Variable-Pitch Liquid Crystal Diffraction Grating for Chromatic Aberration Correction
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Solution Overview
Problem
Traditional diffraction gratings have a fixed pitch, leading to optical artifacts and aberrations in waveguides used for color multiplexing, particularly causing chromatic aberrations like color fringing in head-worn displays, which are difficult to mitigate without increasing weight and size.
Innovation Solution
Implementing a liquid crystal diffraction grating with a variable pitch that changes in response to an applied electric field, allowing for synchronization with color changes in a projector, enabling a single waveguide to multiplex colors while reducing chromatic aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed-pitch diffraction grating is used in waveguides for color multiplexing, then the waveguide structure is simple and stable, but chromatic aberrations and color fringing occur
Solution Approach 1:
The patent applies a liquid crystal layer between the waveguide and the diffraction grating that can dynamically change its refractive index in response to applied voltage. This dynamic adjustment allows the system to compensate for chromatic aberrations by adapting the diffraction characteristics to match the projector's color output, transforming a static harmful effect into a controllable variable parameter
Solution Approach 2:
The patent changes the refractive index parameter of the liquid crystal material in response to voltage changes, which in turn changes the effective pitch of the diffraction grating. This parameter change allows the system to maintain optimal diffraction performance across different colors while eliminating chromatic aberrations, resolving the contradiction between fixed structure and adaptive performance
2Object-generated harmful factors
If multiple waveguides are used to reduce chromatic aberrations, then color fringing is reduced, but weight and size increase
Solution Approach 1:
The patent makes a single waveguide multi-functional by adding a voltage-controllable liquid crystal layer that can adapt to different colors. This single component performs the function that would otherwise require multiple dedicated waveguides, reducing overall system weight while maintaining the ability to handle multiple wavelengths without chromatic aberrations
Solution Approach 2:
Instead of using multiple physical waveguides, the patent creates a virtual copy of the diffraction grating's chromatic correction capability through the liquid crystal layer's voltage-controlled refractive index changes. This software-like adjustment replaces the need for multiple hardware waveguides, reducing weight while maintaining performance
3Object-generated harmful factors
If a variable-pitch liquid crystal diffraction grating is used, then chromatic aberrations are reduced, but device complexity increases
Solution Approach 1:
The patent replaces mechanical or fixed-structural solutions for chromatic aberration correction with an electro-optic system. Instead of physically adjusting the grating pitch through mechanical means or using multiple fixed waveguides, the system uses voltage-controlled refractive index changes in the liquid crystal layer to achieve the same correction effect, simplifying the overall control architecture
Solution Approach 2:
The liquid crystal layer acts as an intermediary between the fixed diffraction grating and the variable color output. This intermediate component translates voltage signals into refractive index changes that dynamically match the projector's color characteristics, providing a simple and effective solution without requiring complex direct control of the grating structure itself
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 reduces chromatic aberrations such as color fringing in head-worn displays by dynamically adjusting the diffraction grating pitch, improving image uniformity and reducing the need for multiple waveguides, thus enhancing the performance and compactness of display systems.
Implementation Method 1
Certain liquid crystals may have properties that allow for their use as switchable diffraction gratings. For example, a layer of liquid crystals may form molecular orientation patterns under an applied electric field. Thus, if the applied electric field is a periodic electric field, the liquid crystal molecules may follow the pattern of the electric field and have the same periodic structure as the electric field pattern.
Implementation Method 2
The refractive index of the liquid crystal molecules may change from minimum to maximum in one pitch. These patterns may function as a diffraction grating.
Implementation Method 3
These patterns may function as a diffraction grating.
Data Source
AI summary
An apparatus may include (1) a planar liquid-crystal structure including a plurality of liquid crystals, and (2) a plurality of electrodes coupled to the planar liquid-crystal structure such that (a) when a first plurality of voltages are applied to at least some of the plurality of electrodes, the plurality of liquid crystals are oriented such that the planar liquid-crystal structure operates as a diffraction grating having a first pitch, and (2) when a second plurality of voltages are applied to at least some of the plurality of electrodes, the plurality of liquid crystals are oriented such that the planar liquid-crystal structure operates as a diffraction grating having a second pitch different from the first pitch.