Patent Publication Number: US-2020292835-A1

Title: Projection apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of China application serial no. 201910192254.0, filed on Mar. 14, 2019. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a projection apparatus, and particularly relates to a projection apparatus for a head-mounted display. 
     Description of Related Art 
     Through the development of display technologies and following the demands for high-techs, near eye displays (NEDs) and head-mounted displays (HMDs) have emerged as products with great potential nowadays. Currently, the applications relating to NED may be classified into augmented reality (AR) technologies and virtual reality (VR) technologies. Amongst the applications, since light field near eye displays (LFNEDs) have current light field information, such displays are capable of refocusing and therefore able to provide image information with depth. Consequently, LFNEDs are broadly applied in AR and VR technologies using NFD technologies. However, in the conventional light field displays, an image beam may easily become stray light through the imaging system and result in cross-talk, and the resolution may drop significantly as the depth of the image information expands. 
     The information disclosed in this Background section is only for enhancement of understanding of the background of the described technology 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. Further, the information disclosed in the Background section does not mean that one or more problems to be resolved by one or more embodiments of the invention were acknowledged by a person of ordinary skill in the art. 
     SUMMARY 
     The invention provides a projection apparatus having favorable image quality and resolution. 
     Other objects and advantages of the present invention can be further illustrated by the technical features broadly embodied and described as follows. 
     In order to achieve one or a portion of or all of the objects or other objects, one embodiment of the present invention provides a projection apparatus. The projection apparatus includes an illumination system and a projection imaging system. The illumination system is adapted to emit an illumination beam, and the illumination system includes a light source module and a light shaping module. The light source module is adapted to emit at least one beam. The light shaping module is located on a transmission path of the at least one beam and adapted to adjust a light shape of the at least one beam. The at least one beam forms the illumination beam after passing through the light shaping module, and the illumination beam has a light imaging matching angle. The light shaping module includes at least one first lens element located on the transmission path of the at least one beam and adapted to adjust uniformity of the at least one beam. The projection imaging system is disposed on a transmission path of the illumination beam, and the projection imaging system includes a reflective light valve disposed on the transmission path of the illumination beam. The reflective valve is adapted to modulate the illumination beam into an image beam. 
     Based on the above, the embodiments of the invention exhibit at least one of the following properties or effects. In the embodiments of the invention, by configuring the light shaping module, the illumination beam formed by the illumination system forms the suitable light imaging matching angle and the sub-beams of the illumination beam also have suitable unit light divergence angles. In addition, with the illumination beam formed by the illumination system, the projection apparatus is also able to meet the requirements of the light path in a specific projection imaging system, thereby eliminating stray light or crosstalk of images and rendering favorable image quality and resolution. 
     Other objectives, features and advantages of the present invention will be further understood from the further technological features disclosed by the embodiments of the present invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1A  is a schematic view illustrating an optical framework of a projection apparatus according to an embodiment of the invention. 
         FIG. 1B  is a schematic view illustrating an optical framework of an illumination system of  FIG. 1A . 
         FIG. 1C  is a schematic diagram illustrating the uniformity distributions of light intensity before and after an illumination beam of  FIG. 1B  passes through a first lens element. 
         FIG. 1D  to  FIG. 1F  are schematic views of different light diffusing elements of  FIG. 1B . 
         FIG. 1G  is a diagram illustrating a light shape distribution of sub illumination beams of  FIG. 1B . 
         FIG. 1H  is a schematic view illustrating a distribution of a plurality of illumination sub-regions formed by the sub illumination beams of  FIG. 1A . 
         FIGS. 2A to 2C  are schematic views illustrating optical frameworks of different illumination systems of  FIG. 1A . 
         FIG. 3  is a schematic view illustrating an optical framework of another projection apparatus according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” etc., is used with reference to the orientation of the Figure(s) being described. The components of the present invention can be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no way limiting. On the other hand, the drawings are only schematic and the sizes of components may be exaggerated for clarity. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. Similarly, the terms “facing,” “faces” and variations thereof herein are used broadly and encompass direct and indirect facing, and “adjacent to” and variations thereof herein are used broadly and encompass directly and indirectly “adjacent to”. Therefore, the description of “A” component facing “B” component herein may contain the situations that “A” component directly faces “B” component or one or more additional components are between “A” component and “B” component. Also, the description of “A” component “adjacent to” “B” component herein may contain the situations that “A” component is directly “adjacent to” “B” component or one or more additional components are between “A” component and “B” component. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. 
