Double-Sided Imaging Light Guide with Dichroic Filters
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Solution Overview
Problem
Conventional optical light guides for near-eye displays face challenges in separating color channels effectively, leading to cross-talk and color shifts, which are difficult to correct without increasing device thickness, weight, and reducing brightness.
Innovation Solution
A double-sided beam expander design using dichroic patches and diffractive optics on a single substrate to separate and manage red and blue-green color channels, reducing cross-talk by selectively transmitting or reflecting light based on wavelength and incidence angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple waveguides are stacked together to separate color channels, then cross-talk between color channels is reduced, but device thickness increases and brightness decreases
Solution Approach 1:
The single waveguide is segmented into different functional regions using dichroic patches that divide the waveguide surface into zones handling different color channels (e.g., red channel region and blue-green channel region). This spatial segmentation allows color channel separation without stacking multiple waveguides, thus avoiding increased thickness.
Solution Approach 2:
Different regions of the waveguide are assigned different local optical properties through dichroic patches. The first dichroic patch has properties optimized for the red channel (transmitting red light while reflecting blue-green light), while the second dichroic patch has properties optimized for the blue-green channel. This local quality differentiation enables effective color separation within a single waveguide layer.
2Reliability
If multiple waveguides are stacked together to separate color channels, then cross-talk between color channels is reduced, but device weight increases
Solution Approach 1:
The patent merges the functions of multiple color channel waveguides into a single waveguide structure. By integrating dichroic patches that can selectively route different color channels within one waveguide, the design combines what would traditionally require separate waveguides into a unified structure, thereby reducing overall device weight.
3Adaptability or versatility
If conventional light guide mechanisms are used, then pupil expansion is achieved, but color channel separation is insufficient leading to cross-talk and color shifts
Solution Approach 1:
Dichroic patches serve as intermediary elements between the input coupling and output coupling within the waveguide. These patches act as wavelength-selective mediators that redirect different color channels along distinct paths within the same waveguide, enabling both pupil expansion and effective color channel separation simultaneously.
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 design allows for efficient separation of color channels within a single waveguide substrate, reducing color shifts and improving color quality without increasing device thickness or weight, while maintaining pupil expansion capabilities.
Implementation Method 1
a first dichroic patch (210BG) having a filter characteristic for handling light in the blue-green wavelength range and a second dichroic patch (210R) having a filter characteristic for handling light in the red wavelength range
Implementation Method 2
The collimated light beams can be directed out of the waveguide by a similar output optical coupling, which can also take the form of a diffractive optic
Implementation Method 3
The collimated light beams can be enlarged in one dimension by offsetting partially reflected portions of the collimated beams
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
An imaging light guide has a waveguide formed as a coated substrate having first and second surface coatings. A first in-coupling diffractive optic on the first coating directs diffracted light of a first wavelength range into the waveguide along a first direction. A second in-coupling diffractive optic on the second coating directs diffracted light of a second wavelength range into the waveguide along a second different direction. A first dichroic patch between the first surface of the substrate and the first surface coating for (a) transmitting the first wavelength range, (b) transmitting the second wavelength range through a limited range of incidence angles, and (c) reflecting the second wavelength range through a higher range of incidence angles. A second dichroic patch between the second surface of the substrate and the second surface coating for transmitting the second wavelength range and reflecting the first wavelength range.