Abstract:
A light beam polarization converter for converting non-polarized light beams of an illumination source into a single polarization state, which may be utilized in various electro-optical devices, such as liquid crystal projection type televisions. A polarization splitter film and a phase retardation film are utilized to make the incident light beams of a light source focused and refracted with an under plate. The light beam, upon passing through the under plate, goes through a series of optical processes of polarization splitting, reflection, total reflection and phase retardation, and subsequently becomes a light beam of a single polarization state output.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to light beam polarization devices and more particularly to a light beam polarization converter for electro-optical devices, such as a liquid crystal projection displays. 
     DESCRIPTION OF THE PRIOR ART 
     With the advent of the information technology (IT) age, there is an increasing demand for various electro-optical displays, such as liquid crystal projection type television displays. In this type of display, the light source is not inherently integrated, and thus an external source may be required for image display. As the demand for higher quality displays increases, it is becoming more and more important that the utilization efficiency of light sources should be enhanced. A conventional way to increase efficiency is to convert the non-polarized light beams of a light source into linearly polarized light beams having a single polarization state, as disclosed in, for example U.S. Pat. No. 5,122,895 (Polarization converter for converting randomly polarized light to linearly polarized light to Takanashi et al.). Wherein a conventional converter, the so-called P-S converter is disclosed. The P-polarized light component refers to the optical component of the electric field oscillation direction that is parallel to the plane of the incident light beam. The S-polarized light component is the optical component perpendicular to that plane. 
     As shown in prior art FIG. 1, in a conventional liquid crystal projection type television, the light beam emitted from a light source  10  is projected through a projection lens onto a display (not shown) through the processing of a parallelizing lens  11 , a diverging plate  12 , a P-S converter  13 , splitter lenses  14  and  15 , a reflecting mirror  16  and respective liquid crystal displays  301 ,  302  and  303 . The main function of the P-S converter  13  is to reduce the optical loss of light beams when screened through the liquid crystal displays  301 ,  302  and  303  for specific polarization. 
     FIG. 2 shows a schematic perspective view of a conventional P-S converter  70 . The non-polarized light beams I emitted from a light source travels from the bottom side of P-S converter  70 , is converted therein and emitted from the top side as a single S-polarized state light beam. 
     FIG. 3 shows a typical optical path of a light beam in a conventional P-S converter. The description is illustrated utilizing one (designated “I1”) of a plurality of light beams emanating from the light source. The light beam I 1  is incident to the P-S converter through an anti-reflection film  70 , and then subsequently becomes a light beam I 2  having both P- and S-polarization states. The light beam I 2  is then incident on a polarization state splitter film  73  with a P-component I 4  penetrating through the splitter film  73  and being converted by a half wave plate  78 . Light beam I 4  then travels further through an anti-reflection film  79  and becomes a light beam  16  of S-polarization state. The component of the light beam I 2  failing to penetrate through the splitter film  73  is reflected and becomes a light beam I 3  of S-polarization state, after which the light beam I 3  is reflected by a highly reflective film  75  and penetrates through an anti-reflection film  77 . Finally, the output thereof is a light beam  16  of S-polarization state. Since the above effect of polarization conversion may not be obtained if the light beam emitted from the light source is incident to the portion  81  as shown in FIG. 3, the conventional P-S converter may only achieve efficiencies of at best 50% in converting the polarization state of light beams. In addition to such lack of efficiency, the configuration of conventional P-S converters is complex and typically involves relatively high costs of production. It is also known in the art that a conventional display incorporating such a conventional converter is notorious for high power consumption. 
     SUMMARY OF THE INVENTION 
     In view of the above problems, the first object of the present invention is to provide a light beam polarization converter for converting an illumination source into a single polarization light source, which may convert the light at extremely low optical loss and is suitable for mass production in terms of production cost. 
     The second object of the present invention is to provide a light beam polarization converter for converting an illumination source into a single polarization light source, which is easy to use or to add on to a conventional apparatus. 
     To achieve the first object, the present invention provides a light beam polarization converter for converting an illumination light source into a polarization light source, comprising an under plate having an undulated lower surface and a ridged upper surface; a substrate having a ridged lower surface, substantially complementary to the upper surface of the under plate and facing therewith, and a ridged upper surface; a phase retardation film of high reflectivity disposed partially between the substrate and the under plate; a top cover having a lower surface, substantially complementary to the upper surface of the substrate and facing therewith, and an upper surface; and a polarization splitter film disposed between the substrate and the top cover. 
     For achieving enhanced optical performance, the ridge pitch of the ridged surfaces may be constant or varied, and the ridge lines thereof are arranged as being not parallel to each other, thus allowing greater freedom of converter design. Moreover, the lower surface of the under plate and the upper surface of the top cover may respectively have various undulations, such as cylindrical, spherical or non-spherical, corresponding to each other in a conjugate way to control the optical output angle, and thus enhance the transmitting efficiency of light beams while passing through the converter. 
     To achieve the second object, the present invention provides a light beam polarization converter for converting an illumination light source into a polarization light source, comprising an under plate having an undulated lower surface and a ridged upper surface; a substrate having a ridged lower surface, substantially complementary to the upper surface of the under plate and facing therewith, and a substantially flat upper surface; a phase retardation film of high reflectivity provided partially between the substrate and the under plate; a top cover film having a flat lower surface, substantially complementary to the upper surface of the substrate and facing therewith, and a ridged upper surface; a top cover having a lower surface, substantially complementary to the upper surface of the top cover film and facing therewith, and an upper surface; and a polarization splitter film provided between the upper surface of the top cover film and the lower surface of the top cover. 
     With the above top cover film, which is soft and flexible when joined with the top cover and the polarization splitter film, it is very convenient to apply this soft configuration onto the under plate and achieve the effect and advantage in accordance with the present invention. 
     With the configuration disclosed in accordance with the present invention, the light beam polarization converter is simple and easy to produce, and achieves optical efficiency no less than that of a conventional one. In particular, the present invention provides a significant advantage of quick adaptation to conventional optical devices. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The above and other features, effects and advantages of the light beam polarization of the present invention may be clearly understood from the following description of preferred embodiments in connection with the accompanying drawings, wherein 
     FIG. 1 is a schematic view of a conventional liquid crystal projection type television, showing an installation position and function of a P-S converter; 
     FIG. 2 is a perspective view showing a conventional P-S converter; 
     FIG. 3 illustrates an exemplary optical path traversing a conventional P-S converter; 
     FIG. 4 is a cross sectional view showing a light beam polarization converter in accordance with one embodiment of the present invention; 
     FIG. 5 shows the optical path occurring in the light beam polarization converter in accordance with one embodiment of the present invention; 
     FIG. 6 shows the optical path occurring in the light beam polarization converter in accordance with another embodiment of the present invention; 
     FIG. 7 is a perspective view of the light beam converter in accordance with one embodiment of the present invention, wherein the ridge lines are not parallel to each other; 
     FIG. 8 shows the relationship between the reflectivity to P-S polarized component and the wavelength of a light beam with respect to a typical phase retardation film of high reflectivity; 
     FIG. 9 shows the relationship between the relative phase difference to P-S polarized component and the wavelength of a light beam with respect to a typical phase retardation film of high reflectivity; 
     FIG. 10 shows the relationship between the transmissivity of a P-S polarized component and the wavelength of a light beam with respect to a typical polarization splitter film; 
     FIG. 11 shows the relationship between the reflectivity to P-S polarized component and the wavelength of a light beam with respect to a typical polarization splitter film; 
     FIG. 12 is a perspective view of the light beam polarization in accordance with one embodiment of the present invention, wherein the upper surface of the top cover has a spherical undulation; 
     FIG. 13 is a perspective view of the light beam polarization in accordance with another embodiment of the present invention, wherein the upper surface of the top cover has a regular square protuberances; and 
     FIG. 14 is a sectional view of the light beam polarization converter in accordance with another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 4, a sectional view of a light beam polarization converter  100  in accordance with one embodiment of the present invention is shown. The converter  100  has a laminate configuration, comprising an under plate  110 , a substrate  120  and a top cover  130 , joined together in the above sequence. A phase retardation film (not shown) is provided partially between the under plate  110  and the substrate  120 , whereas a polarization splitter film is provided between the substrate  120  and the top cover  130 . The under plate  110  has a lower surface of undulation with a layer of anti-reflection film being coated thereon, which may increase the upward transmissivity of the light beam I from the bottom. The under plate  110  has a ridged upper surface, the ridge angle between two neighboring ridges is 90 degrees. Accordingly, the ridge angles of the upper and lower surfaces of the substrate  10  and the lower surface of the top cover are all 90 degrees. The top cover  130  has a substantially flat upper surface on which a layer of anti-reflection film may be optionally coated, to increase the transmissivity of light through the converter. 
     The phase retardation film is provided partially between the under plate  110  and the substrate  120  in a way the incident light beam I which penetrates the under plate  110  may be focused by the undulated surface thereof and then penetrates the substrate  109  through the portions without phase retardation film thereon. The lower surface of the under plate  110  need not be of specific profile, but is designed for the purpose of converging the incident light beam I which thereafter penetrates through the portions having no phase retardation film and then travels into the substrate  120 . The phase retardation film may be applied through evaporation or coating. 
     In one embodiment of the present invention, the ridge angle between two neighboring ridges on the ridged surfaces may be 90 degrees. Therefore, the incident light beam may go through continuous reflection or total reflection on the lower surface of the substrate  120 . For matching the output specification of the converter  100 , the composition of the polarization splitter film between the top cover  130  and substrate  120  may be adjusted. to provide linearly or otherwise polarized light beam output. 
     In producing the converter  100  in accordance with the present invention, the top cover  130  and substrate  120  should be joined together for a simple and feasible polarization splitter film. In other words, both lateral sides of the polarization splitter film should be made of optically transparent material, such as polymethylmethacrylate (PMMA), polycarbonate (PC) or ARTON™. The top cover  130  may be produced through spraying, pouring, injection molding of smooth plating in a mass production therefor. 
     With reference to FIGS. 5 and 6, an optical path is shown of the light beam I entering through the under plate  110 . The S-polarized component of the light beam is represented by a solid arrow, and the P-component by a hollow arrow. The light beam I is converged by the undulated surface and then enters into the substrate  120  through the interface between the under plate  110  of no phase retardation film and the substrate  120 . The P-polarized component is not influenced by this configuration, and may directly emanate from the upper surface  120  of the top cover  130 . The S-polarized component is continuously reflected by the ridged surfaces and is consequentially transformed into a light beam having both P- and S-polarized components simultaneously. Thereafter, the P-component in turn passes through the polarization splitter film and the top cover  130  and emits therefrom. The S-component is progressively reflected and transformed into a light beam having both P- and S-components simultaneously. FIG. 5 shows an embodiment wherein the ridge pitches of the upper and lower ridged surfaces are equal. FIG. 6 shows another embodiment wherein the ridge pitches of the upper and lower surfaces are not equal. The above two arrangements may achieve substantially the same effect. 
     With reference to FIG. 7, there is disclosed another converter  100  in accordance with the present invention, wherein the ridge pitches of the upper and lower ridge lines are not equal and the upper and lower ridge lines are not parallel to each other, which increases the freedom in designing the phase retardation film. It should be noted that any conventional reflection film may be advantageously utilized to achieve the effect by the phase retardation film disclosed in the present invention if the upper and lower ridge lines are not parallel. On the other hand, it will be difficult to design and produce the phase retardation film under the parallel condition. A possible solution is to add certain magnetic material into the film. Since the non-parallel condition for the ridgelines is easy to achieve, the present invention provides a favorable and simple solution. 
     For clarifying the features of the present invention, the configuration and inventive principles of the present invention is in detail described below. 
     The under plate  110  has a lower surface of cylindrical, spherical or non-spherical undulation and an upper ridged surface. The upper surface may be pyramidal if the lower surface of the under plate  110  is of spherical or non-spherical undulation for focusing the incident light beam as a point light source. To sum up, the fundamental function of the under plate is to ensure that the incident light beam enters the substrate and the top cover at high efficiency. The supplementary function of the upper surface of the under plate is to provide a place for applying the phase retardation film, and alternatively the upper surface of the lower plate may be ridged. Notwithstanding the above, any modification of the surface profile other than the ridged surface may be deemed as falling within the scope of the present invention as defined in the claims. 
     The upper and lower surfaces of the substrate are ridged and having ridge angles, different or identical from each other. Their ridge pitches may be neither equal nor constant, so as to avoid the morie effect. The neighboring ridged surfaces should be substantially complementary to each other, so as to facilitate the insertion of a film between the following attachment. 
     In consideration of the production process, the substrate may be made of any optical material, such as PMMA, PC or ARTON™ plastic or various glasses. It is necessary to determine in advance the refractivity of the substrate in designing the optical film. Table 1 shows the relationship between the water absorptivity and refractivity over different wavelengths for ARTON. FIGS. 10 and 11 show the function of the phase retardation film and the corresponding polarization splitter film. 
     It may be noted that in practical production, the phase retardation film is applied partially on the upper surface of the under plate, with exception to the convex portion thereof. Therefore, the phase retardation film may first be applied wholly on the upper surface of the under plate and be partially removed at the unnecessary (convex) portion through polishing. For example, if the substrate is made of PMMA having optical coefficient 1.53, the ridge angle of the lower surface is 90 degrees, and the wavelength of the incident light beam is 400 to 700 nm, the typical composition of the film and its thickness may be inferred from table 2. If the substrate is made of ARTON, under the same conditions as above, table 3 shows the composition. 
     The polarization splitter film is provided between the top cover and the substrate, which may screen particularly polarized light beam as the output while making any differently polarized light beam reflected back to the inside of the substrate, once the top cover and the substrate are joined together. For example, under the condition that the substrate is made of PMMA having optical coefficient 1.53, the ridge angle of the upper surface is 90 degrees and the wavelength of the incident light beam is 400 to 700 nm, the polarization splitter film may be formed through multi-layer evaporation coating with the material and film thickness as shown in table 4. If the substrate is made of ARTON as shown in table 1 under 40° C., the material and its thickness as shown in table 5 may be used. 
     For increasing the transmissivity by the light beam, the upper surface of the top cover may be applied with an anti-reflection film. Moreover, its upper surface may be substantially flat or undulated as shown in FIGS. 12 and 13, for controlling the output angle of the incident light beam as being in parallel or of any other angle. For example, the light beam is incident on the under plate with an angle almost in parallel thereto, since the upper surface of the top cover has an undulated surface complementary with the lower surface of the under plate in a conjugate relationship, and thus the output angle of the polarized light beam may be controlled. In addition, the diffusion angle of the light beam may be controlled to determine the output illumination level over different view angles. 
     With reference to FIG. 14, the ridged portions at the interface between the substrate  120  and the top cover  130  may be avoided to form a one-side flat substrate. The lower surface of the top cover may be applied with a polarization splitter film thereon, and thereafter a top cover film  39  is formed onto the lower surface of the top cover through spraying or pouring. As a result, the top cover made of soft material may be combined with the polarization splitter film and the top cover film to become a soft and flexible configuration, which is easy to use. In use, the converter may be divided into two portions, upper and lower, at the flat surface of the substrate. The thus divided portions may be applied respectively at two sides of a transparent flat optical device to provide the function of polarization splitting. 
     The above description is for an illustrative purpose in accordance with one embodiment of the polarization state converter of the present invention. Any modification or amendment which may be achieved by those skilled in the art will fall within the scope and spirit of the present invention. That is, the real and distinctive scope of the present invention should be defined by the accompanying claims. 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 ARTON FX26 
               
               
                 Main Chain: NORBORNENE 
               
               
                 Branch Chain: polyester function group 
               
             
          
           
               
                   
                 Measured wavelength 
               
             
          
           
               
                   
                 794.76 nm 
                 656 nm 
                 588 nm 
                 486 nm 
                 436 nm 
               
               
                   
                   
               
             
          
           
               
                 Absorptivity (%) 
                   
                   
                   
                   
                   
               
               
                 0.01 
                 1.5161 
                 1.5198 
                 1.5227 
                 1.5298 
                 1.5354 
               
               
                 0.25 
                 1.5163 
                 1.5200 
                 1.5230 
                 1.5300 
                 1.5357 
               
               
                 temperature (° C.) 
               
               
                 30 
                 1.515 
                 1.519 
                 1.521 
                 1.528 
                 1.534 
               
               
                 40 
                 1.514 
                 1.518 
                 1.520 
                 1.527 
                 1.533 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Typical phase retardation film as to composition and thickness 
               
               
                   
                 (unit: nm, substrate: PMMA) 
               
               
                   
                   
               
             
             
               
                   
                 ZnS 202.21, MgF 2  200.00, ZnS 83.66, MgF 2  200.00, 
               
               
                   
                 ZnS 58.46, MgF 2  203.95, ZnS 200.19, MgF 2  202.94, 
               
               
                   
                 ZnS 78.42, MgF 2  184.10, ZnS 210.19, MgF 2  196.22, 
               
               
                   
                 ZnS 235.49, MgF 2  404.42, ZnS 105.38, MgF 2  165.89, 
               
               
                   
                 ZnS 219.69, MgF 2  207.75, ZnS 211.30, MgF 2  184.61, 
               
               
                   
                 ZnS 57.30, MgF 2  264.81, ZnS 168.19, MgF 2  200.24, 
               
               
                   
                 ZnS 95.51, MgF 2  146.82, ZnS 141.62, MgF 2  62.71, 
               
               
                   
                 ZnS 61.65, MgF 2  245.83, ZnS 203.82, MgF 2  110.37, 
               
               
                   
                 ZnS 49.58, MgF 2  136.26, ZnS 92.75, Ag 61.14 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Typical phase retardation film as to composition and thickness 
               
               
                   
                 (unit: nm, substrate: ARTON ™) 
               
               
                   
                   
               
             
             
               
                   
                 ZnS 202.44, MgF 2  200.00, ZnS 83.68, MgF 2  200.00, 
               
               
                   
                 ZnS 60.66, MgF 2  206.53, ZnS 200.00, MgF 2  200.00, 
               
               
                   
                 ZnS 85.56, MgF 2  176.92, ZnS 207.83, MgF 2  186.64, 
               
               
                   
                 ZnS 228.17, MgF 2  450.70, ZnS 102.87, MgF 2  163.44, 
               
               
                   
                 ZnS 223.36, MgF 2  193.18, ZnS 206.10, MgF 2  180.03, 
               
               
                   
                 ZnS 62.29, MgF 2  255.92, ZnS 180.50, MgF 2  238.48, 
               
               
                   
                 ZnS 81.97, MgF 2  133.27, ZnS 132.49, MgF 2  101.40, 
               
               
                   
                 ZnS 62.55, MgF 2  264.24, ZnS 189.91, MgF 2  85.94, 
               
               
                   
                 ZnS 59.96, MgF 2  140.79, ZnS 89.76, Ag 60.92 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Typical polarization splitter film as to composition and thickness 
               
               
                   
                 (Unit: nm, substrate: PMMA) 
               
               
                   
                   
               
             
             
               
                   
                 ZnS 20.99, Na 3 AIF 6  98.19, ZnS 47.15, Na 3 AIF 6  99.16, 
               
               
                   
                 ZnS 29.58, Na 3 AIF 6  141.21, ZnS 40.27, Na 3 AIF 6  94.87, 
               
               
                   
                 ZnS 44.40, Na 3 AIF 6  119.53, ZnS 45.04, Na 3 AIF 6  92.66, 
               
               
                   
                 ZnS 154.73, Na 3 AIF 6  169.16, ZnS 15.99, Na 3 AIF 6  75.86, 
               
               
                   
                 ZnS 87.82, Na 3 AIF 6  283.13, ZnS 65.74, Na 3 AIF 6  96.03, 
               
               
                   
                 ZnS 33.77, Na 3 AIF 6  110.39, ZnS 70.09, Na 3 AIF 6  283.27, 
               
               
                   
                 ZnS 73.35, Na 3 AIF 6  100.38, ZnS 36.82, Na 3 AIF 6  99.62, 
               
               
                   
                 ZnS 46.08, Na 3 AIF 6  316.85, ZnS 97.96, Na 3 AIF 6  239.98, 
               
               
                   
                 ZnS 80.59, Na 3 AIF 6  234.61, ZnS 93.97, Na 3 AIF 6  249.77, 
               
               
                   
                 ZnS 108.62, Na 3 AIF 6  120.21 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
             
           
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 Typical polarization splitter film as to composition and thickness 
               
               
                   
                 (Unit: nm, substrate: ARTON ™) 
               
               
                   
                   
               
             
             
               
                   
                 ZnS 10.57, Na 3 AIF 6  125.72, ZnS 51.25, Na 3 AIF 6  55.35, 
               
               
                   
                 ZnS 48.71, Na 3 AIF 6  147.30, ZnS 28.53, Na 3 AIF 6  110.45, 
               
               
                   
                 ZnS 49.03, Na 3 AIF 6  119.80, ZnS 40.04, Na 3 AIF 6  100.49, 
               
               
                   
                 ZnS 153.25, Na 3 AIF 6  326.16, ZnS 97.71, Na 3 AIF 6  276.36, 
               
               
                   
                 ZnS 56.00, Na 3 AIF 6  93.48, ZnS 35.15, Na 3 AIF 6  113.18, 
               
               
                   
                 ZnS 78.81, Na 3 AIF 6  287.44, ZnS 62.71, Na 3 AIF 6  104.21, 
               
               
                   
                 ZnS 37.74, Na 3 AIF 6  106.49, ZnS 51.39, Na 3 AIF 6  307.32, 
               
               
                   
                 ZnS 91.51, Na 3 AIF 6  254.75, ZnS 80.68, Na 3 AIF 6  236.81, 
               
               
                   
                 ZnS 93.10, Na 3 AIF 6  260.58, ZnS 104.44, Na 3 AIF 6  134.42,