Patent Publication Number: US-2020292821-A1

Title: Near-eye display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of China application serial no. 201910191801.3, 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 
     Technical Field 
     The disclosure relates to a display device, and more particularly to a near-eye display device. 
     Description of Related Art 
     In the near-eye display field of augmented reality (AR), there are two main mechanisms for introducing image information into the human eye: the freeform prism and the waveguide. The main problem of using the freeform prism is the greater thickness and weight and the introduction of severe image distortion. In contrast, the structure using the waveguide plate is significantly thinner and lighter and has a larger eye box. However, although the structure of the waveguide plate does not introduce image distortion, it introduces many flaws in image display, such as ghosting, mirror image, uniformity reduction, chromatic aberration, etc. Currently, there are three main structures of waveguide plates, mainly including a holographic type, a surface relief grating type and a geometrical beam splitter type. The first two face more challenges in the limitations of the chromatic aberration and the influence on the ambient light than the geometrical beam splitter type waveguide plate. 
     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 was acknowledged by a person of ordinary skill in the art. 
     SUMMARY 
     The disclosure provides a near-eye display device that can improve brightness uniformity of an image. 
     Other objects and advantages of the disclosure will become apparent from the technical features disclosed herein. In order to achieve one or a part or all of the above or other objects, an embodiment of the disclosure provides a near-eye display device. The near-eye display device includes a light engine, a first light waveguide and a second light waveguide. The light engine is configured to provide an image. The first light waveguide is configured to reproduce an image of a view angle region in a first direction. The first light waveguide includes a plurality of first beam splitters arranged along the first direction. The second light waveguide is disposed in a light incident area at a side of the first light waveguide. The second light waveguide is configured to reproduce an image of a view angle region in a second direction. The second light waveguide includes a plurality of second beam splitters arranged along the second direction. The first direction and the second direction determine a reference plane. A diameter of a stop of the light engine is P; a projection width of the first beam splitter on the reference plane is d 1 ; a projection width of the second beam splitter on the reference plane is d 2 ; and the diameter P of the stop, the projection width d 1  and the projection width d 2  satisfy the condition of P&gt;1.5d 2 ≥d 1 . 
     Based on the above, the near-eye display device of the embodiments of the disclosure has a two-dimensional geometrical waveguide plate structure which can improve the brightness uniformity of the image. 
     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. 1  is a schematic view of a near-eye display device according to an embodiment of the disclosure. 
         FIG. 2  is a schematic top view of the near-eye display device of the embodiment of  FIG. 1 . 
         FIG. 3  is a schematic side view of the light engine and the second light waveguide of the embodiment of  FIG. 1 . 
         FIG. 4  is a schematic side view of a near-eye display device according to another embodiment of the disclosure. 
         FIG. 5  is a schematic view of an output image of the embodiment of  FIG. 4 . 
         FIG. 6  is a schematic view of an output image of a related example of the disclosure. 
         FIG. 7  is a schematic side view of a near-eye display device according to another embodiment of the disclosure. 
     
    
    
     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. 1  is a schematic view of a near-eye display device according to an embodiment of the disclosure.  FIG. 2  is a schematic top view of the near-eye display device of the embodiment of  FIG. 1 .  FIG. 3  is a schematic side view of the light engine and the second light waveguide of the embodiment of  FIG. 1 . With reference to  FIGS. 1 to 3 , a near-eye display device  100  of the embodiment includes a light engine  130 , a first light waveguide  110  and a second light waveguide  120 .  FIG. 1  illustrates a two-dimensional waveguide plate structure for improving the brightness uniformity of an image. In the embodiment, the near-eye display device  100  projects an image  600  onto a projection target  200 , such as an eye pupil of a user. 
