Abstract:
Described is an optical lens having a light-receiving surface facing a light source and a first structured surface opposite a first portion of the light-receiving surface. The first structured surface includes a plurality of first reflecting surfaces and first refractive surfaces. Each of the first refractive surfaces receives light from a corresponding first reflective surface for refractive transmission therethrough. The optical system may further include a second structured surface opposite a second portion of the light-receiving surface. The second structured surface includes a plurality of second refractive surfaces. Each of the second refractive surfaces receives light directly from the light-receiving surface. Where the first and second structured surfaces are included, the first and second portions of the light-receiving surface can be positioned so that light projected from the light source at an angle above a threshold angle falls on the first portion and light at an angle below the threshold angle falls on the second portion.

Description:
FIELD OF INVENTION  
       [0001]     The invention relates generally to a projection display system and in particular, an optical lens for a projection display system.  
       BACKGROUND INFORMATION  
       [0002]     Several technologies exist for display systems including cathode ray tubes (“CRT”), projection displays, and plasma displays. For large displays (e.g., a screen diagonal greater than 1 m (40 inch)), CRT usually is not practical. Plasma and projection displays are often favored for larger display systems because they may be produced with lighter weights and thinner depths than conventional CRT displays.  
         [0003]     Rear projection systems (e.g., a rear projection television) generally include a projection lens system to project light (e.g., images) on a projection screen. The depth of a rear projection system is limited in part by the angle from which the projection lens is capable of displaying images (i.e., the projection lens angle). Several solutions have been employed to increase the projection lens angle, including the use of a Fresnel lens adjacent to the projection screen. However, as the projection angle is increased, rear projection systems tend to experience low transmission and significant color dispersion.  
       SUMMARY  
       [0004]     The present disclosure is directed to an optical lens having a light-receiving surface that can be disposed facing a light source to receive light therefrom and a first structured surface opposite a first portion of the light-receiving surface. The first structured surface includes a plurality of first reflecting surfaces projecting at a plurality of first angles relative to the light-receiving surface and a plurality of first refractive surfaces projecting at a plurality of second angles relative to the light-receiving surface. Each of the first refractive surfaces receives light from a corresponding one of the first reflective surfaces for transmission therethrough.  
         [0005]     In some exemplary embodiments of the present disclosure, the optical lens may further include a second structured surface opposite a second portion of the light-receiving surface. The second structured surface includes a plurality of second refractive surfaces projecting at a plurality of third angles relative to the light-receiving surface. Each of the second refractive surfaces may receive light from the light-receiving surface for transmission therethrough.  
         [0006]     In the exemplary embodiments that include the first and second structured surfaces, the first and second portions of the light-receiving surface may be positioned so that light from a light source incident on the light-receiving surface at an angle above a threshold angle falls on the first portion and light incident on the light-receiving surface at an angle below the threshold angle falls on the second portion.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0007]     So that those having ordinary skill in the art to which the subject invention pertains will more readily understand how to make and use the subject invention, exemplary embodiments thereof will be described in detail below with reference to the drawings, wherein:  
         [0008]      FIG. 1A  shows a cross-sectional view of an exemplary projection system according to the present disclosure;  
         [0009]      FIG. 1B  shows a front perspective view of the exemplary projection system shown in  FIG. 1A ;  
         [0010]      FIG. 2A  shows a partial schematic cross-sectional view of an exemplary embodiment of an optical lens according to the present disclosure;  
         [0011]      FIG. 2B  shows another partial schematic cross-sectional view of the exemplary embodiment of an optical lens shown in  FIG. 2A ;  
         [0012]      FIG. 3A  shows a partial schematic cross-sectional view of another exemplary embodiment of an optical lens according to the present disclosure;  
         [0013]      FIG. 3B  shows another partial schematic cross-sectional view of the exemplary embodiment of an optical lens shown in  FIG. 3A ;  
         [0014]      FIG. 4A  shows a perspective view of another exemplary embodiment of an optical lens according to the present disclosure;  
         [0015]      FIG. 4B  shows a perspective view of another exemplary embodiment of an optical lens according to the present disclosure;  
         [0016]      FIG. 4C  shows a perspective view of another exemplary embodiment of an optical lens according to the present disclosure;  
         [0017]      FIG. 5A  shows a cross-sectional view of another exemplary projection system according to the present disclosure; and  
         [0018]      FIG. 5B  shows a front perspective view of the exemplary projection system shown in  FIG. 5A . 
