Low Ts Wire Grid Polarizer With Refractive Index Stack
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Solution Overview
Problem
Existing wire grid polarizers face challenges in achieving low transmission of the primarily reflected/absorbed polarization, which is crucial for applications like image projection systems to prevent distortion and ghosting, as high transmission of the opposite polarization can interfere with optical systems.
Innovation Solution
A wire grid polarizer design featuring a stack of thin films with specific refractive index relationships and materials, including aluminum oxide, silicon nitride, silicon oxide, and titanium oxide, is implemented to minimize the transmission of the minimally-transmitted polarization, with a configuration that includes additional thin films extending over the wires and filling channels to optimize light management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a wire grid polarizer is designed for high absorption of s-polarization, then ghosting in image projector is reduced, but transmission of s-polarization (Ts) cannot be sufficiently reduced below a certain threshold
Solution Approach 1:
The polarizer structure is segmented into multiple functional layers: a wire grid layer for primary polarization separation, followed by multiple dielectric layers (including high-index and low-index layers) that work together to progressively reduce Ts. Each layer segment contributes to the overall suppression of transmitted s-polarization, with the stack achieving Ts ≤ 0.0008 through cumulative effect rather than relying on a single layer.
Solution Approach 2:
The patent employs composite material structures including alternating high-index and low-index dielectric layers (such as TiO2/SiO2, HfO2/SiO2, or Ta2O5/SiO2 combinations) deposited on the wire grid. This composite approach allows optimization of both absorption and reflection characteristics to achieve ultra-low Ts while maintaining high Tp, resolving the contradiction between ghosting reduction and transmission control.
2Ease of manufacture
If the polarizer uses simple structure, then manufacturing is easier, but transmission of minimally-transmitted polarization cannot be reduced sufficiently
Solution Approach 1:
The patent optimizes specific parameters of the dielectric layers including thickness (t1, t2, t3 ranging from 10-100 nm), refractive indices (n1 > n2 > n3 relationships), and material composition to achieve the desired Ts ≤ 0.0008 performance. By carefully controlling these parameters during deposition, the complex optical performance is achieved through systematic parameter optimization rather than structural complexity.
3Use of energy by moving object
If high transmission of p-polarization is achieved, then light-source power requirements are minimized, but any residual transmission of s-polarization will distort the projected image
Solution Approach 1:
The dielectric layer stack acts as an intermediary between the wire grid and the final optical output. These layers mediate the interaction between s-polarized light and the wire grid by providing additional reflection and absorption mechanisms, ensuring that Ts is reduced to ≤ 0.0008 while Tp remains high, thus preventing image distortion without compromising energy efficiency.
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 solution effectively reduces the transmission of the minimally-transmitted polarization to ≤0.0008 across a light wavelength range from 450 nm to 700 nm, enhancing image resolution and reducing ghosting effects by optimizing the refractive index stack and materials used in the wire grid polarizer.
Implementation Method 1
an index of refraction of the first layer can be greater than an index of refraction of the substrate, an index of refraction of the second layer can be greater than the index of refraction of the first layer, and an index of refraction of the third layer can be less than the index of refraction of the first layer
Implementation Method 2
A wire grid polarizer (WGP) can primarily transmit one polarization (e.g. p-polarization) and primarily reflect or absorb an opposite polarization (e.g. s-polarization)
Implementation Method 3
High absorption/low reflectivity of the opposite polarization (e.g. low Rs) can be important in other applications
Data Source
AI summary
A wire grid polarizer (WGP) can have low transmission of a primarily reflected/absorbed polarization (e.g. low Ts). The WGP can comprise an array of wires on a substrate and a stack of thin films between the substrate and the array of wires. The stack of thin films can include a first layer closest to the substrate, a second layer over the first layer, and a third layer over the second layer and closest to the array of wires. An index of refraction of the first layer can be greater than an index of refraction of the substrate, an index of refraction of the second layer can be greater than the index of refraction of the first layer, and an index of refraction of the third layer can be less than the index of refraction of the first layer.