Optical Stack With Polar Retarders for Display Privacy
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Solution Overview
Problem
Existing privacy displays struggle to provide high image visibility to on-axis users while maintaining reduced visibility for off-axis snoopers, especially in environments with varying ambient illuminance, and often compromise on luminance uniformity and security factors.
Innovation Solution
A display device comprising a spatial light modulator with a light control film and polar control retarders, including switchable liquid crystal retarders and passive compensation retarders, arranged to modulate off-axis luminance and reflectivity, achieving enhanced security and visibility through controlled transmittance and reflectance profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If switchable liquid crystal retarders and compensation retarders are arranged to modulate off-axis luminance, then off-axis luminance reduction is achieved, but device complexity increases
Solution Approach 1:
The optical stack is divided into distinct functional layers: spatial light modulator, light control film with transmissive and absorptive regions, additional polarizer, and polar control retarder. Each layer performs a specific function in controlling off-axis luminance, allowing independent optimization of each component rather than relying on a single complex element.
Solution Approach 2:
The light control film features spatially varying properties with transmissive regions and absorptive regions positioned at specific locations and orientations. The absorptive regions are arranged to selectively block off-axis light paths while maintaining on-axis transmission, creating local variations in optical properties that achieve privacy control without requiring the entire optical stack to be complex.
2Loss of information
If light control film with absorptive regions is used to reduce off-axis luminance, then image security for off-axis snoopers is improved, but manufacturing precision requirements increase
Solution Approach 1:
The light control film acts as an intermediary element between the spatial light modulator and the viewer. It mediates the light paths by using absorptive regions to block off-axis light and transmissive regions to allow on-axis light passage. This intermediary structure simplifies the overall system by providing a single component that handles both image display and privacy control functions.
Solution Approach 2:
The optical properties of the light control film are optimized by adjusting parameters such as the width, orientation, and spacing of transmissive and absorptive regions. The pitch of transmissive regions and the dimensions of absorptive regions are carefully selected to achieve the desired angular selectivity for privacy control, allowing manufacturing within standard tolerances while maintaining effective off-axis luminance reduction.
3Adaptability or versatility
If polar control retarder with switchable liquid crystal is implemented, then control over off-axis luminance is enhanced, but device thickness increases
Solution Approach 1:
The polar control retarder with switchable liquid crystal performs multiple functions: it controls the polarization state of light, modulates off-axis luminance, and enables switchable privacy modes. This multi-functional component reduces the need for separate elements, thereby controlling overall stack thickness while maintaining enhanced adaptability for luminance control.
Solution Approach 2:
The switchable liquid crystal retarder replaces mechanical privacy controls with an electrically controlled optical element. Instead of physically moving parts or adjusting mechanical structures, the liquid crystal molecules are reoriented using electric fields to change the polarization and transmission properties, achieving privacy control in a thin, solid-state format.
4Illumination intensity
If additional polarizer and polar control retarder are arranged in series, then off-axis reflectivity control is improved, but loss of light increases
Solution Approach 1:
The additional polarizer and polar control retarder are positioned and configured to pre-establish the desired polarization state and reflectivity control before light reaches the viewer. By controlling the polarization and reflectivity in advance through these series-arranged elements, the system achieves effective off-axis reflectivity management while minimizing unnecessary light loss through optimized material selection and geometric arrangement.
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 increased image security and uniformity for off-axis snoopers with reduced off-axis luminance, maintaining high visibility for on-axis users, even in bright environments, while minimizing cost and thickness.
Implementation Method 1
at least one polar control retarder arranged between the additional polariser and the display polariser and including a switchable liquid crystal retarder
Implementation Method 2
the spatial light modulator including a display polariser arranged on a side of the spatial light modulator, the display polariser being a linear polariser
Implementation Method 3
a light control film arranged in series with the spatial light modulator, the additional polariser and the at least one polar control retarder, wherein the light control film comprises an input surface, an output surface facing the input surface, an array of transmissive regions extending between the input surface and the output surface, and absorptive regions between the transmissive regions
Implementation Method 4
an array of transmissive regions extending between the input surface and the output surface, and absorptive regions between the transmissive regions and extending at least partway between the input surface and the output surface
Data Source
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Figure 3A
AI summary
A switchable privacy display apparatus comprises a spatial light modulator, a light control film, and a polar control retarder that comprises plural retarders arranged between a display polariser of the spatial light modulator and an additional polariser. The display achieves high image visibility to an off-axis user in a public mode of operation and high image security to an off-axis snooper in privacy mode of operation.