     
    
     DETAILED DESCRIPTION  
       [0019]     The present disclosure is directed to an optical lens and to an optical system including the optical lens. In particular, the present disclosure is directed to an optical lens including a total internal reflection (“TIR”) Fresnel optical lens. The disclosed invention may be useful, for example, in projection systems and ultra-thin projection systems. The disclosed invention may improve light transmission, minimize dispersion, and reduce ghost light beams in projection systems.  
         [0020]      FIGS. 1A and 1B  show an exemplary embodiment of a projection system  100  according to the present disclosure. The projection system  100  may be, for example, a rear projection television. The projection system  100  includes an enclosure  102 . The enclosure  102  may be of any material, shape, or size known to those skilled in the art. The projection system  100  may include a light source and a projection lens, collectively designated as  104 . The projection lens  104  may be mounted within the enclosure  102  at a projection lens angle β 1  (beta one). The projection lens angle β 1  may be, for example, an angle greater than forty-two (42) degrees.  
         [0021]     An optical lens  110  may be included in the enclosure  102 . In the exemplary embodiment shown in  FIGS. 1A and 1B , the optical lens  110  is positioned substantially parallel to a projection screen  112  and preferably adjacent to the projection screen  112 . The optical lens  110  may receive light (e.g., images) from the projection lens  104 , and transmit at least a substantial portion of the light through the projection screen  112  in a general direction  114 . The general direction  114  may be, for example, towards a viewer (not shown) of the projection system  100 . Further exemplary embodiments of the optical lens  110  are described below.  
         [0022]      FIGS. 2A and 2B  show a partial schematic cross-sectional view of an exemplary embodiment of an optical lens  200  according to the present disclosure. The body of the optical lens  200  may be made of any known material with an appropriate refractive index (e.g., 1.49), such as an acrylic. The optical lens  200  may include an input surface  202  which may be, for example, a substantially planar and refractive surface. A portion of light transmitted from the light source and projection lens  104  may be refracted at the input surface  202  depending on the angle at which the light meets the input surface  202  (e.g., incident angle), the polarization of the light, the wavelength of the light, and the refractive index of the material of the body of the optical lens  200 .  
         [0023]     The optical lens  200  may include a first structured surface  204 . The first structured surface  204  may be rigid or flexible and may be manufactured using a hard or flexible mold. The first structured surface  204  may be, for example, a TIR Fresnel lens. The first structured surface  204  may be disposed opposite to the input surface  202  on the viewing side of a rear projection system (e.g., projection system  100 ). Preferably, a substantial portion of light transmitted from a projection lens (e.g., the projection lens  104 ) is refracted through the input surface  202  in a general direction towards the first structured surface  204 .  
         [0024]     The first structured surface  204  may include a plurality of first reflective surfaces  206   a ,  206   b ,  206   c  (hereinafter collectively called “ 206 ”). The first reflective surfaces  206  may be, for example, TIR surfaces. For example, the first reflective surface  206   a  may be situated at a surface angle α 1  (i.e., alpha one) with respect to a plane generally parallel to the optical lens  200  (e.g., a vertical plane). The first reflective surfaces  206   b  and  206   c  may likewise be situated at surface angles α 3  and α 5 , respectively. The surface angles of the first reflective surfaces  206  may also be unequal (e.g., α 1  not equal to α 3  not equal to α 5 ). At least some of the first reflective surfaces  206  in the exemplary embodiment may be undercut, i.e., having surface angles α greater than ninety (90) degrees (e.g., one hundred (100) degrees). However, in some exemplary embodiments, at least some of the first reflective surfaces  206  may be situated at surface angles α less than ninety (90) degrees.  
