The present invention relates to projection display systems, and more particularly relates to an integrated beam splitter and polarizer for a single panel scrolling color projection display system.

A single panel scrolling color projection display system is characterized by a single light modulator panel such as a liquid crystal display (LCD) panel having a raster of individual picture elements or pixels, which panel is illuminated by horizontally elongated red, green and blue illumination bars or stripes. The stripes are continuously scrolled vertically across the panel while the illuminated rows of pixels are synchronously addressed with display information corresponding to the color of the then incident stripe.

See, for example, United States Patent 5,410, 370, "Single panel color projection video display improved scanning"issued to P. Janssen on March 25,1994, and United States Patent 5,416, 514, "Single panel color projection video display having control circuitry for synchronizing the color illumination system with reading/writing of the light valve"issued to P. Janssen et al. on May 16,1995, the entire specifications of which are hereby incorporated by reference herein.

Such single panel systems are to be distinguished from the more conventional three-panel systems, in which separate red, green and blue beams each fully illuminate and are modulated by a separate light modulator panel. The modulated beams are then superimposed on a display screen to produce a full color display.

In single panel scrolling color systems, incoming white light is split into separate red, green and blue color components by a light engine using dichroic elements. The illumination architecture for a light engine 1 for such a scrolling color projector is shown schematically in Fig. 1. White light from source S is split into a blue component B and a green/red component G/R by dichroic element 2. The B component is directed by lens 3 and mirror 4 to prism scanner 5. The G/R component is passed by dichroic element 2 through lens 6 to dichroic element 7, which splits the G/R component into a green component G and a red component R. The G component is reflected by element 7 to prism scanner 8, while the red component is passed through dichroic element 7 to prism scanner 9. The scanned R, G, B components are then directed to recombination dichroic elements

10 and 11 by mirror 12 and relay lenses 13 through 17.

The dichroic elements and mirrors are tilted at a 45 degree angle to the beam path.

The spectral response of a tilted dichroic filter depends strongly on the incident angle of the light. Therefore, it is not possible to effectively divide white light into non-overlapping color bands when using these filters in divergent light, which is necessary for high light throughput. Consequently, either the color performance or the optical efficiency of the system must be sacrificed.

Where the light modulating panel is an LCD, the light must also be polarized.

Polarization conversion is achieved in a separate step, typically using an optical element known as a McNeill prism. As in the case of dichroic filters, the efficiency of these polarization conversion elements decreases as the light being treated becomes more divergent.

A typical polarization conversion arrangement 20 is shown in Fig. 2. Output light from a light engine, which constitutes an image of scrolling bands of R, G, and B light, is directed through polarizer 22 to a polarizing beam splitter (PBS) 23, having an internal polarized beam splitting surface 23a. Polarizer 22 converts the unpolarized light to light of one polarization state, eg. S. Surface 23a passes this S light to light modulator panel 24, which modulates the light in accordance with a display signal, and reflects the modulated light back to the PBS 23. In the process of modulation and reflection, panel 24 changes the polarization state of the light from S to P, and surface 23a reflects the light out of the PBS 23 to a projection lens for display.

Polarization conversion is often carried out in combination with a light integration step using an integrating array. Light integration is intended to produce light beams having a stripe-shaped cross-section of uniform brightness. However, as presently practiced, polarization conversion in combination with light integration arrays does not work well with beams having cross-sections with such large aspect ratios.

In accordance with the invention, there is provided an integrated system for both splitting unpolarized white light into red, green and blue components, and for converting those components into a single state of polarizion.

According to one aspect of the invention, an integrated beam splitting and polarization conversion system 10 for a projection display system is provided, the system comprising:

