Directional diffuser

Abstract

A diffuser is disclosed which transmits or reflects incident light into a specific range of angles. In a preferred embodiment, this light is uniformly scattered throughout a cone of angles. The diffuser consists of two parts. The first part diffracts or reflects light into a specific offset angle. The second part, in the preferred embodiment, uniformly scatters the light through a range of angles, which is centered on the offset angle. The diffusers have utility in applications such as screens for wrist watches, computers, calculators, and cell phones.

Description

RELATED APPLICATIONS [0001] This application is a divisional application of U.S. Ser. No. 10 / 639,552, filed Aug. 12, 2003, which is a divisional application of U.S. Ser. No. 09 / 920,060, filed Aug. 1, 2001 (now U.S. Pat. No. 6,608,722), which claims priority to U.S. Ser. No. 60 / 222,182, filed on Aug. 1, 2000, both of which are incorporated herein by reference.FIELD OF THE INVENTION [0002] The present invention relates generally to an optical diffuser and method for making the same, and more particularly to an optical diffuser having a high diffraction efficiency, broadband response and cost effective method of producing the same. BACKGROUND [0003] Reflective diffusers are required for many applications, including liquid crystal displays, to enhance their viewability. Often these diffusers, placed behind the liquid crystal element, are simply roughened reflective surfaces. These reflectors utilize no back lighting, but instead rely on the scattered reflection of the ambient light. Unf...

AI Technical Summary

Benefits of technology

The present invention is a blazed diffuser that includes a reflective surface with a sawtooth structure. This structure reflects incident oblique light into a beam that is more or less normal to the device. The sawtooth surface is also superimposed with a second structural component that diffracts incident light into rays, which constitute only those over a restricted narrow angle. This results in a "flat top" scattering, where almost all incident light is utilized and efficiencies approaching 100% for all visible wavelengths are possible. In another embodiment, the blazed diffuser can be made entirely by optical, holographic means, and it can be fabricated in such a way that the broadband spectral colors are properly mixed so that the diffracted light appears white.

Problems solved by technology

Unfortunately, light scattered from these devices is centered around the glare angle, which is in direct line-of-sight with the undesirable reflections from their front surface.

Furthermore in many applications, such as computer screens, and perhaps watches, the preferred orientation of the device is one for which viewing at the glare angle is not optimum.

A major disadvantage is that the surface-relief hologram can be inefficient.

As a result, the surface-relief hologram can appear dim because most of the incident white light falls outside of this select band.

Further processing can increase the bandwidth, thus increasing the apparent brightness, but the resulting diffuser still has a predominant hue, which is in most cases undesirable.

In any event the bandwidth is still somewhat restricted, thus limiting the reflection efficiency.

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