       FIG. 1A  is a schematic view illustrating an optical framework of a projection apparatus according to an embodiment of the invention.  FIG. 1B  is a schematic view illustrating an optical framework of an illumination system of  FIG. 1A .  FIG. 1C  is a schematic diagram illustrating the uniformity distributions of light intensity before and after an illumination beam of  FIG. 1B  passes through a first lens element.  FIG. 1D  to  FIG. 1F  are schematic views of different light diffusing elements of  FIG. 1B .  FIG. 1G  is a diagram illustrating a light shape distribution of sub illumination beams of  FIG. 1B .  FIG. 1H  is a schematic view illustrating a distribution of a plurality of illumination sub-regions formed by the sub illumination beams of  FIG. 1A . Referring to  FIGS. 1A and 1B , in the embodiment, a projection apparatus  200  may be a near eye display apparatus, and is adapted to be disposed in front of at least one eye of a user. Specifically, as shown in  FIG. 1A , the projection apparatus  200  includes an illumination system  100  and a projection imaging system  210 . Specifically, as shown in  FIGS. 1A and 1B , the illumination system  100  is adapted to emit an illumination beam IL, and the illumination system  100  includes a light source module  110  and a light shaping module  120 . The light source module  110  is adapted to emit at least one beam CL, and the light shaping module  120  is located on a transmission path of the at least one beam CL and is adapted to adjust a light shape of the at least one beam CL. After passing through the light shaping module  120 , the at least one beam CL forms the illumination beam IL, and the illumination beam IL has a light imaging matching angle MA. The light shape of the at least one beam CL is a cross-sectional shape of a light spot of the beam, for example, and the cross-sectional shape of the light spot is adjusted by the light shaping module  120 . 
     More specifically, as shown in  FIG. 1B , in the embodiment, the light source module  110  includes at least one light emitting element  111  adapted to provide the at least one beam CL. For example, the at least one light emitting element  111  is a laser light emitting element (e.g., laser diode), and the at least one beam CL is a collimated beam. In general, in order for the illumination beam IL formed after the at least one beam CL exits the illumination system  100  to satisfy the required range of field of view of a light path in the projection imaging system  210  and provide a range of divergence angle that needs to be satisfied when respective sub image beams SIB formed by the projection imaging system  210  are transmitted to a pupil  214 , the overall light shape of the illumination beam IL needs to satisfy a specific range of light emitting angle (i.e., the light imaging matching angle MA), and a plurality of corresponding sub illumination beams SIL in the illumination beam IL for providing the respective sub image beams SIB also need to have divergence angles corresponding to the respective sub image beams SIB. However, in the embodiment, since the light emitting element  111  is a laser light emitting element, the etendue of the light distribution of the provided at least one beam CL is very small and not uniform. Besides, since the etendue of the at least one beam CL is excessively small, the divergence angles of the sub illumination beams SIL of the illumination beam IL for providing the respective sub image beams SIB are also excessively small. Therefore, the light shaping module  120  needs to be used together to adjust the uniformity and the light shape of the at least one beam CL, so as to form the illumination beam IL that meets the requirements of the light path in the projection imaging system  210 . 
     Specifically, as shown in  FIG. 1B , in the embodiment, the light shaping module  120  includes at least one first lens element  121  and a light diffusing element  123 , and the at least one first lens element  121  and the light diffusing element  123  are located on the transmission path of the at least one beam CL. Specifically, the number of the at least one first lens element  121  of the light shaping module  120  is the same as the number of the at least one light emitting element  111  of the light source module  110 , and each light emitting element  111  is disposed in correspondence with each first lens element  121 . In the embodiment, the number of the first lens element  121  and the number of the light emitting element  111  are both one. However, the invention is not limited thereto. In other embodiments, the number of the first lens element  121  and the number of the light emitting element  111  may both be plural. Besides, the number of the first lens element  121  and the number of the at least one light emitting element  111  of the light source module  110  may also be different. Nevertheless, the invention is not limited thereto. 
