Flat-panel picture display device

• US 5,808,713 A
• Filed: 09/20/1996
• Issued: 09/15/1998
• Est. Priority Date: 09/22/1995
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Broer, Dirk J., Henzen, Alexander V., Smid, Reinder
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): TON, MINH TOAN T
• Application Number:
  US08/710,625
• Time in Patent Office: 725 Days
• Field of Search: 349/98, 349/113, 349/74, 349/65, 349/64, 349/115
• US Class Current: 349/98
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/133543 Cholesteric polarisers
• CPC Class Codes: G02F 1/13355 Polarising beam splitters [PBS]
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one
• CPC Class Codes: G02F 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n

Abstract

Flat-panel picture display device comprising a picture display panel for modulating the state of polarization of polarized light coupled into said panel in conformity with a picture to be displayed. The light is polarized by means of a reflective polarizer which is integrated or not integrated with the picture display panel. At least a part of the picture display panel functions as an optical waveguide, notably for the beam component b₂ having the state of polarization which is not suitable for modulation. An analyzer is present at a first surface of the picture display panel. The polarizing means in the form of a reflective polarizer are present at a second surface of the picture display panel, which surface is located opposite the first surface. A light-directing system is present at the surface of the polarizer remote from the picture display panel, which system is used for sending the light leaving the picture display panel at this surface without contributing to the formation of the image to the picture display panel again so that it will as yet have a chance of being converted into light having the desired state of polarization.

Claims

1. A flat-panel picture display device, comprising:

a picture display panel which includes an integral optical waveguide having opposite first and second major surfaces, a first end face which is positioned to receive polarized light, a second end face opposite the first end face, and means for modulating the state of polarization of the received polarized light in accordance with picture information to be displayed;

an analyzer proximate the first major surface;

a reflective polarizer proximate the second major surface;

a light directing system proximate a major surface of the reflective polarizer which is remote from the picture display panel;

wherein the reflective polarizer allows a first portion of the received polarized light having a desired state of polarization to pass therethrough and reflects a second portion of the received polarized light having an unwanted state of polarization;

wherein the reflected second portion of the received polarized light propagates through the optical waveguide in a direction away from the first end face of the optical waveguide, whereby at least a portion of the second portion which propagates through the optical waveguide will be depolarized due to birefringence of the optical waveguide and eventually transformed into the desired state of polarization for passage through the reflective polarizer; and

,

wherein the light directing system is configured to at least partially reflect the first portion of the received polarized light and the at least a portion of the second portion of the received polarized light which is transformed into the desired state of polarization, towards the picture display panel, for use in forming the picture to be displayed.

2. The display device as set forth in claim 1, further comprising:

a light source for generating the polarized light; and

,

a reflector positioned behind the light source for reflecting portions of the polarized light which are emitted away from the first end face of the optical waveguide, back towards the first end face.

3. The picture display device as set forth in claim 1, wherein the light directing system includes:

a reflector disposed in spaced-apart, parallel relationship to the major surface of the reflective polarizer which is remote from the picture display panel;

a diffuser disposed between the reflector and the major surface of the reflective polarizer which is remote from the picture display panel;

wherein the first portion of the received polarized light which passes through the reflective polarizer is incident upon the diffuser; and

,

wherein a first part of the light incident upon the diffuser is diffused towards the picture display panel for use in forming the picture to be displayed, and a second part of the light incident upon the diffuser is diffused away from the picture display panel; and

,

wherein the second part of the light which is diffused away from the picture display panel is reflected by the reflector towards the picture display panel for use in forming the picture to be displayed.

4. The picture display device as set forth in claim 1, wherein the light directing system comprises a plurality of facets formed in the major surface of the reflective polarizer which is remote from the picture display panel.

5. The picture display device as set forth in claim 4, wherein the facets enclose an angle with respect to the major surface of the reflective polarizer which is remote from the picture display panel.

6. A. The picture display device as set forth in claim 1, wherein the reflective polarizer comprises a cholesteric polarizer.

7. The picture display device as set forth in claim 6, wherein the cholesteric polarizer comprises a single layer of a liquid crystalline polymer material, within which single layer the pitch of the molecular helix varies substantially continuously between first and second values which correspond to lower and upper limits, respectively, of a reflection band required to encompass the full visible wavelength range.

8. The picture display device as set forth in claim 1, further comprising a depolarizing reflector disposed proximate the second end face of the optical waveguide.

9. The picture display device as set forth in claim 3, wherein the diffuser comprises a pattern of discrete diffusing elements formed on the major surface of the reflective polarizer which is remote from the picture display panel.

10. The picture display device as set forth in claim 1, further comprising an nλ

/4 plate disposed between the reflective polarizer and the picture display panel, where n is an odd integer.

11. The picture display device as set forth in claim 10, further comprising an nλ

/4 plate disposed between the reflective polarizer and the picture display panel, where n is an odd integer, wherein the nλ

/4 plate serves as a substrate of the cholesteric polarizer.

12. The picture display device as set forth in claim 1, wherein the reflective polarizer is comprised of a plurality of layers, at least one of which is made of a birefringent material.

13. The picture display device as set forth in claim 1, wherein the reflective polarizer is comprised of a plurality of layers each of which is made of a birefringent material.

14. The picture display device as set forth in claim 1, wherein the reflective polarizer is comprised of a plurality of layers, alternating ones of which are made of a birefringent material.