Patent Publication Number: US-2019187354-A1

Title: Optical lens

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of China application serial no. 201711363161.7, filed on Dec. 18, 2017. 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 an optical lens, and particularly relates to a waveguide display having the optical lens. 
     Description of Related Art 
     A display having a waveguide (waveguide display) can be divided into with a self-luminous panel structure, a transmission-type panel structure, and a reflection-type panel structure according to the type of image source. In the waveguide display with the self-luminous or transmission-type panel structure, an image beam provided by the aforementioned various forms of panel passes through an optical lens, and enters into the waveguide via a coupling inlet. Then, the image beam is transmitted to a coupling outlet in the waveguide, and the image beam is projected to the position of human eyes to form an image. In the waveguide display with the reflection-type panel structure, after an illumination beam provided by light source is transmitted by an illumination optical device, the illumination beam is irradiated onto the reflection-type panel by an illumination prism. The reflection-type panel converts the illumination beam into the image beam. Thus, the reflection-type panel transmits the image beam to the optical lens, and the image beam is guided into the waveguide passing through the optical lens. Then, the image beam is transmitted to a coupling outlet in the waveguide, and the image beam is projected to the position of human eyes. The optical lens will make the image generated by the image source (panel) to form a virtual image in a certain distance, and the virtual image is imaged on a retina through the human eyes. When the optical lens is applied to the waveguide display, the considerations of size and weight of the optical lens in the design is an important issue. 
     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 OF THE INVENTION 
     The invention provides an optical lens having small size, light weight, large viewing angle, and high resolution. 
     Other objects and advantages of the 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, an embodiment of the invention provides an optical lens including a first lens, a second lens, and a third lens arranged in sequence from a light emitting side to a light incident side. A light valve is disposed at the light incident side. The optical lens is configured to receive an image beam provided by the light valve. The image beam forms a stop at the light emitting side. The stop has the smallest cross-sectional area of a beam shrinkage of the image beam. 
     Based on the above, the embodiments of the invention have at least one of the following advantages or effects. In the exemplary embodiment of the invention, the design of the optical lens meets the preset specifications, so that the entire length of the optical lens can be shorten, and the appearance of the display becomes smaller. Moreover, when the material of all lenses in the optical lens is considered, the weight of the optical lens becomes lighter. Thereby, the weight of the display becomes lighter. Additionally, to avoid the design of the optical lens will become complicated accordingly when the field of view (FOV) of the waveguide becomes larger; thereby, the size and weight of the display becomes larger and heavier, the optical lens of the invention has the advantages of small size, light weight, large viewing angle, and high resolution. 
     Other objectives, features and advantages of the invention will be further understood from the further technological features disclosed by the embodiments of the 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 diagram illustrating a waveguide display according to an embodiment of the invention. 
         FIG. 2A  is a diagram showing astigmatic field curvature and distortion of an optical lens of  FIG. 1 . 
         FIG. 2B  is a diagram showing lateral color of the optical lens of  FIG. 1 . 
         FIG. 2C  is a diagram showing modulation transfer function curves of the optical lens of  FIG. 1 . 
         FIG. 2D  is a diagram showing an optical path difference of the optical lens of  FIG. 1 . 
         FIG. 2E  is a transverse ray fan plot of the optical lens of  FIG. 1 . 
         FIG. 3  is a schematic diagram illustrating the waveguide display according to another embodiment of the invention. 
         FIG. 4  is a schematic diagram illustrating the waveguide display according to yet another embodiment of the invention. 
         FIG. 5  is a schematic diagram illustrating the waveguide display according to yet another embodiment of the invention. 
         FIG. 6A  is a diagram showing astigmatic field curvature and distortion of the optical lens of  FIG. 5 . 
         FIG. 6B  is a diagram showing lateral color of the optical lens of  FIG. 5 . 
         FIG. 6C  is a diagram showing modulation transfer function curves of the optical lens of  FIG. 5 . 
         FIG. 6D  is a diagram showing an optical path difference of the optical lens of  FIG. 5 . 
         FIG. 6E  is a transverse ray fan plot of the optical lens of  FIG. 5 . 
         FIG. 7  is a schematic diagram illustrating the waveguide display according to yet another embodiment of the invention. 
