Cube Polarizer Asymmetry for Optical Path Equality
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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 issues like wavefront distortion and impractical manufacturing costs.
Innovation Solution
Designing a cube polarizer with aligned prisms and a wire grid polarizer sandwiched between them, where the optical path lengths of reflected and transmitted beams are minimized by adjusting the distances between prism edges and faces, and using thin films to reduce curvature and stress-induced distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a wire grid polarizer with substrate is used in a cube polarizer, then the polarizer can be mechanically stable and allow attachment of other devices, but the optical path length difference between reflected and transmitted beams increases
Solution Approach 1:
The patent applies asymmetry by making the first and second prisms have different dimensions. Specifically, the first prism has a larger size than the second prism, which compensates for the optical path length difference introduced by the substrate. This asymmetric design allows the optical paths of reflected and transmitted beams to be equalized while maintaining mechanical stability through the wire grid polarizer substrate.
2Strength
If the substrate thickness is increased for mechanical support, then the wire grid polarizer can maintain structural integrity, but the optical path length difference between beams increases
Solution Approach 1:
The patent applies parameter changes by adjusting the dimensions of the prisms based on the substrate thickness. The first prism is designed with larger dimensions to compensate for the additional optical path length introduced by a thicker substrate. This allows the use of substrates with sufficient thickness for mechanical support while maintaining optical path equality through careful parameter selection.
3Ease of manufacture
If prisms are made symmetric for ease of manufacture, then manufacturing is simplified, but optical path length difference between beams occurs
Solution Approach 1:
The patent deliberately introduces asymmetry between the first and second prisms to resolve the contradiction. While asymmetric prisms may require slightly more complex manufacturing procedures, the patent provides specific dimensional relationships that guide the manufacturing process. The asymmetric design is necessary to achieve optical path length equality when a substrate is present.
4Ease of manufacture
If the wire grid polarizer is curved due to stress, then manufacturing may be simplified, but wavefront distortion increases
Solution Approach 1:
The patent applies preliminary anti-action by designing the prism configuration to pre-compensate for stress-induced curvature in the wire grid polarizer. The asymmetric prism dimensions are calculated to counteract the expected curvature effects, thereby maintaining wavefront quality even when the polarizer experiences manufacturing stresses.
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 nearly equal optical path lengths for reflected and transmitted beams, reducing wavefront distortion and manufacturing complexities, 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 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
Implementation Method 3
The transmitted beam T can transmit through the polarizer 131 and prismB 136, and exit through a side (outer faceB) of prismB 136. The optical path length OPL is defined as the actual physical distance the light travels through the cube polarizer times an index of refraction n of the material(s)
Data Source
AI summary
Cube polarizers can be designed for substantially equal optical path lengths of a reflected beam and a transmitted beam. For example, d11 of FIG. 1 can define a distance between a plane (face plane2) of the outer face (outer face2) of a second prism 16 and the first edge (first edge1) of the first prism, and d11 can be less than 400 micrometers. As another example, an optical path length differential between a transmitted beam and a reflected beam (|OPLT−OPLR|) can be<0.5*t*np2;where 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.