Projector and illumination system thereof

An illumination system includes an excitation light source, a lens group, a dichroic device and a phosphor wheel. The lens group has an optical axis and a light flux cross-section is perpendicular to the optical axis. The dichroic device includes a dichroic layer for reflecting the excitation beam to the lens group and projecting an overlapping region on the light flux cross-section in a direction of the optical axis. The optical axis does not pass through the overlapping region, and the overlapping region has an area ranged between the ¼ and ½ area of the light flux cross-section. The phosphor wheel receives the excitation beam and has a reflective region and a phosphor region. A projector including the illumination system is also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of China application (CN201710244118.2 filed on 2017 Apr. 14). The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

FIELD OF THE INVENTION

The invention relates to a display device, and more particularly to a projector and an illumination system thereof.

BACKGROUND OF THE INVENTION

A conventional digital light processing (DLP) projector includes an illumination system, a digital micro-mirror device (DMD) and a projection lens. The illumination system is used to provide an illumination beam, the digital micro-mirror device is used to convert the illumination beam into an image beam, and the projection lens is used to project the image beam onto a screen to form an image screen on the screen. In addition, with the development of illumination technology, most of the conventional projectors have employed a laser source as the light source of the illumination system, wherein the laser source may be laser diode LD).

FIG. 1is a schematic view of a conventional illumination system employing a laser source. ReferringFIG. 1. In the illumination system100, the laser source module110can emit a blue beam112. The blue beam112is irradiated to the phosphor wheel140after sequentially passing through the collimating element122, the dichroic mirror130and the lenses123,124. The phosphor wheel140rotates and may have a reflective portion, a green phosphor region, a yellow phosphor region and a transmissive region or an opening region (these elements of the phosphor wheel140are not shown), and the green phosphor region and the yellow phosphor region both are formed on the reflective portion.

When the blue beam112is individually irradiated in the green phosphor region and the yellow phosphor region, the green phosphor region and the yellow phosphor region respectively excite the green beam113and the yellow beam114, and the reflective portion reflects the green beam113and the yellow beam114to the dichroic mirror130. The green beam113and the light beam114reflected by the dichroic mirror130are irradiated to the rotatable color wheel150after passing through the lens125. The opening region of the phosphor wheel140may allow the blue beam112to penetrate. After the blue beam112penetrating the opening region, the blue beam112sequentially passes through the lenses126,127, the reflective portions161,162, the lens128, the reflective portion163, the lens129, the dichroic mirror130and the lens150. Thereafter, the blue beam112is irradiated to the color wheel150.

The color wheel150has a red light filter region, a green light filter region, a transparent region and a diffusion region. The yellow phosphor region corresponds to the red light filter region and the transparent region, the green phosphor region corresponds to the green light filter region, and the opening region corresponds to the diffusion region. The color wheel150and the phosphor wheel140can be rotated in cooperation with each other, so that the green beam113is irradiated to the green light filter region, the yellow beam114is irradiated to the red light filter region and the transparent region, and the blue beam112is irradiated to the diffusion region. The color beam filtered by the color wheel150is a blue, a green beam and a red beam for forming a color image and a yellow beam for increasing the luminance. The color beams then enter the optical integration rod170.

However, according to the above description, it is understood that the conventional illumination system100requires many optical elements (e.g., a plurality of lenses123to128) and has a complicated optical layout. Therefore, the conventional illumination system100has some disadvantages such as high cost, large volume and poor optical efficiency.

The information disclosed in this “BACKGROUND OF THE INVENTION” section is only for enhancement understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Furthermore, the information disclosed in this “BACKGROUND OF THE INVENTION” section does not mean that one or more problems to be solved by one or more embodiments of the invention were acknowledged by a person of ordinary skill in the art.

SUMMARY OF THE INVENTION

The invention provides an illumination system employing fewer optical elements and a simplified optical layout to help to reduce cost and volume.

The invention further provides a projector including the aforementioned illumination system.

Other objectives and advantages of the invention become apparent from the technical features disclosed in the invention.

The invention provides an illumination system, which includes an excitation light source, a lens group, a dichroic device and a phosphor wheel. The excitation light source is adapted for emitting an excitation beam. The lens group has an optical axis and a light flux cross-section perpendicular to the optical axis. The dichroic device includes a dichroic layer. The dichroic layer is adapted for reflecting the excitation beam to the lens group and projecting an overlapping region on the light flux cross-section in a direction parallel to the optical axis. The optical axis does not pass through the overlapping region, and an area of the overlapping region is larger than a ¼ area of the light flux cross-section and smaller than a ½ area of the light flux cross-section. The phosphor wheel is adapted for receiving the excitation beam passing through the lens group and has a reflective region and at least one phosphor region. The at least one phosphor region is adapted for converting the excitation beam into a conversion beam and reflecting the conversion beam to the lens group. The reflective region is adapted for reflecting the excitation beam back to the lens group. The excitation beam and the conversion beam both pass through the light flux cross-section, and the conversion beam penetrates the dichroic layer.