     In the embodiment, the light engine  130  is configured to provide an image  400 . The first light waveguide  110  is configured to reproduce an image of a view angle region in a first direction Y. The first light waveguide  110  includes a plurality of first beam splitters BS 1  arranged along the first direction Y, and the first beam splitters BS 1  are spaced apart from each other between the two opposite surfaces of the first light waveguide  110 . The second light waveguide  120  is disposed in a light incident area  111  at a side of the first light waveguide  110 . The second light waveguide  120  is configured to reproduce an image of a view angle region in a second direction X. The second light waveguide  120  includes a plurality of second beam splitters BS 2  arranged along the second direction X. The first direction Y and the second direction X are perpendicular to each other. The first direction Y and the second direction X determine a reference plane, that is, an XY plane. The reference plane (XY plane) is perpendicular to a third direction Z. A diameter of a stop ST of the light engine  130  is P; a projection width of the first beam splitter BS 1  on the XY plane is d 1 ; a projection width of the second beam splitter BS 2  on the XY plane is d 2 ; and the diameter P of the stop, the projection width d 1  and the projection width d 2  satisfy the condition of P&gt;1.5d 2 ≥d 1 . In more detail, the light incident area  111  of the first light waveguide  110  corresponds to at least one first beam splitter BS 1  (shown as one), and the first beam splitter covered by the light incident area  111  has an oblique direction opposite to that of the other first beam splitters. The oblique direction of the first beam splitters BS 1  is the oblique relationship between the first beam splitters BS 1  and a surface of the side of the first light waveguide  110 ; that is, the oblique direction of the first beam splitter covered by the light incident area  111  is configured to guide the image from the second light waveguide  120  to the other first beam splitters BS 1 , and the oblique direction of the other first beam splitters BS 1  is configured to guide the received image to the outside of the first light waveguide  110  and direct the received image to the projection target  200 . The second beam splitters BS 2  are disposed parallel to each other and spaced apart from each other between the two opposite surfaces of the second light waveguide  120 . The image provided by the light engine  130  enters the second light waveguide  120  and is guided to the light incident area  111  of the first light waveguide  110  via the second beam splitters BS 2 . The image enters the first light waveguide  110  from the light incident area  111  and is guided to the projection target  200  through the first beam splitters BS 1 . 
     In the embodiment, the stop ST of the light engine  130  is located approximately at a light incident surface of the second light waveguide  120 , and the second light waveguide  120  is provided with two second beam splitters  122  and  124  in an area corresponding to the stop ST of the light engine  130 . That is, the second beam splitters  122  and  124  may simultaneously receive the image  400  from the light engine  130 . As shown in  FIG. 3 , the second beam splitter  122  and the second beam splitter  124  are sequentially disposed in the opposite direction of the second direction X. The second beam splitter  122  is, for example, a beam splitter having a reflectance of 100% and can totally reflect the image  400  to the second beam splitter  124 . In other embodiments, the second beam splitter  122  having the reflectance of 100% may be replaced with a reflecting mirror, and any optical component capable of totally reflecting the image  400  from the light engine  130  to the second beam splitter  124  may be used; the disclosure is not limited to the above. The second beam splitter  124  is, for example, a beam splitter having a reflectance of 50% and a transmittance of 50%. The second beam splitter  124  may receive the image  400  from the second beam splitter  122  so that the image  400  is partially transmitted and partially reflected. The second beam splitter  124  may directly receive the image  400  from the light engine  130  so that the image  400  is partially transmitted and partially reflected. A light-outputting effective area  121  of the second light waveguide  120  does not include the second beam splitters  122  and  124 . As shown in  FIG. 3 , the part of the image transmitting through the second beam splitters  122  and  124  is not guided by the first light waveguide and does not enter the eye pupil. According to the two-dimensional waveguide plate structure of the embodiment of  FIGS. 1 to 3 , the near-eye display device  100  can eliminate the clear ghosting stray light in the light field system observed in off-axis places when the human eye drifts away, thereby improving the brightness uniformity of the image. 
       FIG. 4  is a schematic side view of a near-eye display device according to another embodiment of the disclosure. With reference to  FIG. 4 , a near-eye display device  900  of the embodiment further includes a half wave plate  140 . The half wave plate  140  is disposed between the stop ST of the light engine  130  (shown in  FIG. 3 ) and the light incident surface of the second light waveguide  120 . In the embodiment, the light engine  130  provides the image  400  ( 400   a _ 1 ,  400   a _ 2 ) having a first polarization state. In the embodiment, the second light waveguide  120  is provided with two second beam splitters  126  and  128  in an area corresponding to the stop ST of the light engine  130  (shown in  FIG. 3 ). That is, the second beam splitters  126  and  128  may simultaneously receive the image  400  from the light engine  130  (shown in  FIG. 3 ), as shown in  FIG. 4 . The second beam splitter  126  and the second beam splitter  128  are sequentially disposed in the opposite direction of the second direction X, and the second beam splitter  128  is, for example, a polarization beam splitter. The half wave plate  140  is disposed between the second beam splitter  128  (polarization beam splitter) and the light engine  130  (shown in  FIG. 3 ) and does not correspond to the second beam splitter  126 , and the image  400  having the first polarization state includes an image  400   a _ 1  directly transmitted to the second beam splitter  126  and an image  400   a _ 2  transmitted to the half wave plate  140 . The half wave plate  140  converts the image  400   a _ 2  having the first polarization state into an image  400   b _ 2  having a second polarization state and then transmits it to the second beam splitter  128  (polarization beam splitter). In the embodiment, the first polarization state is, for example, a p-polarization state, and the second polarization state is, for example, an s-polarization state. In other embodiments, the first polarization state is, for example, an s-polarization state, and the second polarization state is, for example, a p-polarization state. 
