Front-lit LCOS for AR displays

Abstract

Augmented reality (AR) displays are recognized as an important human–machine interface for next-generation computing platforms. They consist of a micro projector and a waveguide combiner. Researchers are looking for a compact and powerful projector to power up the waveguide combiner. The projector itself is comprised of microdisplays [liquid-crystal-on silicon (LCOS), MicroLED, laser beam scanning, and organic light-emitting diode] that generate the virtual image and a collimating optics module that collimates the image toward the waveguide’s entrance aperture. However, the microdisplays mentioned above suffer from different problems, such as being too bulky, having too low brightness, reliabilities issue, or too high power consumption. In particular, projectors using LCOS are too bulky and heavy to fit into an AR glasses form factor. Therefore, we proposed a new illumination system called front-lit for LCOS. In the front-lit system, the conventional polarization beam splitter (PBS) in the LCOS projector is replaced by a polarized waveguide plate with a micro mirror array. The polarized waveguide functions like a PBS. It reflects the s-polarized beam and transmits to the p-polarized beam. Moreover, the polarized waveguide input beam is shaped to a profile with two intensity peaks from a Lambertian profile by our coupling lens, which is located between the LED and waveguide. Having this profile, the polarized waveguide efficiency is improved, and a larger display illumination area is obtained. From our real measurement results, it is proven that the front-lit LCOS significantly reduces the size and weight of the illumination system. It weighs less than 1 g, and the size of the full module is as small as 0.47cc. The color filter front-lit LCOS and color sequential LCOS deliver 30,000 nits / 175 mW and 100,000 nits / 300 mW, respectively. The color sequential front-lit LCOS also provides high image quality with a 500:1 contrast ratio and 140% sRGB color gamut.