         FIG. 8  is a schematic diagram illustrating the waveguide display according to yet another 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 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 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 diagram illustrating a waveguide display according to an embodiment of the invention. Referring to  FIG. 1 , a waveguide display  100  of the embodiment is applied to a head-mounted display device having a waveguide element  130 , but the invention is not limited thereto. In the embodiment, the waveguide display  100  includes an optical lens  110 , an illumination prism (second prism)  120 , the waveguide element  130 , and a light valve  150 . The light valve  150  is disposed at a light incident side IS opposite to the optical lens  100 . The light valve  150  may be a digital micromirror device (DMD), a transflective liquid crystal display (liquid crystal on silicon (LCoS)), or other image display elements. In other embodiments, the light valve  150  may be a transparent spatial light modulator, such as a transparent liquid crystal panel. When using the removable illumination prism  120 , the types and species of the light valve  150  are not limited to the invention. The illumination prism  120  is disposed between the optical lens  110  and the light valve  150 . An image beam IM provided by the light valve  150  passes through the illumination prism  120  and enters into the optical lens  110 . The optical lens  110  is adapted to receive the image beam IM. In the embodiment, a cover glass  140  is disposed between the light valve  150  and the illumination prism  120  to protect the light valve  150  from the effects of dust. 
     In the embodiment, after the image beam IM passing through the optical lens  110 , a stop ST is formed at a light emitting side ES opposite to the optical lens  110 . In the embodiment, the stop ST formed by the image beam IM is located in the waveguide element  130 . The stop ST has the smallest cross-sectional area of a beam shrinkage of the image beam IM. For instance, in the embodiment, on a reference plane formed by an X-axis and a Y-axis, the stop ST is circular, for example, and the diameter size thereof in the X-axis direction is consistent with that in the Y-axis. In the embodiment, the image beam IM forms the stop ST after passing through the optical lens  110 , and the stop ST has the smallest cross-sectional area of the beam shrinkage of the image beam IM. Thus, the image beam IM is shrunk to the stop ST after passing through the optical lens  110 , and is dispersed after passing through the stop ST. In the embodiment, the image beam IM is transmitted in the waveguide element  130  after the stop ST, and then is projected to a preset target. In one embodiment, the preset target is human eyes, for example. 
     In the embodiment, one condition is that the optical lens  110  meets 0.3&lt;B/D&lt;2.5, wherein B is a total lens length of the optical lens  110 , and D is a clear aperture of the largest lens in the optical lens  110 . In the embodiment, D is the clear aperture of the first lens  112 , for example. In the embodiment, another condition is that the optical lens  110  meets 0.1&lt;A/B&lt;3.5, wherein A is a distance between the stop ST and the optical lens  110  on an optical axis OA, i.e., a distance between the stop ST and a light emitting surface of the first lens  112 . In the embodiment, yet another condition is that the optical lens  110  meets 2&lt;(A+C)×FOV/(B×D)&lt;30, wherein C is a distance between the optical lens  110  and the light valve  150  on the optical axis OA, which may be a distance between a surface of the illumination prism  120  close to the light emitting side ES and the light valve  150  on the optical axis OA, and FOV is a field of view of the optical lens  110 . In the embodiment, yet another condition is that the optical lens  110  meets E/F&lt;1, wherein a shape of the stop ST is circular, E is a diameter of the stop ST, the light valve  150  is rectangular or square, and F is a diagonal length of the light valve  150 . In the embodiment, yet another condition is that the optical lens  110  simultaneously meets 0.3&lt;B/D&lt;2.5, 0.1&lt;A/B&lt;3.5, 2&lt;(A+C)×FOV/(B×D)&lt;30, and E/F&lt;1. The aforementioned parameters A, B, C, D, E, F, and FOV are as defined above. In the embodiment, the aforementioned parameters A, B, C, D, E, and F are respectively 15.5 millimeters (mm), 7.51 mm, 10.4 mm, 8.6 mm, 3.76 mm, and 7.93 mm, for example. The values of these parameters are not intended to limit the invention. In the embodiment, the field of view of the optical lens  110  is 40 degrees. 
     In the embodiment, the optical lens  110  includes the first lens  112 , a second lens  114 , and a third lens  116  arranged in sequence from the light emitting side ES to the light incident side IS. Diopters of the first lens  112 , the second lens  114 , and the third lens  116  are positive, negative, and positive in sequence. In the embodiment, the first lens  112  is a biconvex lens, the second lens  114  is a biconcave lens, and the third lens  116  is a biconvex lens. In the embodiment, the first lens  112  and the third lens  116  are glass aspheric lenses, and the second lens  114  is a plastic aspheric lens. In another embodiment, the first lens  112 , the second lens  114 , and the third lens  116  are plastic aspheric lenses. 
     An embodiment of the optical lens  110  is provided below. It should be noted that data provided below is not used for limiting the invention, and those skilled in the art may suitably modify parameters or settings of the following embodiment with reference of the invention without departing from the scope or spirit of the invention. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Curvature 
                   
