Waveguide Air Pocket Cavities to Reduce Light Loss in TIR
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Solution Overview
Problem
Existing augmented reality viewing devices face challenges in achieving total internal reflection (TIR) without light loss, as projected light often escapes the waveguide, reducing the clarity and brightness of the image seen by the user.
Innovation Solution
A method of manufacturing an optical system involving a waveguide with a cap layer and a cavity filled with optical gas, enhancing the refractive index difference between the waveguide and air to promote reflection and minimize light loss, using a sequence of cap layers with varying refractive indices to absorb and reflect ambient light effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a simple waveguide structure is used, then the device complexity is low, but light loss occurs due to insufficient total internal reflection
Solution Approach 1:
The waveguide structure is segmented into multiple functional layers: a core waveguide layer, cladding layers with different refractive indices, and periodic modulation structures. This segmentation enables each layer to perform specific optical functions that collectively achieve total internal reflection while maintaining structural feasibility
Solution Approach 2:
Cladding layers with intermediate refractive indices are introduced between the core waveguide and external environment. These intermediary layers create the necessary refractive index gradient to enable total internal reflection at the core-cladding interfaces, preventing light loss without requiring complex external optical elements
2Manufacturing precision
If the waveguide uses uniform material composition, then the manufacturing process is simple, but optical image quality suffers from reflections and ghost artifacts
Solution Approach 1:
Different regions of the waveguide structure are assigned different material compositions and refractive indices. The core layer, cladding layers, and modulation regions each have optimized local properties tailored to their specific optical functions, enabling high-quality total internal reflection while using standard manufacturing techniques for each individual layer
Solution Approach 2:
The waveguide employs composite material structures combining multiple transparent materials with different refractive indices. This composite approach creates the necessary optical contrast for total internal reflection and eliminates ghost artifacts, while each material layer can be deposited using conventional thin-film fabrication methods
3Reliability
If no cap layer is added to the waveguide, then the manufacturing process is simpler, but ambient light transmission and optical gas cavity formation are compromised
Solution Approach 1:
The cap layer is deposited over the waveguide structure before final assembly, preliminarily creating the sealed cavity environment and protecting the optical surfaces. This preliminary action ensures proper ambient light transmission characteristics and maintains the optical gas cavity integrity throughout subsequent manufacturing steps
Solution Approach 2:
The cap layer serves as an intermediary protective and functional element between the waveguide core and the external environment. It mediates the interaction between ambient light and the internal optical structures while maintaining the sealed cavity, simplifying the overall manufacturing by integrating multiple functions into a single component
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
Improves optical image quality by increasing transmissivity, reducing reflections, and enhancing diffraction efficiency, resulting in clearer and brighter real-world object visibility while minimizing ghost artifacts and rainbow defects.
Implementation Method 1
Total internal reflection (TIR) is an ideal situation where there are no losses of the projected light out of the waveguide and 100 percent of the projected light reaches the eye of the user
Implementation Method 2
enhancing the refractive index difference between the waveguide and air to promote reflection and minimize light loss
Data Source
AI summary
Recesses are formed on a front side and a rear side of a waveguide. A solid porogen material is spun onto the front side and the rear side and fills the recesses. First front and rear cap layers are then formed on raised formations of the waveguide and on the solid porogen material. The entire structure is then heated and the solid porogen material decomposes to a porogen gas. The first front and rear cap layers are porous to allow the porogen gas to escape and air to enter into the recesses. The air maximizes a difference in refractive indices between the high-index transparent material of the waveguide and the air to promote reflection in the waveguide from interfaces between the waveguide and the air.