     More specifically, as shown in  FIG. 1B  and  FIG. 1C , in the embodiment, the at least one first lens element  121  is adapted to adjust the uniformity and the light shape of the at least one beam CL. As shown in  FIG. 1C , after passing through the at least one first lens element  121 , the at least one beam CL may have an increased light etendue as well as a light shape with uniform light intensity, so as to be projected to the light diffusing element  123 . Accordingly, as shown in  FIG. 1B , the at least one beam CL may pass through the at least one first lens element  121  and form the illumination beam IL having the light imaging matching angle MA. 
     Then, as shown in  FIG. 1B , in the embodiment, the at least one beam CL may also have a plurality of sub-beams SCL. The light diffusing element  123  is located on transmission paths of the sub-beams SCL. For example, in the embodiment, the light diffusing element  123  may be any one of a microstructure diffuser  123   a,  a surface-scattering diffuser  123   b,  a volume-scattering diffuser  123   c,  and a diffraction optical element (DOE), and is adapted to diffuse the unit light divergence angles of the sub-beams SCL and thereby form the sub illumination beams SIL of the illumination beam IL. Further details will be described in the following with reference to  FIGS. 1D to 1F . 
     For example, in the embodiment of  FIG. 1D , the light diffusing element  123  may be a microstructure diffuser  123   a,  and may have a plurality of microstructure diffusion units  123   u . As shown in  FIG. 1B and 1D , the microstructure diffusion units  123   u  correspond to the sub-beams SCL, and a size of each of the microstructure diffusion units  123   u  is in a range between 10 um to 500 um. Before passing through the light diffusing element  123 , each of the sub-beams SCL has a first unit light divergence angle. After passing through the light diffusing element  123 , the unit light divergence angles of the sub-beams SCL are expanded, and the sub-beams SCL may form the sub illumination beams SIL required in the light path of the projection imaging system  210 . In other words, in the embodiment of  FIG. 1D , each of the sub illumination beams SIL may have a second unit light divergence angle, and the second unit light divergence angle is greater than the first unit light divergence angle. The first unit light divergence angle and the second unit light divergence angle are defined as light cone angles of beams known by people skilled in the art. 
     Meanwhile, in the embodiment of  FIG. 1E , the light diffusing element  123  may also be a surface-scattering diffuser  123   b,  and the surface thereof has a plurality of uneven structures that are concave or convex, so as to be able to diffuse the unit light divergence angles of the sub-beams SCL and achieve the same function of the microstructure diffuser  123  of  FIG. 1D . Details in this regard will not be repeated again in the following. Also, in the embodiment of  FIG. 1F , the light diffusing element  123  may also be a volume-scattering diffuser  123   c  having a plurality of scattered particles PA inside. Therefore, the volume-scattering diffuser  123   b  is able to diffuse the unit light divergence angles of the sub-beams SCL and achieve the same function as that of the microstructure diffuser  123   a  of  FIG. 1D . Details in this regard will not be repeated in the following. 
     Accordingly, as shown in  FIGS. 1A and 1B , the illumination beam IL formed after the at least on beam CL passes through the light shaping module  120  has the light imaging matching angle MA, and the sub illumination beams SIL of the illumination beam IL for providing the respective sub image beams may also have greater second unit light divergence angles (as shown in  FIG. 1G ), so as to meet the requirements of the light path in the projection imaging system  210 . 
     Specifically, referring to  FIG. 1A  again, in the embodiment, the projection imaging system  210  is disposed on a transmission path of the illumination beam IL, and the projection imaging system  210  includes a polarizer beam splitter (PBS)  211 , a reflective light valve  213 , and the pupil  214 . The reflective light valve  213  may be a reflective liquid crystal on silicon (LCOS) device or a digital micro-mirror device (DMD), etc. Specifically, as shown in  FIG. 1A , in the embodiment, the polarizer beam splitter  211  and the reflective light valve  213  are disposed on the transmission path of the illumination beam IL, and the pupil  214  is disposed on a transmission path of the image beam IB. For example, in the embodiment, the pupil  214  may be at the location of an exit pupil of the projection imaging system  210  or the location of the pupil of the user&#39;s eye. When the pupil  214  is located at the pupil of the user&#39;s eye, the projection apparatus may be used for virtual reality (VR). 
