Diffractive Polarizing Beam Splitter for Liquid Crystal Stability
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Solution Overview
Problem
Optical elements with polarized beam-splitting functions, such as wire-grid polarized-beam splitting elements, often cause destabilization in liquid crystal panels due to reflected light, which is undesirable in projection displays and other optical devices.
Innovation Solution
An optical element with a diffractive structure featuring concave and convex portions and a grid of fine lines on a transparent substrate, where the grid reflects one polarized component and transmits the other, with the reflected light being diffracted at a large angle and totally reflected at the substrate interface, preventing its return to the previous stage on the optical path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a wire-grid polarized-beam splitting element is used to achieve high polarized-beam splitting capability and high optical-damage threshold, then the polarized beam splitting performance is improved, but reflected light returns to the liquid crystal panel causing operation destabilization
Solution Approach 1:
The patent converts the harmful reflected light into a useful diffracted beam. The diffractive structure is designed to diffract the reflected light at a specific angle (first-order diffraction) that directs it away from the liquid crystal panel. By setting the diffraction angle to satisfy the relationship θ > arcsin(1/n), the reflected light undergoes total internal reflection at the substrate-air interface and is guided to the sides of the substrate, thus converting the harmful reflection into a beneficial diffraction effect that eliminates the harmful feedback while maintaining the polarized beam splitting function.
Solution Approach 2:
The patent addresses the reflected light problem by introducing a spatial dimension solution. Instead of trying to control the reflection in the same optical path dimension, the diffractive structure redirects the reflected light into a different spatial dimension (diffraction angle θ) that leads it away from the problematic feedback path. This dimensional redirection through diffraction allows the reflected light to be separated from the main optical path and directed to safe exit paths at the substrate edges.
2Illumination intensity
If high intensity light is input to improve luminance of displayed images, then the luminance is improved, but the reflected light intensity increases causing greater destabilization of the liquid crystal panel
Solution Approach 1:
The diffractive structure converts the intensified reflected light (which would be more harmful at higher intensities) into a beneficial diffracted beam. The same diffraction mechanism that works for low intensity light effectively redirects the high intensity reflected light away from the liquid crystal panel. The relationship θ > arcsin(1/n) ensures that even at high light intensities, the reflected light is diffracted at an angle that causes total internal reflection and guides it to the substrate edges, preventing feedback destabilization regardless of the input light intensity level.
3Object-affected harmful factors
If a diffractive structure is added to diffract reflected light, then the harmful reflected light is redirected, but the device complexity increases
Solution Approach 1:
The patent merges the polarized beam splitting function (performed by the wire grid) and the reflected light redirection function (performed by the diffractive structure) into a single integrated optical element. Both functions are implemented on the same substrate, with the diffractive structure and wire grid working together in a unified design. This merging eliminates the need for separate components and reduces overall system complexity despite adding functional capabilities.
Solution Approach 2:
The optical element achieves multi-functionality by combining polarized beam splitting and reflected light diffraction redirection in a single component. The substrate with both the diffractive structure and wire grid serves multiple purposes: it splits polarized beams for the liquid crystal panel operation and simultaneously diffracts redirects reflected light to prevent feedback. This universal design allows one element to perform multiple functions that would otherwise require separate components.
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 solution effectively suppresses the negative influence of reflected light, improving the stability and performance of liquid crystal devices and displays by ensuring that most reflected light does not re-enter the optical path, thereby enhancing light use efficiency and preventing malfunctions.
Implementation Method 1
one of polarized components of the incident light is reflected by the grid, whereas the other one of the polarized components is transmitted
Implementation Method 2
The reflected polarized component (the reflected light) is diffracted at a sufficiently large angle by the diffractive structure
Implementation Method 3
allows the diffracted reflected light to be totally reflected at an interface between a second surface of the substrate and a medium surrounding the substrate
Data Source
AI summary
An optical element having a function of splitting incident light into polarized beams includes a substrate transparent for the incident light; a diffractive structure that includes a plurality of concave portions and a plurality of convex portions alternately arranged with each other, each of the plurality of concave portions and convex portions having a rectangular sectional shape and that is provided on a first surface of the substrate; and a grid that includes a plurality of fine lines extending in a single direction and that is provided across a top surface of the diffractive structure on the first surface of the substrate, wherein conditions: d<λ and λ/n<δ≦λ are satisfied when λ represents a wavelength of the incident light; d represents a distance between the neighboring fine lines; δ represents a distance between the convex portions; and n represents a refractive index of a material forming the substrate.