Optical Stack for Directional Display Privacy
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Solution Overview
Problem
Existing display technologies face challenges in providing effective privacy by reducing off-axis visibility while maintaining on-axis luminance, particularly due to high losses in head-on illumination and the occurrence of Moiré artefacts, and require complex configurations that increase inventory and cost.
Innovation Solution
A display device comprising a spatial light modulator, display polarizers, and passive retarders with specific orientations and configurations to reduce off-axis luminance, including crossed retarders and retarders with slow axes at 45° and 135°, 0°, and 90°, which are integrated with a directional waveguide and polarizers to control light distribution and minimize stray light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If micro-louvre optical films are used to provide privacy function, then off-axis visibility is reduced, but head-on illumination losses are high
Solution Approach 1:
The optical system is segmented into multiple functional layers: a first optical stack with polarizers and retarders for privacy control, and a second optical stack with additional polarizers and retarders for stray light reduction. Each layer performs a specific function, allowing independent optimization of privacy and illumination efficiency.
Solution Approach 2:
The patent employs multiple passive retarders with different orientations (0°, 45°, 90°, 135° slow axes) to modify the optical parameters of light propagation. By changing the orientation parameters of retarder layers, the system achieves directional control of light transmission, maintaining high on-axis luminance while reducing off-axis visibility.
2Object-affected harmful factors
If micro-louvre films are used for privacy, then off-axis visibility is reduced, but Moiré artefacts occur due to beating with pixels
Solution Approach 1:
The patent replaces the mechanical micro-louvre structure with an optical system based on polarizers and passive retarders. This substitution eliminates the physical grating structure that causes Moiré effects while maintaining the privacy function through polarization-based directional control of light transmission.
3Manufacturing precision
If pitch of micro-louvre is selected for panel resolution, then privacy function is optimized, but inventory and cost increase
Solution Approach 1:
The optical stack design is universal and can be applied to different panel resolutions without requiring custom pitch optimization. The polarizer-retarder combination provides privacy control that is independent of pixel pitch, allowing the same optical components to be used across multiple product lines, thereby reducing inventory complexity and cost.
4Illumination intensity
If additional polarizers and passive retarders are added, then off-axis luminance is reduced, but device complexity increases
Solution Approach 1:
The patent combines multiple optical functions into integrated stacks: the first optical stack merges privacy control functions (polarizer + retarder), and the second optical stack merges stray light reduction functions (additional polarizer + additional retarder). This merging approach achieves complex optical control while maintaining a structured, modular architecture that simplifies manufacturing and assembly.
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 effectively reduces off-axis visibility and stray light, maintaining high on-axis luminance, and allows for flexible operation in landscape and portrait modes without requiring matching to panel pixel resolution, thus enhancing privacy and reducing costs.
Implementation Method 1
at least one passive retarder arranged between the additional polariser and the display polariser
Implementation Method 2
The display polariser may have an electric vector transmission direction that is parallel to the electric vector transmission direction of the additional polariser
Data Source
AI summary
A privacy display comprises a spatial light modulator and a passive retarder arranged between first and second polarisers arranged in series with the spatial light modulator. On-axis light from the spatial light modulator is directed without loss, and off-axis light has reduced luminance. The visibility of the display to off-axis snoopers is reduced by means of luminance reduction over a wide polar field of view. Off-axis visibility of the display in an automotive vehicle can be reduced.