Optical system for miniature personal displays using reflective light valves

Abstract

An illumination system and display are disclosed that include a light for providing light, a polarizing beam splitter (PBS) having a first surface that receives the light from the backlight. The PBS passes a first polarization of the received light to a curved mirror located at a second PBS face, which second PBS face is opposite the first PBS face. The curvature of the mirror provides the optical power necessary for proper imaging, while limiting the reflecting area of the mirror provides an aperture stop that determines the numerical aperture of the optical system. The display also includes a quarter wave plate and a spatial light modulator (SLM). The quarter wave plate is located between the PBS and mirror and changes the first polarization of light, directed from the PBS to the mirror, to a second polarization which is reflected from the mirror back to the PBS. The SLM receives this second polarization of light after reflection thereof by the PBS, and selectively rotates the second polarization of light to form an image forming light having the first polarization, which is reflected back to the PBS. Through an exit face, the PBS provides the rotated image forming light to a viewer. Between the viewer and the PBS exit surface, an imaging lens system is provided that includes at least one folding mirror.

Description

BACKGROUND OF THE INVENTION[0001] 1. Field of the Invention[0002] The present invention is directed to an optical system for illuminating and imaging a reflective light valve, and more particularly, to systems using compact lightweight, and foldable optics for personal miniature displays using reflective light valves.[0003] 2. Discussion of the Prior Art[0004] Typically, conventional miniature displays, such as head mounted displays (HMDs), are based on miniature cathode ray tube (CRT) or transmission-based liquid crystal light valve technology. The CRT-based systems are bulky, expensive, and heavy, and primarily used for military helmet-mounted applications. This technology is not suitable for lightweight, compact personal displays.[0005] Transmission-based liquid crystal (LC) technology is the preferred technology for these portable miniature displays today. Although appropriate for the low resolution displays currently available, such as sub-VGA to VGA (640.times.480 pixels), thi...

AI Technical Summary

Benefits of technology

[0019] The object of the present invention is to provide an optical system that eliminates the problems of conventional optical systems.

[0020] Another object of the present invention is to provide an optical system which is compact, efficient, has reduced background stray light and ghost images, and has enhanced contrast and brightness.

[0021] Yet another object of the present invention is to provide an optical system that has high optical performance and accommodates folding mirrors suitable for compact portable displays and head mounted displays (HMDs).

[0022] A further object of the present invention is to provide an optical system that provides the imaging and light controlling optics, including providing a desired numerical aperture, in a compact and folded optical package.

Problems solved by technology

The CRT-based systems are bulky, expensive, and heavy, and primarily used for military helmet-mounted applications.

This technology is not suitable for lightweight, compact personal displays.

Although appropriate for the low resolution displays currently available, such as sub-VGA to VGA (640.times.480 pixels), this transmission-based LC technology is not adequate for high resolution miniature portable displays.

Thus, the pixel size is only limited by the CMOS technology required to fabricate the drive circuitry, which today is less than 10 microns per pixel.

However, reflection-based light valves, such as liquid crystal (LC) spatial light modulators (SLMS) have complex illumination requirements.

A simple backlight structure typically used in transmission-based displays is not directly applicable for reflective SLMS.

The addition of light brightness enhancing polymer films improves the directionality of the light, but cannot produce a collimated light source.

Although the conventional optical system 10 provides useful illumination to the SLM 14, the optical system 10 is not optimal and suffers from a number of disadvantages.

First, light coupling to the SLM 14 is inefficient.

Second, there is no control for the numerical aperture (NA) of the illumination.

This produces poor contrast in the resulting image.

Furthermore, light at the extreme angles will scatter off the numerous optical surfaces producing additional depolarized background stray light and ghost images that will further degrade the image contrast.

Although the conventional illumination optical system 50 is adequate for illuminating the reflective SLM 14, the optical system 50 is large and bulky.

In addition, the optical system 50 is not suitable for portable personal displays, particularly compact, lightweight, head mounted displays.

Images