Directional Display Retarder Stack for Low-Loss Off-Axis Privacy
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Solution Overview
Problem
Existing privacy displays face challenges with high luminance loss and Moiré artefacts due to micro-louvre optical films, which increase inventory and cost, and require complex control of off-axis optical output.
Innovation Solution
A display device with a configuration of switchable retarders and polarisers, including reflective and transmissive spatial light modulators, to control off-axis output and enhance privacy by adjusting retardance values and alignment layers, reducing privacy switch-on angles and increasing security levels.
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 employs switchable liquid crystal retarders that can dynamically change their optical properties between different states. By applying voltage, the retarders switch between providing privacy (reducing off-axis visibility) and maintaining normal visibility (preserving head-on luminance), thus making the privacy function dynamic rather than static.
Solution Approach 2:
The invention changes the optical parameters of the light modulation system by using variable retardance elements. The liquid crystal retarders modify the polarization state of light passing through them, and by controlling their retardance values, the system can adjust the balance between privacy protection and luminance transmission without permanently sacrificing head-on brightness.
2Object-affected harmful factors
If micro-louvre optical films are used for privacy, then Moiré artefacts occur due to beating with pixels, but these films are simple in structure
Solution Approach 1:
The patent introduces liquid crystal retarders as intermediary elements between the display pixels and the viewer. These retarders modify the polarization state of light in a way that prevents the periodic interference patterns (Moiré artefacts) that occur with direct micro-louvre structures, while still achieving the desired privacy effect.
Solution Approach 2:
The invention replaces the mechanical micro-louvre structure with an optical field-based solution using liquid crystal retarders. Instead of physically blocking light with angled structures that create Moiré effects, the system uses controlled modification of light polarization to achieve privacy, eliminating the mechanical source of Moiré artefacts.
3Object-affected harmful factors
If switchable retarders with different retardance values are used to extend polar regions, then security level is improved, but device complexity increases
Solution Approach 1:
The patent divides the light modulation function into multiple segments: a first switchable liquid crystal retarder and a second switchable liquid crystal retarder with different retardance characteristics. Each retarder handles specific aspects of the privacy control, allowing the system to achieve extended polar regions and higher security levels while maintaining manageable complexity through functional segmentation.
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 and reduced luminance loss, with increased security levels and reduced Moiré artefacts, allowing for efficient operation in both landscape and portrait modes.
Implementation Method 1
Each of the at least one first polar control retarder and the at least one second polar control retarder comprises a switchable liquid crystal retarder
Implementation Method 2
the switchable liquid crystal retarder of said one of the at least one first polar control retarder and the at least one second polar control retarder has a retardance for light of a wavelength of 550nm having a first retardance value
Implementation Method 3
the reflective polariser may be arranged between the first additional polariser and the at least one second polar control retarder
Implementation Method 4
the reflective polariser, the reflective polariser being a linear polariser
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A switchable privacy display comprises a spatial light modulator, a first switchable liquid crystal retarder and first passive retarder arranged between a first pair of polarisers and a second switchable liquid crystal retarder and second passive retarder arranged between a second pair of polarisers. The first switchable liquid crystal retarder comprises two homeotropic alignment layers and the second switchable liquid crystal retarder comprises two homogeneous alignment layers. 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. The display may also be operated to switch between day-time and night-time operation, for example for use in an automotive environment.