                   
                   
               
               
                   
                   
                 radius 
                 Interval 
                 Refractive 
                 Abbe 
               
               
                 Element 
                 Surface 
                 (mm) 
                 (mm) 
                 index 
                 number 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 First lens 112 
                 S1 
                 8.44 
                 2.02 
                 1.8 
                 40.88 
               
               
                   
                 S2 
                 −20.71 
                 1.26 
               
               
                 Second lens 114 
                 S3 
                 −16.64 
                 1.00 
                 1.63 
                 23.33 
               
               
                   
                 S4 
                 3.85 
                 0.99 
               
               
                 Third lens 116 
                 S5 
                 9.87 
                 1.89 
                 1.85 
                 40.39 
               
               
                   
                 S6 
                 −12.95 
                 0.25 
               
               
                   
               
            
           
         
       
     
     Referring to  FIG. 1  and Table 1, the surface of each lens (including the first lens  112  to the third lens  116 ) are listed in Table 1. For instance, a surface S 1  is the surface of the first lens  112  facing the light emitting side ES, and a surface S 2  is the surface of the first lens  112  facing the light incident side IS, and so on. Additionally, an interval represents a linear distance between two adjacent surfaces on the optical axis OA. For instance, the interval corresponding to the surface S 1  is the linear distance between the surface S 1  and the surface S 2  on the optical axis OA, and the interval corresponding to the surface S 2  is the linear distance between the surface S 2  and the surface S 3  on the optical axis OA, and so on. 
     In the embodiment, the first lens  112 , the second lens  114 , and the third lens  116  may be aspheric lenses. A formula of the aspheric lens is as follows: 
     
       
         
           
             X 
             = 
             
               
                 
                   Y 
                   2 
                 
                 
                   R 
                    
                   
                     ( 
                     
                       1 
                       + 
                       
                         
                           1 
                           - 
                           
                             
                               ( 
                               
                                 1 
                                 + 
                                 k 
                               
                               ) 
                             
                             * 
                             
                               
                                 Y 
                                 2 
                               
                               / 
                               
                                 R 
                                 2 
                               
                             
                           
                         
                       
                     
                     ) 
                   
                 
               
               + 
               
                 
                   A 
                   2 
                 
                  
                 
                   Y 
                   2 
                 
               
               + 
               
                 
                   A 
                   4 
                 
                  
                 
                   Y 
                   4 
                 
               
               + 
               
                 
                   A 
                   6 
                 
                  
                 
                   Y 
                   6 
                 
               
               + 
               
                 
                   A 
                   8 
                 
                  
                 
                   Y 
                   8 
                 
               
               + 
               
                 
                   A 
                   10 
                 
                  
                 
                   Y 
                   10 
                 
               
               + 
               
                 
                   A 
                   12 
                 
                  
                 
                   Y 
                   12 
                 
                  
                 
                     
                 
                  
                 … 
               
             
           
         
       
     
     In the above formula, X is a sag along the optical axis OA, and R is a radius of an osculating sphere, i.e., a curvature radius close to the optical axis OA (e.g. the curvature radius listed in Table 1). k is a conic coefficient, Y is an aspheric height, i.e., the height from the center to the edge of the lens, and coefficients A2, A4, A6, A8, A10, and A12 are aspheric coefficients. In the embodiment, the coefficient A2 is 0. The values listed in Table 2 below are the parameter values of the surface of each lens. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 S1 
                 S2 
                 S3 
                 S4 
                 S5 
                 S6 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 k 
                 0 
                 0 
                 −3.38E−001 
                 −3.20E+000 
                 −4.99E+000 
                 0 
               
               
                 A4 
                 −1.10E−004 
                 9.48E−004 
                 −2.19E−003 
                 −1.18E−003 
                 2.45E−004 
                 7.06E−004 
               
