Switchable Privacy Display Using Liquid Crystal Retarder
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Solution Overview
Problem
Existing privacy displays face challenges with high losses for head-on illumination and Moiré artefacts due to micro-louvre optical films, which also require panel resolution-specific pitch selection, increasing inventory and cost, and struggle with controlling off-axis optical output effectively.
Innovation Solution
A display device comprising a spatial light modulator, display and additional polarizers, quarter-wave plates, and a liquid crystal retarder that introduces phase shifts to polarisation components, allowing for reduced luminance along inclined axes, providing a switchable privacy mode with circular symmetry and low stray light, and adjustable transmission and reflectivity profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If micro-louvre optical films are used for privacy display, then off-axis visibility is reduced, but head-on illumination losses increase and Moiré artefacts occur
Solution Approach 1:
The patent changes the optical parameters by using a liquid crystal layer that can dynamically adjust its birefringence properties. By controlling the liquid crystal orientation through voltage application, the system transforms from a static micro-louvre structure to a dynamically controllable optical system that can switch between privacy mode (reducing off-axis visibility) and normal mode (maintaining head-on illumination efficiency) without the energy losses and Moiré artefacts of traditional micro-louvre films
Solution Approach 2:
The invention employs a composite optical structure combining polarising films, quarter-wave plates, and liquid crystal layers. This composite approach integrates multiple optical functions: the polarising films control polarisation states, the quarter-wave plates convert between linear and circular polarisation, and the liquid crystal layer provides dynamic modulation. Together, they achieve privacy display functionality with superior head-on illumination efficiency compared to single-material micro-louvre solutions
2Manufacturing precision
If micro-louvre pitch is selected for panel resolution, then image quality is maintained, but inventory and cost increase
Solution Approach 1:
The liquid crystal-based privacy display system serves multiple functions with a single optical stack configuration. It can operate in privacy mode to prevent off-axis viewing, in normal mode for standard viewing, and can be switched between these states dynamically. This multi-functionality eliminates the need for multiple panel variants with different micro-louvre pitches, reducing inventory complexity and manufacturing costs while maintaining image quality across different viewing conditions
3Adaptability or versatility
If switchable privacy mode is implemented, then off-axis optical output is controlled, but device complexity increases
Solution Approach 1:
The patent replaces mechanical or physical structures (like micro-louvre elements) with a field-controlled liquid crystal system. Instead of relying on fixed geometric structures to control light, the system uses electric fields to modulate the optical properties of the liquid crystal layer. This substitution enables dynamic control of off-axis optical output through voltage application, achieving adaptability without the complexity of mechanical switching mechanisms or multiple physical components
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 for privacy displays, reducing off-axis luminance and reflections, improving visual security while maintaining high on-axis efficiency and color uniformity, and allowing operation in landscape and portrait modes with reduced inventory and cost.
Implementation Method 1
the first and second quarter-wave plates and the at least one retarder are arranged to introduce phase shifts to polarisation components of light
Implementation Method 2
the at least one retarder comprises a liquid crystal retarder comprising a layer of liquid crystal material
Implementation Method 3
the first quarter-wave plate being arranged to convert a linearly polarised polarisation state into a circularly polarised polarisation state, and the second quarter-wave plate being arranged to convert a circularly polarised polarisation state into a linearly polarised polarisation state
Implementation Method 4
causes reduction of the luminance of light passed by the other of the display polariser and the additional polariser along axes that are inclined to the optical axis
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A switchable privacy display comprises a spatial light modulator, and switchable liquid crystal retarder arranged between crossed quarter-wave plates and polarisers. 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 to reduce the visibility of the display to off-axis snoopers. The display may be rotated to achieve privacy operation in landscape and portrait orientations. Further, display reflectivity may be reduced for on-axis reflections of ambient light, while reflectivity may be increased for off-axis light to achieve increased visual security. In a public mode of operation, the liquid crystal retardance is adjusted so that off-axis luminance and reflectivity are unmodified. The display may also be operated to switch between day-time and night-time operation, for example for use in an automotive environment.