Optical Unit With Polarization Diffraction for Uniform Display Brightness
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Solution Overview
Problem
Existing image display systems using liquid crystal diffraction elements suffer from brightness unevenness due to low diffraction efficiency near the end parts, leading to reduced image quality and increased thickness.
Innovation Solution
An optical unit comprising a first and second partial reflection element, and a polarization diffraction element with a liquid crystal layer having a specific alignment pattern and twisted angles, which selectively focuses polarized light to reduce brightness unevenness and enhance field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a liquid crystal diffraction element is used instead of a lens, then the system thickness is reduced, but brightness unevenness occurs due to low diffraction efficiency near the end parts
Solution Approach 1:
The patent applies local quality by varying the liquid crystal alignment pattern across different regions of the diffraction element. Specifically, the optical axis orientation and twisted angles are adjusted locally in different areas to compensate for position-dependent diffraction efficiency variations, ensuring uniform brightness across the entire field of view while maintaining the thin profile of the liquid crystal-based optical system
2Ease of manufacture
If the liquid crystal layer has a simple alignment pattern, then the manufacturing is easier, but the field of view and image quality are limited
Solution Approach 1:
The patent employs dynamics by implementing a liquid crystal alignment pattern with spatially varying optical axis orientations and twisted angles. This dynamic configuration allows the diffraction element to effectively guide light across a wide field of view, achieving enhanced adaptability and image quality while remaining compatible with conventional liquid crystal manufacturing processes
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 optical unit achieves reduced brightness unevenness and wider field of view by optimizing the liquid crystal alignment pattern and twisted angles, improving image quality and reducing system thickness.
Implementation Method 1
polarization diffraction element with a liquid crystal layer having a specific alignment pattern and twisted angles, which selectively focuses polarized light
Implementation Method 2
polarization diffraction element with a liquid crystal layer having a specific alignment pattern and twisted angles, which selectively focuses polarized light
Data Source
AI summary
An optical unit that enables observation of an image with reduced brightness unevenness, and an image display system including the unit, are provided. The optical unit includes first and second partial reflection elements that reflect part of incident light and transmit part of it, and a polarization diffraction element including a liquid crystal layer. The liquid crystal layer has an alignment pattern in which an optical axis orientation continuously rotates in one in-plane direction. Regions of the layer have different single period lengths, where a single period is defined as a 180° rotation of the optical axis. The layer also includes regions where the optical axis is twisted in the thickness direction and regions with different total twisted angles.