         [0025]     The first structured surface  204  may also include a plurality of first refractive surfaces  208   a ,  208   b ,  208   c  (hereinafter collectively called “ 208 ”). For example, the first refractive surface  208   a  may be situated at a surface angle α 2  (i.e., alpha two) with respect to a plane generally parallel to the optical lens  200  (e.g., a vertical plane), and the first refractive surfaces  208   b  and  208   c  may be situated at surface angles α 4  and α 6  respectively. In the exemplary embodiment, the surface angles of the first refractive surfaces  208  (e.g., α 2  and α 4 ) are preferably similar or equal to the complementary (90 degrees−alpha) angles to the expected exit angles (e.g., exit angle Φ 4  and Φ 8 ) of light beams passing through the optical lens  200 . As one of ordinary skill in the art will understand, this may result in a substantial portion of light being directed in the direction  114  (shown in  FIG. 1 ), e.g., a substantially horizontal direction.  
         [0026]     As one of ordinary skill in the art will know, the amount of refraction a light beam experiences while passing from one medium into another medium (e.g., into one of different density) is determined by the relative refractive indexes and Snell&#39;s Law. Based on the principles of Snell&#39;s Law, when light encounters, or is incident upon, a medium having a lesser refractive index, the light beam is bent away from the normal at an exit angle greater than the incident angle. Snell&#39;s Law can be expressed by the formula: 
 
 n   i *sin Φ i   =n   t *sin Φ t , 
        where, 
            n i =the refractive index of the material on the side of incident light,     Φ i =the incident angle,     n t =the refractive index of the material on the side of transmitted light, and     Φ t =the exit angle.    
               
 
         [0032]     As shown in  FIG. 2B , a light beam  210  transmitted from the projection lens (e.g., the projection lens  104 ) at a projection angle Φ 0  (i.e., phi zero) may encounter the input surface  202  at the angle Φ 0  relative to a normal to the input surface  202 . As one of ordinary skill in the art will understand, the incident angle Φ 0  at the input surface  202  and the projection angle Φ 0  of the light beam may be the same. In the present example, the light beam  210  will refract and pass through the input surface  202 . The light beam  210  may exit the input surface  202  at a first exit angle Φ 1  determined from the Snell&#39;s Law equation.  
         [0033]     Shown in  FIG. 2B , the light beam  210  may encounter the first reflective surface  206   a  at an incident angle Φ 2 . In the exemplary embodiment, the first reflective surface  206   a  is situated at the surface angle α1 such that a substantial portion of light beams that encounter the first reflective surface  206   a  will have an incident angle (e.g., Φ 2 ) to the first reflective surface  206   a  greater than a predetermined critical angle Φ c2 . As one of ordinary skill in the art would understand, a light beam traveling from a higher refractive index material to one of lower refractive index will generally refract when its incident angle to a surface is less than a predetermined critical angle Φ c  (e.g., Φ c2 ) and reflect when equal to or greater than the critical angle Φ c  (e.g., Φ c2 ).  
         [0034]     One of ordinary skill will further understand that the critical angle Φ c  at a surface (e.g., the first reflective input surface  206   a ) may be determined according to the Snell&#39;s Law (described above) by setting the exit angle Φ t  to ninety (90) degrees and solving for the incident angle Φ i . It may be noted that incident angles and critical angles are often represented with respect to a normal to the surface (e.g., surface  206   a ), however, in the present disclosure some angles may likewise be discussed with respect to the surface, i.e., their complement angle.  
         [0035]     As discussed above, the incident angle Φ 2  in the present example is greater than the critical incident angle Φ c2 . Therefore, there may be total internal reflection of the light beam  210  at the first reflective surface  206   a  (i.e., the light beam will be reflected rather than being refracted and transmitted through the surface). The light beam  210  reflected from the first reflective surface  206   a  may then encounter the first refractive surface  208   a  at an incident angle Φ 3 . The incident angle Φ 3  may be less than a critical angle Φ c3  at the fist refractive surface  208   a . Therefore, the light beam  210  may pass through the first refractive surface  208   a  at a second exit angle Φ 4  (e.g., in a general direction  114  or similar direction).  
         [0036]     Shown in  FIG. 2B , a light beam  212  with a projection angle Φ 5  may encounter the input surface  202 . The light beam  212  may be refracted and pass through the input surface  202  with a first exit angle Φ 6 . The refracted light beam  212  may encounter the first reflective surface  206   b  at an angle Φ 7  with respect to the first reflective surface  206   b  and reflect at substantially the same angle Φ 7  (i.e., total internal reflection occurs). The reflected light beam  212  may next encounter the first refractive surface  208   b  and pass through the first refractive surface  208   b  at a second exit angle Φ 8  (e.g., in the general direction  114 ).  
