Switchable Liquid Crystal Retarder for Privacy Display
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Solution Overview
Problem
Existing privacy displays face challenges in providing effective control of off-axis optical output, leading to high losses for head-on illumination and potential Moiré artefacts due to micro-louvre optical films.
Innovation Solution
A display device comprising a spatial light modulator, a display polariser, an additional polariser, and plural retarders, including a switchable liquid crystal retarder and at least one passive compensation retarder, arranged to control luminance and phase shift of light, enabling a switchable privacy display with extended field of view and reduced off-axis luminance.
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 losses increase and Moiré artefacts occur
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 (reducing off-axis visibility) and wide-angle mode (maintaining head-on illumination). This dynamic switching resolves the contradiction by allowing the system to adapt its optical characteristics based on operational requirements rather than being 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., half-wave or quarter-wave at specific wavelengths) and by controlling the orientation of liquid crystal molecules through electric fields. This allows precise control over the phase shift of light waves, enabling the system to maintain high transmission for on-axis viewing while blocking off-axis views, thus resolving the illumination loss problem.
2Object-affected harmful factors
If micro-louvre optical films are used to provide privacy function, then off-axis visibility is reduced, but Moiré artefacts are generated
Solution Approach 1:
The patent removes the micro-louvre structure from the optical stack and replaces it with liquid crystal retarders positioned at different locations (input side and/or output side of the spatial light modulator). This extraction eliminates the Moiré artefact problem caused by the interaction between micro-louvre pitch and pixel pitch, while maintaining the privacy function through the liquid crystal's ability to control light polarization and phase.
Solution Approach 2:
The liquid crystal retarders act as an intermediary between the light source and the display panel, controlling the optical properties of light before it interacts with the micro-louvre or exits the display. By mediating the light's polarization and phase state, the liquid crystal retarders enable privacy control without requiring the micro-louvre structure that causes Moiré artefacts.
3Adaptability or versatility
If switchable liquid crystal retarders are added to control privacy, then privacy control capability is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple functions into the liquid crystal retarder assembly: privacy control, wide-angle viewing control, and optical compensation are all achieved through the same liquid crystal retarder component by switching between different voltage states. This merging reduces the need for separate optical elements for each function, thereby managing complexity while maintaining versatility.
Solution Approach 2:
The liquid crystal retarder is designed to perform multiple functions: it provides privacy control when switched to the privacy state, enables wide-angle viewing when switched to the wide-angle state, and compensates for optical phase delays. This multi-functionality allows a single component to address multiple requirements, reducing overall device complexity compared to using separate elements for each function.
4Object-affected harmful factors
If liquid crystal bias tilt is adjusted to control off-axis privacy, then contrast reduction is achieved, but control flexibility is limited
Solution Approach 1:
Instead of fixed liquid crystal bias tilt adjustment, the patent uses switchable liquid crystal retarders that can dynamically change their optical state through voltage control. This allows real-time switching between privacy and wide-angle modes, providing much greater control flexibility compared to static bias tilt adjustment while achieving the same off-axis contrast reduction effect.
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 switchable privacy display that maintains on-axis luminance while reducing off-axis luminance, enhancing privacy and reducing Moiré artefacts, with the ability to switch between wide angle and privacy modes without substantial power consumption.
Implementation Method 1
a switchable liquid crystal retarder comprising a layer of liquid crystal material arranged between the display polariser and the additional polariser
Implementation Method 2
The switchable liquid crystal retarder may be arranged to introduce no phase shift to polarisation components of light passed by the one of the display polariser and the additional polariser on the input side of the plural retarders along an axis along a normal to the plane of the switchable liquid crystal retarder and/or to introduce a phase shift to polarisation components of light passed by the one of the display polariser and the additional polariser on the input side of the plural retarders along an axis inclined to a normal to the plane of the switchable liquid crystal retarder
Implementation Method 3
at least one passive compensation retarder. The at least one passive compensation retarder may be arranged to introduce no phase shift to polarisation components of light passed by the one of the display polariser and the additional polariser on the input side of the plural retarders along an axis along a normal to the plane of the at least one passive compensation retarder and/or to introduce a phase shift to polarisation components of light passed by the one of the display polariser and the additional polariser on the input side of the plural retarders along an axis inclined to a normal to the plane of the at least one passive compensation retarder
Implementation Method 4
a spatial light modulator; a display polariser arranged on a side of the spatial light modulator; an additional polariser arranged on the same side of the spatial light modulator as the display polariser
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.