Liquid crystal display system and light projection system

[0002] This application claims the priority benefit of Taiwan application serial no. 87108197, filed May 26, 1998, the full disclosure of which is incorporated herein by reference.

[0003] 1. Field of the Invention

[0004] This invention relates to an electronic optical system, and more particularly to a light projection system suitable for a use in a liquid crystal display system (LCD) to display image.

[0005] 2. Description of Related Art

[0006] Recently, a LCD device is widely used in TV, computer, monitor or other display system. Comparing with a conventional display apparatus with a picture tube, the LCD system is lighter and has a smaller dimension. It becomes a necessary part to display system, such as a notebook computer.

[0007] FIG. 1 is a structure diagram, illustrating a polarization light projection system used in a reflection-type color display board as disclosed by U.S. Pat. No. 5,530,489. In FIG. 1, a reading light source 100 can emit a white light. The white light is polarized by a polarization beam splitter (PBS) 102 and split into an S-state polarized beam and a P-state polarized beam, both which are also reflected so that both light polarized beams are deflected by 90 degrees. The S-state polarized beam forms the WS beam. The P-state polarized beam is converted into an S-polarization beam WS′ through a half-wave plate 106. The WS and WS′ beams are incident to a polarization analyzer 108 and are deflected by 90 degrees again, in which the polarization analyzer 108 further ensures that the Ws and the WS′ beams are polarized into an S polarized state.

[0008] The WS and the WS′ beams enter a dichroic prism 110, which deflects a blue light BS of the WS and WS′ beams by 90° and allows a red light RS and a green light GS to continuously transmit. The blue light BS passes a light path compensation plate 112 and enters a blue liquid crystal light valve (LCLV) 114, which converts the blue light BS into a blue light BP with P-state polarization and reflect the blue light BP back to the dichroic prism 110 through the light path compensation plate 112. The blue light BP is deflected to a projection lens 122 through the polarization analyzer 108. The projection lens 122 project the blue light BP onto an image screen (not shown). For the red light RS and the green light GS, they continuously travel to a color filter prism 116, which deflects the green light GS by 90° into a red LCLV 118, and allows the red light RS to pass and reach a green LCLV 120. The red LCLV 118 reflects the green light GS back and converts it into a green light GP with P-state polarization. Similarly, the green LCLV 120 reflects the red light GS back and converts it into a red light GP with P-state polarization. The red light RP and the green light GP are also deflected to the projection lens 122 and projected to the image screen like the blue light BG.

[0009] In this system shown in FIG. 1, the system includes two light splitters and several prisms, resulting in a large system dimension. This display system cannot be efficiently applied in a large displaying area and is not portable. Moreover, a poor focusing quality severely occurs due to a too large distance between the LCLVs and the projection lens. This further limits its applications.

[0010] Another system is disclosed by U.S. Pat. No. 5,153,752 to reduce the distance of the projection lens and the system dimension. FIG. 2 is a structure diagram, illustrating a polarization light projection system used in a reflection-type color display board as disclosed by U.S. Pat. No. 5,153,752. In FIG. 2, a light source 200 can emit a white unpolarized light S+P, which enters a PBS 201 and is split into an S-state polarized beam S1 and a P-state polarized beam P2. The S-state polarized beam S1 is deflected by 90° and enters a dichroic prism set 204, which includes several dichroic prisms 204a,204b,204c,and 204d.After passing the dichroic prism set 204, the S-state polarized beam S1 are split into a red light RS, a green light GS, and a blue light BS, which respectively travel to LCD panels 205R, 205G and 205B. The LCD panels 205R, 205G and 205B respectively convert the red light RS, the green light GS, and the blue light BS into a red light RP, a green light GP, and a blue light BP with P-state polarization, and reflect the lights RP, GP, and BP onto a projection lens 206, which projects passing light onto a screen (not shown).

[0011] For the P-state polarized beam P2, as it passes the PBS 201, it enters a half-wave plate 202 and is polarized to an S-state polarized beam S2. The S-state polarized beam S2, similar to the S-state polarized beam S1, is reflected by the LCD panels 205R, 205G and 205G and reach the screen at the end.

[0012] In this conventional projection system of FIG. 2, the dimension and the light focusing issues of the conventional projection system of FIG. 1 is reduced. However, since the system of FIG. 2 is very complicate, production yield rate is low and fabrication cost is high. Moreover, since several prisms are used in the system, a little misalignment may cause a large error. Its requirement of alignment precision is much higher that a usual level.

[0013] It is at least an objective of the present invention to provide a LCD system, particularly suitable for a color LCD system. The LCD system includes a projection system with a denser layout so that system dimension and back focal length are effectively reduced. A light path needs no a complicate reflection set so that there is no need of high alignment precision. Fabrication cost is also effectively reduced.

[0014] In accordance with the foregoing and other objectives of the present invention, a projection system used in a LCD system is provided. The projection system includes a light source, a polarization set which further includes a double dove prism, a vertical prism and a half-wave plate, a polarization beam splitter (PBS), a dichroic prism, and a projection lens. The light source emits a white light, which enters the polarization set and is split into a P-state polarized blue light and a mixed light. The mixed light includes an S-state polarized red light and an S-state polarized green light. The PBS allows the P-state polarized blue light to transmit and enter onto a blue light LCD panel, and deflects the mixed light by 90°. The dichroic prism splits the S-state polarized red light and the S-state polarized green light of the mixed light, which respectively enter a red light LCD panel and a green light LCD panel. The projection lens collects lights from the red, green, blue LCD panels and project the lights onto a screen.