a light guide array 32 comprising at least four light guide elements (W, Gr, Gg, Gb), a first of the light guide elements (W) having a light exit face 34, and second, third and fourth light guide elements having light entrance faces (36,38, 40) with a wide aspect ratio (1/w> 2), the entrance faces (36,38, 40) each having a first side (36a, 38a, 40a) and a second side (36b, 38b, 40b); a polarizing beam splitter 42 for converting white light from exit face 34 of light guide element W into a first beam having a first state of polarization and a second beam having a second state of polarization, the polarizing beam splitter 42 comprising an entrance face 44, an internal polarizing-beam-splitting surface 46 oriented at an angle to the entrance face 44, surface 46 having a polarizing-beam-splitting side 46a for reflecting light of the first state of polarization and for transmitting light of the second state of polarization, and an opposing side 46b for transmitting light of the second state of polarization, polarizing beam splitter 42 also having a first exit face 48 facing side 46a, and a second exit face 50 facing side 46b; a first filter set Fl opposing first exit face 48, filter set F1 comprising red, green and blue filters (Rl, G1, Bl), the filters (Rl, G1, B1) positioned to reflect red, green and blue light, respectively, of the first state of polarization toward the first sides (36a, 38a, 40a) of entrance faces (36, 38, 40) of light guides (Gr, Gg, Gb), respectively, after reflection by side 46a of surface 46; a second filter set F2 opposing second exit face 50, filter set F2 comprising red, green and blue filters (R2, G2, B2), the filters (R2, G2, B2) positioned to reflect red, green and blue light, respectively, of the second state of polarization toward the second sides (36b, 38b, 40b) of entrance faces (36, 38, 40) of light guides (Gr, Gg, Gb), respectively; a first lens LI opposing light guide array 32, for imaging light from exit face 34 of light guide W onto entrance face 44 of polarizing beam splitter 42, and for imaging light from polarizing beam splitter 42 onto entrance faces (36, 38, 40) of light guides (Gr, Gg, Gb) ; a second lens L2 for collimating light from exit face 34 of light guide W; and a wave-plate 52 positioned between the lens L2 and the second sides (36b, 38b, 40b) of the entrance faces (36, 38, 40) of light guides (Gr, Gg, Gb), for converting light of the second state of polarization to light of the first state of polarization.

The light guide W is preferably positioned below the light guides (Gr, Gg, Gb), but may alternatively positioned above or to one side of the light guides (Gr, Gg, Gb).

The filters (Rl, G1, B1) and (R2, G2, B2) of filter sets F1 and F2 are preferably positioned in series in the order B, G, R from the exit faces 48 and 50, respectively, but alternatively may be positioned in another order, such as B, R, G, from the exit faces 48 and 50, respectively.

According to another aspect of the invention, a projection display system 50 is provided, the system comprising: a source 52 of white light; an integrated beam splitting and polarization conversion system 54 according to the first aspect of the invention, system 54 for splitting the source 52 into polarized red, green and blue beams having a cross-section with a wide aspect ratio; a light modulating panel 56, for modulating light in accordance with a display signal; means 58 for continuously and sequentially scrolling the red, green and blue beams across the light modulating panel 56; and a projection lens 60 for projecting the modulated light onto a display surface.

The light modulating panel 56 is preferably a liquid crystal display panel, although other types of display panels such as deformable mirror devices may alternatively be employed. The means 58 for scrolling the beams may be a single large rotating prism, or alternatively, three smaller rotating prisms, one for each of the red, green and blue beams.

The projection display system 50 may include a light guide system 62 for guiding the red, green and blue beams from the beam splitting and polarization conversion system 54 to the scrolling means 58. A loss-less, etendue-preserving light guide suitable for use in the present invention is described in co-pending United States Patent Application Serial Number, filed, (Attorney Docket PHUS 020,170), the entire specification of which is hereby incorporated herein by reference.

The projection display system 50 may also include means 64 for synchronously and continuously supplying red, green and blue components of a color display signal to the light modulating panel 56 during scrolling of the red, green and blue light beams across the light modulating panel 56. Suitable means are described, for example, in United States Patents 5,410, 370 and 5,416, 514, already referenced hereinabove.

Fig. 1 is a schematic representation of the illumination architecture of a light engine for a single panel scrolling color projection system of the prior art; Fig. 2 is a schematic representation of a polarization conversion architecture for a single panel scrolling color projection system of the prior art; Figs. 3A through 3E are different views of a schematic illustration of one embodiment of an integrated beam splitter and polarizer for a projection display system of the invention; Figs. 4A through 4G are different views of a schematic illustration of additional embodiments of an integrated beam splitter and polarizer for a projection display system of the invention; and Fig. 5 is a block diagram illustrating one embodiment of a projection display system incorporating an integrated beam splitter and polarizer of the invention.

