Switchable Liquid Crystal Retarder for Privacy Display
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Solution Overview
Problem
Existing privacy displays face challenges in controlling off-axis illumination, leading to high losses for head-on illumination and potential Moiré artefacts due to micro-louvre pitch requirements, which increase inventory and cost, and struggle to effectively manage contrast and luminance for privacy modes.
Innovation Solution
A display device comprising a backlight, a transmissive spatial light modulator, and a switchable compensated retarder system with a liquid crystal retarder and passive compensation retarder, arranged to provide adjustable luminance and contrast control, allowing switching between narrow and wide angle modes for privacy and visibility control.
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 efficiency deteriorates with high losses
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 adapt between privacy mode (reducing off-axis visibility) and wide-angle mode (maintaining head-on illumination efficiency), eliminating the fixed trade-off inherent in micro-louvre films
Solution Approach 2:
The invention changes the optical parameters of the system by using liquid crystal retarders with specific retardance values (500-1000 nm) and controlling their molecular orientation through electric fields. By adjusting the pretilt angles and retardance of the liquid crystal layers, the system can control the polarization state of light differently for on-axis and off-axis viewing angles, thereby achieving privacy protection without sacrificing head-on illumination efficiency
2Manufacturing precision
If micro-louvre pitch is selected for panel resolution, then display quality is improved, but inventory and cost increase
Solution Approach 1:
The patent removes the micro-louvre optical films from the display structure and replaces them with liquid crystal retarders positioned at different locations (input and/or output sides of the spatial light modulator). This extraction eliminates the need for precise micro-louvre pitch selection and the associated inventory complexity, while maintaining or improving display quality through the liquid crystal-based optical control
Solution Approach 2:
The invention uses liquid crystal retarders that can optically replicate or simulate the light-modulating effect of micro-louvres without requiring the physical micro-louvre structure. The liquid crystal layers create equivalent optical functionality through controlled birefringence and polarization effects, avoiding the manufacturing precision and inventory requirements of actual micro-louvre structures
3Object-affected harmful factors
If micro-louvre structure is used for privacy control, then off-axis privacy is improved, but Moiré artefacts occur due to beating with pixels
Solution Approach 1:
The patent converts the potential harm of visible pixel structures into a benefit by using liquid crystal retarders that operate independently of the pixel pitch. The liquid crystal layers modulate light based on polarization control rather than physical spacing, eliminating the beating effect that causes Moiré artefacts while maintaining effective privacy protection through controlled light transmission at different viewing angles
4Object-affected harmful factors
If switchable backlights are used to control off-axis output, then privacy control is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges the privacy control function with the existing liquid crystal spatial light modulator structure by incorporating switchable retarder layers at the input and/or output sides. This integration allows the same liquid crystal technology to perform both spatial light modulation and privacy control functions, eliminating the need for separate switchable backlight systems and reducing overall device complexity and cost
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 enables efficient control of illumination, reducing off-axis luminance for privacy while maintaining high on-axis visibility, thereby enhancing privacy and reducing costs by eliminating the need for precise micro-louvre pitch selection and minimizing Moiré artefacts.
Implementation Method 1
a layer of liquid crystal material having a retardance for light of a wavelength of 550 nm in a range from 500 nm to 1000 nm
Implementation Method 2
two surface alignment layers disposed adjacent to the layer of liquid crystal material and on opposite sides thereof, each of the surface alignment layers being arranged to provide homogeneous alignment in the adjacent liquid crystal material
Implementation Method 3
a passive retarder having its optical axis perpendicular to the plane of the retarder and having a retardance for light of a wavelength of 550 nm in a range from −300 nm to −900 nm
Data Source
AI summary
A privacy display comprises a spatial light modulator and a compensated 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.