Waveguide Deformation Sensing in Head-Mounted Displays
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Solution Overview
Problem
Electronic devices, particularly head-mounted devices with optical components, face challenges in maintaining satisfactory display performance due to potential deformation caused by drop events, thermal effects, and other stressing events, which can lead to misalignment and distortion of images.
Innovation Solution
A head-mounted device with a housing featuring a first and second portion, each equipped with a projector and waveguide, and an optical bridge sensor that detects deformation by analyzing a calibration pattern in the image light, allowing control circuitry to identify and mitigate any misalignment or distortion through point spread function comparison.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If waveguides are used to direct image light in head-mounted devices, then optical performance is improved, but the waveguides become susceptible to deformation from drop events and thermal effects that impacts display performance
Solution Approach 1:
The system performs preliminary calibration by capturing images of a calibration pattern through the waveguide before normal operation. This establishes a baseline point spread function that accounts for any existing waveguide deformation, allowing the system to compensate for these deformations during actual display operation to maintain optical performance
Solution Approach 2:
The system continuously monitors the point spread function of the calibration pattern during operation and compares it to the nominal point spread function. When deviations are detected indicating waveguide deformation, the system can trigger recalibration or compensation mechanisms to restore optimal display performance, creating a closed-loop feedback system
2Measurement precision
If calibration patterns are analyzed to detect waveguide deformation, then measurement precision is improved, but device complexity increases due to additional sensors and processing requirements
Solution Approach 1:
The optical bridge sensor serves multiple functions: it captures the calibration pattern for deformation detection, captures images for display output, and can potentially serve other sensing functions. This multi-functionality reduces the need for separate dedicated deformation sensors, thereby limiting the increase in device complexity while maintaining high measurement precision
Solution Approach 2:
Instead of using complex direct measurement instruments to detect waveguide deformation, the system creates an optical copy of the calibration pattern through the waveguide and analyzes its point spread function. This indirect measurement approach uses simple imaging components rather than complex specialized sensors, achieving high measurement precision with minimal added device complexity
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 detects and mitigates waveguide deformation in real-time, ensuring optimal display performance by adjusting the image data or mechanical alignment, thereby maintaining clear and undistorted images in the eye boxes.
Implementation Method 1
The first waveguide may direct a first portion of the first image light to a first eye box and may direct a second portion of the first image light to the optical bridge sensor
Data Source
AI summary
A head-mounted device may have projector, a first waveguide, a second waveguide, and an optical bridge sensor coupled between the first and second waveguides. An input coupler may couple light with a calibration pattern into the first waveguide. The calibration pattern may be included in visible or infrared light produced by the projector or may be included in infrared light produced by infrared emitters mounted to the first waveguide. An output coupler may couple the light having the calibration pattern out of the first waveguide. An additional output coupler may be used to couple visible light from the projector out of the waveguide and towards an eye box. An image sensor may generate image sensor data based on the light having the calibration pattern. Control circuitry may process the calibration pattern in the image sensor data to detect deformation or warping of the first waveguide.