               
                 A6 
                 1.23E−005 
                 −5.98E−005 
                 2.08E−004 
                 1.54E−004 
                 −4.95E−005 
                 −3.66E−005 
               
               
                 A8 
                 −1.06E−006 
                 3.44E−006 
                 −5.46E−006 
                 −1.17E−006 
                 6.20E−006 
                 4.64E−006 
               
               
                 A10 
                 3.74E−008 
                 −1.02E−007 
                 −5.52E−008 
                 −2.32E−007 
                 −2.96E−007 
                 −2.54E−007 
               
               
                 A12 
                 1.30E−012 
                 1.61E−009 
                 3.14E−009 
                 6.60E−009 
                 5.40E−009 
                 4.93E−009 
               
               
                   
               
            
           
         
       
     
       FIG. 2A  is a diagram showing astigmatic field curvature and distortion of the optical lens of  FIG. 1 .  FIG. 2B  is a diagram showing lateral color of the optical lens of  FIG. 1 , which is an analog data diagram made based on the light with the wavelength of 465 nm, 525 nm, and 630 nm, and the ordinate is an airy disc.  FIG. 2C  is a diagram showing modulation transfer function curves of the optical lens of  FIG. 1 , wherein the abscissa is a focus shift, and the ordinate is a modulus of the OTF.  FIG. 2D  is a diagram showing the optical path difference of the optical lens of  FIG. 1 .  FIG. 2E  is a transverse ray fan plot of the optical lens of  FIG. 1 , based on 525 nm, for example. The figures shown in  FIG. 2A  to  FIG. 2E  are within in the standard range. Thus, it can be verified that the optical lens  110  of the embodiment can achieve good effects of imaging. Additionally, from  FIG. 2D , on the active surface of the light valve  150 , the range of the OPD of the image beam IM is −2.0λ&lt;OPD&lt;2.0λ, wherein the OPD is the optical path difference at each field of view, λ is the wavelength of each color light, and the image beam IM includes red light, green light, and blue light. The active surface of the light valve  150  is the surface where the image beam IM emits. Further explanation, the design of the optical path difference, those skilled in the art can easily understand that when designing the optical lens, the optical path difference of the image beam at each field of view to be provided by the image source is reversely obtained from a light plane by a method of optical analogy. In the embodiment, the design of the optical lens  110  meets the preset specifications, which can at least resolve the image with a resolution of 931 p/mm, and thus, the optical lens  110  has small size, light weight, large viewing angle, and high resolution. 
       FIG. 3  is a schematic diagram illustrating the waveguide display according to yet another embodiment of the invention. Referring to  FIG. 3 , a waveguide display  200  of the embodiment is similar to the waveguide display  100  of  FIG. 1 , but the main difference between the two is that the waveguide display  200  further includes the design of a deflecting prism  260  (first lens) and a waveguide element  230 , for example. In the embodiment, the deflecting prism  260  is disposed between the optical lens  110  and the stop ST. The image beam IM leaves the optical lens  110 , a transmission direction thereof is changed after passing through the deflecting prism  260 , and then the image beam IM is converged toward the stop ST. The image beam IM is dispersed after passing through the stop ST. In the embodiment, the waveguide element  230  includes a coupling inlet  232  and a coupling outlet  234 . The coupling inlet  232  and the coupling outlet  234  are a surface area of the waveguide element  230  where the image beam incidents thereto and a surface area of the waveguide element  230  where the image beam leaves therefrom. The stop ST is formed at the coupling inlet  232  of the waveguide element  230 . The image beam IM enters into the waveguide element  230  passing through the stop ST via the coupling inlet  232 , is transmitted to the coupling outlet  234  of the waveguide element  230 , and then is projected to a target  900 . The projection target  900  herein is human eyes, for example. 
     In the embodiment, one condition is that the optical lens  110  meets 0.3&lt;B/D&lt;2.5; another condition is that the optical lens  110  meets 0.1&lt;A/B&lt;3.5; yet another condition is that the optical lens  110  meets 2&lt;(A+C)×FOV/(B×D)&lt;30; yet another condition is that the optical lens  110  meets E/F&lt;1; yet another condition is that the optical lens  110  simultaneously meets 0.3&lt;B/D&lt;2.5, 0.1&lt;A/B&lt;3.5, 2&lt;(A+C)×FOV/(B×D)&lt;30, and E/F&lt;1. A is the distance between the stop ST and the optical lens  110  on the optical axis OA. In the embodiment, A is the sum of the distance between the surface S 1  of the first lens  112  and a surface S 7  of the deflecting prism  260  on the optical axis OA and the distance between the surface S 7  of the deflecting prism  260  and the surface of the stop ST on the optical axis OA. In the embodiment, the aforementioned parameters A, B, C, D, E, and F are respectively 11.8 mm, 7.51 mm, 10.4 mm, 8.6 mm, 3.76 mm, and 7.93 mm, for example. The values of these parameters are not intended to limit the invention. 
       FIG. 4  is a schematic diagram illustrating the waveguide display according to yet another embodiment of the invention. Referring to  FIG. 4 , a waveguide display  300  of the embodiment is similar to the waveguide display  100  of  FIG. 1 , but the main difference between the two is that the design of the waveguide element  230 , for example. Additionally, in the embodiment, there is no glass block or lens between the stop ST and the first lens  112 . After leaving the optical lens  110 , the image beam IM is transmitted in the air and then is converged toward the stop ST. 
