Switchable Guest-Host Liquid Crystal Retarder for Privacy Displays
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Solution Overview
Problem
Existing privacy displays face challenges in effectively reducing off-axis illumination while maintaining high image visibility for on-axis users, due to high losses in head-on illumination and the potential for Moiré artefacts from micro-louvre optical films.
Innovation Solution
A display device comprising a spatial light modulator, a guest-host liquid crystal retarder, and a control system that adjusts the voltage applied to switchable liquid crystal retarders to control the optical stack's operation between share mode, privacy mode, and low stray light mode, thereby managing off-axis luminance and maintaining high on-axis visibility.
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
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 optical stack between share mode (high transmission), privacy mode (off-axis blocking), and low stray light mode, thereby dynamically adjusting the balance between off-axis visibility reduction and head-on illumination maintenance
Solution Approach 2:
The invention changes the optical parameters of the liquid crystal retarder by applying different voltages, which alters the refractive index and orientation of the liquid crystal molecules. This parameter change enables the system to switch between different operational modes, optimizing both privacy protection and illumination efficiency for different viewing conditions
2Object-affected harmful factors
If micro-louvre optical films are used to provide privacy function, then off-axis visibility is reduced, but Moiré artefacts occur
Solution Approach 1:
The patent introduces liquid crystal retarders as an intermediary element between the display panel and the viewer. These retarders mediate the light transmission by controlling the polarization state of light, thereby achieving privacy protection without the need for micro-louvre structures that cause Moiré artefacts. The liquid crystal layer acts as a controllable intermediary that can switch between transparent and privacy states
Solution Approach 2:
The invention replaces the mechanical micro-louvre structure with an electro-optical liquid crystal system. Instead of using physical louvres that create Moiré patterns when interacting with pixel structures, the patent uses electrically controlled liquid crystal molecules to achieve the same privacy function through optical property changes, eliminating the mechanical structure that causes Moiré artefacts
3Object-affected harmful factors
If switchable liquid crystal retarders are used to control off-axis luminance, then privacy security factor is improved, but device complexity increases
Solution Approach 1:
The patent designs the optical stack with multi-functional liquid crystal retarders that can perform multiple operations based on applied voltage. The same liquid crystal layer provides privacy protection, stray light control, and viewing angle management functions, reducing the need for separate components and thereby managing device complexity while maintaining enhanced privacy security
Solution Approach 2:
The invention merges multiple optical control functions into a single integrated optical stack structure. The liquid crystal retarder is combined with the display panel's existing polarizers and optical layers, creating a unified system that achieves privacy protection without requiring entirely separate complex mechanisms
4Object-affected harmful factors
If liquid crystal bias tilt is adjusted to control contrast reduction, then off-axis privacy is improved, but on-axis image visibility decreases
Solution Approach 1:
The patent employs dynamically switchable liquid crystal retarders that can change their tilt angle and optical properties in real-time based on applied voltage. This dynamic control allows the system to achieve off-axis privacy protection while maintaining high on-axis image visibility, as the liquid crystal molecules can be precisely controlled to block off-axis light without affecting on-axis transmission
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 achieves a high security factor for off-axis viewers while ensuring high image visibility for on-axis users, with low thickness and cost, and an aesthetically desirable appearance for snoopers.
Implementation Method 1
a guest-host liquid crystal retarder arranged between the additional polariser and the reflective polariser, the guest-host liquid crystal retarder comprising a liquid crystal layer comprising a guest material and a host material
Implementation Method 2
the optical axis of the guest-host liquid crystal retarder has an alignment component perpendicular to the plane of the guest-host liquid crystal retarder
Implementation Method 3
a reflective polariser arranged on an output side of the display polariser, the reflective polariser being a linear polariser
Implementation Method 4
The anisotropic material may be an anisotropic optical absorber. The anisotropic material may be a dichroic dye or a pleochroic dye
Data Source
AI summary
A switchable privacy display comprises a spatial light modulator and a compensated switchable guest-host liquid crystal retarder arranged between an output display polariser of the spatial light modulator and an additional polariser. A reflective polariser is arranged between the guest-host liquid crystal retarder and the output display polariser. In privacy mode, 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 luminance reduction and reflection increase over a wide polar field. The colour of the reflected light may be modified by selection of the spectral absorption of the guest material in correspondence to the spectral transmission of the additional polariser. An aesthetically desirable display appearance may be achieved in privacy mode from non-viewing directions. In wide-angle mode, the switchable liquid crystal retardance is adjusted so off-axis luminance and reflectance is substantially unmodified.