Optical Stack With Guest-Host Retarder for Switchable Privacy
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Solution Overview
Problem
Privacy displays face challenges with high luminance loss for head-on illumination and Moiré artefacts due to micro-louvre interactions with spatial light modulators, increasing inventory and cost, and existing switchable privacy displays are inefficient in controlling off-axis optical output.
Innovation Solution
A display device comprising a spatial light modulator, a display polariser, and a guest-host liquid crystal retarder with anisotropic materials, including dichroic or pleochroic dyes and metallic nanomaterials, to control off-axis privacy by reducing stray light and recirculating off-axis light, combined with passive retarders to enhance efficiency and reduce field of view.
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 luminance is significantly lost
Solution Approach 1:
The patent employs switchable liquid crystal retarders that can dynamically change their optical properties between different states. By applying voltage, the liquid crystal molecules reorient, switching the optical path between two configurations. This dynamic control allows the system to adjust privacy levels and luminance transmission in real-time, resolving the static trade-off between privacy and brightness
Solution Approach 2:
The invention changes the optical parameters of the light modulation system by using liquid crystal retarders with specific retardance values (e.g., quarter-wave, half-wave) that can be switched between different states. This parameter switching enables control over the polarization state of light, thereby controlling both privacy and luminance without the fixed limitations of micro-louvre structures
2Object-affected harmful factors
If micro-louvre optical films are used to provide privacy function, then off-axis visibility is reduced, but Moiré artefacts are generated
Solution Approach 1:
The patent replaces the mechanical micro-louvre structure with an optical field-based solution using liquid crystal retarders and polarizers. This substitution eliminates the physical interaction between micro-louvre features and display pixels that causes Moiré artefacts, while still achieving privacy control through polarization manipulation
Solution Approach 2:
The invention introduces liquid crystal retarders as intermediary elements between the display and the viewer. These retarders mediate the light path by controlling polarization states, providing privacy control without the direct structural interaction that causes Moiré effects in micro-louvre systems
3Object-affected harmful factors
If switchable backlights are used to control off-axis optical output, then privacy function is provided, but power consumption increases
Solution Approach 1:
The patent implements light recirculation by using reflective polarizers and liquid crystal retarders to redirect off-axis light back into the optical path. Instead of allowing light to be lost or requiring additional power to compensate, the system recovers and reuses the light, improving efficiency while maintaining privacy control
Solution Approach 2:
The optical system is designed to be self-regulating through the use of switchable liquid crystal elements that automatically adjust the optical path based on applied voltage. The system controls its own light distribution and privacy characteristics without requiring external power-intensive components, reducing overall power consumption
4Object-affected harmful factors
If liquid crystal bias tilt is adjusted to control off-axis privacy, then contrast is reduced, but privacy function is achieved
Solution Approach 1:
The patent uses dynamically switchable liquid crystal retarders that can change their optical configuration between different voltage states. This dynamic control allows selective adjustment of privacy and contrast for different viewing angles without the fixed compromise required by static bias tilt adjustments
Solution Approach 2:
The invention segments the optical control function by using multiple independent liquid crystal retarder layers with different orientations and retardance values. Each layer can be independently controlled to manage specific aspects of light modulation, allowing simultaneous optimization of privacy and contrast that cannot be achieved through single-parameter bias tilt adjustment
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 a privacy display with low stray light, reduced off-axis luminance, and increased efficiency by reflecting off-axis ambient light, while allowing switching between privacy and wide-angle modes with reduced power consumption.
Implementation Method 1
off-axis ambient light may be reflected to provide reduced image contrast to an off-axis observer
Implementation Method 2
the guest material is an anisotropic material and the host material is a liquid crystal material
Implementation Method 3
The anisotropic material may be an anisotropic absorber. The anisotropic absorber may be a dichroic dye or a pleochroic dye
Implementation Method 4
the display polariser being a linear polariser
Implementation Method 5
The metallic nanomaterial may comprise a transparent electrically insulating surface layer. The insulating surface layer may be coating or may be formed chemically such as a transparent oxide for example
Implementation Method 6
the host material is a liquid crystal material
Data Source
AI summary
A privacy display comprises a spatial light modulator and a switchable liquid crystal retarder arranged between first and second polarisers arranged in series with the spatial light modulator. In a privacy mode of operation, on-axis light from the spatial light modulator is directed without loss, whereas 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. In a wide angle mode of operation, the switchable liquid crystal retardance is adjusted so that off-axis luminance is substantially unmodified.