Reflective Optical Stack for Switchable Privacy Displays
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Solution Overview
Problem
Existing privacy displays lack switchable functionality to control off-axis optical output, limiting them to privacy mode only and not allowing for wide viewing angle modes with high contrast images.
Innovation Solution
A display device incorporating a switchable liquid crystal retarder with passive retarders and linear polarizers, which adjusts luminance and reflectivity based on viewing angle to provide high reflectivity and low luminance for off-axis positions and low reflectivity and high luminance for on-axis positions.
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 applies a switchable liquid crystal retarder that can dynamically change its optical properties between different states. In the first state, it provides privacy by reducing off-axis luminance through controlled phase shifts. In the second state, it allows wide viewing angles with high contrast. This dynamic switching capability resolves the contradiction by making the privacy function controllable rather than fixed.
Solution Approach 2:
The liquid crystal retarder changes its retardance parameter (phase shift) based on applied voltage to achieve different optical states. By controlling the retardance parameter, the system can switch between privacy mode (reduced off-axis luminance) and wide viewing angle mode (high contrast), thereby achieving both reduced off-axis luminance and switchability.
2Object-affected harmful factors
If switchable backlights are used to control off-axis optical output, then privacy function is achieved, but device complexity increases
Solution Approach 1:
Instead of modifying the backlight system directly, the patent introduces a liquid crystal retarder as an intermediary optical element between the backlight and the display panel. This intermediary component controls the polarization state of light to achieve privacy function without requiring complex switchable backlight mechanisms, thereby reducing overall device complexity.
3Object-affected harmful factors
If liquid crystal bias tilt is adjusted to control contrast, then off-axis privacy is improved, but on-axis image quality may be compromised
Solution Approach 1:
The patent segments the optical control function into two independent components: the liquid crystal display panel handles on-axis image quality, while the separate liquid crystal retarder handles off-axis privacy control. This segmentation allows each component to be optimized for its specific function without compromising the other, maintaining high on-axis image quality while achieving off-axis privacy.
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
Enables a privacy display that switches between privacy and wide viewing angle modes, providing enhanced visual security and high contrast images while maintaining high luminance for on-axis viewers.
Implementation Method 1
a switchable liquid crystal retarder comprising a layer of liquid crystal material and at least one passive retarder, and the plural polar direction control retarders are arranged, in a switchable state of the switchable liquid crystal retarder, simultaneously to introduce 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 plural polar direction control retarders and to introduce 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 plural polar direction control retarders
Implementation Method 2
a reflective polariser arranged between the output polariser and the additional polariser, the reflective polariser being a linear polariser
Data Source
Figure 1A
Figure 1B
Figure 2A
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.