Lightguide Surface Parallelism Measurement via Optical Interference
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Solution Overview
Problem
Existing head-mounted displays (HMDs) with lightguides that rely on Total Internal Reflection (TIR) face issues with image misdirection due to non-parallel surfaces, leading to improper light delivery to the user's eye, which is undesirable and affects the overall performance of augmented reality applications.
Innovation Solution
A system and method for measuring parallelism in lightguide surfaces using a wavefront generator, Polarized Beam Splitter (PBS), camera module, and logic unit, which generates interference patterns to determine the angle between the lightguide surfaces, ensuring accurate alignment and proper image delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lightguide surfaces are manufactured with tight tolerances to ensure parallelism, then image delivery accuracy is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies preliminary action by performing parallelism measurement during the manufacturing process itself, rather than as a separate post-processing step. The measurement system is integrated into the manufacturing workflow, allowing parallelism to be verified and adjusted while the lightguide is still being fabricated, thereby preventing defects before they propagate through subsequent manufacturing steps.
Solution Approach 2:
The patent replaces complex mechanical measurement systems with an optical measurement approach. By using optical interference patterns and wavefront analysis, the system achieves high-precision parallelism measurement without requiring complex mechanical fixtures, alignment mechanisms, or contact-based measurement tools, thus reducing manufacturing process complexity.
2Measurement precision
If traditional mechanical measurement methods are used to measure lightguide parallelism, then measurement setup is simple, but measurement precision is insufficient
Solution Approach 1:
The patent replaces traditional mechanical measurement methods (such as autocollimators, interferometers with mechanical components, or contact-based profilometers) with a purely optical measurement system. The system uses wavefront generation and optical interference patterns to measure surface parallelism, eliminating mechanical moving parts, complex alignment mechanisms, and contact probes, thereby achieving high precision without proportionally increasing device complexity.
Solution Approach 2:
The patent changes the measurement parameter from direct physical displacement or angle measurement to optical path difference and interference pattern analysis. By measuring the phase shifts and interference fringes created by wavefront reflections from the lightguide surfaces, the system achieves sub-microradian angular precision and sub-micrometer surface parallelism accuracy, far exceeding the capabilities of traditional mechanical measurement systems.
3Ease of manufacture
If non-parallel lightguide surfaces are used, then manufacturing is easier, but light delivery accuracy deteriorates
Solution Approach 1:
The patent enables the lightguide to self-verify its parallelism through the optical measurement system. The wavefront generation and interference pattern analysis allow the lightguide surfaces to essentially measure themselves, providing immediate feedback on manufacturing quality. This self-service capability allows manufacturers to quickly identify and correct parallelism deviations without requiring complex external calibration standards or reference artifacts.
Solution Approach 2:
The patent implements a feedback mechanism where the optical measurement system continuously monitors lightguide surface parallelism during manufacturing. The interference patterns provide real-time feedback on surface alignment, allowing operators to adjust manufacturing parameters or rework components before they leave the production line. This closed-loop feedback ensures that only lightguides meeting the specified parallelism tolerances proceed to final assembly, maintaining high image delivery accuracy.
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 system effectively measures and ensures the parallelism of lightguide surfaces, preventing image misdirection and enhancing the performance of HMDs by ensuring precise light delivery, thereby improving the accuracy and effectiveness of augmented reality applications.
Implementation Method 1
If the lightguide depends on the optical phenomenon of Total Internal Reflection ("TIR") to deliver an image to the eye of a user, the surfaces of the lightguide that facilitate the TIR must be manufactured within design parameters.
Implementation Method 2
A system and method for measuring parallel surfaces in lightguides... generates interference patterns to determine the angle between the lightguide surfaces
Data Source
AI summary
A system for measuring transparent optical elements includes a beam generator, optomechanics, an imaging module, and a logic unit. The beam generator is driven to emit a beam directed at a transparent optical element that is aligned by optomechanics. An image is captured of the beam after the beam reflects off of surfaces of the transparent optical element. The image is analyzed to measure tolerances of the transparent optical element.