     In the embodiment, one condition is that the optical lens  110  meets 0.3&lt;B/D&lt;2.5; another condition is that the optical lens  110  meets 0.1&lt;A/B&lt;3.5; yet another condition is that the optical lens  110  meets 2&lt;(A+C)×FOV/(B×D)&lt;30; yet another condition is that the optical lens  110  meets E/F&lt;1; yet another condition is that the optical lens  110  simultaneously meets 0.3&lt;B/D&lt;2.5, 0.1&lt;A/B&lt;3.5, 2&lt;(A+C)×FOV/(B×D)&lt;30, and E/F&lt;1. In the embodiment, the aforementioned parameters A, B, C, D, E, and F are respectively 8 mm, 7.51 mm, 10.4 mm, 8.6 mm, 3.76 mm, and 7.93 mm, for example. The values of these parameters are not intended to limit the invention. 
       FIG. 5  is a schematic diagram illustrating the waveguide display according to yet another embodiment of the invention. Referring to  FIG. 5 , a waveguide display  400  of the embodiment is a head-mounted display device having the waveguide element  130 , for example, but the invention is not limited thereto. In the embodiment, the waveguide display  400  includes an optical lens  410 , the illumination prism (second prism)  120 , the waveguide element  130 , and the light valve  150 . The light valve  150  is disposed at the light incident side IS. The illumination prism  120  is disposed between the optical lens  410  and the light valve  150 . The image beam IM provided by the light valve  150  passes through the illumination prism  120  and enters into the optical lens  410 . The optical lens  410  is adapted to receive the image beam IM. In the embodiment, the cover glass  140  is disposed between the light valve  150  and the illumination prism  120  to protect the light valve  150 . 
     In the embodiment, the image beam IM forms the stop ST at the light emitting side ES after passing through the optical lens  410 . The stop ST has the smallest cross-sectional area of the beam shrinkage of the image beam IM. In the embodiment, the image beam IM enters into the waveguide element  130  after passing through the stop ST, and then is projected to the preset target. In one embodiment, the preset target is human eyes, for example. 
     In the embodiment, one condition is that the optical lens  410  meets 0.3&lt;B/D&lt;2.5, wherein B is a total lens length of the optical lens  410 , and D is a clear aperture of the largest lens in the optical lens  410 . In the embodiment, D is the clear aperture of a second lens  414 , for example. In the embodiment, another condition is that the optical lens  410  meets 0.1&lt;A/B&lt;3.5, wherein A is the distance between the stop ST and the optical lens  410  on the optical axis OA. In the embodiment, yet another condition is that the optical lens  410  meets 2&lt;(A+C)×FOV/(B×D)&lt;30, wherein C is the distance between the optical lens  410  and the light valve  150  on the optical axis OA, and FOV is the field of view of the optical lens  410 . In the embodiment, yet another condition is that the optical lens  410  meets E/F&lt;1, wherein the shape of the stop ST is circular, E is the diameter of the stop ST, the light valve  150  is rectangular or square, and F is the diagonal length of the light valve  150 . In the embodiment, yet another condition is that the optical lens  410  simultaneously meets 0.3&lt;B/D&lt;2.5, 0.1&lt;A/B&lt;3.5, 2&lt;(A+C)×FOV/(B×D)&lt;30, and E/F&lt;1. The aforementioned parameters A, B, C, D, E, F, and FOV are as defined above. In the embodiment, the aforementioned parameters A, B, C, D, E, and F are respectively 12.49 mm, 11.55 mm, 10.4 mm, 8.4 mm, 3.84 mm, and 7.93 mm, for example. The values of these parameters are not intended to limit the invention. In the embodiment, the field of view of the optical lens  410  is 40 degrees. 
     In the embodiment, the optical lens  410  includes the first lens  412 , the second lens  414 , a third lens  416 , and a fourth lens  418  arranged in sequence from the light emitting side ES to the light incident side IS. The diopters of the first lens  412 , the second lens  414 , the third lens  416 , and the fourth lens  418  are negative, positive, negative, and positive in sequence. In the embodiment, the first lens  412  is a convex-concave lens and has a convex surface toward the light incident side IS, the second lens  414  is a biconvex lens, the third lens  416  is a convex-concave lens and has a convex surface toward the light emitting side ES, and the fourth lens  418  is a biconvex lens. In the embodiment, the first lens  412 , the second lens  414 , the third lens  416 , and the fourth lens  418  are plastic aspheric lenses, but is not limited thereto. 
     For instance, the optical lens  410  has four lenses, but is not limited thereto. The diameter of the stop ST is about 4 mm, close to the size of the pupil of normal human eyes (about 3-6 mm). The size of the stop ST is also close to a width of a short side of the light valve  150  (e.g., 3.888 mm), but smaller than the diagonal of the light valve  150  (e.g., 7.93 mm), wherein the diagonal of the light valve  150  represents an image circle IMA of the optical lens  410 . The light valve is to use a 0.3-inch  720 P DMD device, for example. In the design of the optical lens  410 , the human eyes can see which is equivalent to a 57-inch virtual image outside 2 meters (M), and the magnification is about 190 times at this time. 
     Additionally, the optical lens  410  in the embodiment has a relational expression between the focal distance and the image height as follows: image height=focal distance×tan (half field of view), wherein the image height is 3.965 mm, for example. The field of view is designed to be 40 degrees, and the half field of view is 20 degrees. Thereby, the effective focal distance of the optical lens  410  is approximately 10.89 mm. 
     An embodiment of the optical lens  410  is provided below. It should be noted that data provided below is not used for limiting the invention, and those skilled in the art may suitably modify parameters or settings of the following embodiment with reference of the invention without departing from the scope or spirit of the invention. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                 Curvature 
                   