     Specifically, as shown in  FIG. 1A , in the embodiment, the polarizer beam splitter  211  has a first surface S 1 , a second surface S 2 , and a third surface S 3 . The first surface S 1  is connected with the second surface S 2  and the third surface S 3 , and the second surface S 3  and the third surface S 3  are opposite to each other. The illumination beam IL has a first polarization direction (e.g., the S-polarization direction). After entering the polarizer beam splitter  211  through the first surface S 1 , the illumination beam IL is reflected by the polarizer beam splitter  211 , exits the polarizer beam splitter  211  through the second surface, and is transmitted to the reflective light valve  213 . Then, as shown in  FIG. 1A , in the embodiment, the reflective light valve  213  is adapted to modulate the illumination beam IL into the image beam IB having the sub image beams SIB. In addition, the image beam IB has a second polarization direction (e.g., the P-polarization direction), and the first polarization direction is perpendicular to the second polarization direction. The image beam IB is transmitted to the polarizer beam splitter  211 , enters the polarizer beam splitter  211  through the second surface S 2 , and passes through the polarizer beam splitter  211 . Then, the image beam IB exits the polarizer beam splitter  211  through the third surface S 3  of the polarizer beam splitter  211  and is transmitted to the pupil  214 . 
     In addition, as shown in  FIGS. 1A and 1H , in the embodiment, the projection imaging system  210  further includes a micro lens array  212 . The respective sub illumination beams SIL form a plurality of illumination sub-regions SLR (as shown in  FIG. 1H ) on the reflective light valve  213  through the corresponding micro lenses in the micro lens array  212 , and the sub image beams SIB are formed through the reflective light valve  213 . In addition, as shown in  FIGS. 1A and 1G , on the light path of the projection imaging system  210 , since the main rays of all the sub illumination beams SIL on the light path are parallel light before entering the reflective light valve  213 , and as shown in  FIG. 1G , the second unit light divergence angles of the sub illumination beams SIL are within a range of ±10°, the light emitted by the sub illumination beams SIL and the sub image beams SIB formed from the sub illumination beams SIL travel reciprocally along the same light path and do not pass through other micro lenses adjacent to the corresponding micro lenses in the micro lens array  212 . Therefore, neither stray light nor crosstalk of images may occur. 
     More specifically, as shown in  FIG. 1A , in the embodiment, the angle at which the illumination beam IL enters the polarizer beam splitter  211  through the first surface S 1  of the polarizer beam splitter  211  corresponds to the angle at which the image beam IB exits the polarizer beam splitter  211  through the third surface S 3  of the polarizer beam splitter  211 . In addition, the light shape of the illumination beam IL when the illumination beam IL enters the polarizer beam splitter  211  through the first surface S 1  of the polarizer beam splitter  211  is similar to the light shape of the image beam IB when the image beam IB exits the polarizer beam splitter  211  through the third surface S 3  of the polarizer beam splitter  211 . For example, the cross-sectional areas of the light shapes are proportional to each other. Accordingly, the light imaging matching angle MA of the illumination beam IL is matched with a field of view FOV of the pupil  214 , so as to meet the requirements of the light path design for the field of view FOV required in the projection imaging system  210 . 
     Meanwhile, the second unit light divergence angles of the sub illumination beams SIL also correspond to the divergence angles of the sub image beams SIB of the image beam IB. Accordingly, the size of the pupil  214  may correspond to the size of the light emitting surface of the image beam IB, and the formed image may be sufficiently bright and of favorable quality. 
     Accordingly, the projection apparatus  200  is able to meet the requirements of the light path in the projection imaging system  210  through the illumination beam IL formed by the illumination system  100 , thereby eliminating stray light or crosstalk of images and rendering favorable image quality and resolution. 
       FIGS. 2A to 2C  are schematic views illustrating optical frameworks of different illumination systems of  FIG. 1A . Referring to  FIGS. 2A to 2C , illumination systems  300 A,  300 B, and  300 C in the embodiments of  FIGS. 2A to 2C  are similar to the illumination system  100  of  FIG. 1B , and the differences therebetween will be described in the following. 
