Light modulator including a collimator comprising an interferenc

Details Light modulator including a collimator comprising an interferenc Light modulator including a collimator comprising an interferenc

1999-10-25

2000-06-20

Ben, Loha

Optical: systems and elements

Optical modulator

359350, 359359, 359360, 359588, 359589, 359722, 362 31, 349 64, 428216, G02B 2600, G02B 528

Patent

active

060784210

DESCRIPTION:

BRIEF SUMMARY
This invention relates to an improved collimator, particularly for use with a liquid-crystal display system of the type using a photoluminescent screen, such as are discussed, for instance, in WO 95/27920 (Crossland et al).
Means for producing collimated light suitable for use with liquid-crystal display cells are known. For example, IBM Technical Disclosure Bulletin (1987) discloses at page 4838 a system involving a light guide plate and a lens plate with a plurality of moulded lenslets placed in front of the plate. The moulded lenslets collimate the light passing through holes in the light guide plate. A similar arrangement is disclosed in European patent application No. 529 832 (Rockwell International). In that case, phosphors are used to provide small spots of light to be focused by a lens array.
Collimators can be desirable in liquid-crystal displays for various reasons, one being that when a diffuse light source is used the light passing through a single cell, not being collimated, will spread and cover a substantial area of the photoluminescent screen, leading to crosstalk. This will impair the resolution of the screen, and is of particular significance for LCDs using a photoluminescent screen, where in colour displays it may result in a phosphor of the wrong colour being illuminated. For the standard kinds of liquid-crystal cells increasing the collimation of the backlighting has the disadvantageous effect of reducing the angle of view of the display, though the display is brighter in the collimation direction. The light from the display thus has to be spread out again using, for instance, a diffuser plate. In photoluminescent LCDs (PLLCDs), however, the phosphor on the front screen performs the diffusing Function to great advantage, as explained in WO 95/27920. However, prior art collimators are bulky and require expensive manufacturing techniques to produce the lens array accurately.
Anti-reflection coatings for optical components are also known. These work on the principle that all the light incident normal to a transparent surface of refractive index n.sub.1 is transmitted if the surface is covered with a thin film of refractive index n.sub.2 which satisfies the relations: .lambda. is the wavelength of the light used. At other angles of incidence (and at other wavelengths) some of the light is reflected.
The anti-reflection coating only works optimally for light at normal incidence at a specific wavelength. However, by using a plurality of dielectric layers of varying refractive index and thickness the spectral pass band at normal incidence can be improved. The invention is based on the recognition that thin dielectric coatings can be put to novel use in displays.
Collimator-like devices based on dielectric coatings are also known. For example, JP 07-43528 (Fuji Photo Film Co. Ltd.) discloses a filter device designed to protect a photo-sensitive material from light entering at angles other than a specified angle and wavelength and JP 59-67503 (Matsushita Electric Industrial Co. Ltd.) describes a spectroscopic dispersion element which uses wedge-shaped interference filters to pass only light perpendicular to the plane of the filter, further spectrally narrowing the passed light as a consequence of the spectral dispersion of the elements of the filter. U.S. Pat. No. 5,572,500 (Pioneer) uses an interference filter to eliminate diffractive lobes to make a smaller beam spot in a laser recording system.
According to a first aspect of the invention there is provided a collimator for light in a narrow band around a predetermined wavelength, comprising an interference filter having a stack of dielectric layers with optical thicknesses adapted to transmit light in the band incident at a predetermined range of angles of incidence centred at normal incidence more efficiently than light in the band incident at other angles, in which the interference filter has the form of a low-pass filter with a cut-off wavelength longer than the predetermined wavelength.
In an alternative aspect the collimator comprises a

REFERENCES:
patent: 5173808 (1992-12-01), Auer et al.
patent: 5572500 (1996-11-01), Ikeya et al.
patent: 5933273 (1999-08-01), Ferrante et al.
patent: 5956107 (1999-09-01), Hashimoto et al.
patent: 5965365 (1999-10-01), Shirai
patent: 5966240 (1999-10-01), Lange et al.
patent: 5978134 (1999-11-01), Chaton et al.
patent: 5993950 (1999-11-01), Novis et al.
patent: 5999322 (1999-12-01), Cushing
Patent Abstracts of Japan, vol. 095, No. 005, Jun. 30, 1995, & JP 07 0435238 A (Fuji Photo Film Co. Ltd), 141 Feb. 1995.
Patent Abstracts of Japan, vol. 008, No. 171 (P-293), Aug. 8, 1984 & JP 59 067503 A (Matsushita Denki Sangyo KK), Apr. 17, 1984.
Patent Abstracts of Japan, vol. 017, No. 669 (P-1657), Dec. 9, 1993 & JP 05 224002 A (Fuji Photo Optical Co Ltd.), Sep. 3, 1993.
Soviet Journal of Optical Technology, vol. 46, No. 1, Jan. 1979, pp. 57-58, XP002073633, .N. Cherepanova et al., "Optical Properties of Narrow-Band Interference Filters as Function of Incidence Angle and Polarization of the Incident Light".
IBM Technical Disclosure Bulletin, vol. 29, No. 11, Apr. 1, 1987, pp. 4838-4839, XP002001571, "Backlighting For Liquid Crystal Display".

Affiliated with

Also associated with

Rating

Light modulator including a collimator comprising an interferenc does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Light modulator including a collimator comprising an interferenc, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light modulator including a collimator comprising an interferenc will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1858039