                   
                   
               
               
                   
                   
                 radius 
                 Interval 
                 Refractive 
                 Abbe 
               
               
                 Element 
                 Surface 
                 (mm) 
                 (mm) 
                 index 
                 number 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 First lens 412 
                 S1 
                 −3.71 
                 1.15 
                 1.63 
                 23.33 
               
               
                   
                 S2 
                 −4.74 
                 0.10 
               
               
                 Second lens 414 
                 S3 
                 6.51 
                 2.23 
                 1.53 
                 55.74 
               
               
                   
                 S4 
                 −40.49 
                 0.10 
               
               
                 Third lens 416 
                 S5 
                 6.30 
                 2.50 
                 1.63 
                 23.33 
               
               
                   
                 S6 
                 2.57 
                 0.92 
               
               
                 Fourth lens 418 
                 S7 
                 6.44 
                 2.74 
                 1.53 
                 55.74 
               
               
                   
                 S8 
                 −13.30 
                 0.25 
               
               
                   
               
            
           
         
       
     
     Referring to  FIG. 5  and Table 3, the surface of each lens (including the first lens  412  to the fourth lens  418 ) are listed in Table 3. For instance, the surface S 1  is the surface of the first lens  412  facing the light emitting side ES, and the surface S 2  is the surface of the first lens  412  facing the light incident side IS, and so on. Additionally, the interval represents the linear distance between two adjacent surfaces on the optical axis OA. For instance, the interval corresponding to the surface S 1  is the linear distance between the surface S 1  and the surface S 2  on the optical axis OA, and the interval corresponding to the surface S 2  is the linear distance between the surface S 2  and the surface S 3  on the optical axis OA, and so on. 
     In the embodiment, the first lens  412 , the second lens  414 , the third lens  416 , and the fourth lens  418  may be aspheric lenses. A formula of the aspheric lens is as follows: 
     