     Referring to  FIG. 2A , in the embodiment, a light shaping module  320 A of the illumination system  300 A further includes a second lens element  322  located on the transmission path of the at least one beam CL, the at least one beam CL forms the illumination beam IL after passing through the at least one first lens element  121  and the second lens element  322 , and the light imaging matching angle MA of the illumination beam IL is matched with the field of view FOV of the pupil  214 . For example, in the embodiment, the second lens element  322  is a condensing lens, and may serve to converge the light imaging matching angle MA of the illumination beam IL. Specifically, as shown in  FIG. 2A , in the embodiment, the second lens element  322  may be located between the first lens element  121  and the light diffusing element  123  (e.g., at the location of a second lens element  322   a  shown in  FIG. 2A ) or between the light diffusing element  123  and the projection imaging system  210  (e.g., at the location of a second lens element  322   b  shown in  FIG. 2A ). Accordingly, when the light divergence angles of the sub illumination beams SIL of the illumination beam IL are being formed, the light imaging matching angle MA of the illumination beam IL is prevented from being excessively large, so as to be adapted for the projection imaging system  210  whose pupil  214  has a smaller field of view FOV. 
     Meanwhile, referring to  FIG. 2B , in the embodiment, a light source module  310 B of the illumination system  300 B includes at least one light emitting element  311  and at least one collimating lens  312 . The at least one light emitting element  311  is a light emitting diode, is adapted to provide the at least one beam CL, and corresponds to the at least one collimating lens  312 . The at least one beam CL is collimated by the corresponding at least one collimating lens  312 . Accordingly, the light source module  310 B may serve to replace the light source module  110  shown in  FIG. 1B  and attain a similar function. Besides, as shown in  FIG. 2B , in the embodiment, the second lens element  322  may also be additionally disposed in a light shaping module  320 B of the illumination system  300 B to attain a function similar to the light shaping module  320 A shown in  FIG. 2A . Relevant descriptions may be referred to the above and therefore will not be repeated in the following. Besides, in the embodiment, since the divergence angle of the light emitting diode is greater, the light diffusing element  123  may be omitted, and it is not necessary to further diffuse the unit light divergence angles of the sub-beams SCL. When the light diffusing element  123  is omitted, the second lens element  322  is located between the at least one first lens element  121  and the projection imaging system  210  and serves to converge the light imaging matching angle MA. In other embodiments, the at least one collimating lens  312  and the at least one first lens element  121  may be replaced by a single cemented lens. The single cemented lens has the optical functions of the at least one collimating lens  312  and the at least one first lens element  121  and is also able to attain the effect shown in  FIG. 2B . 
     Besides, referring to  FIG. 2C , in the embodiment, the number of the at least one first lens element  121  and the number of the at least one light emitting element  111  of the illumination system  300 C are plural, and the at least one light emitting element  111  includes a red laser element  111 R, a green laser element  111 G, a blue laser element  111 B respectively adapted for providing a red beam R, a green beam G, and a blue beam B. In addition, the respective first lens elements  121  are disposed in front of the respective light emitting elements  111  and are respectively adapted to adjust the uniformity of the light intensity and the light shape of the red beam R, the green beam G, or the blue beam B. 
     Besides, as shown in  FIG. 2C , in the embodiment, the light shaping module  320 C further includes a plurality of dichroic mirrors DN 1  and DN 2 . The dichroic mirrors DN 1  and DN 2  respectively correspond to at least part of the light emitting elements  111 R,  111 G, and  111 B, and the dichroic mirrors DN 1  and DN 2  are disposed between the corresponding part of the light emitting elements  111 R,  111 G, and  111 B and the projection imaging system. Specifically, as shown in  FIG. 2C , in the embodiment, the dichroic mirror DN 1  of the light shaping module  320 C is located on transmission paths of the green beam G and the blue beam B, and the dichroic mirror DN 1  is adapted to reflect the green beam G and allow the blue beam B to pass through, thereby allowing the green beam G and the blue beam B to be transmitted to the other dichroic mirror DN 2 . The other dichroic mirror DN 2  is located on transmission paths of the red beam R as well as the green beam G and the blue beam B from the dichroic mirror DN 1 . The dichroic mirror DN 1  is adapted to allow the green beam G and the blue beam B to pass through and reflect the red beam R. Accordingly, the green beam G, the blue beam B, and the red beam R are transmitted to the light diffusing element  123  of the light shaping module  320 C and form the subsequent illumination beam IL. 
