Directional Privacy Display Waveguide Light Extraction
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Solution Overview
Problem
Spatially multiplexed autostereoscopic displays suffer from reduced spatial resolution, image flicker, and increased cross-talk due to non-uniform viewing windows and gaps between pixels, which limit viewing freedom and are not suitable for privacy displays.
Innovation Solution
A directional display apparatus with a waveguide and an array of light sources that uses total internal reflection and light extraction features to direct light into optical windows, a transmissive spatial light modulator, and a control system to synchronize light sources and modulator operation, creating a primary image for a primary observer and a secondary image with reduced luminance and contrast for a secondary observer, enhancing privacy and reducing cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If spatially multiplexed autostereoscopic displays use pixel aperture shapes and parallax components to create viewing windows, then viewing freedom is enabled, but image flicker occurs and spatial resolution is reduced
Solution Approach 1:
The display divides the viewing area into multiple discrete optical windows corresponding to different viewing positions. Each window is formed by directing light from specific pixel sets through the parallax component at defined angles, creating separate viewing zones that eliminate flicker by ensuring continuous image availability at each position.
Solution Approach 2:
The system transitions from temporal multiplexing to spatial multiplexing by using a parallax barrier or lenticular screen to direct light from multiple pixel sets into different spatial directions simultaneously. This creates multiple viewing windows in the spatial domain, enabling viewing freedom without the temporal flicker associated with sequential display methods.
2Ease of operation
If defocusing optical elements is done to reduce image flicker, then viewing freedom is improved, but image cross-talk increases and visual strain increases
Solution Approach 1:
The parallax component is designed with localized optical properties at different positions to direct light from specific pixel sets into different directions. Each local region of the parallax barrier handles specific viewing angles, ensuring that light from adjacent pixels remains confined to its designated viewing window, thereby preventing cross-talk while maintaining viewing freedom.
3Reliability
If pixel aperture shape is adjusted to reduce flicker, then image stability is improved, but display brightness is reduced
Solution Approach 1:
The system dynamically assigns different pixel sets to different viewing windows based on the desired display content and viewing position. By flexibly controlling which pixels illuminate which viewing windows, the system maintains high brightness by utilizing the full pixel aperture area without being constrained by fixed aperture shapes, while still achieving image stability through coordinated control of multiple pixel sets.
4Object-affected harmful factors
If directional backlight is used to provide privacy display, then off-axis visibility is reduced, but viewing freedom for primary observer is limited
Solution Approach 1:
The directional backlight creates multiple discrete optical windows at different viewing angles, each optimized for a specific viewing position. The parallax component segments the light paths so that each window provides directional illumination for its designated viewing zone, enabling privacy protection through angle-selective visibility while maintaining viewing freedom within the defined zones.
Solution Approach 2:
The system uses the angular dimension to provide privacy by directing light into specific cones corresponding to authorized viewing positions. The parallax barrier or lenticular screen creates angularly selective optical windows that allow the primary observer at authorized positions to view the display freely while blocking off-axis viewing, thus achieving privacy without sacrificing viewing freedom for legitimate users.
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 high luminance and contrast for a primary observer while obscuring the image for a secondary observer, improving privacy and reducing power consumption, and enabling autostereoscopic operation with low visibility of the secondary image.
Implementation Method 1
the first guide surface is arranged to guide light by total internal reflection
Implementation Method 2
the second guide surface comprises a plurality of light extraction features arranged to deflect light guided through the waveguide out of the waveguide through the first guide surface as output light
Data Source
AI summary
A directional privacy display may include a waveguide; and an array of light sources and spatial light modulator that operate in a time sequential manner. The waveguide may include light extraction features arranged to direct light from an array of light sources by total internal reflection to an array of viewing windows and a reflector arranged to direct light from the waveguide by transmission through extraction features of the waveguide to the same array of viewing windows. First and second phases may be temporally multiplexed with respective primary and secondary images and primary and secondary angular illumination distributions. An efficient and bright privacy display may be provided with obscured primary image visibility for off-axis observers.