     In the embodiment, the second beam splitter  126  has a first reflectance Ra of 100% and reflects the image  400   a _ 1  having the first polarization state to the second beam splitter  128 . The first reflectance Ra refers to the reflectance of the beam splitter for a beam or image having the first polarization state. In other embodiments, the second beam splitter  126  having the first reflectance Ra of 100% may be replaced with a reflecting mirror, and any optical component capable of totally reflecting the image  400   a _ 1  having the first polarization state to the second beam splitter  128  may be used; the disclosure is not limited to the above. 
     In the embodiment, the second beam splitter  128  (polarization beam splitter) has a first reflectance Ra, a second reflectance Rb, a first transmittance Ta, and a second transmittance Tb. The first reflectance Ra, the second reflectance Rb, the first transmittance Ta, and the second transmittance Tb satisfy the conditions of Rb=Ta and Tb=Ra. The second reflectance Rb refers to the reflectance of the beam splitter for a beam or image having the second polarization state. The first transmittance Ta refers to the transmittance of the beam splitter for a beam or image having the first polarization state. The second transmittance Tb refers to the transmittance of the beam splitter for a beam or image having the second polarization state. Therefore, the second beam splitter  128  may receive the image  400   a _ 1  from the second beam splitter  126  so that the image  400   a _ 1  is partially transmitted and partially reflected. The second beam splitter  128  may directly receive the image  400   b _ 2  from the half wave plate  140  so that the image  400   b _ 2  is partially transmitted and partially reflected. The light-outputting effective area  121  of the second light waveguide  120  includes the second beam splitter  128  (polarization beam splitter) and other second beam splitters BS 2  but does not include the second beam splitter  126 , as shown in  FIG. 4 . That is, the part of the image  400   a _ 1  reflected by the second beam splitter  128  and the part of the image  400   b _ 2  transmitting through the second beam splitter  128  are guided by the first light waveguide and enter the eye pupil. 
       FIG. 5  is a schematic view of an output image of the embodiment of  FIG. 4 .  FIG. 6  is a schematic view of an output image of a related example of the disclosure. With reference to  FIGS. 5 to 6 , an output image  600  shown in  FIG. 5  is, for example, an image  600  output from the first light waveguide  110  to the projection target  200 , as shown in  FIG. 2 . 
     In the embodiment of  FIG. 4 , the near-eye display device  900  further includes the half wave plate  140 , and the reflectance and transmittance of the second beam splitters  126  and  128  adopt the design manner described in the embodiment of  FIG. 4 . Therefore, the overall brightness of the output image  600  of  FIG. 5  is more uniform than the brightness of an output image  800  of the related example of  FIG. 6 . Therefore, according to the two-dimensional waveguide plate structure of the embodiment of  FIG. 4 , the near-eye display device  900  can eliminate the clear ghosting stray light in the light field system observed in off-axis places when the human eye drifts away, thereby improving the brightness uniformity of the image. 
       FIG. 7  is a schematic side view of a near-eye display device according to another embodiment of the disclosure. With reference to  FIG. 7 , in a near-eye display device  700  of the embodiment, the diameter of the stop of the light engine  130  is P; the projection width of the first beam splitter BS 1  on the XY plane is d 1  (as shown in the first light waveguide  110  shown in  FIG. 2 ); the projection width of the second beam splitter on the XY plane is d 2 ; and the diameter P of the stop, the projection width d 1  and the projection width d 2  satisfy the condition of P=d 2 ≥1.5d 1 . In addition, as shown in  FIG. 7 , the stop ST of the light engine corresponds to one of the second beam splitters BS 2  in the second light waveguide  120 . That is, the diameter P of the stop ST is equal to the projection width d 2  of the second beam splitter on the XY plane, and thus the second light waveguide  120  has a greater thickness t correspondingly. Therefore, according to the two-dimensional waveguide plate structure of the embodiment of  FIG. 7 , the near-eye display device  700  can eliminate the clear ghosting stray light in the light field system observed in off-axis places when the human eye drifts away, thereby improving the brightness uniformity of the image. 
     In summary, the embodiments of the disclosure have at least one of the following advantages or effects. In the embodiments of the disclosure, the near-eye display device has a two-dimensional waveguide plate structure including two light waveguides, and the diameter of the stop of the light engine, the projection width of the first beam splitter on the reference plane, and the projection width of the second beam splitter on the reference plane satisfy the preset design conditions. Therefore, in the structures of the embodiments of the disclosure, the brightness uniformity of the image can be improved. 
     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. 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.