     Accordingly, the illumination beams IL formed by the illumination systems  300 A,  300 B, and  300 C are all formed with the suitable light imaging matching angle MA by disposing the first lens element  121 , and the sub-beams SCL of the illumination beam IL also have suitable unit light divergence angles, thereby meeting the requirements of the light path in the projection imaging system  210  and attaining the effects and properties similar to those of the illumination system  100 . Thus, details in this regard will not be repeated in the following. Moreover, when the illumination systems  300 A,  300 B, and  300 C are applied to the projection apparatus  200  of  FIG. 1A , the projection apparatus  200  is also able to attain the same functions and effects. Other details in this regard will not be repeated in the following. 
       FIG. 3  is a schematic view illustrating an optical framework of another projection apparatus according to an embodiment of the invention. Referring to  FIG. 3 , a projection imaging system  410  of a projection apparatus  400  in the embodiment of  FIG. 3  is similar to the projection imaging system  210  of the projection apparatus  200  of  FIG. 1A , and the difference therebetween will be described in the following. The projection imaging system  410  further includes at least one optical waveguide  415 . The at least one optical waveguide  415  is located between a pupil  414  and the reflective light valve  213 . More specifically, the at least one optical waveguide  415  is located between the pupil  414  and the polarizer beam splitter  211 . For example, in the embodiment, the pupil  414  is the pupil of at least one eye EY of a user. In other words, in the embodiment, the at least one optical waveguide  415  is adapted to transmit the image beam IB to the at least one eye EY of the user. In addition, in the embodiment, the at least one optical waveguide  415  also allows an ambient beam SL to pass through and is therefore applicable in the field of augmented reality display technologies. 
     Moreover, with the illumination beam IL formed by the illumination system  100 , the projection apparatus  400  may also meet the requirements of the light path in the projection imaging system  410 , thereby eliminating stray light or crosstalk of images and rendering favorable image quality and resolution. Therefore, the projection apparatus  400  may also attain similar effects and properties of the projection apparatus  200 . Details in this regard will not be repeated in the following. 
     A projection imaging system (not shown) of a projection apparatus according to another embodiment of the invention is similar to the projection imaging system  210  of the projection apparatus  200  shown in  FIG. 1A , and the difference therebetween will be described in the following. The technical difference of the projection apparatus of the embodiment from the projection apparatus  200  of  FIG. 1A  lies in that the at least one beam CL of the embodiment does not have a single polarization direction. Therefore, a total reflection prism assembly in the projection imaging system of the embodiment may replace the polarizer beam splitter  211  of  FIG. 1A . The projection imaging system of the embodiment is disposed on the transmission path of the illumination beam IL. The projection imaging system includes the total reflection prism assembly. The total reflection prism assembly includes a first prism and a second prism, and there is an air gap between the first prism and the second prism. In the embodiment, the reflective light valve of the projection imaging system includes a digital micro-mirror device (DMD). Specifically, in the embodiment, the total reflection prism assembly and the reflective light valve are disposed on the transmission path of the illumination beam IL. The total reflection prism assembly and the pupil  214  are disposed on the transmission path of the image beam IB. For example, in the embodiment, the pupil  214  may be at the location of the exit pupil of the projection imaging system  210  or the location of the pupil of the user&#39;s eye. When the pupil  214  is located at the pupil of the user&#39;s eye, the projection apparatus may be used for virtual reality (VR). Specifically, in the embodiment, the total reflection prism assembly has a first surface, a second surface, and a third surface. The first prism includes the first surface and the second surface. The second prism includes the third surface. The first surface is connected with the second surface. The second surface is opposite to the third surface. After the illumination beam IL enters the total reflection prism assembly through the first surface, the illumination beam IL is reflected by the total reflection prism assembly, exits the total reflection prism assembly through the second surface, and is transmitted to the reflective light valve. Then, the reflective light valve is adapted to modulate the illumination beam IL into the image beam IB having the sub image beams SIB. The image beam IB is transmitted to the total reflection prism assembly, enters the total reflection prism assembly through the second surface S 2 , and passes through the total reflection prism assembly. Then, the image beam IB exits the total reflection prism assembly through the third surface S 3  of the total reflection prism assembly and is transmitted to the pupil  214 . 