The invention further provides a projector including the aforementioned illumination system, a light valve unit and a projection lens. The light valve unit is disposed on the transmission path of the illumination beam converted by a light integration rod and is adapted for converting the illumination beam into an image beam. The projection lens is disposed on the transmission path of the image beam.

In summary, by the disposing means between the aforementioned dichroic layer and the lens group, the overlapping area projected by the dichroic layer on the light flux cross-section is not passed through by the optical axis of the lens group and the area of the overlapping region is larger than the ¼ area of the light flux cross-section and smaller than the ½ area of the light flux cross-section. Thus, the optical axis of the lens group does not pass through the dichroic layer and the axis of the excitation beam is noncoaxial with the optical axis of the lens group, so that the lens group can deflect the excitation beam and the excitation beam emitted from the phosphor wheel is not all blocked by the dichroic layer, or even completely not blocked by the dichroic layer. Compared with the conventional illumination systems, the invention apparently employs fewer optical elements and has a simpler optical layout, thereby helping to reduce cost and volume.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 2Ais a schematic view of an illumination system in accordance with an embodiment of the invention. Referring toFIG. 2A. The illumination system200includes an excitation light source210, a dichroic device220and a lens group230. The excitation light source210can emit an excitation beam L10and may be a laser light source such as a laser diode and therefore the excitation beam L10may be a laser beam, or may be a light emitting diode (LED) light source. In addition, the excitation beam L10may be a blue beam having a wavelength of 445 nm or 455 nm for example. The dichroic device220includes a dichroic layer221and a transparent substrate222. The transparent substrate222is, for example, a glass plate or an acrylic plate. The transparent substrate222has a plane222f, and the dichroic layer221is formed on the plane222fand covers the plane222f.

The dichroic layer221can reflect a beam of a specific wavelength range and allow a beam of a wavelength range other than the specific wavelength range to penetrate. For example, the dichroic layer221is disposed on the transmission path of the excitation beam L10and can reflect the excitation beam L10to the lens group230. In addition, the dichroic layer221is, for example, a dichroic mirror or an interference filter film and has an optical multilayer structure.

The lens group230is also disposed on the transmission path of the excitation beam L10and may include at least one lens. Taking the embodiment ofFIG. 2Aas an example. The lens group230includes two lenses231and232. However, in other embodiments, the lens group230may include only one lens or three or more lenses. Therefore, the number of lenses included in the lens group230is not limited to two as shown inFIG. 2A. In the embodiment ofFIG. 2A, the excitation beam L10sequentially pass through the lens231and the lens232. The lens231and the lens232overlap each other, and the size of the lens231is larger than the size of the lens232. The lens232does not protrude the edge231eof the lens231, that is, the lens232does not cover the edge231eof the lens231, thereby controlling the light divergence angle of the excitation beam L10.

The lens group230has an optical axis230a. The optical axis230apenetrates the lenses231and232along the axis of the lenses231and232, so that the lenses231and232are coaxial with each other. In addition, the transparent substrate222may have a beveled edge222ethat may be parallel to the optical axis230a. The lens group230further has a light flux cross-section231f. The optical axis230ais perpendicular to the light flux cross-section231fand passes through the light flux cross-section231f, wherein the optical axis230apasses through the center position of the light flux cross-section231f.

The excitation beam L10also passes through the light flux cross-section231f, but the axis of the excitation beam L10does not overlap the optical axis230a. The axis of the excitation beam L10refers to the axis of the main ray of the excitation beam L10. Therefore, the axis of the excitation beam L10is noncoaxial with the optical axis230aof the lens group230, so that the lens group230can deflect the traveling direction of the excitation beam L10, as shown inFIG. 2A. In addition, the drawings of the invention illustrate the main ray of the excitation beam L10as a straight line, and the straight line can be regarded as the axis of the excitation beam L10. Therefore, as shown inFIG. 2A, it is apparent that the axis of the excitation beam L10is noncoaxial with the optical axis230aof the lens group230, so that the excitation beam L10can be deflected by the lens group230, as shown inFIG. 2A.