[0015] The invention can be more fully understood by reading the following detailed description of the preferred embodiment, with reference made to the accompanying drawings as follows:

[0016] FIG. 1 is a structure diagram, illustrating a polarization light projection system used in a reflection-type color display board as disclosed by U.S. Pat. No. 5,530,489;

[0017] FIG. 2 is a structure diagram, illustrating a polarization light projection system used in a reflection-type color display board as disclosed by U.S. Pat. No. 5,153,752;

[0018] FIG. 3 is a structure diagram, schematically illustrating a polarization light projection system using reflection-type LCD panels, according to a preferred embodiment of the invention;

[0019] FIG. 4 is a reflection factor distribution, schematically illustrating a reflection spectrum of the optical film 302 in FIG. 3; and

[0020] FIG. 5 is a reflection factor distribution, schematically illustrating a reflection spectrum of the optical film 304 in FIG. 3

[0021] The conventional projection system used in a LCD system includes issues of, for example, large dimension, poor focusing quality, complicate system, or high fabrication cost. The invention introduces a projection system used in a LCD system so as to at least solve the above issues.

[0022] FIG. 3 is a structure diagram, schematically illustrating a polarization light projection system using reflection-type LCD panels, according to a preferred embodiment of the invention. In FIG. 3, a greatly simplified projection system is designed so that dimension is greatly reduced, a back focal length is also reduced. The system has a large tolerance of misalignment. Fabrication cost is also reduced.

[0023] The projection system of the invention includes a light source 300, a double dove prism 301A, a vertical prism 301B, a half-wave plate 305, a polarization beam splitter (PBS) 306, a color filter prism 309, and a projection lens 311. The double dove prism 301A further includes optical films 302 and 304, in which the optical film 302 behaves as a PBS for blue light but behaves as a dichroic mirror for red light and green light. The light source 300, such as a lamp, emits a light, such as a white light, which is incident on the optical film 302. A red light R and a green light G of the white light are reflected and a blue light B is split into a blue light BS with S-state polarization and a blue light BP with P-state polarization. The blue light BS is also reflected by the optical film 302 so as to form a mixed light RG+BS.

[0024] The blue light BP continuously travels to a reflection mirror 303 so that the blue light BP is deflected by 90°, travelling in parallel to the mixed light RG+BS. The blue light BP then directly travels to a blue LCD panel 310B through the optical film 302 and the BPS 306.

[0025] The mixed light RG+BS resulting from the optical film 302 keep travelling to the optical film 304, which behaves as a PBS for red light and green light but behaves as a dichroic mirror for blue light. So, the red/green light RG of the mixed light RG+BS is split into a red/green light RPGP with P-state polarization and a red/green light RSGS with S-state polarization. The red/green light RPGP continuously travels in the same direction but the red/green light RSGS is deflected by 90° onto the optical film 302. Due to the property of the optical film 304, the blue light BS just transmits the optical film 304 and combines with the red/green light RPGP to form a mixed light RPGP+BS, which enters the half-wave plate 305 through the vertical prism 301B. The purpose of the vertical prism 301B is used to compensate a corner of the double dove prism 301A to form a box corner for easy assembling. The half-wave plate 305, for example, located on the vertical prism 301B so as to only allow the mixed light RPGP+BS to pass. The half-wave plate 305 changes polarization state of passing light so that the red/green light RPGP is converted into a red/green light RS′GS′ with S-state polarization, and the blue light BS is converted into a blue light BP′. The blue light BP′ travels to the blue LCD panel 310B through the PBS 306 but the red/green light RS′GS′ is deflected by the PBS 306 by 90° onto the dichroic prism 309.

[0026] As the red/green light RSGS is incident on the optical film 302, it is deflected again by 90° so that the red/green light RSGS is reflected to the PBS 306, which deflects the red/green light RSGS again. As a result, the red/green light RS′GS′ and the red/green light RSGS do travel in parallel and both enter the dichroic prism 309. The red/green light RS′GS′ and the red/green light RSGS are respectively split by the dichroic prism 309 into a green-content light G and a red-content light. The red-content light R travels to a red LCD panel 310R, and the green-content light G travels to a green LCD panel 310G. All the red LCD panel 310R, the green LCD panel 310G, and the blue LCD panel 310B respectively reflect incident lights back along the same light path to the PBS 306, in which all polarization states are inverted also. Through the PBS 306, a mixed light RPGP+BS and a mixed light RP′GP′+BS′ therefor are formed and travel to the projection lens 311. The projection lens 311 can project incident light onto a screen (not shown).

[0027] In this projection system of the invention, the optical film 302 can be formed to include, for example, a stacked-layer structure by alternatively depositing layers of materials with high and low refractive indices as listed in Table 1. Similarly, the optical film 304 can also be formed, for example, like the optical film 302 with two different film materials as listed in Table 2. Their reflection factors are shown in FIG. 4 and FIG. 5. FIG. 4 is a reflection factor distribution, schematically illustrating a reflection spectrum of the optical film 302 in FIG. 3. FIG. 5 is a reflection factor distribution, schematically illustrating a reflection spectrum of the optical film 304 in FIG. 3. An incident angle is 45° so as to deflect light by 90°. Each S and P curves in FIG. 4 and FIG. 5 respectively represent an S-state polarized light and a P-state polarized light. An observable range of wavelength (λ) is, for example, about between 400 nm and 690 nm. Both the optical films 302 and 304 may also be formed by deposition of more than two film materials. For example, some layers with medium refractive index may be further included in the stack-layer structure of the optical films 302 and 304.

[0028] The invention has been described using an exemplary preferred embodiment. However, it is to be understood that the scope of the invention is not limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements. The scope of the claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.