     In the embodiment, the projection imaging system further includes the micro lens array  212 . The respective sub illumination beams SIL form the illumination sub-regions SLR (as shown in  FIG. 1H ) on the reflective light valve  213  through the corresponding micro lenses in the micro lens array  212 , and the sub image beams SIB are formed through the reflective light valve  213 . On the light path of the projection imaging system, since the main rays of all the sub illumination beams SIL on the light path are parallel light before entering the reflective light valve  213 , and the second unit light divergence angles of the sub illumination beams SIL are within a range of ±10°, the light emitted by the sub illumination beams SIL and the sub image beams SIB formed from the sub illumination beams SIL travel reciprocally along the same light path and do not pass through other micro lenses adjacent to the corresponding micro lenses in the micro lens array  212 . Therefore, neither stray light nor crosstalk of images is generated. 
     More specifically, in the embodiment, the angle at which the illumination beam IL enters the total reflection prism assembly through the first surface of the total reflection prism assembly corresponds to the angle at which the image beam IB exits the total reflection prism assembly through the third surface of the total reflection prism assembly. In addition, the light shape of the illumination beam IL when the illumination beam IL enters the total reflection prism assembly through the first surface of the total reflection prism assembly is similar to the light shape of the image beam IB when the image beam IB exits the total reflection prism assembly through the third surface of the total reflection prism assembly. For example, the cross-sectional areas of the light shapes are proportional to each other. Accordingly, the light imaging matching angle MA of the illumination beam IL is matched with the field of view FOV of the pupil  214 , so as to meet the requirements of the light path design of the field of view FOV required in the projection imaging system. 
     Meanwhile, the second unit light divergence angles of the sub illumination beams SIL also correspond to the divergence angles of the sub image beams SIB of the image beam IB. Accordingly, the size of the pupil  214  may correspond to the size of the light emitting surface of the image beam IB, and the formed image may be sufficiently bright and of favorable quality. 
     Moreover, with the illumination beam IL formed by the illumination system, the projection apparatus of the embodiment may also meet the requirements of the light path in the projection imaging system, thereby eliminating stray light or crosstalk of images and rendering favorable image quality and resolution. Therefore, the projection apparatus may also attain similar effects and properties of the foregoing projection apparatus. Details in this regard will not be repeated in the following. 
     In view of the foregoing, the embodiments of the invention exhibit at least one of the following properties or effects. In the embodiments of the invention, by configuring the light shaping module, the illumination beam formed by the illumination system forms the suitable light imaging matching angle and the sub-beams of the illumination beam also have suitable unit light divergence angles. In addition, with the illumination beam formed by the illumination system, the projection apparatus is also able to meet the requirements of the light path in the projection imaging system, thereby eliminating stray light or crosstalk of images and rendering favorable image quality and resolution. 
     The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiments disclosed. Accordingly, the foregoing description should be regarded as illustrative rather than restrictive. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. The embodiments are chosen and described in order to best explain the principles of the invention and its best mode practical application, thereby to enable persons skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents in which all terms are meant in their broadest reasonable sense unless otherwise indicated. Therefore, the term “the invention”, “the present invention” or the like does not necessarily limit the claim scope to a specific embodiment, and the reference to particularly preferred exemplary embodiments of the invention does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is limited only by the spirit and scope of the appended claims. Moreover, these claims may refer to use “first”, “second”, etc. following with noun or element. Such terms should be understood as a nomenclature and should not be construed as giving the limitation on the number of the elements modified by such nomenclature unless specific number has been given. The abstract of the disclosure is provided to comply with the rules requiring an abstract, which will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Any advantages and benefits described may not apply to all embodiments of the invention. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention as defined by the following claims. Moreover, no element and component in the present disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims.