Waveguide FOV Expansion via Polarization Grating Tiling
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Solution Overview
Problem
Conventional optical waveguides used in near-eye displays, such as head-mounted displays, are limited to a diagonal field of view (FOV) of about 35 degrees due to the critical angle of the materials used, which cannot be easily expanded without increasing the index of refraction or using expensive materials.
Innovation Solution
The optical assembly includes an input-coupler with Bragg polarization gratings that diffract polarized light in a time-division multiplexed scheme to two intermediate components, allowing the light to be steered in different directions, thereby increasing the FOV to around 70 degrees without modifying the display engine or using high-index materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional optical waveguides are used with standard materials, then the device structure remains simple and materials remain inexpensive, but the field of view is limited to about 35 degrees
Solution Approach 1:
The input-coupler is segmented into multiple polarization gratings (first and second polarization gratings) that diffract light into separate first and second portions. Each grating handles a specific polarization state and directs it to appropriate intermediate components, enabling the system to achieve an expanded field of view through coordinated action of multiple segmented elements rather than relying on a single material property
Solution Approach 2:
The system changes the parameter of light polarization to achieve field of view expansion. By manipulating polarized light through polarization gratings and time-division multiplexing, the system directs different polarization states along different optical paths, effectively doubling the field of view without changing the base material's index of refraction
2Area of stationary object
If the index of refraction is increased to expand field of view, then the field of view can be increased, but the material cost increases significantly
Solution Approach 1:
The patent replaces the mechanical/material-based approach (using high-index materials) with an optical/polarization-based approach. Instead of changing the physical material properties to achieve field of view expansion, the system uses polarization optics and diffraction gratings to achieve the same effect, thereby avoiding the need for expensive high-index materials
3Area of stationary object
If a single intermediate component is used, then the device complexity remains low, but the field of view is limited by the critical angle
Solution Approach 1:
The intermediate component function is segmented into multiple specialized components (first and second intermediate components), each optimized for handling specific portions of the polarized light. This segmentation allows each component to operate within its optimal performance range while collectively achieving an expanded field of view that would be impossible with a single component
Solution Approach 2:
Multiple intermediate components are introduced to handle different functions: the first intermediate component handles the first portion of polarized light, the second intermediate component handles the second portion, and together they contribute to the expanded field of view. Each component has a specialized function that contributes to the overall system capability
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 significantly expands the diagonal FOV to nearly 70 degrees, doubling the conventional limit, while maintaining the same display engine size and avoiding the need for expensive high-index materials.
Implementation Method 1
The one or more polarization gratings diffract polarized light from the image in two different directions according to a time-division multiplexed scheme
Implementation Method 2
The input-coupler includes one or more polarization gratings, which in embodiments may be configured according to the Bragg regime
Implementation Method 3
Light propagating at some non-zero angle of incidence to a surface of the waveguide will travel within the waveguide, bouncing back and forth between the surfaces, so long as the angle of incidence with respect to the surface normal is greater than some critical angle
Data Source
AI summary
An input-coupler of an optical waveguide includes one or more Bragg polarization gratings for coupling light corresponding to the image in two different directions into the optical waveguide. The input-coupler splits the FOV of the image coupled into the optical waveguide into first and second portions by diffracting a portion of the light corresponding to the image in a first direction toward a first intermediate component, and diffracting a portion of the light corresponding to the image in a second direction toward a second intermediate component. An output-coupler of the waveguide combines the light corresponding to the first and second portions of the FOV, and couples the light corresponding to the combined first and second portions of the FOV out of the optical waveguide so that the light corresponding to the image and the combined first and second portions of the FOV is output from the optical waveguide. The input-coupler splitting the light to two or more intermediate components provides an increased FOV.