Abstract:
A method, apparatus and system for polarization conversion and recycling by using a half-pyramid shaped reflector with multiple reflective surfaces, or said reflector assembly, to obtain a desirable polarization rotation effect. The disclosed half-pyramid reflector comprises a plurality of reflective surfaces, which are formed so that an incoming beam passing perpendicularly through the entrant surface is reflected three times inside the device and leaves the exit surface with the direction of polarization being rotated 90 degrees. The preferred embodiments of polarization conversion systems using the invented apparatus are included. Without employing any waveplate component, the disclosed system is not sensitive to wavelength variations of the light source, temperature changes, and polarization alignment errors. Typical application of this invention includes polarization conversion and recycling for projection systems with polarization dependent spatial light modulation panels, such as LCD (Liquid Crystal Display) and LCOS (Liquid Crystal On Silicon).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is in-part a continuation of the U.S. provisional Patent Application Ser. No. 60/424,171 filed Nov. 7, 2002, entitled “Polarization conversion and recycling method and apparatus”. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to a polarization conversion and recycling method that features a polarization converting apparatus using a uniquely designed half-pyramid shaped reflector with multi-reflection to achieve a desirable polarization rotation function. The present invention further relates to polarization conversion and recycling systems using the same.  
           [0004]    2. Description of the Prior Art  
           [0005]    Polarized light sources are utilized in various applications such as LCD (Liquid Crystal Display) and LCOS (Liquid Crystal On Silicon) projection systems. An un-polarized light source can be decomposed by a polarizing beam splitter (PBS) into a linear s-polarization component and an orthogonal p-polarization component.  
           [0006]    A commonly used method of producing polarized light for a LCD projection panel comprises the use of a PBS prism cube or a reflective PBS plate to separate s and p polarized beams into reflection and transmission, respectively. One linearly polarized component of the light is transmitted by the PBS and directed to the LCD panel, while the orthogonal component is reflected away in a different direction. The regular PBS could only be used near 45 degrees incidence with small numerical apertures. Another kind of PBS, the wire grid PBS, has attracted special interest because it can be used in a perpendicular incidence with a large incident cone angle, as disclosed in U.S. Pat. No. 6,208,463 and U.S. Pat. No. 6,243,199.  
           [0007]    It is evident that conventional reflective polarizers with no polarization conversion and recycling device attached are inefficient, due to the fact that, during s-p polarization split, severe loss of light occurs and only a maximum of one-half of the available light from the source can be converted to polarized light for transmission.  
           [0008]    Many efforts have been made to increase the efficiency of polarization conversion and the results can be found in the prior arts and commercial products. Some of the polarizing converting systems incorporate a waveplate with polarizing beam splitter to make use of both polarizations. For example, by introducing a half waveplate, one could convert a p-beam into a s-beam or vice versa to recover otherwise wasted component. A mirror or a prism has to be employed to reflect the converted beam in the same direction as the other beam does. Examples can be found in U.S. Pat. No. 6,046,856 and U.S. Pat. No. 5,884,991.  
           [0009]    Another commonly proposed approach involves the implementation of units that incorporate a plurality of prisms arranged in an array with PBS coating or reflecting surfaces formed between the prisms. Light from the source is directed towards the prisms by a multi-lens optical array. One polarization is passed directly through the prisms while the other polarization is directed sideways towards the mirror surfaces between the prisms. Mirrors redirect the other polarization again into the useful beam. Waveplate strips, arranged on the exiting surfaces, rotate the other polarization so that it is the same as the passed polarization. The width of the elements in the lens array is twice the width of the PBS prism elements so that the structure can make full use of the illumination area. Implementations of such mechanism can be found in U.S. Pat. No. 6,337,759 and U.S. Pat. No. 6,154,320.  
           [0010]    In summary, previous work shows that almost all current polarization conversion systems have to utilize half-wave or quarter-wave phase retardation plates to increase conversion efficiency. However, the methodology of employing waveplates in a polarization converter inevitably leads to some problems. One of the disadvantages is that the waveplates will not work properly if the wavelengths of the illumination beam deviate considerably from the center wavelength. Another disadvantage is that the waveplates are sensitive to changes of the incident angles and the direction of polarization. Furthermore, a waveplate made of polymer is thermally unstable, while although a waveplate made of crystal can tolerate high temperature and rapid temperature change, its cost is usually too high. These issues have restricted the use of waveplate in some practical applications, particularly in those applications where working with a high flux of broadband light and/or a high operation temperature is unavoidable.  
           [0011]    In some literature from the prior arts, a variety of proposals have been made to achieve polarization rotation and conversion by using prisms. Among them, U.S. Pat. No. 4,822,150 disclosed an optical device for rotating the polarization of a light beam. In one embodiment of the invention, the device comprises a prism, which is adapted to rotate the polarization of a linearly polarized beam of radiation by 90 degrees and the propagation direction of the beam is altered by 90 degrees. U.S. Pat. No. 4,252,410 disclosed a method and apparatus for rotating the polarization vector of a substantially linearly polarized beam through a selected angle by using three or four reflections with the output beam being substantially free of ellipticity. U.S. Pat. No. 5,751,482 disclosed an achromatic polarization rotating right angle prism system for rotating the plane of polarization by 90 degrees. The direction of travel of the beam may be altered by 90 degrees or the beam may continue on in the same line. These findings and derived systems are often too complicated to be used in practical polarization applications.  
           [0012]    To address the problems and drawbacks in prior art polarization conversion systems, the current invention introduces a unique apparatus of a half-pyramid shaped reflector, either a half-pyramid shaped prism reflector or a half-pyramid shaped hollow reflector, which can be assembled and integrated in a polarization conversion system to achieve the required polarization rotation, conversion and recycling. Unlike the polarization converting systems published in the prior arts or used in the commercial products, no waveplate or retardation plate is employed in the invented systems.  
         SUMMARY OF INVENTION  
         [0013]    The primary objective of the present invention is to provide polarization rotation and converting devices and systems for rotating the direction of polarization of the incoming beam and efficiently converting the otherwise wasted polarizing beam from a light source into the wanted polarization.  
           [0014]    It is yet another objective of the present invention to provide a reflector apparatus for polarization rotation, which is not sensitive to wavelength variations of the light source.  
           [0015]    It is yet another objective of the present invention to provide a reflector apparatus for polarization rotation, which is not sensitive to temperature changes.  
           [0016]    It is yet another objective of the present invention to provide a reflector apparatus for polarization rotation, which is not sensitive to polarization alignment errors.  
           [0017]    It is yet another objective of the present invention to provide a polarization recovery system without any waveplate employed.  
           [0018]    It is a further objective of the present invention to provide a polarization recovery apparatus and systems for use in image projection, light projection and other display applications.  
           [0019]    To achieve the above objectives, the present invention discloses an apparatus of a half-pyramid shaped reflector, comprising three reflective surfaces, not mutually perpendicular, but formed at such angles that the incoming beam perpendicularly passing through the entrant surface is reflected three times inside said reflector and leaves the exit surface with the direction of polarization being rotated 90 degrees.  
           [0020]    Several preferred sample embodiments are disclosed by integrating or combining said apparatus into different optical arrangements, each configuration comprising one or more said apparatus of half-pyramid shaped reflectors, such as, said reflector with triangular entrance/exit surface, an assembly of two said reflectors with square entrance/exit surface, a strip of said reflectors, and an array of said reflectors. The disclosed polarization converting system has the advantage of high converting efficiency, stability at high light flux and tolerance to high temperature. Other advantages of the disclosed system, resulting from no waveplate employed in the disclosed system, include its insensitivity to wavelength variations of the light source, to temperature changes, and to polarization alignment errors.  
           [0021]    In addition, for its simplicity in structure and ease in fabrication, the invented apparatus of half-pyramid shaped reflectors and derived polarizing converter systems have substantial benefits over waveplate-dependent polarization conversion systems and are potentially useful in many polarization conversion applications. A typical application of this invention is to provide a polarized light source with improved efficiency for the projection systems utilizing polarization dependent spatial light modulation panels, either transmissive or reflective, such as LCD (Liquid Crystal Display) and LCOS (Liquid Crystal On Silicon). By further customizing and configuring the disclosed apparatus, the disclosed method can encompass more embodiments and be adopted into more polarization converting systems, including the polarization systems where no polarization recovering device exists previously, and polarization conversion systems where the waveplate works as the key polarization converting and recycling component.  
           [0022]    The other features and advantages of the present invention will become more evident from the following descriptions and the preferred embodiments as set forth hereinafter. For convenience of illustration, the abbreviation “HP” will be used to identify the Half-Pyramid structure of said reflector in the description thereafter. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0023]    The detailed description, not intended to limit the present invention solely will best be understood in conjunction with the accompanying drawings, where similar elements will be represented by the same reference symbol, in which:  
         [0024]    [0024]FIG. 1 is a perspective structural view of a model of the half pyramid reflector, illustrating the geometry and basic concept of operation of the invented apparatus.  
         [0025]    FIGS.  2 ( a )- 2 ( d ) present an embodiment of the invented half pyramid reflector shown in FIG. 1, illustrating the geometry and structure of a disclosed HP prism reflector. FIG. 2( a ) shows a front view of the HP prism reflector thereof, FIG. 2( b ) shows a side view of the apparatus in FIG. 2( a ), FIG. 2( c ) shows a top view of the apparatus in FIG. 2( a ), and FIG. 2( d ) shows a perspective view of the HP prism reflector thereof. The optical path inside the disclosed HP prism reflector is also shown in FIG. 2, for a beam perpendicularly incident to the entrance surface.  
         [0026]    FIGS.  3 ( a )- 3 ( f ) are explanatory views to exhibit the optical path inside the invented HP prism reflector shown in FIG. 2, for an incident beam generally not perpendicular to the entrance surface. Similar to FIGS.  2 ( a )- 2 ( d ), FIG. 3( a ) is a front view of the HP prism reflector thereof, FIG. 3( b ) is a side view of the apparatus in FIG. 3( a ), FIG. 3( c ) is a top view of the apparatus in FIG. 3( a ), and FIG. 3( d ) is a perspective view of the HP prism reflector thereof. FIG. 3( e ) and FIG. 3( f ) are cross-sectional views taken along lines E-E and F-F in FIG. 3( a ), respectively.  
         [0027]    [0027]FIG. 4 illustrates a pyramid shaped polarizing converter with a square entrance/exit surface, which comprises an assembly of two HP prism reflectors shown in FIG. 2.  
         [0028]    FIGS.  5 ( a )- 5 ( c ) illustrate a variation on the embodiments of a polarizing converter with a square entrance/exit surface, which comprises four HP prism reflectors shown in FIG. 2. FIG. 5( a ) is a front view of said prism reflector assembly thereof. FIG. 5( b ) is a side view of FIG. 5( a ). FIG. 5( c ) is a perspective view of said apparatus thereof.  
         [0029]    FIGS.  6 ( a )- 6 ( d ) present another embodiment of the invented half pyramid reflector shown in FIG. 1, illustrating the geometry and structure of a disclosed HP hollow reflector being formed by three reflecting mirror plates. FIG. 6( a ) shows a front view of the HP hollow reflector thereof, FIG. 6( b ) shows a side view of the apparatus in FIG. 6( a ), FIG. 6( c ) shows a top view of the apparatus in FIG. 6( a ), and FIG. 6( d ) shows a perspective view of the HP hollow reflector thereof.  
         [0030]    [0030]FIG. 7 illustrates a pyramid shaped polarizing converter with a square entrance/exit surface, which comprises an assembly of two HP hollow reflectors as shown in FIG. 6.  
         [0031]    FIGS.  8 ( a )- 8 ( c ) illustrate a variation on the embodiments of a polarizing converter with a square entrance/exit surface, which comprises four HP hollow reflectors as shown in FIG. 6. FIG. 8( a ) is a front view of said hollow reflector assembly thereof. FIG. 8( b ) is a side view of FIG. 8( a ). FIG. 8( c ) is a perspective view of FIG. 8( a ) thereof.  
         [0032]    FIGS.  9 ( a )- 9 ( d ) illustrate a schematic configuration of a polarizing converter with a strip shaped entrance/exit surface, which comprises a plural number of pyramid shaped HP assemblies. FIG. 9( a ) shows a front view of the HP reflector strip thereof, FIG. 9( b ) shows a side view of the apparatus in FIG. 9( a ), FIG. 9( c ) shows a top view of the apparatus in FIG. 9( a ), and FIG. 9( d ) shows a perspective view of the HP reflector strip thereof.  
         [0033]    FIGS.  10 ( a )- 10 ( c ) show a schematic configuration of a polarizing converter comprising a HP prism reflector array. FIG. 10( a ) shows a front view of the HP reflector array thereof, FIG. 10( b ) shows a side view of the apparatus in FIG. 10( a ), FIG. 10( c ) shows a perspective view of the HP reflector array thereof.  
         [0034]    [0034]FIG. 11 illustrates the principle of operation for a polarization conversion and recovery system according to an embodiment of the invention, which comprises a pyramid shaped HP prism reflector assembly as shown in FIG. 4, a polarizing beam splitter and a right angle prism.  
         [0035]    FIGS.  12 ( a )- 12 ( b ) illustrate another schematic configuration of a polarization conversion and recovery system, which comprises multiple HP prism reflector strips shown in FIG. 9, and multiple polarizing beam splitter prism strips. FIG. 12( a ) is a front schematic view of the system thereof. FIG. 12( b ) is a perspective schematic view of the system shown in FIG. 12( a ).  
         [0036]    [0036]FIG. 13 shows a schematic view of an illumination system for an image projection application utilizing linearly polarized light source. The system consists of a pyramid shaped HP prism assembly, a PBS plate, a reflective mirror, a light source, a collimation lens, a focusing lens and an integrator rod.  
         [0037]    FIGS.  14 ( a )- 14 ( c ) present a schematic configuration for a polarization recycling system according to an embodiment of the invention, which includes a HP hollow reflector assembly as shown in FIG. 8, a reflective PBS plate and a light pipe integrator. FIG. 14( a ) is a cross-sectional view of the system. FIG. 14( b ) shows a side view of the system. FIG. 14( c ) is a perspective schematic view of the system thereof.  
     
    
     DETAILED DESCRIPTION  
       [0038]    The present invention is further described based on several sample embodiments, but embodiments of this invention are not limited to these examples. All embodiments demonstrate the usefulness of the invention and its versatility in a variety of polarization rotating, converting, and recycling applications.  
         [0039]    [0039]FIG. 1 is a conceptual construction view showing a model of HP reflector, which comprises four triangular surfaces with four vertexes A, C, B, and D, wherein the surface s 1  (BCD), in the shape of an isosceles right triangle, denotes the incident light entrance surface and light exit surface; the surface s 2  (CDA), surface s 3  (BAC) and surface s 4  (DBA) denote three reflecting surfaces adjacent to each other. The reflecting surface s 3  is perpendicular to the entrance/exit surface s 1 . The other two reflecting surfaces, surface s 2  and surface s 4 , are both at a 45 degrees angle with respect to surface s 1  to form a half-pyramid shaped reflector.  
         [0040]    To illustrate the basic principle of the polarization rotation mechanism of said HP reflector, a linearly polarized beam  11 , perpendicular to surface s 1 , is transmitted through s 1  plane to reach the first reflective surface s 2 . The beam is continually reflected from the surface s 2  to the second reflective surface s 3 . The surface s 3  then reflects the beam to the third reflective surface s 4 . Finally, the surface s 4  redirects the beam toward the surface s 1 . As the result of multiple reflections inside said reflector, the beam  12 , exiting through the surface s 1  in the reverse direction, has its polarization direction being rotated 90 degrees from the polarization direction of the incoming beam  11 , as shown in FIG. 1.  
         [0041]    Consequently, it can be derived that the linear polarized beam, perpendicularly entering on the left (or right) portion of the surface s 1 , being reflected three times internally in the HP reflector, will exit from the right (or left) portion of the surface s 1  with the polarization direction being rotated by 90 degrees from the polarization direction of the incoming beam. Therefore, the characteristics of said HP reflector can be well used as a polarizing rotation apparatus for polarization conversion systems.  
         [0042]    FIGS.  2 ( a )- 2 ( d ) present an embodiment of the invented half pyramid reflector shown in FIG. 1. FIG. 2( a ) is a front view of the HP prism reflector  20 , wherein the surface s 1  (BCD) is the beam entrance/exit surface, in the shape of an isosceles right triangle. FIG. 2( b ) is a side view of said HP prism reflector in FIG. 2( a ), wherein the surface s 3  (BAC) is a reflective surface perpendicular to the surface s 1 . FIG. 2( c ) is a top view of said HP prism reflector wherein the triangular surface s 4  (DBA) and s 2  (CDA) are two reflective surfaces, both at a 45 degrees angle respect to surface s 1 . FIG. 2( d ) is a perspective view of said HP prism reflector. Normally, the surfaces s 2 , s 3  and s 4  should have high reflection coatings and surface s 1  should have anti-reflection coating.  
         [0043]    The light path sequence for an incident beam perpendicular to the entrance surface s 1  is also shown in FIG. 2. Cartesian coordinates X, Y are shown in FIG. 2 ( a ) and a Z-axis (not shown) perpendicular to the XY plane points out of the page. Cartesian coordinates Y, Z are shown in FIG. 2( b ) with a X-axis (not shown) perpendicular to the YZ plane and pointing into the page. Cartesian coordinates X, Z are shown in FIG. 2( c ) with a Y-axis (not shown) perpendicular to the XZ plane and pointing out of the page. The incident beam  21  normal to surface s 1  is reflected three times inside the HP prism reflector  20 , sequentially by surfaces s 2 , s 3 , and s 4 , and exits surface s 1  in the reverse direction (denoted by beam  22 ). The arrow tail (a circle with a cross inside) in FIG. 2( a ) denotes the beam entrance point on surface s 1 . The arrowhead (a circle with a dot in it) in FIG. 2( a ) denotes the beam exit point on surface s 1 . It is concluded that, for a normal incident lineally polarized beam, the exiting beam from HP reflector has its polarization direction being rotated 90 degrees from the polarization direction of the incoming beam.  
         [0044]    FIGS.  3 ( a )- 3 ( f ) further exhibit the optical path inside an invented HP prism reflector, for an incident beam generally not perpendicular to the entrance surface. Similar to FIGS.  2 ( a )- 2 ( d ), FIG. 3( a ) is a front view of the HP prism reflector, FIG. 3 ( b ) is a side view of the apparatus in FIG. 3( a ), FIG. 3( c ) is a top view of the apparatus in FIG. 3( a ), and FIG. 3( d ) is a perspective view of the HP prism reflector. FIG. 3( e ) and FIG. 3( f ) are cross-sectional views taken along lines E-E and F-F in FIG. 3( a ), respectively. In FIG. 3( a ), Cartesian coordinates X, Y are shown and a Z-axis (not shown) perpendicular to the X- and Y-axes points out of the page. Cartesian coordinates Y, Z are shown in FIG. 3( b ) and a X-axis (not shown) perpendicular to the YZ plane points into the page. The YZ plane defines the plane parallel to the plane of incident beam  31  (the E-E plane in FIG. 3( a ) and FIG. 3( e )). In FIG. 3( c ), Cartesian coordinates X, Z are shown and a Y-axis (not shown) perpendicular to the X- and Z-axes points out of the page. The XZ plane defines the plane parallel to the plane of exit beam  32  (the F-F plane in FIG. 3( a ) and FIG. 3( f )).  
         [0045]    As shown, a lineally polarized beam  31  is incident at a tilted angle with respect to the Y-axis and Z-axis in a plane (the E-E plane) parallel to the YZ plane. The incident beam  31  is refracted when it enters into the surface s 1  (BCD) toward surface s 2  (CDA), where the refraction angle is dependent on the refractive indices (air and glass) and the orientation of incident light. The beam is further reflected from the surface s 2  to the surface s 3 . The reflective surface s 3  then continually reflects the beam toward the surface s 4 . The reflective surface s 4  redirects the beam toward the surface s 1 . Finally, the beam is refracted from the surface s 1  and exits the HP prism reflector in a plane (the F-F plane) parallel to the XZ plane. As the result of tilted incidence, the exiting beams  32  emerged from the surface s 1  has its polarization direction being rotated from the polarization direction of the incoming beam  31 , but by an angle generally not equal to 90 degrees (or the exit beam may be elliptically polarized). The arrow tail (a circle with a cross inside) in FIG. 3( a ) denotes the beam entrance point on surface s 1 . The arrowhead (a circle with a dot in it) in FIG. 3( a ) denotes the beam exit point on surface s 1 .  
         [0046]    [0046]FIG. 4 shows a perspective view of a pyramid shaped polarizing converter  40 , which is assembled by two HP prism reflectors (HP prism reflector  20  as shown in FIG. 2), with their side reflective surfaces (s 3  in FIG. 2) cemented together and their entrance surfaces (s 1  in FIG. 2) coplanar, to form a square shaped entrance/exit surface. The pyramid shaped prism reflector assembly has the similar polarization rotating property of its HP reflector component. In addition, due to its square entrance/exit surface, the pyramid shaped prism reflector  40  is more useful in many practical applications.  
         [0047]    Alternatively, FIGS.  5 ( a )- 5 ( c ) illustrate a variation on the embodiments of a polarizing converter with square entrance/exit surface, which comprises four HP prism reflectors shown in FIG. 2, wherein four isosceles right triangular shaped entrance/exit surfaces of  20  (s 1  in FIG. 2) coplanarly joint together to form a flat square entrance/exit surface, with four reflecting surfaces (s 3  in FIG. 2), perpendicular to the entrance/exit surface, facing outside to outline said reflector assembly  50 . The operation of the HP reflector assembly is identical to its HP reflector components. FIG. 5( a ) is a front view of said prism reflector assembly  50 . FIG. 5( b ) is a side view and FIG. 5( a ). FIG. 5( c ) is a perspective view of FIG. 5( a ).  
         [0048]    Another implementation of the HP reflector, described in FIG. 1, is formed by mirrors cemented together to be shaped in a hollow half pyramid. FIGS.  6 ( a )- 6 ( d ) present a front view, side view, top view and perspective view of a HP hollow reflector  60 , according to the invention. A HP hollow reflector is a hollow half pyramid shaped structure with three reflective inner wall surfaces, made up of three mirror plates. The entrance/exit surface s 1  (BCD) is an open surface while the surface s 2  (CDA), s 3  (BAC) and s 4  (DBA) are inner reflecting surfaces. The open surface s 1  (surface BCD) is the beam entrance/exit surface, in the shape of an isosceles right triangle. The surface s 3  is a reflective surface perpendicular to the open surface s 1 . The triangular surface s 2  and s 4  are two reflective surfaces, both at a 45 degrees angle respect to surface s 1 . The surfaces s 2 , s 3  and s 4  normally have high reflection coatings. Working on the same principle, a beam perpendicularly incident to open plane s 1 , reflected three times inside said reflector sequentially by surfaces s 2 , s 3  and s 4 , will exit open surface s 1  in a reversed direction to the incident beam with the polarization direction rotated by 90 degrees.  
         [0049]    Like HP prism reflector  20 , HP hollow reflector  60  could also be further assembled in a variety of configurations for different polarization rotation applications. FIG. 7 shows a pyramid shaped polarizing converter  70 , which is formed by two HP hollow reflectors  60  shown in FIG. 6, made up of thin reflective mirror plates, with their side plates (s 3  in FIG. 6) cemented together and two open surfaces (s 1  in FIG. 6) coplanar, to form a square shaped open entrance/exit surface. In practice, two side plates (s 3  in FIG. 6) can be replaced by one plate with both sides high-reflection coated.  
         [0050]    FIGS.  8 ( a )- 8 ( c ) present another embodiment of a polarizing converter with a square entrance/exit surface, comprising four HP hollow reflectors  60  shown in FIG. 6, wherein four isosceles right triangular shaped open entrance/exit surfaces of  60  (s 1  in FIG. 6) coplanarly joint together to form a flat open square entrance/exit surface, while four reflecting surfaces (s 3  in FIG. 6), perpendicular to entrance/exit surface, are facing outside to outline said reflector assembly  80 . The working principle of the HP reflector assembly  80  is identical to its HP hollow reflector components. FIG. 8( a ) is a front view of said apparatus  80 . FIG. 8( b ) is a side view of FIG. 8( a ). FIG. 8( d ) is a perspective view of FIG. 8( a ).  
         [0051]    FIGS.  9 ( a )- 9 ( d ) present a schematic configuration of a strip polarizing converter  90 , comprising multiple pyramid shaped HP prism reflectors  40  shown in FIG. 4, for using in an application where a strip shaped polarizing converter is needed. One of the sample applications will be described in FIG. 12. The element types in said strip reflector include, but are not limited to, the prism reflector assemblies shown in FIG. 4 and FIG. 5, and the hollow reflector assembly shown in FIG. 7 and FIG. 8. The number of the elements in the strip is decided by the actual application. FIG. 9( a ) shows a front view of the strip, FIG. 9( b ) shows a side view of the apparatus in FIG. 9 ( a ), FIG. 9( c ) shows a top view of the apparatus in FIG. 9( a ), and FIG. 9( d ) shows a perspective view of the strip.  
         [0052]    FIGS.  10 ( a )- 10 ( d ) shows a schematic configuration of a HP prism reflector array assembly  100 , comprising multiple pyramid prism reflectors  40  shown in FIG. 4. The element types in the array include, but are not limited to, the prism reflector assemblies shown in FIG. 4 and FIG. 5, and the hollow reflector assembly shown in FIG. 7 and FIG. 8. The number of the elements in the array and the shape of the array can be varied, being determined by the requirements of the actual application. The array assembly may reduce the size, weight and cost when the aperture of the polarizing converter is very large. FIG. 10( a ) shows a front view of the HP reflector array. FIG. 10( b ) shows a side view of the apparatus in FIG. 10( a ). FIG. 10( c ) shows a perspective view of the HP reflector array in FIG. 10( a ).  
         [0053]    [0053]FIG. 11 illustrates a schematic diagram of a polarization conversion and recovery system with the invented apparatus. The un-polarized light beam  100  is incident to a polarizing beam splitter (PBS)  101 . The p-component of the beam  111  passes through the PBS  101 , while the s-component  112  is reflected downward and incident to the HP reflector assembly  103 , which can be, but is not limited to, any one of the embodiments of the HP prism reflector assembly described above with square entrance surface, such as the prism reflector assemblies shown in FIG. 4 and FIG. 5, the hollow reflector assembly shown in FIG. 7 and FIG. 8, and the prism reflector array shown in FIG. 10. As described in FIG. 1 and FIG. 2, when the collimated incident s-beam strikes the entrance surface of  103 , the exiting beam emerging from said reflector  103  has its polarization rotated and becomes a p-polarized beam. Then, the newly p-polarized beam from  103 , passing through the PBS  101  and reflected by the right angle prism  102 , exits  102  in a desired direction parallel to the p-component  111 . Thus, by integrating an invented HP prism reflector assembly in a polarizing converter, the otherwise unused s-component  112  is converted into a p-component  113 , with the wanted polarization direction and propagation direction, as shown in FIG. 11.  
         [0054]    [0054]FIG. 12 shows an embodiment of a polarization converting and recovery system with invented HP reflector strips shown in FIG. 9, combined with a PBS strip array and used in a fly-eye lens array polarization converting system. The un-polarizing light beam  120 , coming from the fly-eye lens array (not shown in FIG. 12), is incident to the primary PBS strip  121 . The p-component  124  of the incident beams passes through the primary PBS strip  121  while the s-component is reflected downward, and is further reflected by the secondary PBS strip  122  onto the HP strip reflector  123 . As described before, the exiting beam from  123  becomes p-polarized so it passes through the PBS strip  122 . The exiting beam  125  is in a direction parallel to the p-component  124 , as shown in FIG. 12( a ). The same processes are repeated in the other rows of the PBS strips. As a result, with multiple strip reflector assembly  123  installed in the system, which converts otherwise wasted s-polarization components into p-polarization components and redirects them back to the desired direction, the un-polarized incident light from the fly-eye lens array can be converted into polarized light with high converting efficiency. FIG. 12( a ) is a front schematic view of the system and FIG. 12( b ) is a perspective schematic view of the system shown in FIG. 12( a ).  
         [0055]    [0055]FIG. 13 presents another embodiment of the current invention for an application in an image projection system utilizing linearly polarized light source. Light from light source  131  is reflected by an elliptic reflector  132  and then collimated by lens  133 . The collimated light exiting from the right side of the lens  133  is incident to a PBS plate  134 . The p-component of the incident light  130  passes the PBS plate  134  while the s-component is reflected downwards to HP reflector assembly  135 . As described previously, when the incident beam to HP reflector assembly  135  is s-polarized, the exiting beam from  135  becomes p-polarized, which passes through the PBS plate  134 , and then is reflected by mirror  136 , propagating in a direction parallel to the direction of beam  130 . The p-polarized beam  139  from mirror  136  and the p-polarized beam  130  from PBS  134  are collected by lens  137  onto the entrance of the integrator rod  138 .  
         [0056]    For LCD or LCOS based projection applications, the integrator rod  138  in FIG. 13 usually has square or rectangular cross section to match the shape of the light valves panel used in the image projection system. The HP reflector assembly  135  could be, but is not limited to, any one of the embodiments of the HP prism reflector assemblies described above with the square entrance surface, such as the prism reflector assemblies shown in FIG. 4 and FIG. 5, the hollow reflector assemblies shown in FIG. 7 and FIG. 8, and the prism reflector array shown in FIG. 10. Alternatively, the PBS plate  134 , reflecting mirror  136 , and integrator rod  138  in FIG. 13 could be replaced with a PBS cube, a right angle prism and an integrator pipe, respectively.  
         [0057]    FIGS.  14 ( a )- 14 ( c ) present a polarization recycling system employing a HP hollow reflector assembly for image projection systems utilizing a linearly polarized light source, such as a polarized light source for illuminating LCD or LCOS panels. As shown in FIGS.  14 ( a )- 14 ( c ), a HP hollow reflector assembly  141  of the type shown in FIG. 8, with a small opening  144  in the center for incident light to enter in, is mounted on the top of the light pipe integrator  143 , which is assembled by four thin mirror plates to form multiple reflective inner wall surfaces. A PBS plate  142 , either a wire grid PBS or another type of reflective PBS plate, is mounted on the bottom of the light pipe integrator  143 .  
         [0058]    An incident light, passing through the opening  144 , is multi-reflected by the reflective inner walls of the light pipe integrator  143  before reaching the reflective PBS plate  142 . The p-component of incident beam passes through  142  while the s-component is reflected back onto the inner walls of the light pipe integrator  143 . The reflected s-components that enter in the HP hollow reflector assembly  141  will be reflected back from  141  to the light pipe  143 , with the direction of polarization being rotated. For a normal incident polarized beam, the beam reflected from  141  becomes p-polarized, while for a tilt incident beam, the beam exiting from  141  may have some portion not totally p-polarized, as described previously (see FIG. 3). The reflected beam from the reflector  141 , through multi-reflection inside the pipe  143 , travels toward to the PBS plate  142 , where the recycled p-components will pass through while residual s-components will be reflected back to  143  for further recycling.  
         [0059]    Similar to other embodiments illustrated before, the HP reflector assembly  141  in FIG. 14 is the key component in this polarization recycling system to perform the wanted polarization rotation. The polarization rotation apparatus  141  in FIG. 14 could be made from, but is not limited to, any one of the types of the disclosed HP prism reflector assemblies with triangular or square entrance surface, such as the HP prism reflector shown in FIG. 2, the HP hollow reflector in FIG. 6, the prism reflector assemblies shown in FIG. 4 and FIG. 5, the hollow reflector assemblies shown in FIG. 7 and FIG. 8, or the prism reflector array shown in FIG. 10, with a small opening in the center to allow light to enter the system. An integrator rod, with a reflective PBS layer at its end, could replace the light pipe integrator  143  and the PBS plate  142 . FIG. 14( a ) is a cross-sectional view of the system taken along line A-A in FIG. 14 ( b ). FIG. 14( b ) is a side view of the system. FIG. 14( c ) is a perspective schematic view of the system.