Waveguide Cladding and Polishing for Pupil Expander Light Guidance
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Solution Overview
Problem
Conventional pupil expanders face challenges in efficiently guiding diffractive or diverging light fields, often resulting in light loss through unintended surfaces and compromised image quality due to imperfections in waveguide edges and corners.
Innovation Solution
A waveguide with a core of high refractive index material, surrounded by protective layers of lower refractive index, is manufactured using specific polishing and bonding techniques to ensure sharp edges and internal reflections, preventing light loss and maintaining image quality by using total internal reflection and protective cladding to manage diffracted light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional polishing techniques are used on waveguide surfaces, then manufacturing simplicity is maintained, but edge imperfections and surface defects occur that compromise image quality
Solution Approach 1:
The polishing process is divided into multiple sequential stages (coarse polishing, fine polishing, and super-fine polishing), each using progressively finer abrasives to achieve the required edge sharpness without creating defects
Solution Approach 2:
Protective layers are applied to the waveguide surfaces before polishing to prevent edge damage and surface defects during the manufacturing process, ensuring sharp edges are maintained throughout polishing
2Loss of energy
If the waveguide core has high refractive index material for efficient light guidance, then light guidance efficiency is improved, but light loss through unintended surfaces occurs due to insufficient edge protection
Solution Approach 1:
Protective layers with appropriate refractive indices are applied to the waveguide surfaces to act as intermediaries that prevent light loss through unintended surfaces while maintaining total internal reflection at the core boundaries
Solution Approach 2:
The waveguide structure combines the high refractive index core material with protective layer materials of different refractive indices to create a composite structure that simultaneously achieves efficient light guidance and prevents light loss through edges and corners
3Reliability
If protective layers are applied to waveguide surfaces to prevent light loss, then light guidance efficiency is improved, but manufacturing complexity increases due to additional bonding steps
Solution Approach 1:
The refractive indices of protective layers are carefully selected to be between that of air and the waveguide core material, enabling total internal reflection to occur at the protective layer boundaries while preventing light loss through waveguide surfaces
Solution Approach 2:
Protective layers serve as intermediary structures that provide both mechanical protection and optical functionality, preventing light loss while the bonding process integrates them into the waveguide structure
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 expands the eye-box for holographic projections, ensuring high-quality image reproduction while maintaining a compact and efficient optical system, capable of handling diffracted light fields with improved light guidance and reduced edge imperfections.
Implementation Method 1
Each surface of the second pair of opposing surfaces is clad with a respective layer of material having a refractive index less than that of the transparent medium
Implementation Method 2
a first pair of opposing surfaces arranged to guide a light field through the transparent medium from the input port to the output port by reflection therebetween
Data Source
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AI summary
A method is provided of manufacturing a waveguide (1114) comprising an input port, an output port, a transparent medium (1104) having a first refractive index (n1), a first pair of opposing surfaces (1116, 1118) and a second pair of opposing surfaces. The method comprises polishing at least one surface of the second pair of opposing surfaces to achieve a separation therebetween, bonding a protective layer (1110, 1112) to at least one polished surface of the second pair of opposing surfaces; and polishing at least one surface of the first pair of opposing surfaces to achieve a separation therebetween.The waveguide (1114) is used as a pupil expander in a head-up display.