       
         
           
             X 
             = 
             
               
                 
                   Y 
                   2 
                 
                 
                   R 
                    
                   
                     ( 
                     
                       1 
                       + 
                       
                         
                           1 
                           - 
                           
                             
                               ( 
                               
                                 1 
                                 + 
                                 k 
                               
                               ) 
                             
                             * 
                             
                               
                                 Y 
                                 2 
                               
                               / 
                               
                                 R 
                                 2 
                               
                             
                           
                         
                       
                     
                     ) 
                   
                 
               
               + 
               
                 
                   A 
                   2 
                 
                  
                 
                   Y 
                   2 
                 
               
               + 
               
                 
                   A 
                   4 
                 
                  
                 
                   Y 
                   4 
                 
               
               + 
               
                 
                   A 
                   6 
                 
                  
                 
                   Y 
                   6 
                 
               
               + 
               
                 
                   A 
                   8 
                 
                  
                 
                   Y 
                   8 
                 
               
               + 
               
                 
                   A 
                   10 
                 
                  
                 
                   Y 
                   10 
                 
               
               + 
               
                 
                   A 
                   12 
                 
                  
                 
                   Y 
                   12 
                 
                  
                 
                     
                 
                  
                 … 
               
             
           
         
       
     
     In the above formula, X is the sag along the optical axis OA, and R is the radius of the osculating sphere, i.e., the curvature radius close to the optical axis OA (e.g. the curvature radius listed in Table 1). k is the conic coefficient, Y is the aspheric height, i.e., the height from the center to the edge of the lens, and the coefficients A2, A4, A6, A8, A10, and A12 are aspheric coefficients. In the embodiment, the coefficient A2 is 0. The values listed in Table 4 below are the parameter values of the surface of each lens. 
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 S1 
                 S2 
                 S3 
                 S4 
                 S5 
                 S6 
                 S7 
                 S8 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 k 
                 −7.13E−001 
                 0.00E+000 
                 0.00E+000 
                 0.00E+000 
                 −3.38E−001 
                 −2.45E+000 
                 −3.58E+000 
                 0.00E+000 
               
               
                 A4 
                 2.95E−003 
                 6.13E−004 
                 −1.66E−004 
                 2.43E−003 
                 −5.24E−003 
                 −1.61E−004 
                 1.64E−003 
                 1.42E−003 
               
               
                 A6 
                 −4.78E−004 
                 −9.29E−005 
                 −2.08E−005 
                 −1.77E−004 
                 1.87E−004 
                 3.33E−005 
                 −5.77E−005 
                 −4.97E−005 
               
               
                 A8 
                 3.99E−005 
                 6.10E−006 
                 −5.94E−007 
                 6.03E−006 
                 −1.00E−006 
                 6.44E−006 
                 6.44E−006 
                 6.60E−006 
               
               
                 A10 
                 −2.13E−006 
                 −2.58E−008 
                 3.37E−008 
                 −1.08E−007 
                 −1.42E−007 
                 −4.02E−007 
                 −3.34E−007 
                 −3.52E−007 
               
               
                 A12 
                 5.33E−008 
                 −5.21E−033 
                 −5.21E−033 
                 1.61E−009 
                 3.14E−009 
                 6.60E−009 
                 5.40E−009 
                 4.93E−009 
               
               
                   
               
            
           
         
       
     