Referring toFIGS. 2A and 2B.FIG. 2Bis a schematic side view of the lens group230taken along the direction V1inFIG. 2A, wherein the direction V1is parallel to the optical axis230a. Since the size of the lens231is larger than the size of the lens232and the lens231and the lens232are coaxial with each other, it is observed that the lens231completely covers the lens232while viewing the lens group230in the direction V1, so that only the lens231is shown inFIG. 2B. The light flux cross-section231fis an imaginary plane of the lens group230, and the contour of the light flux cross-section231fis equivalent to the edge of the lens having the effective and largest size in the lens group230. TakingFIG. 2Bas an example, the contour of the light flux cross-section231fis equivalent to the edge231eof the lens231. That is, the region surrounded by the edge231eis equivalent to the light flux cross-section231finFIG. 2B.

The dichroic device220, the lens231and the lens232all are arranged along the optical axis230a, and the dichroic device220overlaps the lens group230. Specifically, the dichroic layer221projects the overlapping region Z2bon the light flux cross-section231fin the direction parallel to the optical axis230a, as shown inFIG. 2B. As shown inFIG. 2B, the area of the overlapping area Z2bhaving a rectangular shape is clearly larger than the ¼ area of the light flux cross-section231f(i.e., the region surrounded by the edge231e) and smaller than the ½ area of the light flux cross-section231f. In addition, the optical axis230adoes not pass through the overlapping region Z2b, that is, the optical axis230adoes not pass through the dichroic layer220.

FIG. 2Cis a schematic view of another overlapping region between the dichroic layer and the light flux cross-section inFIG. 2A. Referring toFIGS. 2A and 2C. In addition to the overlapping region Z2bshown inFIG. 2B, the dichroic layer221may also project the overlapping region Z2con the light flux cross-section231fin the direction parallel to the optical axis230a, as shown inFIG. 2C. Unlike the overlapping region Z2bhaving a rectangular shape inFIG. 2B, the overlapping region Z2cinFIG. 2Chas a fan shape. In addition, as shown inFIG. 2C, the area of the overlapping region Z2cis also clearly larger than the ¼ area of the light flux cross-section231fand smaller than the ½ area of the light flux cross-section231f, and the optical axis230adoes not pass through the overlapping region Z2c. Therefore, it can be seen that the overlapping region projected on the light flux cross-section231fby the dichroic layer221may have various shapes, for example, a rectangular overlapping region Z2bor a fan-shaped overlapping region Z2c.

Referring toFIG. 2A. The illumination system200further includes a phosphor wheel240disposed on the transmission path of the excitation beam L10. The lens group230is disposed between the dichroic device220and the phosphor wheel240, so that the phosphor wheel240can receive the excitation beam L10passing through the lens group230. The phosphor wheel240can be rotated relative to the dichroic device220, so that the excitation beam L10can be irradiated to a plurality of different sections of the phosphor wheel240. At least one section of the phosphor wheel240can convert the excitation beam L10into at least one conversion beam L11and reflect the conversion beam L11to the lens group230, and another section of the phosphor wheel240can directly reflect the excitation beam L10back to the lens group230, so that the excitation beam L10and the conversion beam L11both pass through the light flux cross-section231f. The conversion beam L11can penetrate the dichroic device220, that is, the conversion beam L11penetrates the dichroic layer221.

FIG. 2Dis a front view of the phosphor wheel inFIG. 2A. Referring toFIGS. 2A and 2D. The phosphor wheel240has a reflective region24b, and the reflective region24bcan reflect the excitation beam L10back to the lens group230. In addition, the phosphor wheel240further has at least one phosphor region. Taking the embodiment of FIG.2D as an example. The phosphor wheel240has two phosphor regions24yand24g, wherein the phosphor regions24yand24gcan convert the excitation beam L10into two conversion beams L11having different wavelengths and reflect the conversion beams L11to the lens group230, respectively.

For example, the conversion beam L11converted by the phosphor region24ymay be a yellow light and the conversion beam L11converted by the phosphor region24gmay be a green light. Therefore, the conversion beams L11generated by the phosphor regions24yand24ghave different wavelengths, so that the phosphor wheel240can provide a green light and a yellow light. In addition, these conversion beams L11(e.g., yellow light and green light) all penetrate the dichroic device220and its dichroic layer221. Although the phosphor wheel240has two phosphor regions24yand24gin the embodiment ofFIG. 2D, the phosphor wheel240may have only one phosphor region24yin other embodiments, so that the number of phosphor regions that the phosphor wheel240has may be one and is not limited to be plural.