         [0037]     As discussed above, light transmitted from a projection lens (e.g., the projection lens  104 ) may encounter the optical lens  200 , reflect off one of the first reflective surfaces  206 , and pass through one of the first refractive surfaces  208 . To direct multiple light beams originating from the same projection lens in substantially the same general directions (e.g., the direction  114 ), the surface angles α may be varied (e.g., α 1  not equal to α 3 , α 4  not equal to α 6 ) at different locations along the first structured surface  204 . For example, the optical lens  200  may be employed in the projection system  100  (shown in  FIG. 1 ). Given a fixed projection lens  104  location (e.g., fixed angle β 1 ), incident angles of light received in the vicinity of the first reflective surface  206   b  and the first refractive surface  208   b  may be estimated. The surface angles α 3  and α 4  of the first reflective surface  206   b  and the first refractive surface  208   b , respectively, may then be chosen such that a substantial portion of the received light is refracted in the general direction  114 . For example, the angle α 4  may be chosen so as to situate the first refractive surface  208   b  slightly more horizontal than the expected direction of a light beam (e.g., the light beam  212 ).  
         [0038]     In the exemplary embodiment, the refractive surface  208   b  may be situated such that the expected angle of light beams (e.g., angle Φ 6  of the light beam  212 ) is greater than the surface angle of the first refractive surface  208   b  (i.e., 90 minus α 4 ) by an angle δ (delta). Angle δ may be approximately equal to two (2) degrees. Therefore, light beams received in the vicinity of the first reflective surface  206   b  and the first refractive surface  208   b  may generally encounter the first reflective surface  206   b  before the first refractive surface  208   b . As one of ordinary skill in the art will understand, preferred surface angles α may be similarly chosen for each of the first reflective surfaces  206  and/or for each of the first refractive surfaces  208  in the first structured surface  204  according to the present disclosure.  
         [0039]      FIGS. 3A and 3B  show a cross-sectional view of another exemplary embodiment of the optical lens  110  according to the present disclosure (e.g., an optical lens  300 ). The body of the optical lens  300  may be made of any known material with an appropriate refractive index, such as an acrylic. The optical lens  300  may include an input surface  302  which may be, for example, a substantially planar and refractive surface. The optical lens  300  may include a first structured surface  304 . The first structured surface  304  may be, for example, a TIR Fresnel lens. The first structured surface  304  may include a plurality of first reflective surfaces  306   a ,  306   b ,  306   c  (hereinafter collectively called “ 306 ”). For example, the first reflective surface  306   a  may be situated at a surface angle α 7  with respect to a plane generally parallel to the optical lens (e.g., a vertical plane). The first reflective surfaces  306   b  and  306   c  may likewise be situated at surface angles α 9  and α 11  respectively. The first reflective surfaces  306  may be, for example, TIR surfaces.  
         [0040]     The first structured surface  304  may also include a plurality of first refractive surfaces  308   a ,  308   b ,  308   c  (hereinafter collectively called “ 308 ”). For example, the first refractive surface  308   a  may be situated at a surface angle α 8  with respect to the vertical, and the first refractive surfaces  308   b  and  308   c  may be situated at surface angles α 10  and α 12 , respectively.  
         [0041]     The optical lens  300  may include a second structured surface  310  separated from the first structured surface  304  by a transition region  312 . The second structured surface  310  may be, for example, a Fresnel lens (e.g., conventional refractive Fresnel lens). The second structured surface  310  may include a plurality of second refractive surfaces  314   a ,  314   b  (hereinafter collectively called “ 314 ”) and riser surfaces  316   a ,  316   b  (hereinafter collectively called “ 316 ”). The second refractive surfaces  314  may be situated at surface angles α 13  and α 15  with respect to a plane parallel to the optical lens (e.g., a vertical plane). The riser surfaces  316  may likewise be situated at surface angles α 14  and α 16  respectively.  
