LUNGERSHAUSEN ARNOLD W (US)
| US5967635A | 1999-10-19 | |||
| US20020114079A1 | 2002-08-22 | |||
| EP0848274A1 | 1998-06-17 | |||
| US6344929B1 | 2002-02-05 | |||
| EP0905542A2 | 1999-03-31 |
| 1. | Apparatus for illuminating an LCD utilization device comprising in combination : a. A first lens array comprising a first plurality of lens elements adapted to receive illuminating beams from an illumination source; b. A second plurality of polarizing beam splitters, arranged in pairs, each pair of beam splitters correlated to a lens element in said first array, one beam splitter of each pair being adapted to receive the illuminating beam from the corresponding lens element of said first array, the other beam splitter of each pair being shielded from the illuminating beam, said beam splitters being adapted to transmit and re flect respective first and second polarized illumination beams in complementary polarizations; c. A second lens array comprising a second plurality of lens elements, each lens element being associated with a beam splitter of said second plurality of beam splitters and adapted to receive a polarized beam from its associated beam splitter for supplying overall illumination to a utilization device; and d. a first plurality of polarization shifting elements interposed in the light path between said beam splitters and the LCD utilization device, each polarization shifting element being associated with one beam splitter of each of said pairs and its associated lens element to impart the same polariza tion to said first and second beams; whereby every lens element of said second array transmits radiation uniformly polarized in the same orientation for overall illumination of the entire LCD utilization device. |
| 2. | The apparatus of claim 1, further including a first plurality of masking elements, each applied to one of each pair of beam splitters to block impinging illumination from the corresponding lens element in said first lens array. |
| 3. | The apparatus of claim 1 wherein the beam splitters of each pair are arranged so that an impinging illuminating beam on the input face of one beam splitter is transmitted as a first output beam in one polarization orientation and is reflected into the other beam splitter of the pair to emerge as a second output beam in a second polarization orientation substantially parallel to said first output beam. |
| 4. | A module for use with a plurality of similar modules for illuminating a utilization device with uniform polariza tion comprising in combination: a. a first lens element adapted to receive an unpolar ized illuminating beam; b. a pair of polarizing beam splitters in an adjacent relationship and arranged so that a beam reflected in one of the beam splitters is further reflected by the other beam splitter to exit in a path that is parallel to the beam trans mitted by said one beam splitter but in a different polariza tion; c. masking means associated with the other beam splitter to prevent entry of the unpolarized illuminating beam; d. a pair of second lens elements, each associated with a beam splitter of said pair for directing illumination to the utilization device; and e. polarization modification means interposed in the beam exit path of one of said beam splitter pair to change the polarization of the exiting beam to that of the beam emerging from the other of said beam splitter pair; whereby the illumination reaching the utilization device is uniformly polarized. |
| 5. | Apparatus for illuminating a LCD utilization device comprising : a plurality of modules according to claim 4 for illuminating an LCD utilization device. |
| 6. | Apparatus for illuminating a LCD utilization device comprising: a. a plurality of lens elements; b. a plurality of beam splitter pairs, each pair being associated with a lens element of said plurality of lens elements for producing first and second exit beams of comple mentary polarization one beam splitter of each pair transmit ting a portion of impinging radiation as said first exit beam and reflecting a portion of impinging radiation to the other beam splitter of the pair to produce said second exit beam; c. a plurality of lens elements, each lens element being adapted to transmit the exit beam from an associated beam splitter to the LCD utilization device; and d. a plurality of polarization modification elements, each in the path of one of said first and second exit beams for changing the polarization of the beam impinging thereon to that of the non impinging exit beam; whereby the LCD utilization device receives illumination of uniform polarization. |
| 7. | The device of claim 6, above, wherein said polariza tion modification means include a polarization modification device in the path of each of said first exit beams. |
| 8. | The device of claim 6, above, wherein said polariza tion modification means include a polarization modification device in the path of each of said second exit beams. |
| 9. | The device of claim 6, above, further including masking means for said other beam splitter of each said beam splitter pair to block all illumination save that reflected from said one beam splitter of the pair. |
2. Description of the Related Art In recent years, liquid crystal display ("LCD") devices have come into widespread use. Because they generally require polarized light, most prior art systems have been plagued with low efficiency in their utilization of light sources. Unless special steps are taken, at least 50% of the illumination is lost in the polarizing process. Moreover, if relatively large sources are employed to illuminate a relatively small diameter display, the light efficiency can fall to less than 40%.
The prior art, as exemplified by the patent to W. Geffcken et al, No. 2, 748, 659, taught a light source for polarized light. In that patent, a light source is placed within a parabolic mirror structure to provide a substantially collimat- ed beam. The beam is applied to a polarizing structure which collects virtually all of the light and polarizes it in a desired orientation. In some embodiments, where only polarized light is permitted, alternate prism faces are blackened or metalized to prevent the leakage of undesired radiation compo- nents.
The more recent patent to Sarayeddine, U. S. Pat. No.
5,877, 824, taught a system in which unpolarized light from a source is applied to a polarizing beam splitter combination which transmits a pair of beams to the target, each polarized in the direction that is used by the LCD display. The two beams emerge at defined angles and are applied to a microlens array, each lens of which directs the light from one of the
beams to a first pixel element and the other to an adjacent pixel element If the source suffers from fluctuations in the luminance, this can adversely effect the performance of a liquid crystal display device. In an attempt to correct the problem, lenticu- lar arrays have been used to"integrate"the luminance so to make the illumination on the LCD device more uniform. This is shown in the patent to Watanabe, U. S. Pat. No. 5,786, 939.
It would be desirable to combine the elements of these prior art patents into a system which would be particularly useful in an LCD device, whether as a projector or as a reflec- tive display device.
SUMMARY OF THE INVENTION In a preferred embodiment, a conventional light source, such as a lamp with an parabolic reflector, directs its radiant energy to a first lenslet array of x lenslets which produces a plurality of beams that is focused on a second array of 2x polarizing beam splitters each combined with a lenslet. In the second array, however, half of the beam splitters are arranged so that each of these receives a converging beam from a corre- sponding lenslet of the first array.
The polarizing beam splitters that receive illumination pass approximately half of the illumination to the LCD device.
This half of the illumination has its polarization rotated by 90° by going through a half wave retarder plate located between the beam splitter and its lenslet resulting in a beam having a first polarization orientation.
The other half of the illumination is reflected by the beam splitter to the other beam splitter of the pair and emerg- es as polarized light of the same first polarization orienta- tion which is directed to its associated lenslet. As a result, virtually all of the applied illumination is polarized in the same orientation and is applied to illuminate the entire LCD device.
According to the present invention, the source is inte-
grated by the lenslets for uniformity and is polarized with a first component being polarized in a first orientation by transmission through the beam splitter. The other component of the illumination, which is polarized in a second orientation by reflection to the adjacent beam splitter and transmission by the adjacent beam splitter. Depending upon whether orientation in the first or second polarization is desired, the beam with the undesired polarization is returned to the desired orienta- tion by means of a half wave retarder.
Both components are transmitted to the utilization device through the second lenslets functioning as an optical system that focuses all of the illumination on the utilization device, for example, a liquid crystal display ("LCD") device.
The novel features which are characteristic of the inven- tion, both as to structure and method of operation thereof, together with further objects and advantages thereof, will be understood from the following description, considered in con- nection with the accompanying drawings, in which the preferred embodiment of the invention is illustrated by way of example.
It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and they are not intended as a definition of the limits of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side sectional view of a prior art device; FIG. 2 is a side sectional view of an illumination enhancement device according to the present invention; FIG. 3 is a top view of the device of FIG. 2; FIG. 4. is a front view of an idealized first lens array; FIG. 5 is a front view of an idealized second lens array; and FIG. 6 is a top view of one row of beam splitter-lenslet combinations in the second array of FIG. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning first to FIG. 1, there is shown the prior art
device of FIG la of the patent to Sarayeddine, U. S. Pat. No.
5,877, 824. The system 10 includes a lamp 12 inside of a para- bolic reflector 14. The illumination from the lamp 12 is directed to a polarizing beam splitter 16 with cholesteric filters or other polarization sensitive components.
The light is split into two parts including a first beam 18 and a second beam 20 of complementary polarizations. One of the beams is rotated through a half-wave by a liquid crys- tal cell 21. Using a pair of mirrors 22,24, the beams 18,20 are recombined in a double prism 26 which redirects the com- bined beam to a lenslet array 28. Each microlens 30 of the lenslet array 28 focuses its beam on at least two pixels 32 of a display device so that the first beam 18 illuminates a first pixel 32 and the second beam 20 illuminates a second pixel 32'. Using this technique, all of the light passes through the liquid crystal display.
This approach, however, requires as many lenslets and potentially prisms as pixels in the display. For a sizable display, a substantial number of lenslets and prisms are required, and at no small cost.
An alternative system, according to a preferred embodiment of the present invention is shown in FIGS. 2 and 3.
An illumination device 40 combines with a light source 42 with a parabolic reflector 44. The radiant energy from the device 40 is directed to first lenslet array 46. Each lenslet 48 of the first array 46 is focused upon one of a corresponding pair of lenslets 50 in a second lenslet array 52. Every lenslet 50 of the second array has, associated with it, a polarizing beam splitter 56 which transmits light with a first polarization orientation and reflects, at right angles, light with a second polarization orientation.
Alternating ones of the beam splitters 56 of the second array include a light baffle 54 to prevent the entrance of light from the first array 46. As a result, only one beam splitter 56 of each row pair receives illumination from the first array 46. Light impinging upon the non baffled beam
splitter 56 of a pair is split into a transmitted beam, which proceeds to a utilization device, and a reflected beam, which is directed into the lenslet 50 associated with the baffled one of the beam splitter pair. The entering beam is then reflected by that beam splitter 56 into its associated lenslet and is then directed to the utilization device which, in the preferred embodiment is a liquid crystal display 58.
As shown in the preferred embodiment, associated with each of the unbaffled beam splitters 56 is a half wave plate 60. The half wave plate 60 converts the polarization orienta- tion of the transmitted beams to the second orientation which is identical to the orientation of the beams transmitted from the baffled beam splitter lenslet combinations, therefore resulting in light of uniform polarization impinging upon the utilization device or liquid crystal display 58.
In alternative embodiments, the half wave plates could be associated with the unbaffled beam splitter lenslet combina- tions to result in uniform polarization of the opposite orien- tation.
The arrangement of the first and second arrays can be seen in FIGS. 4 and 5 which are idealized views of a first array 46'of only twenty lenslets 48'and a corresponding second array 52'of forty beam splitter 56'lenslets 50' combinations, half of them being shielded by a baffle 54 As better seen in FIG. 6, the unshielded lenslets 50'have, interposed between the beam splitter 56'and its associated lenslet 50', a half wave plate 60'.
In FIG. 6, the light path through the second lenslet array 52 can easily be seen. Light from each lenslet 48'of the first array 46'is directed to the unbaffled one of the corresponding pair of lenslets 50'of the second array 52'.
That light beam enters the beam splitter 56'and one half of the beam is transmitted through the beam splitter 56'and the associated half wave plate 60'and enters the lenslet 50'.
The other half of the beam is reflected by the beam- splitter 56'and enters the adjacent beam splitter 56'where
it is redirected to the corresponding lenslet 50'. The half wave plate 60'in the path of the transmitted beam changes the polarization of the beam to match that of the beam emerging from adjacent lenslet 50'so that substantially all of the radiant energy from the source is transmitted to the liquid crystal display in the same polarization state.
As can be seen, the second lenslet array provides uniform illumination to the utilization device which, in this embodi- ment, is a liquid crystal display.
As may be appreciated, the present invention efficiently converts unpolarized illumination into illumination of optimum polarization for a liquid crystal display without substantial loss.
Other variations and modifications may occur to one skilled in the art and, accordingly, the scope of the inven- tion should only be limited by the claims appended below.
WHAT IS CLAIMED AS NEW IS :