FIG. 2Eis a schematic cross-sectional view of a phosphor wheel taken along the line2E-2E inFIG. 2D. Referring toFIGS. 2D and 2E. The phosphor wheel240includes a turntable241and at least one phosphor material. The turntable241may be a metal plate or a substrate coated with a reflective layer, wherein the reflective layer is a metal film (not shown) and the substrate is a glass plate or a ceramic plate for example. The turntable241has a light receiving surface241swhich can reflect rays, and the aforementioned phosphor material is disposed on the light receiving surface241s.

In the embodiment shown inFIGS. 2D and 2E, the light receiving surface241sis divided into the reflective region24band the phosphor regions24yand24g. The phosphor wheel240includes two different phosphor materials, for example, phosphor powder. Among the two phosphor materials, one of the phosphor materials is a phosphor material242ywhich is disposed in the phosphor region24yand may be a yellow phosphor. Another phosphor material (not shown) is disposed in the phosphor region24gand may be a green phosphor. Thus, the two phosphor materials can respectively convert the excitation beam L10into different conversion beams L11, such as the yellow and green light conversion beams L11. The light receiving surfaces241sunder these phosphor materials can reflect these conversion beams L11, so that these conversion beams L11are incident on the lens group230.

When the aforementioned phosphor material (including the phosphor material242y) is a phosphor powder, the conversion beams L11emitted from the phosphor regions24yand24gboth are scattered lights and may have a Lambertian distribution. That is, these conversion beams L11, which have just been emitted from the phosphor regions24yand24g, are divergent beams. The lens group230can collect these divergent conversion beams L11and concentrate, collimate and emit out these conversion beams L11to reduce the loss of the conversion beams L11.

The phosphor wheel240further includes a light diffusion film242bfor scattering rays. The light diffusion film242bis formed on the light receiving surface241sand located in the reflective region24b. The light diffusion film242bcan scatter a portion of the excitation beam L10when the excitation beam L10is incident on the light diffusion film242b. Since the excitation beam L10is a laser beam, the excitation beam L10has coherence and so that the excitation beam L10incident on a smooth surface tends to generate speckles due to interference, thereby resulting in a reduced image quality. The scattering of the excitation beam L10by the light diffusion film242bcan reduce or destroy the effect of the coherence, thereby reducing or eliminating the generation of the speckles. However, in the embodiment, the light diffusion film242bmay scatter only a small portion of the excitation beam L10. That is, to maintain a certain optical efficiency, the excitation beam L10emitted from the light diffusion film242bmay not have a Lambertian distribution.

Referring toFIGS. 2A and 2D. When the excitation light beam L10is reflected back to the lens group230by the reflective region24b, since the excitation light beam L10has been deflected by the lens group230before being incident on the reflective region24b, the axis of the excitation beam L10reflected back to the lens group230does not pass through the dichroic layer221, that is, the excitation beam L10is not directly incident on the dichroic layer221. Thus, the dichroic layer221does not block the excitation beam L10transmitted by the lens group230. Therefore, the excitation beam L10emitted from the phosphor wheel240is not completely blocked by the dichroic layer221, so that the excitation beam L10and the conversion beam L11can be received by the subsequent optical element and converted into the illumination beam L13. In addition, since the beveled edge222eof the transparent substrate222is parallel to the optical axis230a, the excitation light beam L10emitted from the phosphor wheel240is prevented from being incident to the rays in the transparent substrate222, thereby increasing the optical efficiency.

Referring toFIG. 2A. The illumination system200may further include a light receiving member260and a filter wheel250, wherein the light receiving member260and the filter wheel250are sequentially disposed on the transmission path of the excitation beam L10and the conversion beam L11. The dichroic device220is disposed between the light receiving member260and the lens group230, the lens group230and the light receiving member260both are disposed between the filter wheel250and the phosphor wheel240, so that the excitation light beam L10and the conversion light beam L11emitted from the phosphor wheel240sequentially pass through the light receiving member260and the filter wheel250after passing through the lens group230.

The light receiving member260can converge the excitation beam L10and the conversion beam L11, wherein the light receiving member260is a convex lens for example, but is not limited thereto. The filter wheel250can be rotated relative to the dichroic device220, so that the excitation beam L10and the conversion beam L11can be irradiated to different sections of the filter wheel250. The filter wheel250can filter the conversion beam L11to form a plurality of filter beams L12(only one filter beam is shown in the drawing), and the filter wheel250may further allow the excitation beam L10to penetrate. In addition, in the embodiment, the color of the excitation beam L10after penetrating the filter wheel250does not change, but is not limited thereto.

FIG. 2Fis a front view of the filter wheel inFIG. 2A. Referring toFIGS. 2A and 2F. The filter wheel250may have a plurality of light penetrating portions25band25yand a plurality of filter portions25rand25g. The light penetrating portion25bis used to allow the excitation beam L10to penetrate, and the light penetrating portion25yis used to allow a portion of the conversion beam L11to penetrate. The filter portions25rand25gcan filter the other portion of the conversion beam L11to form these filter beams L12, wherein these filter beams L12may be a primary color light or a beam having a color close to a primary color, but is not limited thereto.

Specifically, these conversion beams L11incident on the filter wheel250may be a yellow light and a green light, respectively. The yellow conversion beam L11penetrates the filter portion25rand the light penetrating portion25y, wherein the color of the yellow conversion beam L11after penetrating the light penetrating portion25ydoes not change. Since a yellow light can be formed by mixing a red light and a green light, a yellow light contains a red light and a green light. Therefore, the yellow conversion beam L11after penetrating the filter portion25ris converted into the red filter beam L12. The green conversion beam L11penetrates the filter portion25gand is converted into the green filter beam L12by the filter portion25g, wherein the green filter light beam L12may be a green primary color light or a beam having a color closer to a green primary light than the green conversion beam L11has. In addition, since a yellow light contains a red light and a green light, the green filter beam L12may be formed by filtering the yellow conversion beam L11by the filter portion25gin another embodiment, and the phosphor wheel240may include only one yellow phosphor material, such as the phosphor material242y.

FIG. 2Gis a schematic cross-sectional view of a filter wheel taken along the line2G-2G inFIG. 2F. Referring toFIGS. 2F and 2G. In the embodiment, the light penetrating portion25bmay have a surface scattering structure S1for scattering the excitation beam L10, so that the excitation beam L10can be uniformly emitted from the filter wheel250and the speckle generated by the interference can be effectively reduced or eliminated. As shown inFIG. 2G, the surface scattering structure S1has a serrated structure and the surface scattering structure S1has a plurality of protrusions (not shown), wherein the shapes of these protrusions are substantially the same. These protrusions are substantially identical in width and have a width of 1 μm or more, so that the surface scattering structure S1is difficult to generate a visible light diffraction.

In the embodiment ofFIG. 2G, these protrusions are arranged in a regular manner and the surface scattering structure S1may be the same as the surface prism rod structure of the prism sheet, so that the light penetrating portion25bcan deflect the excitation beam L10, as shown inFIG. 2G. However, these protrusions of the surface scattering structure S1may be arranged in an irregular manner in other embodiments, wherein at least two of the protrusions may be different from each other in size (e.g., width) or shape. In addition, the protrusions of the surface scattering structure S1may be replaced with recesses having the same size and shape. Alternatively, the protrusion of the surface scattering structure S1may also be replaced with recesses arranged in an irregular manner, wherein at least two of the recesses are different from each other in size or shape.

Referring toFIG. 2A. The illumination system200further includes a light integration rod270located on the transmission path of the filter beam L12and the excitation beam L10. The filter wheel250is located between the light integration rod270and the dichroic device220, so that the light integration rod270can receive and concentrate the filter beam L12and the excitation beam L10from the filter wheel250and convert the filter beam L12and the excitation beam L10into the illumination beam L13. The illumination beam L13may be applied to the projector and may be incident on the light valve unit and the projection lens so as to be converted into an image beam capable of forming an image screen on the screen.

FIG. 3is a schematic cross-sectional view of a phosphor wheel in accordance with another embodiment of the invention. Referring toFIG. 3. The phosphor wheel340ofFIG. 3Ais similar to the phosphor wheel240ofFIG. 2E. The phosphor wheel340also has a reflective region34band at least one phosphor region (not shown) and includes a turntable341and a phosphor material (not shown). Since the phosphor rotors340and240are similar, the same structural features of the two will not be described herein, andFIG. 3only illustrates the difference between the two, that is, the reflective region34bof the phosphor wheel340.

Specifically, the turntable341has an optical microstructure342b. The optical microstructure342bis formed on the light receiving surface341sand located in the reflective region34b. The optical microstructure342bcan scatter the excitation beam L10, and the optical microstructure342bmay be a plurality of recesses (not shown) formed on the light receiving surface341s, as shown inFIG. 3. The size of the recess of the optical microstructure342bmay be identical with the size of the protrusion of the surface scattering structure S1inFIG. 2G, so that the optical microstructure342bis also difficult to generate a visible light diffraction.

In the embodiment ofFIG. 3, the shapes of these recesses of the optical microstructure342bmay be substantially the same, and these recesses may have substantially the same width and may be arranged in a regular manner. However, these recesses may be arranged in an irregular manner in the optical microstructure342bof other embodiments, wherein at least two of the recesses may be different from each other in size or shape. In addition, the optical microstructure342bmay be a plurality of protrusions formed on the light receiving surface341s, and the structure thereof is the same as the surface scattering structure S1ofFIG. 2G.

FIG. 4Ais a schematic front view of a filter wheel in accordance with another embodiment of the invention, andFIG. 4Bis a schematic cross-sectional view of a filter wheel taken along the line4B-4B ofFIG. 4A. Referring toFIGS. 4A and 4B. The filter wheel450ofFIG. 4Ais similar to the filter wheel250ofFIG. 2F. For example, the filter wheel450also has a plurality of light penetrating portions45band25yand a plurality of filter portions25rand25g. However, unlike the filter wheel250, the light penetrating portion45bof the filter wheel450has a plurality of light scattering particles451. The effect of these light scattering particles451is similar to the surface scattering structure S1inFIG. 2G, that is, these light scattering particles451are used to scatter the excitation beam L10. It can be seen that the filter wheel disclosed in the plurality of embodiments of the invention may use the surface scattering structure S1or the plurality of scattering particles451to realize the scattering of the excitation beam L10, such as the aforementioned filter wheels450and250.

FIG. 5Ais a schematic top view of a phosphor wheel in accordance with another embodiment of the invention, andFIG. 5Bis a schematic cross-sectional view of a phosphor wheel taken along the line5B-5B inFIG. 5A. Referring toFIGS. 5A and 5B. The phosphor wheel540ofFIGS. 5A and 5Bis similar to the phosphor wheel240ofFIG. 2D. For example, the phosphor wheel540also has a reflective region54band two phosphor regions24yand24gand includes a turntable241and a phosphor material242y. However, unlike the phosphor wheel240, the phosphor wheel540further includes an auxiliary phosphor material542b, which is disposed in the reflective region54band capable of converting the excitation beam L10into an auxiliary color light (not shown).

TakingFIG. 5Bas an example. The auxiliary phosphor material542bmay be a phosphor powder and completely cover the reflective region54b. As shown inFIG. 5B, the thickness of the auxiliary phosphor material542bis smaller than the thickness of the phosphor material242y, and the auxiliary phosphor material542bmay be a thin layer of the phosphor power, so that the auxiliary phosphor material542bcan only convert a portion of the excitation beam L10into the auxiliary color light and does not convert all or most of the excitation beam L10into the auxiliary color light. In addition, the auxiliary phosphor material542band the phosphor material in the phosphor region24gmay be the same phosphor material, that is, the auxiliary color light and the conversion beam L11emitted from the phosphor region24ghave the same color.

In the embodiment, the conversion beam L11emitted from the phosphor region24gmay be a green light, and the auxiliary color light may be a green light too. The excitation beam L10may be a blue light having a wavelength of 445 nm or 455 nm, and this blue light is actually a purplish blue light. However, since the auxiliary phosphor material542bconverts a portion of the excitation beam L10into the auxiliary color light (green light), the excitation beam L10and the auxiliary color light can be mixed with each other to form a beam having a color close to a blue primary color, and even form a blue primary color light, thereby increasing the image color.

FIG. 6is a schematic view of a phosphor wheel640in accordance with another embodiment. The phosphor wheel640is similar to the phosphor wheel540ofFIG. 5Aand also has a reflective region64b. The phosphor wheel640and the phosphor wheel540have the same function and can convert a portion of the excitation beam L10into an auxiliary color light. However, unlike the phosphor wheel540, although the phosphor wheel640also includes an auxiliary phosphor material642bdisposed in the reflective region64b, the auxiliary phosphor material642bpartially covers the reflective region64b, that is, the auxiliary phosphor material642bdoes not completely cover the reflective region64b. TakingFIG. 6as an example, the auxiliary phosphor material642bis distributed in the reflective region64bin dotted form. Of course, the auxiliary phosphor material642bmay also be formed in the reflective region64bin other distributions, such as a fringe distribution or a grid distribution. Therefore, the auxiliary phosphor material642bis not limited to a dotted distribution.

The thickness of the auxiliary phosphor material642bmay be the same as the thickness of the phosphor material242y(not shown inFIG. 6) in the phosphor region24y, that is, the thickness of the auxiliary phosphor material642bofFIG. 6may be greater than the thickness of the auxiliary phosphor material542bofFIG. 5B. In addition, it is to be noted that the auxiliary phosphor materials542band642bshown inFIGS. 5A, 5B and 6may also be used for the phosphor wheels240and340ofFIGS. 2D and 3. That is, the auxiliary phosphor material542bor642bmay be formed in the reflective region24bof the phosphor wheel240or formed in the reflective region34bof the phosphor wheel340.

