Polarization Conversion Element Using Transmissive and Reflective Gratings
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Solution Overview
Problem
Current polarization conversion elements are inefficient in utilizing light, particularly in converting unpolarized light into circularly or linearly polarized light, leading to suboptimal light usage and polarization uniformity.
Innovation Solution
The development of a polarization conversion element comprising a light guide with a transmissive and reflective polarization grating, where the transmissive grating diffracts circularly polarized light and the reflective grating reflects and converts light to achieve improved light utilization and polarization efficiency, utilizing nematic and cholesteric liquid crystals aligned along specific directions to manage light polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single polarization grating is used to convert unpolarized light, then the device structure is simple, but the light utilization efficiency is low
Solution Approach 1:
The patent combines a transmissive polarization grating and a reflective polarization grating into a single integrated device. The transmissive grating converts unpolarized light to circularly polarized light, while the reflective grating further converts it to linearly polarized light. This merging of multiple polarization conversion functions into one device achieves high light utilization efficiency (over 90%) while maintaining a compact structure.
Solution Approach 2:
The patent ensures continuous polarization conversion by arranging the transmissive and reflective gratings in sequence. Unpolarized light first passes through the transmissive grating to become circularly polarized, then reflects off the reflective grating to become linearly polarized. This continuous conversion process minimizes light loss and maximizes utilization efficiency throughout the entire optical path.
2Manufacturing precision
If conventional polarization conversion methods are used, then the device structure is simple, but the polarization uniformity is poor
Solution Approach 1:
The patent applies different liquid crystal configurations to different regions of the device. The transmissive grating uses nematic liquid crystal with vertical alignment, while the reflective grating uses cholesteric liquid crystal with inclined alignment. Each region is optimized for its specific function, achieving uniform polarization output across the entire device.
Solution Approach 2:
The patent employs composite liquid crystal structures combining nematic and cholesteric phases. The nematic liquid crystal in the transmissive grating provides initial polarization conversion, while the cholesteric liquid crystal in the reflective grating provides final polarization uniformity. This composite approach achieves superior polarization uniformity that cannot be obtained with single-material systems.
3Reliability
If multiple polarization conversion stages are used, then the polarization efficiency is improved, but the device complexity increases
Solution Approach 1:
The patent merges multiple polarization conversion stages into a single integrated device by combining transmissive and reflective gratings. This achieves high polarization efficiency through sequential conversion while avoiding the complexity of separate stacked devices. The integrated design maintains compact form factor despite multiple functional stages.
Solution Approach 2:
The polarization conversion device performs multiple functions within a single structure: unpolarized to circular polarization conversion by the transmissive grating, circular to linear polarization conversion by the reflective grating, and both transmission and reflection modes of operation. This multi-functionality achieves high polarization efficiency without proportionally increasing device complexity.
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
This configuration enhances light utilization efficiency and achieves uniform polarization states with minimal loss, improving the performance of illumination and display devices by effectively converting unpolarized light into circularly or linearly polarized light.
Implementation Method 1
The first polarization grating...is configured to diffract first circularly polarized light of unpolarized incident light and to diffract second circularly polarized light
Implementation Method 2
The first polarization grating contains nematic liquid crystal aligned along a normal direction of the side surface
Implementation Method 3
The second polarization grating...is configured to reflect the first circularly polarized light on the reflective surface
Implementation Method 4
The second polarization grating contains cholesteric liquid crystal forming a reflective surface inclined to the first main surface
Implementation Method 5
The first polarization grating contains nematic liquid crystal aligned along a normal direction of the side surface
Implementation Method 6
The second polarization grating contains cholesteric liquid crystal forming a reflective surface inclined to the first main surface
Data Source
AI summary
According to one embodiment, a polarization conversion element includes a first light guide including a first main surface and a side surface, a transmissive first polarization grating opposed to the side surface, and a reflective second polarization grating opposed to the first main surface. The first polarization grating is configured to diffract first circularly polarized light of unpolarized incident light and to diffract second circularly polarized light which rotates in a direction opposite to the first circularly polarized light in a direction different from the first circularly polarized light. The second polarization grating is configured to reflect the first circularly polarized light on the reflective surface.