Lightguide Optical Element Testing Without Coupling Prisms
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Solution Overview
Problem
Conventional methods for assessing waveguide performance in near-eye displays are time-consuming and expensive, limiting the availability and adoption of high-quality HMDs due to the need for precise design and manufacturing of facets with parallel alignment and homogeneous refractive index.
Innovation Solution
A novel technique for measuring lightguide optical elements (LOE) performance that eliminates the use of coupling prisms, allowing for efficient measurement of facet parallelism and refractive index homogeneity by coupling light through major surfaces and measuring reflections and transmissions across facets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods using coupling prisms are used to measure facet parallelism and refractive index homogeneity, then measurement precision can be maintained, but device complexity and testing time increase significantly
Solution Approach 1:
The patent extracts and eliminates the coupling prism component from the measurement system. Instead of using a coupling prism to interface with the waveguide, the method directly couples light into the waveguide's major surfaces, removing the intermediate coupling component and simplifying the overall measurement apparatus while maintaining measurement capability
Solution Approach 2:
The measurement system is designed to measure multiple waveguide parameters (facet parallelism, refractive index homogeneity, surface quality) using a single integrated setup without requiring different specialized components for each measurement type, thereby reducing device complexity while maintaining comprehensive measurement precision
2Measurement precision
If conventional coupling prism methods are used for waveguide measurement, then optical performance assessment is accurate, but testing time and production costs increase
Solution Approach 1:
The measurement process enables continuous assessment of waveguide optical performance by eliminating the need for complex coupling prism alignment procedures. Light can be continuously coupled into the waveguide through its major surfaces, allowing for faster, uninterrupted measurement of facet parallelism and refractive index homogeneity throughout production
Solution Approach 2:
The waveguide itself serves as the measurement medium without requiring external coupling prisms. The measurement system utilizes the waveguide's inherent optical properties and geometry, allowing the component being measured to facilitate its own characterization process, thereby reducing external complexity and improving testing speed
3Reliability
If precise design and manufacturing of facets are implemented to ensure parallel alignment and homogeneous refractive index, then waveguide optical performance is optimized, but manufacturing complexity and costs increase
Solution Approach 1:
The patent replaces complex mechanical measurement and alignment systems with optical measurement methods. By using light coupling through the waveguide's major surfaces and analyzing the reflected or transmitted light, the system can assess facet parallelism and refractive index homogeneity without requiring complex mechanical positioning equipment, thereby simplifying both measurement and manufacturing processes
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 method simplifies the measurement process, improving testing efficiency and reducing production costs while ensuring optimal waveguide performance for enhanced image quality and user comfort in near-eye displays.
Implementation Method 1
Waveguides function based on total internal reflection along their major surfaces to propagate light and use reflection off facets placed along the waveguides to direct the light to the user's eyes
Implementation Method 2
coupling light into the waveguide through one or more of the major surfaces to reflect off or transmit through one or more of the facets
Data Source
AI summary
Examining a light optical element (LOE) may include placing a first slit optically between a projector configured to emit light and the LOE's first major surface and placing a second slit optically between the LOE's second major surface and a detector. Facet parallelism between two facets may be deduced based on a shift of the image reflected from the first facet to the second facet relative to light transmitted normal to the first and second major surfaces through a portion of the substrate not including a facet. Facet refractive index homogeneity or deviation may be deduced based on the light transmitted through the facet relative to light transmitted normal to the first and second major surfaces through a portion of the substrate not including a facet.