Thin Liquid Crystal Polarization Stack for Low-Loss Near-Eye Displays
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Solution Overview
Problem
Existing polarization converters and polarization beam generators are bulky and have high loss, leading to low conversion efficiency, which is undesirable for applications in near-eye displays.
Innovation Solution
A stack of thin liquid crystal layers, including a Pancharatnam-Berry phase grating and angular selective waveplate, is used to convert the polarization state of light beams, achieving low thickness and low loss, thereby enhancing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional polarization converters are used, then polarization conversion can be achieved, but the device becomes bulky and heavy
Solution Approach 1:
The conventional single thick liquid crystal layer is segmented into multiple thin liquid crystal layers stacked together. Each thin layer has a specific orientation angle, and the stack achieves the overall polarization conversion function through the cumulative effect of these oriented layers, reducing total thickness while maintaining functionality.
Solution Approach 2:
The solution transitions from a single thick layer in one dimension to multiple thin layers stacked in the thickness dimension. By distributing the polarization conversion function across multiple thin layers with different orientations, the system achieves the same optical function with reduced overall thickness and weight.
2Ease of operation
If conventional polarization converters are used, then polarization conversion can be achieved, but the device has high loss and low conversion efficiency
Solution Approach 1:
By dividing the thick liquid crystal layer into multiple thin layers, each layer operates in a regime with lower optical absorption and scattering losses. The segmented structure reduces cumulative loss while achieving the same total polarization conversion through the oriented stack configuration.
Solution Approach 2:
The invention changes the key parameter of layer thickness from thick to thin, and introduces the parameter of layer orientation angles. By optimizing the thickness and orientation of each thin layer, the system achieves efficient polarization conversion with minimal light loss, as each thin layer operates in a low-loss regime.
Data Source
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AI summary
A polarization conversion device includes a geometric phase grating and an angular selective waveplate. The geometric phase grating includes a first liquid crystal layer and is configured to diffract a unpolarized or partially polarized incident light beam into a first light beam and a second light beam (e.g., in two different diffraction orders). The first light beam is characterized by a first polarization state and propagates in a first direction. The second light beam is characterized by a second polarization state and propagates in a second direction. The angular selective waveplate includes a second liquid crystal layer, and functions as a zero or full-wave plate for the first light beam incident in the first direction and a half-wave plate for the second light beam incident in the second direction.