Pixel Shifting Optical Systems for Compact AR Displays
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Solution Overview
Problem
Designing optical systems for virtual and augmented reality displays is challenging due to the need for compact, power-efficient components that achieve desired optical performance and resolution, often resulting in unsightly and bulky devices.
Innovation Solution
The use of a head-mounted device with a display module incorporating a ferroelectric liquid crystal on silicon (fLCOS) display panel, illumination optics, a twisted nematic (TN) cell, and a birefringent crystal, along with control circuitry to toggle the TN cell between states, maximizing effective image resolution at the eye box through spatial or angular pixel shifting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If traditional display components are used in head-mounted devices, then the device can display images, but the device becomes bulky and unsightly
Solution Approach 1:
The patent implements a nested arrangement where the quarter-wave plate is positioned between the fLCOS display panel and the waveguide, and the geometric phase grating is integrated within the waveguide structure. This nested configuration allows multiple optical components to occupy overlapping or adjacent spatial volumes, reducing the overall device size while maintaining the necessary optical functions for image display and polarization control.
Solution Approach 2:
The patent utilizes angular pixel shifting through the geometric phase grating to distribute image light across different output angles. This transforms the display from a single-plane projection to a multi-angular distribution, effectively increasing the field of view and resolving power without requiring proportional increases in physical display area or device volume.
2Measurement precision
If higher resolution display components are used, then image resolution improves, but power consumption increases
Solution Approach 1:
The patent replaces traditional high-resolution spatial light modulators with a lower-resolution fLCOS panel combined with a geometric phase grating. The grating performs angular pixel shifting that effectively multiplies the resolution through diffraction, substituting a passive optical structure for an active high-resolution display component. This reduces the computational and electrical power demands while achieving equivalent or superior effective resolution.
Solution Approach 2:
The patent changes the operational parameters of the display system by using polarization control through the quarter-wave plate and TN cell in combination with angular diffraction. This parameter-based approach (using polarization states and diffraction angles) allows a lower-resolution physical display to achieve higher effective resolution, reducing the power consumption associated with driving high-resolution pixel arrays.
3Measurement precision
If more optical components are added to improve resolution, then effective resolution increases, but device complexity increases
Solution Approach 1:
The patent merges the quarter-wave plate and geometric phase grating into a compact integrated optical path within the waveguide. The quarter-wave plate is positioned immediately adjacent to the fLCOS panel, and the geometric phase grating is embedded within the waveguide substrate. This merging of components reduces the number of discrete elements and simplifies alignment requirements compared to traditional multi-component optical systems.
Solution Approach 2:
The geometric phase grating serves multiple functions: it performs angular pixel shifting to increase effective resolution, it diffracts light to create the eye box, and it integrates with the waveguide to direct light to the user's eye. This multi-functionality reduces the need for separate components for each function, thereby reducing overall system complexity despite achieving high effective resolution.
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 configuration enhances the effective resolution and field of view of images provided to the user without increasing device size or power consumption, providing seamless integration of virtual and real-world content in augmented reality systems.
Implementation Method 1
A twisted nematic (TN) cell may be optically interposed between the fLCOS display panel and the waveguide. The TN cell may have a first state in which the TN cell transmits the image light with the first linear polarization. The TN cell may have a second state in which the TN cell transmits the image light with a second linear polarization that is different from the first linear polarization.
Implementation Method 2
The birefringent crystal may transmit the image light with the first linear polarization within a first beam. The birefringent crystal may transmit the image light with the second linear polarization within a second beam that is spatially offset from the first beam.
Implementation Method 3
The quarter waveplate may convert the first and second linear polarizations to left and right hand circular polarizations.
Implementation Method 4
The geometric phase grating may diffract left hand circular polarized image light onto a first output angle and may diffract right hand circular polarized image light onto a second output angle.
Data Source
AI summary
A display may include illumination optics, a ferroelectric liquid crystal on silicon (fLCOS) panel, and a waveguide. A twisted nematic cell may be optically interposed between the fLCOS panel and the waveguide. A birefringent crystal may be optically interposed between the cell and the waveguide. The cell may have a first state in which the cell transmits the image light with a first polarization and a second state in which the cell transmits the image light with a second polarization. The crystal may transmit the image light within spatially offset beams based on polarization. In another arrangement, a quarter waveplate may be optically interposed between the cell and the waveguide and a geometric phase grating may be optically interposed between the quarter waveplate and the waveguide. Control circuitry may toggle the cell between the first and second states to maximize the effective resolution of images at an eye box.