Switchable Privacy Display Using Birefringent Polarisation Control
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Solution Overview
Problem
Privacy displays face challenges with high luminance losses for head-on illumination and Moiré artefacts due to micro-louvre interactions with spatial light modulators, leading to increased inventory and cost.
Innovation Solution
A display device comprising a structured birefringent component, out-of-plane polariser, and a polarisation switch arranged between these components to switch between privacy and wide-angle modes, reducing luminance in non-viewing directions and enhancing security.
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 changes the optical parameters of the films by using birefringent materials with specific retardance values (e.g., 1/4 wave, 1/2 wave) and controlling the pitch ratios relative to pixel pitch. This allows the optical stack to achieve both privacy (off-axis blocking) and maintain head-on luminance by precisely tuning the film properties rather than relying on micro-louvre geometry alone.
Solution Approach 2:
The patent employs a composite optical stack comprising multiple layers including birefringent films, polarising films, and diffusion films. This composite structure combines the privacy function of birefringent materials with the light transmission properties of polarising and diffusion films, achieving both off-axis blocking and head-on luminance maintenance that single-layer micro-louvre films cannot achieve.
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 creates a universal optical stack design where the birefringent film pitch is defined as a ratio (e.g., 0.5x, 0.25x, 0.125x) of the pixel pitch. This ratio-based approach allows the same optical film design to be adapted to different panel resolutions without requiring custom micro-louvre pitches for each resolution, thereby reducing inventory complexity and cost while maintaining display quality.
3Adaptability or versatility
If switchable backlights are used for LCD, then privacy control is achieved, but device thickness and complexity increase
Solution Approach 1:
The patent introduces an optical stack comprising birefringent films and polarising films as an intermediary layer between the backlight and the display panel. This optical stack provides switchable privacy control by manipulating light polarization and diffusion, replacing the need for complex switchable backlight mechanisms while achieving similar privacy functionality with reduced thickness and complexity.
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 low thickness, low-cost display with increased security factor and reduced luminance in off-axis positions, while maintaining high image visibility in the on-axis direction.
Implementation Method 1
a structured birefringent component
Implementation Method 2
an out-of-plane polariser
Data Source
AI summary
A switchable privacy display comprises at least one light source, a structured birefringent component, an out-of-plane polariser, a polarisation switch, and an in-plane polariser. The polarisation switch is arranged between the out-of-plane polariser and the in-plane polariser, and the polarisation switch is also arranged between the structured birefringent component and the in-plane polariser. The display device is arranged to output an image formed using light which has been output from the at least one light source and which has passed through the structured birefringent component, the out-of-plane polariser, the polarisation switch and the in-plane polariser. The display can operate in a privacy mode of operation that provides a high security factor in non-viewing directions and high image visibility in viewing directions, or in a wide-angle mode of operation that provides high image visibility for a relatively wider field of view.