         [0042]     In the exemplary embodiment, the surface angles α 14  and α 16  of the riser surfaces  316  may be greater than expected first exit angles from the input surface  302  (e.g., first exit angles Φ 15  and Φ 19 , respectively) and less than or about equal to ninety (90) degrees. As one of ordinary skill in the art will understand, surface angles α 14  and α 16  chosen within such limits will result in light beams (e.g.,  320 ,  322 ) from the input surface  302  generally encountering the second refractive surfaces  314  rather than the riser surfaces  316 . Further, light beams (e.g.,  322 ) exiting the second refractive surface  314  will generally not impinge on the riser surfaces  316 .  
         [0043]     The second structured surface  310  may be disposed next to the first structured surface  304  and positioned to receive light from the projection lens  104  at lower projection angles than light received by the first structured surface  304 . The projection angle (e.g., Φ 9 , Φ 14 , Φ 18 ) below which a light beam may encounter the second structured surface  310  rather than the first structured surface  304  will be referred to as a threshold angle. Those of ordinary skill in the art will understand that where the transition region  312  has an appreciable extent, the threshold angle will become a threshold angle range. The threshold angle may be any angle chosen to suit the specific application of the optical lens  300 .  
         [0044]     To avoid visible light transmission discontinuities at the transition region  312 , the threshold angle may be the angle at which the percent transmission through the first structured surface  304  is essentially the same as the percent transmission through the second structured surface  310 . However, other appropriate criteria for selecting the threshold angle or the threshold angle range may be used depending on a particular application. This may occur, for example, when α 11  is equal to ninety (90) degrees and α 12  is essentially equal to α 13 . For example, the optical lens  300  may have a threshold angle approximately equal to forty-three (43) degrees and an angle δ (shown in  FIG. 2B ) approximately equal to two (2) degrees. Thus, in such exemplary embodiments, a light beam transmitted from the projection lens  104  with a projection angle of at least about forty-three (43) degrees (i.e., the threshold angle) may encounter the first structured surface  304 , and light with a projection angle less than about forty-three (43) degrees may encounter the second structured surface  310 .  
         [0045]     In exemplary embodiments of the present disclosure, the threshold angle or the threshold angle range may be selected based on the transmission of S- and P-polarized light through a conventional Fresnel lens as compared to a TIR Fresnel lens and the dispersion caused by these respective structures. For example, it may be determined by mathematical modeling of performance of an acrylic optical lens  300  that at angles greater than about 43 degrees, the transmission of both polarizations through the TIR Fresnel is higher than transmission through a conventional Fresnel lens. In addition, it may be determined by mathematical modeling of performance of an acrylic optical lens  300 , that for input angles greater than about 43 degrees, the dispersion caused by TIR Fresnel is less than that of the conventional Fresnel. Thus, the angle of about 43 degrees may be advantageously selected as a threshold angle for such exemplary embodiments. In other exemplary embodiments the optical lens  300  may have a threshold angle range of about 42 degrees to about 43 degrees. However, other threshold angles may be suitable for optical lenses made of other materials or constructed to achieve different optical performance.  
         [0046]     As shown in  FIG. 3B , a light beam  318  with a projection angle Φ 9  greater than the predetermined threshold angle may encounter the input surface  302 . The light beam  318  may be refracted at a first exit angle Φ 10 . The light beam  318  may next encounter the first structured surface  304  at the first reflective surface  306   b . The light beam  318  may approach at an incident angle Φ 11  (e.g., greater than a critical angle Φ c ) and reflect at substantially the same angle Φ 11  (e.g., total internal reflection occurs). The light beam  318  may then encounter the first refractive surface  308   b  at an incident angle Φ 12  and pass through the refractive surface  308   b  at a second exit angle Φ 13 .  
         [0047]     A light beam  320  may encounter the input surface  302  with a projection angle Φ 14  being less than the threshold angle. Therefore, the light beam  320  may be refracted at a first exit angle Φ 15  and encounter the second refractive surface  314   a  in the second structured surface  310  at an incident angle Φ 16 . The incident angle Φ 16  may be less than a critical angle Φ c16  at the second refractive surface  314   a , and therefore the light beam  320  may refract at a second exit angle Φ 17 . Similarly, a light beam  322  may encounter the input surface  302  with a projection angle Φ 18 . The projection angle Φ 18  may be less than the threshold angle and less than the projection angle Φ 14  of light beam  320 . The light beam may be refracted (e.g., at a first exit angle Φ 19 ) in a general direction towards the second structured surface  310 . The light beam  322  may encounter the second refractive surface  314   b  of the second structured surface  310  at an incident angle Φ 20  and refract at a second exit angle Φ 21 .  
         [0048]      FIGS. 4A-4C  show an optical lens  400  according the present disclosure. As one of ordinary skill in the art will understand, the optical lens  400  may be a semicircular shape. Although the entire semicircular shape is shown in  FIGS. 4A and 4B  for the purposes of the present disclosure, the optical lens  400  may generally be limited (e.g., trimmed) to the rectangular size of a projection screen  428  as shown in  FIG. 4C . The optical lens  400  may include a first structured surface  404  and a second structured surface  410  meeting at a transition region  412 . The first structured surface  404  and the second structured surface  410  may include a plurality of reflective and refractive surfaces (e.g., which are substantially similar to the surfaces  306 ,  308 ,  314 ,  316 ). In the exemplary embodiment, the first structured surface  404  may include a TIR Fresnel lens and the second structured surface  410  may include a conventional refractive Fresnel lens.  
         [0049]     As shown in  FIG. 4A , a projection lens  424  may transmit a plurality of light beams  426 . The light beams  426  may be transmitted at various projection angles in general directions towards the optical lens  400  and the projection screen  428 . As one of ordinary skill in the art will understand, the projection angle for each of the light beams  426  may lie in planes different from one another. For example, the projection angle for each of the light beams  426  may be determined in a plane including the light beam and a parent axis point  430  shown in  FIGS. 4A-4C . In the exemplary embodiment, the parent axis point  430  is situated outside a rectangular area of the optical lens  400  that corresponds to the projection screen  428 . In other embodiments, however, the parent axis point  430  may be situated within the rectangular area (e.g., centered within the projection screen  428 ).  
         [0050]     As shown in  FIG. 4A , those light beams  426  transmitted at projection angles greater than or equal to a predetermined threshold angle may encounter the first structured surface  404 ; and those light beams  426  transmitted at a projection angle less than the predetermined threshold angle may encounter the second structured surface  410 . In some exemplary embodiments, the threshold angle may be about forty-three (43) degrees. However, the threshold angle may be any angle chosen to suit the specific application, or it may be a threshold angle range.  
         [0051]      FIGS. 5A and 5B  show another exemplary embodiment of projection system  500  according to the present disclosure. The projection system  500  may include an enclosure  502  and a projection lens  504  with a projection lens angle β 2  (beta two). The projection system  500  may include an optical lens  510  and a projection screen  512  situated within the enclosure  502 . The projection system  500  may be, for example, an ultra-thin rear projection system. As one or ordinary skill in the art will understand, an ultra-thin rear projection system (e.g., projection system  500 ) may have an enclosure depth of less than twenty (20) percent of a diagonal of the projection screen (e.g.,  512 ).  
         [0052]     The projection system  500  may further include an aspheric mirror  506 . As one of ordinary skill in the art will understand, the aspheric mirror  506  may allow for a thinner enclosure  502  by employing offset optics, thus reducing the horizontal distance from the projection lens to the projection screen  512 . The exemplary embodiment may further include a cabinet mirror  508  within the enclosure  502 ; however, other embodiments may not require the cabinet mirror  508 . The cabinet mirror  508  may be useful for reflecting light transmitted from the projection lens  504  and the aspheric mirror  506 . For example, a light beam  516  may be transmitted from the projection lens  504  and reflected off the aspheric mirror  506  and the cabinet mirror  508  in a general direction towards the optical lens  510 . The light beam  516  may pass through the optical lens  510  in a general direction  514  towards a viewer of the projection system  500 .  
         [0053]     It will be apparent to those skilled in the art that various modifications and variations can be made in the structure and the methodology of the present disclosure, without departing from the spirit or scope of the invention. Thus, it is intended that the present disclosure cover the modifications and variations of the exemplary embodiments described herein, provided that they come within the scope of the appended claims and their equivalents.