Directional Backlight Optical Stack for Privacy Viewing Windows
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Solution Overview
Problem
Spatially multiplexed autostereoscopic displays suffer from reduced spatial resolution, non-uniform viewing windows, image flicker, and increased image cross talk due to pixel gaps and optical element defocusing, which compromise brightness and viewing freedom.
Innovation Solution
A directional illumination apparatus with a waveguide and polarizers, including a switchable liquid crystal retarder, is used to direct light into specific viewing windows, reducing visibility to snoopers and maintaining luminance for primary users, while allowing for wide-angle viewing and privacy modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optical elements are defocused to reduce image flicker, then image flicker is reduced, but image cross talk increases and visual strain increases
Solution Approach 1:
The patent changes the optical parameters by replacing conventional diffusers with engineered holographic diffusers that have specific diffuser functions. These diffusers are designed with particular scattering characteristics that maintain image quality while reducing flicker, avoiding the need to defocus optical elements and thereby preventing increased cross talk and visual strain.
2Reliability
If pixel aperture shape is adjusted to reduce image flicker, then image flicker is reduced, but display brightness is reduced and addressing electronics are compromised
Solution Approach 1:
The patent introduces engineered holographic diffusers as intermediary optical elements between the pixel array and the viewing window. These diffusers mediate the light distribution to eliminate flicker effects without requiring changes to the pixel aperture shape, thereby preserving both display brightness and the integrity of addressing electronics.
3Ease of operation
If conventional diffusers are used in imaging directional backlight, then light distribution is provided, but viewing window uniformity is poor and spatial resolution is reduced
Solution Approach 1:
The patent changes the diffuser parameters by using engineered holographic diffusers with specifically designed diffuser functions rather than conventional diffusers. These engineered diffusers provide the necessary light distribution while maintaining superior viewing window uniformity and spatial resolution through controlled light scattering patterns.
4Ease of operation
If imaging directional backlight is used to direct light into viewing windows, then directional illumination is achieved, but snoopers can still see the display from certain angles
Solution Approach 1:
The patent applies local quality by using engineered holographic diffusers with position-dependent diffuser functions. Different regions of the display have diffusers tailored to their specific viewing requirements, creating highly directional illumination that directs light precisely to intended viewing windows while preventing light leakage to snooper positions, thereby achieving both directional control and privacy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides improved privacy and reduced visibility to snoopers, maintains luminance for primary users, and enhances viewing freedom by controlling light distribution and luminance across different angles.
Implementation Method 1
a waveguide arranged to receive input light from the light sources at different input positions... for guiding the input light along the waveguide
Implementation Method 2
a switchable liquid crystal retarder arranged between the waveguide and the spatial light modulator
Implementation Method 3
an input polariser arranged on the input side of the spatial light modulator between the backlight and the spatial light modulator; an output polariser arranged on the output side of the spatial light modulator
Data Source
AI summary
A backlight device includes a first array of plural light sources, a second array of plural light sources, and a control system arranged to control the first and second arrays of plural light sources. In some embodiments, the control system is arranged to provide switching between, in a first mode of operation, the first array of plural light sources being operated along a first input end of a first waveguide and a first applied voltage across a switchable liquid crystal retarder and, in a second mode of operation, the second array of plural light sources being operated along a second input end of a second waveguide and a second applied voltage across the switchable liquid crystal retarder. In some embodiments, the second applied voltage is different to the first applied voltage.