FIGS. 7A to 7Care perspective views of a phosphor wheel in accordance with the other three embodiments of the invention. The phosphor wheels740a,740band740cshown inFIGS. 7A to 7Care similar to the phosphor wheels240,540and640in the aforementioned embodiments, and the overall functions of the phosphor wheels740a,740band740care the same. However, unlike the aforementioned phosphor wheels240,540and640, the phosphor wheels740a,740band740chave bevels74a,74band74c, respectively. The bevels74a,74band74cmay be used to reflect and deflect the excitation beam L10to assist the excitation beam L10emitted from the phosphor wheel (e.g., the phosphor wheel240) from being blocked by the dichroic layer221(seeFIG. 2A).

Referring toFIG. 7A. The phosphor wheel740aincludes a turntable741a. The turntable741ahas a light receiving surface741asand an inclined portion743alocated on the light receiving surface741as, wherein the inclined portion743ais located in the reflective region74ab. The inclined portion743ahas a bevel74ainclined with respect to the light receiving surface741as, wherein the angle A1between the bevel74aand the light receiving surface741asmay be ranged between 0 and 10 degrees. In addition, the height of the inclined portion743awith respect to the light receiving surface741asdecreases from the center of the turntable741atoward the direction away from the center.

Referring toFIG. 7B. The phosphor wheel740bis similar to the phosphor wheel740aand also includes a turntable741b. The turntable741bhas a light receiving surface741bsand an inclined portion743blocated on the light receiving surface741bs, wherein the inclined portion743bis located in the reflective region74bb. The inclined portion743bhas a bevel74binclined with respect to the light receiving surface741bs, wherein the angle (not labeled) between the bevel74band the light receiving surface741bsmay be equal to the angle A1inFIG. 7A. In addition, unlike the phosphor wheel740a, the height of the inclined portion743bwith respect to the light receiving surface741bsincreases from the center of the turntable741btoward the direction away from the center, as shown inFIG. 7B.

Referring toFIG. 7C. The phosphor wheel740cis similar to the phosphor wheels740aand740bof the aforementioned embodiments and has a light receiving surface741csand a reflective region74cb. However, unlike the phosphor wheels740aand740b, the turntable741cof the phosphor wheel740chas a plurality of inclined portions743clocated on the light receiving surface741cs. Each of the inclined portions743cis located in the reflective region74cband has a bevel74c. Each of the bevels74cis inclined with respect to the light receiving surface741csand the angle (not labeled) between each of the bevels74cand the light receiving surfaces741csmay be equal to the angle A1. As shown inFIG. 7C, it is apparent that these inclined portions743care arranged in a straight line along the radius of the turntable741c, and the height of each of the inclined portions743cwith respect to the light receiving surface741csincreases from the center of the turntable741ctoward the direction away from the center. However, in other embodiments, the height of each of the inclined portions743cwith respect to the light receiving surface741csmay decrease from the center of the turntable741ctoward the direction away from the center.

FIG. 8is a schematic view of an illumination system in accordance with another embodiment of the invention. Referring toFIG. 8. The illumination system801is similar to the illumination system200of the embodiment ofFIG. 2A. The illumination systems801and200have the same effect and include the same elements, such as an excitation light source210, a lens group230, a phosphor wheel840and a filter wheel850. The phosphor wheel840may be the phosphor wheel240,340,540,640,740bor740cof the aforementioned embodiment and the filter wheel850may be the filter wheel250or450of the aforementioned embodiment. The same features of the illumination systems801and200will not be described herein, and only the main difference between the illumination systems801and200, that is, the dichroic device821, will be described below.

Specifically, compared with the dichroic device220ofFIG. 2A, the dichroic device821also includes a dichroic layer221and a transparent substrate21hand the dichroic layer221is also formed on the plane21fof the transparent substrate21h; however, unlike the dichroic device220, the dichroic layer221partially covers the plane21fand exposes a portion of the plane21fin the dichroic device821. That is, the dichroic layer221does not completely cover the plane21f. In addition, inFIG. 8, the optical axis230apasses through the dichroic device821but does not pass through the dichroic layer221. Further, the overlapping region projected by the dichroic layer221on the light flux cross-section231fin the direction parallel to the optical axis230amay be the same as the overlapping region Z2bor Z2cshown inFIGS. 2B and 2C. That is, the overlapping region projected by the dichroic layer221on the light flux cross-section231finFIG. 8is also larger than the ¼ area of the light flux cross-section231fand smaller than the ½ area of the light flux cross-section231f.