Referring now to Fig. 3A, one embodiment of an integrated beam splitter and polarizer 30 of the invention is shown in a side view. A light guide array 32 includes four light guide elements (W, Gr, Gg, Gb). Light guide element W has a light exit face 34, and light guide elements Gr, Gg, Gb have light entrance faces 36,38 and 40, respectively.

As shown in the section view A-A of Figs. 3C through 3E, entrance faces 36, 38 and 40 have a first side (36a, 38a, 40a) and a second side (36b, 38b, 40b). These entrance faces also have a wide aspect ratio characterized by a length-to-width ratio of 2 or greater (1/w > 2), to enable the stripe-shaped beam cross-sections needed for scrolling the light modulator panel.

The integrated beam splitter and polarizer 30 also includes a polarizing beam splitter (PBS) 42 for converting white light from exit face 34 of light guide element W into a first beam having a first state of polarization and a second beam having a second state of polarization. Unpolarized white light (U) from exit face 14 of light guide W is imaged onto entrance face 44 of PBS 42, and collimated by a second lens L2. Lens L2 also helps to preserve tele-centricity of the light. Upon striking the internal polarizing-beam-splitting side 46b of surface 46, the U light is converted to S light and reflected toward exit face 48 and filter set F1. Filters Bl, G1 and Rl separate out blue, green and red light, respectively, from the S-polarized white light. Filters B1, Gl and Rl are retro-reflective and tilted at different angles so that after retro-reflection, the light is re-imaged by lens LI into a corresponding light guide. Filters B1, G1 and Rl are also tilted in a plane normal to the

drawing, such that the light falls into the left half of light guides (36a, 38a, 40a) (view A- A).

At the same time, P-polarized light (Fig. 3B) is transmitted by surface 46 of PBS 44 to exit face 50. A second filter set F2 is positioned opposite exit face 50, and the individual retro-reflective filters B2, G2, R2 are tilted so that, after retro-reflection, the light is again transmitted by surface 46 and re-imaged by lens Ll into the right-hand half of the corresponding light guides (36b, 38b, 40b).

A wave-plate 52 (Fig. 3E) placed before the right-hand half of light guide array 32 transforms the polarization state of the P light to S light, so that the polarization state of all of the light entering the light guides Gr, Gg, Gb matches, as indicated by the matched cross hatching on the entrance faces 36,38 and 40 (Fig. 3F).

An alternative, side-by-side, disposition of the light guides is shown in the system 60 of Figs. 4A through 4G. In the depiction of this arrangement, Figs. 4A and 4B are side views similar to those of Figs. 3A and 3B, except for the different placement of the light guide W in the array 62, and the order of placement of the filters in the filter sets F1 and F2. In this arrangement, the positions of filters R and G are switched from those of the previous embodiment.

Fig 4C is a top view of the arrangement, showing light guide W placed on the left side of the array 62. Figs. 4D through 4G are section views along A-A, with Figs. 4E and 4G showing the unmatched polarization states prior to wave plate 72, and Figs. 4D and 4F showing the matched polarization states after wave plate 72, for the side and top views, respectively.

The above integrated systems combine both the polarization conversion and color splitting functions into one compact unit. Moreover, the use of dichroic filters for color separation is eliminated, and the accompanying degradation of color purity in divergent light systems is avoided.

Fig. 5 shows a projection display system 80 incorporating an integrated beam splitter and polarizer 82 in accordance with the invention, a light modulation panel 84, means 86 for scrolling colored light beams across the panel 84, and a projection lens 88 for projecting the modulated light onto a display surface.

The system 80 also includes a light guide system 90 for guiding white light from a source S to the integrated beam splitter and polarizer 82, and for guiding colored light

beams from the integrated beam splitter and polarizer 82 to means 86. Addressing means 92 is provided for supplying display signals to the panel 84 synchronously with the impingement of the scrolling bands of colored light, to produce a color display image.

The details of operation as well as exemplary structures for light guide systems are provided in previously referenced co-pending United States Patent Application Serial Number, filed, (Attorney Docket PHUS 020,170).

The invention has necessarily been described in terms of a limited number of embodiments. However, other embodiments and variations of embodiments will be apparent to those skilled in the art, and these are intended to be encompassed within the scope of the appended claims.