Reflective Privacy Display Stack for Switchable Off-Axis Dimming
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Solution Overview
Problem
Current privacy displays lack the ability to dynamically control off-axis privacy, relying on fixed micro-louvre optical films or liquid crystal displays that are not switchable, limiting their functionality to only privacy mode and not accommodating varying viewer positions effectively.
Innovation Solution
A display device incorporating a spatial light modulator (SLM) with a linear polarizer, an additional polarizer, a reflective polarizer, and a polar control retarder that can introduce relative phase shifts to orthogonal polarization components, allowing for high reflectivity at off-axis positions and high luminance at on-axis positions, enabling switchable privacy modes.
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 luminance is reduced, but the display becomes non-switchable and limited to privacy mode only
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 display between privacy mode (off-axis luminance reduced) and public mode (full viewing angle). This dynamic switching capability resolves the contradiction by making the privacy function controllable rather than fixed.
Solution Approach 2:
The invention changes the optical parameters of the display system by using liquid crystal retarders with specific retardance values (e.g., quarter-wave, half-wave) that can be switched. By altering the phase shift parameter introduced by the liquid crystal layer, the system achieves different viewing angle characteristics, enabling both privacy and public viewing modes from the same hardware configuration.
2Adaptability or versatility
If switchable backlights are used to control off-axis optical output, then privacy can be switched, but device complexity increases
Solution Approach 1:
Instead of modifying the backlight system directly, the patent introduces liquid crystal retarders as intermediary elements between the backlight and the display panel. These retarders act as optical mediators that control the polarization state of light, enabling privacy switching without requiring complex imaging directional backlights. This approach simplifies the overall system while achieving the desired switchable privacy function.
Solution Approach 2:
The invention replaces the mechanical/optical complexity of imaging directional backlights with a simpler liquid crystal-based optical control system. By using electrically controllable liquid crystal retarders instead of complex optical valve mechanisms, the patent achieves switchable privacy with reduced device complexity and easier integration into standard display architectures.
3Object-affected harmful factors
If liquid crystal bias tilt is adjusted to control contrast, then off-axis privacy can be controlled, but manufacturing precision requirements increase
Solution Approach 1:
The patent achieves off-axis contrast control by changing the retardance parameter of liquid crystal layers rather than relying on precise bias tilt adjustment. By using liquid crystal materials with specific birefringence values and controlling the layer thickness, the system achieves the desired optical effect with more relaxed manufacturing tolerances compared to precision mechanical tilt control.
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 enhanced privacy performance by reducing luminance for off-axis viewers while maintaining high luminance for on-axis viewers, offering increased visual security and flexibility in ambient illumination environments.
Implementation Method 1
the at least one polar control retarder is capable of simultaneously introducing no net relative phase shift to orthogonal polarisation components of light passed by the reflective polariser along an axis along a normal to the plane of the at least one polar control retarder and introducing a relative phase shift to orthogonal polarisation components of light passed by the reflective polariser along an axis inclined to a normal to the plane of the at least one polar control retarder
Implementation Method 2
Control may be provided by means of luminance reduction, for example by means of switchable backlights for a liquid crystal display (LCD) spatial light modulator (SLM). Display backlights in general employ waveguides and light sources arranged along at least one input edge of the waveguide. Certain imaging directional backlights have the additional capability of directing the illumination through a display panel into viewing windows.
Data Source
AI summary
A privacy display comprises a polarised output spatial light modulator, reflective polariser, plural polar control retarders and a polariser. 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. Further, display reflectivity is reduced for on-axis reflections of ambient light, while reflectivity is increased for off-axis light. The visibility of the display to off-axis snoopers is reduced by means of luminance reduction and increased frontal reflectivity to ambient light. In a public mode of operation, the liquid crystal retardance is adjusted so that off-axis luminance and reflectivity are unmodified.