Laser illuminated backlight for liquid crystal displays
A flat panel display includes a backlight with a plurality of lasing elements. A light distributor distributes light from the lasing elements across the flat panel display. In edge-lit backlights, the light distributor may be a light guide. In direct-lit backlights, the light distributor may be one or more light diffusers that randomize the polarization of light. A polarization enhancement film increases the polarization of light from the light distributor by allowing light of a first polarization to pass through the film and reflecting light that is not of the first polarization back into the backlight. The light reflected back into the backlight is randomly re-polarized within the backlight. An array of light modulators arranged across the flat panel display modulates light emitted by the backlight.
1. A flat panel display, comprising:
a backlight including a plurality of lasing elements of at least one primary color arranged in a plurality of laser assemblies, wherein the plurality of lasing elements of at least one primary color are selected such that each lasing element emits a laser beam with a center wavelength λ 0i and a spectral bandwidth Δλ i , wherein the center wavelength of at least one of the lasing elements is wavelength-shifted with respect to the center wavelength of at least one other lasing element, and wherein said laser beams, when combined, have an ensemble spectrum Λ with an overlap parameter γ= Δλ i / S i , with Δλ i , being a mean spectral bandwidth of the lasing elements and S i being a mean wavelength shift between the center wavelengths λ 0i , of the at least one and the at least one other lasing elements, with Δλ i and S i , selected such that γ≧1;
a light distributor for substantially distributing light output by the plurality of lasing elements across the flat panel display;
a polarization enhancement film that increases the polarization of light from the light distributor by:
allowing light of a first polarization to pass through the film, and
reflecting light that is not of the first polarization back into the backlight for random re-polarization within the backlight; and
an array of light modulators arranged across the flat panel display for modulating light emitted by the backlight.
2. The flat panel display of claim 1 , wherein the light distributor randomizes the polarization of incident light.
3. The flat panel display of claim 1 , wherein the array of light modulators comprises a liquid crystal display (LCD) panel.
4. The flat panel display of claim 1 , wherein the plurality of lasing elements are positioned about an exterior edge of the light distributor.
5. The flat panel display of claim 4 , wherein the light distributor comprises a light guide.
6. The flat panel display of claim 1 , wherein the plurality of laser assemblies of the backlight are configured to directly illuminate the array of light modulators from behind.
7. The flat panel display of claim 6 , wherein the light distributor comprises a first and second light diffuser.
8. The flat panel display of claim 1 , wherein the polarization enhancement film includes a plurality of prisms.
9. The flat panel display of claim 8 , wherein the prisms are arranged in rows on the polarization enhancement film.
10. The flat panel display of claim 9 , wherein a pitch of the prisms is less than or equal to that of the light modulators of the array of light modulators.
11. The flat panel display of claim 8 , wherein the prisms are arranged in columns on the polarization enhancement film.
12. The flat panel display of claim 8 , wherein the prisms are arranged in a circular pattern on the polarization enhancement film.
13. The flat panel display of claim 8 , wherein the prisms are randomly positioned on the polarization enhancement film.
14. The flat panel display of claim 8 , wherein cross-sections of the prisms are triangular.
15. The flat panel display of claim 14 , wherein the cross-sections of the prisms are right triangles.
16. The flat panel display of claim 15 , wherein the polarization enhancement film is made of a first material, and wherein the angles of a prism cross-section at a surface of the polarization enhancement film are a right angle and a Brewster angle of the first material.
17. The flat panel display of claim 16 , wherein the polarization enhancement film is made of polyester and the Brewster angle is about 56° .
18. The flat panel display of claim 14 , wherein the cross-sections of the prisms are isosceles triangles.
19. The flat panel display of claim 18 , wherein the polarization enhancement film is made of a first material, and wherein equal angles of each triangle are each equal to about a Brewster angle of the first material.
20. The flat panel display of claim 19 , wherein the polarization enhancement film is made of polyester and the Brewster angle is about 56° .
21. The flat panel display of claim 8 , wherein cross-sections of the prisms are trapezoidal.
22. The flat panel display of claim 21 , wherein the polarization enhancement film is made of a first material, and wherein the angles of a prism cross-section at a surface of the polarization enhancement film are each equal to about a Brewster angle of the first material.
23. The flat panel display of claim 22 , wherein the polarization enhancement film is made of polyester and the Brewster angle is about 56° .
24. The flat panel display of claim 1 , wherein Δλ i and S i are selected such that γ>1.