Hologram optical element and surface light source device using the hologram optical element

Abstract

A hologram optical element having a thin form and a high degree of light transmittance, moreover that provides superior handling ease, as well as a surface light source device employing this hologram optical element. The angle at which light can be bent in this hologram optical element, has low wavelength dependency, and the hologram optical element enables prevention of spectral separation in white light incident from an oblique direction which is bent to a vertical direction and emitted. A transmitting diffraction grating, when light of wavelengths λ1, λ2 and λ3 within the ranges 0.46≦λ1≦0.50 μm (blue light), 0.53≦λ2≦0.57 μm (green light), 0.60≦λ3≦0.64 μm (red light) is incident at angle θi, the maximum diffraction angle for diffractive efficiency of each wavelength is within the range from −5 degrees to +5 degrees.

Description

[0001]This application is a Divisional application of prior application Ser. No. 10 / 555,591, filed Nov. 7, 2005, the contents of which are incorporated herein by reference in their entirety. No. 10 / 555,591 is a National Stage Application, field under 35 USC §371, of International (PCT) Application No. PCT / JP2004 / 006486, filed May 7, 2004.TECHNICAL FIELD[0002]The present invention relates to a hologram optical element that bends incident white light entering from an oblique direction to a vertical direction and a surface light source device that uses the hologram optical element. More specifically, the present invention relates to improving the degree of brightness in the direction in front of an observer by using the invention in a backlight of a liquid crystal display.BACKGROUND ART[0003]Liquid crystal displays are used as displays for computers, displays for the control panels of consumer electronic products and displays for mobile telephones. Desired improvements for liquid cryst...

AI Technical Summary

Benefits of technology

"The present invention provides a hologram optical element with high diffractive efficiency and low color and wavelength dispersion. This hologram optical element can bend white light emitted from a surface light source device in a vertical direction. The hologram optical element has a sawtooth form with a cross-sectional form of the grating groove, and can be designed to have a maximum diffraction angle of -5 degrees to +15 degrees. The hologram optical element is a transmitting diffraction grating with a refractive index of n and an average depth of h. The hologram optical element can be used in a surface light source device, which can emit light in a range of angles from 20° to 70°. The hologram optical element can also have polarized light separating, color separating, or reflection preventing functionality. The surface light source device with the hologram optical element has a high diffractive efficiency and can be used in various applications such as lighting and display."

Problems solved by technology

Spectral separation causes a reduction in display qualities such as in the deterioration of color reproduction in the color display of liquid crystals.

The method of geometric optics theory systems for bending of emitted light presents a problem in that substantial height irregularities mean that sheet film thickness increases, making it difficult to achieve a thin form.

Further, in the case of conventional prism sheets, individual prisms perform the function of bending light, and if there are defects on the prism or impurities, light passing that prism may engender display abnormalities such as a luminescent spot of abnormal light rays.

A display device of a conventional art being extremely sensitive to defects and impurities, may give rise to display abnormalities that degrade the quality of the product.

Hologram optical elements have the problems that 1) diffractive light other than that of an order of diffraction of vertically refracted incident light arises, 2) the diffractive efficiency of such an order of diffraction is low and 3) wavelength dispersion is substantial.

Images