it. No dedicated dichroic mirror is necessary and hence the number of components can be reduced.

In the illumination optical system according to the invention, the main body of the light guide175may be the light tunnel175hwhich includes four flat-plate mirrors (side walls). This contributes to reduction in the cost of components and weight reduction.

In the illumination optical system according to the invention, the fluorescence wheel101has the green fluorescence region and the light transmission region which are arranged in the circumferential direction. Light emitted from the blue light-emitting device70(laser diodes) is caused to pass through the light transmission region of the fluorescence wheel101, and resulting high-directivity laser light is applied to the diffusing plate175awhich serves as the incidence surface175eof the light guide175. Therefore, blue-wavelength-band light can be captured reliably and more efficiently.

The light source device according to the invention can increase the efficiency of light utilization because it is equipped with the illumination optical system in which laser light is diffused by the diffusing plate175aprovided in the light guide175and resulting diffused laser light can be captured more efficiently.

The projector10according to the invention can increase the efficiency of light utilization because it is equipped with the light source device in which laser light is diffused by the diffusing plate175aprovided in the light guide175and resulting diffused laser light can be captured reliably and more efficiently.

The invention is not limited to the above embodiment, and various modifications and improvements can be made freely without departing the spirit and scope of the invention. For example, the invention can also be applied to the following projector. Only excitation light emitted from the blue light-emitting device70is used as a light-source light. In the fluorescence wheel101, a green fluorescent light emitting region which emits fluorescent light in a green wavelength band when receiving, as excitation light, light emitted from the blue light-emitting device70, a light transmission region which transmits the light emitted from the blue light-emitting device70, and a red fluorescent light emitting region which emits fluorescent light in a red wavelength band when receiving, as excitation light, the light emitted from the blue light-emitting device70are arranged in the circumferential direction. Red-wavelength-band light, green-wavelength-band light, and blue-wavelength-band light are thus generated using light emitted from the blue light-emitting device70.

While the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. It is aimed, therefore, to cover in the appended claim all such changes and modifications as fall within the true spirit and scope of the present invention.