Cube Polarizer Asymmetric Wire Grid for Optical Path Length Difference
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Solution Overview
Problem
Cube polarizers with wire grid polarizers often exhibit a substantial difference in optical path length between reflected and transmitted beams due to substrate thickness, leading to wavefront distortion and practical manufacturing challenges.
Innovation Solution
Designing cube polarizers with aligned prisms and wire grid polarizers sandwiched between substrates, where the wire grid polarizer's substrate thickness is minimized to equalize optical path lengths and reduce curvature-induced wavefront distortion by using thin films to balance stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a wire grid polarizer with a thick substrate is used in a cube polarizer, then the mechanical strength and structural stability are improved, but the optical path length difference between reflected and transmitted beams increases, causing wavefront distortion
Solution Approach 1:
The patent applies asymmetry by making the substrate thickness asymmetric relative to the wire grid position. The wire grid is positioned closer to one surface of the substrate than the other, creating an asymmetric configuration that equalizes the optical path lengths for reflected and transmitted beams while maintaining adequate mechanical strength through the overall substrate thickness
Solution Approach 2:
The patent changes the geometric parameters of the substrate-wire grid assembly. Specifically, it adjusts the distance from the wire grid to each substrate surface (creating different air gaps) to control and equalize the optical path lengths, while maintaining the substrate thickness sufficient for mechanical strength
2Manufacturing precision
If the substrate thickness is reduced to minimize optical path length difference, then wavefront distortion is reduced, but the mechanical strength and structural stability decrease
Solution Approach 1:
The asymmetric positioning of the wire grid within the substrate allows the use of a thinner overall substrate while maintaining mechanical strength. The wire grid is positioned such that it is closer to one surface, creating an asymmetric configuration that equalizes optical paths while the overall substrate thickness remains sufficient for structural support
3Manufacturing precision
If the wire grid polarizer is positioned asymmetrically within the substrate, then optical path length equality is achieved, but the manufacturing alignment precision requirements increase
Solution Approach 1:
The patent incorporates preliminary action by including alignment features and registration marks on the substrate that guide the precise positioning of the wire grid during assembly. These pre-built alignment structures make it easier to achieve the required asymmetric positioning and optical path equality during manufacturing
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
Achieves minimal difference in optical path lengths between reflected and transmitted beams, reducing wavefront distortion and manufacturing costs, suitable for applications like interferometry and 3D projection displays.
Implementation Method 1
An unpolarized light beam U can enter one side (outer faceA) of prismA 135 and can be polarized into a reflected beam R and a transmitted beam T. The reflected beam R can reflect off the wires 131w of the wire grid polarizer 131
Implementation Method 2
The transmitted beam T can transmit through the polarizer 131 and prismB 136, and exit through a side (outer faceB) of prismB 136
Implementation Method 3
The reflected beam R can reflect off the wires 131w of the wire grid polarizer 131, continue through prismA 135, and exit through another side (outer sideA) of prismA 135
Data Source
AI summary
The cube polarizer can have modified prism dimensions to satisfy the following equation:OPLT-OPLR<0.5*t*np2,where an optical path length is a distance of light travel through a material times an index of refraction of the material, OPLT is an optical path length of the transmitted beam, OPLR is an optical path length of the reflected beam, t is a thickness of the substrate between the first surface and the second surface of the substrate, and np is an index of refraction of the first prism.