Switchable Diffuser Illuminator for Exit Pupil and Speckle Control
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Solution Overview
Problem
Near-eye displays face challenges with bulky, unbalanced, and heavy devices due to inefficient light sources and illuminators, leading to image distortions and artifacts, and laser illumination causes speckle patterns and reduced exit pupil size.
Innovation Solution
A lightguide-based directional illuminator with a switchable diffuser that modulates light beams using spatially variant amplitude or phase delay, controlled by an external signal, to optimize exit pupil size and reduce speckle patterns, utilizing components like switchable polarization volume holograms, Pancharatnam-Berry phase liquid crystal gratings, and fluidic gratings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If laser illumination is used to illuminate the display panel, then the light source efficiency is improved, but speckle patterns are generated and exit pupil size is reduced
Solution Approach 1:
A light guide is introduced as an intermediary component between the laser light source and the display panel. The light guide receives collimated light from the laser, expands it spatially, and redistributes it to illuminate the display panel uniformly. This mediator converts the highly directional laser light into expanded, diffused illumination, eliminating speckle patterns while maintaining laser efficiency.
Solution Approach 2:
The light guide expands the light beam in spatial dimensions (x and y directions) perpendicular to the original propagation direction. By transforming the one-dimensional collimated laser beam into a two-dimensional expanded illumination field, the system maintains the energy efficiency of laser sources while eliminating the harmful speckle effect through spatial redistribution.
2Area of stationary object
If a light guide is used to expand the light beam, then the exit pupil size is increased, but the device becomes more complex
Solution Approach 1:
The light guide is implemented as a thin planar optical waveguide structure rather than a bulky three-dimensional optical system. This thin-film approach achieves beam expansion and exit pupil enlargement while maintaining a compact, lightweight form factor suitable for near-eye displays, thereby increasing exit pupil size without proportionally increasing device complexity.
3Area of stationary object
If the light guide expands the light beam in x and y directions, then the illumination area is increased, but the light intensity is reduced
Solution Approach 1:
A periodic diffraction grating structure is embedded within the light guide to periodically modulate and redirect the expanded light beam. This periodic optical element ensures uniform light distribution across the display panel surface while maintaining adequate illumination intensity by efficiently coupling light into the panel through repeated diffraction events.
Data Source
AI summary
A directional illuminator for a display apparatus includes a switchable diffuser for tuning a divergence of a light beam illuminating a display panel of the display apparatus. The tunable divergence of the illuminating light beam translates into a tunable exit pupil size at the eyebox of the display apparatus, which may be matched to a pupil size of a user's eye, thus providing a configurable illumination of the eye pupil. A tiltable reflector in an optical path of the illuminating light beam may be used to shift the location of the exit pupil at the eyebox of the display apparatus.