       FIG. 6A  is a diagram showing astigmatic field curvature and distortion of the optical lens of  FIG. 5 .  FIG. 6B  is a diagram showing lateral color of the optical lens of  FIG. 5 , which is an analog data diagram made based on the light with the wavelength of 465 nm, 525 nm, and 630 nm, and the ordinate is the airy disc.  FIG. 6C  is a diagram showing modulation transfer function curves of the optical lens of  FIG. 5 , wherein the abscissa is the focus shift, and the ordinate is the modulus of the OTF.  FIG. 6D  is a diagram showing an optical path difference of the optical lens of  FIG. 5 .  FIG. 6E  is a transverse ray fan plot of the optical lens of  FIG. 5 , based on 525 nm, for example. The figures shown in  FIG. 6A  to  FIG. 6E  are within in the standard range. Thus, it can be verified that the optical lens  410  of the embodiment can achieve good effects of imaging. Additionally, from  FIG. 6D , on the active surface of the light valve  150 , the range of the OPD of the image beam IM is −1.5λ&lt;OPD&lt;1.5λ, wherein the OPD is the optical path difference at each field of view, λ is the wavelength of each color light, and the image beam IM includes red light, green light, and blue light. In the embodiment, the design of the optical lens  410  meets the preset specifications, and thus, the optical lens  410  has small size, light weight, large viewing angle, and high resolution. 
       FIG. 7  is a schematic diagram illustrating the waveguide display according to yet another embodiment of the invention. Referring to  FIG. 7 , a waveguide display  500  of the embodiment is similar to the waveguide display  400  of  FIG. 5 , but the main difference between the two is that the waveguide display  500  further includes the design of the deflecting prism  260  (first lens) and the waveguide element  230 , for example. In the embodiment, the deflecting prism  260  is disposed between the optical lens  410  and the stop ST. The image beam IM leaves the optical lens  410 , the transmission direction thereof is changed after passing through the deflecting prism  260 , and then the image beam IM is converged toward the stop ST. The image beam IM is dispersed after passing through the stop ST. In the embodiment, the waveguide element  230  includes the coupling inlet  232  and the coupling outlet  234 . The stop ST is formed at the coupling inlet  232  of the waveguide element  230 . The image beam IM enters into the waveguide element  230  passing through the stop ST via the coupling inlet  232 , is transmitted to the coupling outlet  234  of the waveguide element  230 , and then is projected to the target  900 . The projection target  900  herein is human eyes, for example. 
     In the embodiment, one condition is that the optical lens  410  meets 0.3&lt;B/D&lt;2.5; another condition is that the optical lens  410  meets 0.1&lt;A/B&lt;3.5; yet another condition is that the optical lens  410  meets 2&lt;(A+C)×FOV/(B×D)&lt;30; yet another condition is that the optical lens  410  meets E/F&lt;1; yet another condition is that the optical lens  410  simultaneously meets 0.3&lt;B/D&lt;2.5, 0.1&lt;A/B&lt;3.5, 2&lt;(A+C)×FOV/(B×D)&lt;30, and E/F&lt;1. A is the distance between the stop ST and the optical lens  410  on the optical axis OA. In the embodiment, A is the sum of the distance between the surface S 1  of the first lens  412  and the surface S 7  of the deflecting prism  260  on the optical axis OA and the distance between the surface S 7  of the deflecting prism  260  and the surface of the stop ST on the optical axis OA. In the embodiment, the aforementioned parameters A, B, C, D, E, and F are respectively 9.6 mm, 11.55 mm, 10.4 mm, 8.4 mm, 3.84 mm, and 7.93 mm, for example. The values of these parameters are not intended to limit the invention. 
       FIG. 8  is a schematic diagram illustrating the waveguide display according to yet another embodiment of the invention. Referring to  FIG. 8 , a waveguide display  600  of the embodiment is similar to the waveguide display  400  of  FIG. 5 , but the main difference between the two is that the design of the waveguide element  230 , for example. Additionally, in the embodiment, there is no glass block or lens between the stop ST and the first lens  412 . After leaving the optical lens  410 , the image beam IM is transmitted in the air and then is converged toward the stop ST. 
     In the embodiment, one condition is that the optical lens  410  meets 0.3&lt;B/D&lt;2.5; another condition is that the optical lens  410  meets 0.1&lt;A/B&lt;3.5; yet another condition is that the optical lens  410  meets 2&lt;(A+C)×FOV/(B×D)&lt;30; yet another condition is that the optical lens  410  meets E/F&lt;1; yet another condition is that the optical lens  410  simultaneously meets 0.3&lt;B/D&lt;2.5, 0.1&lt;A/B&lt;3.5, 2&lt;(A+C)×FOV/(B×D)&lt;30, and E/F&lt;1. In the embodiment, the aforementioned parameters A, B, C, D, E, and F are respectively 6.45 mm, 11.55 mm, 10.4 mm, 8.4 mm, 3.84 mm, and 7.93 mm, for example. The values of these parameters are not intended to limit the invention. 
     In summary, the embodiments of the invention have at least one of the following advantages or effects. In the exemplary embodiment of the invention, the design of the optical lens meets the preset specifications, and thus, the optical lens has small size, light weight, large viewing angle, and high 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 invention as defined by the following claims. Moreover, no element and component in the disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims.