Patent Application
20100027238
This invention relates to polarization-recovery illumination systems.
Lens array polarization-recovery illumination systems are widely used in display applications.
The polarization-recovery light integrator consists of first plano-convex lens array 103, second plano-convex lens array 104, strip-mask plate 105, polarization beam splitter (“PBS”) prism bar plate 106, plate 107 of half-wave retardation strips, and focusing lens 108. Lens arrays 103 and 104 are two-dimensional arrays containing the same number of plano-convex lenslets (individual lenses) arranged in the same plural number of rows and the same plural number of columns. PBS prism bar plate 106 is a one-dimensional array of PBS prism bars. The number of PBS prism bars is the same as the number of rows of lenslets in lens array 103 or 104.
Collimated light beam 102 passes through the lenslets of first lens array 103 to form initial partial light fluxes (or sub-beams) 111i traveling generally parallel to optical axis 110. Each initial partial flux 111i consists of the light which passed through a different one of the lenslets of lens array 103. As viewed along optical axis 110, light fluxes 111i are thus distributed in rows and columns respectively corresponding to the rows and columns of lens array 103. The total number of light fluxes 111i equals the number of lenslets in lens array 103 or 104. Light fluxes 111i pass respectively through the lenslets of second lens array 104 and then respectively through openings in strip-mask plate 105 which blocks extraneous (unwanted) light.
Light fluxes 111i in each light-flux row impinge on a corresponding different one of the PBS prism bars in PBS prism bar plate 106. Each PBS prism bar transmits the p linearly polarized component of each incident light flux 111i to produce p linearly polarized light flux 112i. The s linearly polarized component of each incident light flux 111i goes through two reflections in its PBS prism bar. The s linearly polarized components of light fluxes 111i then pass through the half-wave strips of half-wave strip plate 107 and are respectively converted into p linearly polarized light fluxes 113i. Directly passed p polarized light fluxes 112i and converted p polarized light fluxes 113i propagate in the same direction generally parallel to optical axis 110. Focusing lens 108 focuses p polarized light fluxes 112i and 113i onto panel 109 so that light fluxes 112i and 113i mix across panel 109. This causes the light illumination on panel 109 to be moderately uniform.
As
It would be desirable to have a lens array polarization-recovery illumination system that utilizes considerably more, ideally nearly all, of the aperture of the PBS prism bar plate so as to increase the illumination efficiency and cause the illumination to be highly uniform. It would also be desirable to have embodiments which accommodate different numbers of light sources.
The present invention furnishes a polarization-recovery illumination system that provides highly uniform illumination and has high illumination efficiency. The illumination system of the invention contains a light-source structure, a light-pipe structure, and a polarization-recovery light integrator. The light-source structure, formed with one or more light sources, provides light across a light-source area. The light-pipe structure, which contains one or more light pipes, has a light-entrance area and a light-exit area. Light provided from the light-source structure generally across its light-source area enters the light-pipe structure at its light-entrance area, passes largely through the light-pipe structure, and exits the light-pipe structure across largely all of its light-exit area.
The polarization-recovery light integrator performs polarization-recovery light integration by first splitting light which exited the light-pipe structure across its light-exit area into multiple initial partial light fluxes. The polarization-recovery light integrator then converts orthogonally linearly polarized components of the initial light fluxes into multiple partial fluxes of linearly polarized light, i.e., light of substantially only a single linear polarization type. Finally, the polarization-recovery light integrator mixes the fluxes of linearly polarized light so as integrate them.
The polarization-recovery light integrator is characterized by a light-transmission area, referred to as an aperture, through which light can pass in traveling through the integrator. Each flux of linearly polarized light passes through a portion, referred to here as a light spot, of the integrator's aperture. Each light spot is normally largely an image of the light-exit area of the light-pipe structure. By appropriately choosing the shape of the light-exit area of the light-pipe structure, the light spots occupy a very large fraction of the total aperture area. The usage efficiency of the integrator aperture is very high. As a result, the intensity of the mixed fluxes of linearly polarized light is highly uniform and is achieved in a highly efficient manner.
The light-exit area of the light-pipe structure is typically of rectangular shape. The light spots are then of the same rectangular shape and can be packed very close to one another in the integrator aperture. Additionally, the light-pipe structure enables the shape of the light spots to be largely independent of the shape of the light-source area of the light-source structure. The light-source area of the light-source structure can therefore be of a materially different shape than the light-exit area of the light-pipe structure. If, for example, the light-source area is of circular or elliptical shape or of different rectangular shape, i.e., different length-to-width ratio, than a rectangular shape chosen for the exit area of the light-pipe structure, the illumination efficiency of the present illumination system is still very high.
The polarization-recovery light integrator of the present illumination system normally contains a first lens array, a second lens array, a PBS prism bar plate, and a half-wave retardation strip plate. The first lens array splits light which exited the light-pipe structure across its light-exit area into the initial light fluxes. In particular, a selected plurality of the initial light fluxes are so formed. The second lens array images the initial light fluxes on respective locations close to the PBS prism bar plate.
The PBS prism bar plate splits the initial light fluxes into a like plurality of respective primary light fluxes of a first linear polarization type and a like plurality of respective light fluxes of a second linear polarization type opposite to the first linear polarization type. Light of the primary fluxes of the first linear polarization type passes through the PBS prism bar plate.
The PBS prism bar plate directs, typically by double reflection, light of the fluxes of the second linear polarization type to the half-wave retardation strip plate which converts them into a like plurality of respective further light fluxes of the first linear polarization type propagating in generally the same direction as the primary light fluxes of the first polarization type. The primary and further light fluxes of the first polarization type thereby largely form the aforementioned fluxes of linearly polarized light. The polarization-recovery light integrator normally includes a focusing lens that directs the fluxes of linearly polarized light, i.e., the primary and further light fluxes of the first polarization type, toward a target location so that they mix with one another.
The PBS prism bar plate has a light-transmission area, or aperture, through which the primary light fluxes of the first linear polarization type pass through the bar plate's beam-splitting elements and through which the further light fluxes of the second polarization type are directed to the sides of the beam-splitting elements. The aperture of the PBS prism bar plate typically implements the aperture that characterizes the polarization-recovery light integrator. The presence of the light-pipe structure in combination with choosing the shape of its light-exit area in the above described manner enables the light spots of the primary light fluxes of the first linear polarization type and the light spots of the light fluxes of the second linear polarization type to occupy a very large fraction of the bar plate's aperture. Hence, the illumination efficiency is very high. This enables the illumination at the target location to be highly uniform.
The illumination system of the invention preferably includes a collimator for collimating light exiting the light-pipe structure across the light-exit area into a beam of collimated light. The polarization-recovery light integrator then splits collimated light provided from the collimator into the aforementioned initial light fluxes.
When only one light source is present in the light-source structure so that the light-source area is substantially a single continuous area, only one light pipe is typically present in the light-pipe structure. Both the light-entrance and light exit areas of the light pipe are typically rectangular at different length-to-width ratios. Consequently, the light pipe is tapered.
In situations where a plurality of light sources are present in the light-source structure includes, the light-pipe structure typically has an input light-pipe section and an output light-pipe section. The input light-pipe section includes like plurality of input light pipes. Each input light pipe directs light from a different one of the light sources to the output light-pipe section. The output light-pipe section combines light from the input light pipes to produce the light exiting the light-pipe structure. The output light-pipe section typically includes one or more output light pipes and one or more light reflectors which direct light to the output light pipe or pipes.
To summarize, the polarization-recovery illumination system of the invention furnishes highly uniform illumination and high illumination efficiency. The light-pipe structure enables the light distribution across the aperture of the polarization-recovery light integrator to be substantially independent of the shape of the light-source area of the light-source structure. High illumination efficiency can thereby be achieved with various different shapes for the shape of the light-source area of the light-source structure. Consequently, the invention provides a substantial advance over the prior art.
Like reference symbols are used in the drawings and in the description of the preferred embodiments to represent the same, or very similar, item or items.
Referring to
Circular image light spots 201i of directly passed light fluxes 112i and circular image light spots 202i of converted light fluxes 113i in
The shape and size of the images 301i and 302i depend on the size and shape of the lenslets in lens arrays corresponding to lens arrays 103 and 104 in the illumination system of
Components 402-408 are configured, arranged, and operable largely the same as components 102-108 in the conventional illumination system of
Each of lens arrays 403 and 404 is (analogous to lens arrays 103 and 104) a two-dimensional array of row and columns of plano-convex lenslets. Lens arrays 403 and 404 contain the same plural number of lenslet rows and the same plural number of lenslet columns so the number of lenslets in lens arrays 403 and 404 is the same. PBS prism bar plate 406 is (similarly analogous to PBS prism bar plate 106) a one-dimensional array of PBS prism bars. The number of PBS prism bars in prism bar plate 406 is the same as the number of rows of lenslets in lens array 403 or 404.
Light source 401 has a light-source area from which unpolarized (or randomly polarized) light is provided. Light pipe 420 has (a) a light-entrance area 421 situated next to the light-source area of light source 401 and (b) a light-exit area 422 facing collimating lens 402. Unpolarized light provided from light source 401 generally across its light-source area enters light pipe 420 at light-entrance area 421, passes largely through pipe 420, and exits pipe 420 across largely all of light-exit area 422 propagating toward collimating lens 402.
Light pipe 420 has four lateral sides, an entrance side that presents light-entrance area 421, and an exit side that presents light-exit area 422. Each lateral side of light pipe 420 is typical largely flat but can be somewhat curved.
An example of light pipe 420 is illustrated in
Light pipe 420 is preferably a solid glass bar as represented in the example of
When light pipe 420 is implemented as a solid glass bar, the entrance side of pipe 420 is provided with an anti-reflective coating (not shown) to inhibit reflection of the unpolarized light from light source 401. The exit side of light pipe 420 is similarly provided with an anti-reflective coating (likewise not shown) to inhibit reflection of the light traveling toward collimating lens 402.
Alternatively, light pipe 420 can be a hollow body with four lateral glass walls. The entrance and exit ends of the hollow body are open. When light-entrance area 421 and light-exit area 422 of the hollow body are rectangles, the exit-side aspect ratio of the length of the long edges of light-exit area 422 to the length of the short edges of light-exit area 422 normally differs from the entrance-side aspect ratio of the length of the long edges of light-entrance area 421 to the length of the short edges of light-entrance area 421.
Whether implemented as a solid glass bar or a hollow body with four lateral glass walls and open entrance/exit ends, light pipe 420 is normally tapered. Light is substantially inhibited from leaving light pipe 420 through its four lateral sides due to internal reflection at the glass-air interfaces of the lateral sides.
The size of light-entrance area 421 of light pipe 420 preferably substantially fully encompasses the size of the light-source area of light source 401 without exceeding the size of the light-source area by any amount more than that needed to accommodate a predetermined shape, e.g., rectangular, for light-entrance area 421. Consider the situation in which light pipe 420 is a solid glass bar and in which light-entrance area 421 is a rectangle formed by the entrance side of light pipe 421. The light-source area is typically shaped as a rectangle. The length of long light-pipe entrance edges 423 then preferably substantially equals the length of the long edges of the light-source rectangle while the length of short light-pipe entrance edges 424 preferably substantially equals the length of the short edges of the light-source rectangle. The rectangular shape of the light-source area can devolve to a square. In that case, the lengths of light-pipe edges 423 and 424 are substantially the same and are substantially equal to the length of each edge of the square.
If the light-source area is shaped as an ellipse, the length of long light-pipe edges 423 preferably substantially equals the length of the long axis of the ellipse while the length of short light-pipe edges 424 preferably substantially equals the length of the short axis of the ellipse. The elliptical shape of the light-source area can devolve to a circle (as represented in
Similar to what happens to the unpolarized light emitted from light source 101 in the conventional illumination system of
Each initial partial flux 411i consists of the light which passed through a corresponding different one of the lenslets of lens array 403. As viewed along optical axis 410, i.e., in a plane perpendicular to axis 410, light fluxes 411i are thereby distributed in rows and columns respectively corresponding to the rows and columns of lens array 403. The total number of light fluxes 411i equals the number of lenslets in lens array 403 or 404. Partial light fluxes 411i pass respectively through the plano-convex lenslets of second lens array 404 and then respectively through openings in strip-mask plate 405. Strip-mask plate 405 blocks the transmission of extraneous (unwanted) light other than light that passed through the light-pipe structure formed with light pipe 420.
Light fluxes 411i in each light-flux row impinge on a corresponding different one of the PBS prism bars in PBS prism bar plate 406. Each PBS prism boar of prism bar plate 406 splits each of partial light fluxes 411i incident on that PBS prism bar into a linearly polarized component of p linear polarization type and a linearly polarized component of s linear polarization type opposite to p linear polarization type. Light of the p linearly polarized component of each incident partial flux 411i is transmitted through its PBS prism bar to produce a divergent linearly polarized partial flux 412i of p linear polarization type. As viewed along optical axis 410, i.e., in a plane perpendicular to axis 410, directly passed p polarized light fluxes 412i are distributed in rows and columns respectively corresponding to the rows and columns of initial light fluxes 411i and thus respectively corresponding to the rows and columns of lens array 403 or 404.
Light of the s linearly polarized component of each incident partial flux 411i goes through two reflections in its PBS prism bar of PBS prism bar plate 406. The first reflection is by approximately 90°. The second reflection is likewise by approximately by 90° so that light of the s linearly polarized component of each incident partial flux 411i now propagates forward generally along optical axis 410. Light of the s linearly polarized components of partial fluxes 411i passes through the half-wave strips of half-wave strip plate 407. This causes the s linearly polarized components of partial fluxes 411i to be respectively converted into divergent linearly polarized partial fluxes 413i of p linear polarization type. As viewed along optical axis 410, i.e., in a plane perpendicular to axis 410, converted p polarized light fluxes 413i are likewise distributed in rows and columns respectively corresponding to the rows and columns of initial light fluxes 411i and thereby respectively corresponding to the rows and columns of lens array 403 or 404.
Directly passed p polarized partial fluxes 412i and converted p polarized partial fluxes 413i propagate forward generally parallel to optical axis 410 and thus in generally the same direction. As a consequence, each directly passed p polarized partial flux 412i and converted p polarized partial flux 413l that underwent double reflection in the PBS prism bar plate which transmitted that directly passed p polarized partial flux 412i form a partial flux 412i/413i of linearly polarized light of p linear polarization type. Since the number of initial partial light fluxes 411i equals the number of lenslets in lens array 403, the number of partial fluxes 412i/413i of p linearly polarized light equals the number of lenslets in lens array 403.
Focusing lens 408 focuses p partial light fluxes 412i/413i, i.e., directly passed p polarized partial fluxes 412i and converted p polarized partial fluxes 413i, onto the target location formed by panel 109 so that each p partial flux 412i/413i of linearly polarized light is distributed across the panel target location. P partial light fluxes 412i/413i thereby mix across panel 409 so as to become integrated.
The polarization-recovery light integrator formed with components 402-408 is characterized by a light-transmission aperture represented by the aperture at the exit surface of PBS prism bar plate 406. Referring back to
The shape and size of light-exit area 422 of light pipe 401 are generally selected so that the integrator aperture is virtually fully filled by directly passed light spots 301i and converted light spots 302i as shown in
The strategy of using a light-pipe structure to increase the illumination efficiency works with multiple light sources.
The light-pipe structure in the illumination system of
Unpolarized light provided from light source 501 generally across its light-source area passes largely through first input light pipe 503, is reflected approximately 90° by first light reflector 503, passes through output light pipe 507, and exits output pipe 507 across at least part of light-exit area 508. Unpolarized light provided from light source 502 generally across its light-source area similarly passes largely through second input light pipe 504, is reflected approximately 90° by second light reflector 506, passes through output light pipe 507, and exits output pipe 507 across at least part of light-exit area 508 such that the combination of light provided by light sources 501 and 502 is distributed across all of light-exit area 508. Consequently, output light pipe 507 combines the light provided from light sources 501 and 502. The unpolarized light exiting output pipe 507 is thereafter provided to collimating lens 402 and processed in the polarization-recovery light integrator in the same manner as in the illumination system of
The shape and size of light-exit area 508 of output light pipe 507 are preferably selected so that the characteristic aperture of the polarization-recovery light integrator in the illumination system of
In the illumination system of
Output light pipes 511 and 512 do not actually combine the light passing through them. However, output pipes 511 and 512 are preferably so close together that the light passing through them is effectively combined. Also, when output light pipes 511 and 512 consist of largely adjoining glass bars, there is essentially no space between their light-exit areas 513 and 514. Hence, the light exiting second output pipe 512 substantially “adjoins” the light exiting first output pipe 511 so that the exiting light substantially forms a single light beam.
The shapes and sizes of light-exit areas 513 and 514 of output light pipes 511 and 512 are preferably selected so that the characteristic aperture of the polarization-recovery light integrator in the illumination system of
While the invention has been described with reference to preferred embodiments, this description is solely for the purpose of illustration and is not to be construed as limiting the scope of the invention claimed below. For instance, light pipes 420, 503, 504, 507, 511, and 512 can be recycling light pipes to further increase the illumination efficiency. The light-source structure can be implemented with more than two light sources.
A half-wave retardation plate or a plate of half-wave retardation strips can be placed in the optical path (at various locations) so that the directly passed partial fluxes 412i and converted partial fluxes 413i are s linearly polarized. The light-source and light-pipe structures in the illumination system of
This claims priority to U.S. provisional patent application 61/137,688, filed 1 Aug. 2008, the contents of which are incorporated by reference to the extent not repeated herein.
| Number | Date | Country | |
|---|---|---|---|
| 61137688 | Aug 2008 | US |