FIG. 9is a schematic view of an illumination system in accordance with another embodiment of the invention. Referring toFIG. 9. The illumination system802is similar to the illumination system801of the embodiment ofFIG. 8and the illumination systems802and801include the same elements. The main difference between the illumination systems802and801is that the dichroic device822including the prism group22h. Specifically, the prism group22his a symmetrical prism group and includes a pair of prisms P1and P2, as shown inFIG. 9. The prisms P1and P2have prism surfaces PS1and PS2, respectively. These prisms PS1and PS2face each other to form an interface surface (not labeled) between these prism surfaces PS1and PS2. The dichroic layer221may be formed on one of the prism surfaces PS1and PS2, that is, the dichroic layer221is formed on the interface surface. In addition, the dichroic layer221may cover these prism surfaces PS1and PS2.

FIG. 10is a schematic view of an illumination system in accordance with another embodiment of the invention. Referring toFIG. 10. The illumination system803is similar to the illumination system802of the embodiment ofFIG. 9, and the illumination systems803and802include the same elements. The main difference between the illumination systems803and802is that the asymmetric prism group23hincluded in the dichroic device823of the illumination system803, as shown inFIG. 10.

Specifically, the prism group23hof the dichroic device823includes prisms P1and P4, wherein the volume of the prism P4is significantly larger than the volume of the prism P1, as shown inFIG. 10. The prism P4has a prism surface PS4and a light penetrating surface PF4, and the light penetrating surface PF4is adjacent to the prism surface PS4. The excitation beam L10, the conversion beam L11and the optical axis230apenetrate the prism P4from the light penetrating surface PF4, but the optical axis230adoes not penetrate the dichroic layer221of the dichroic device823. In the embodiment ofFIG. 10, the optical axis230amay be perpendicular to the light penetrating surface PF4to reduce the deflection of the light penetrating surface PF4to the excitation beam L10and the conversion beam L11, thereby assisting most or all of the excitation beam L10and the conversion beam L11to enter the light integration rod270.

FIG. 11is a schematic view of an illumination system in accordance with another embodiment of the invention. Referring toFIG. 11. The illumination system804is similar to the illumination system802of the embodiment ofFIG. 9, and only the difference between the illumination systems804and802, i.e., the dichroic device824of the illumination system804, will be described below. Same as the dichroic device822ofFIG. 9, the dichroic device824also includes a symmetrical prism group24h. The prism group24hincludes a pair of prisms P5and P6. The prisms P5and P6have prism surfaces PS5and PS6, respectively, and these prism surfaces PS5and PS6face each other. However, unlike the dichroic device822, the volume of the prism group24his significantly larger than the volume of the prism group22hofFIG. 9, and the dichroic layer221partially covers the prism surfaces PS5and PS6in the dichroic device824, that is, the dichroic layer221does not cover a portion of each of the prism surfaces PS5and PS6, and the optical axis230adoes not pass through the dichroic layer221.

The illumination systems described in the aforementioned embodiments all can be used for a projector. Referring toFIG. 12, which is a schematic view of a projector900in accordance with an embodiment of the invention. The projector900includes an illumination system910, a light valve unit930and a projection lens940, wherein the illumination system910is the illumination system200,801,802,803or804of the aforementioned embodiments and can generate the illumination beam L13. The light valve unit930is disposed on the transmission path of the illumination beam L13and can convert the illumination beam L13into the image beam L14. The projection lens940is disposed on the transmission path of the image beam L14and can project the image beam L14on the screen to form an image screen. In addition, the light valve unit930may include a reflective liquid crystal on silicon (LCOS) or a digital micro-mirror device (DMD), a transmissive spatial light modulator such as a transparent liquid crystal panel, etc. In addition, depending on the input control signal, the light modulator120is, for example, an optical addressable spatial light modulator (OASLM) or an electrically addressed spatial light modulator (EASLM), and the invention does not limit the type of the light modulator120.

In summary, by the disposing means between the aforementioned dichroic layer and the lens group, the overlapping area projected by the dichroic layer on the light flux cross-section is not passed through by the optical axis of the lens group and the area of the overlapping region is larger than the ¼ area of the light flux cross-section and smaller than the ½ area of the light flux cross-section. Thus, the optical axis of the lens group does not pass through the dichroic layer and the axis of the excitation beam is noncoaxial with the optical axis of the lens group, so that the lens group can deflect the excitation beam and the excitation beam emitted from the phosphor wheel is not all blocked by the dichroic layer, or even completely not blocked by the dichroic layer. Compared with the conventional illumination systems, the invention apparently employs fewer optical elements and has a simpler optical layout, thereby helping to reduce cost and volume.