Dual Waveguide Structure for Wide-Band Color HUDs
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Solution Overview
Problem
Existing waveguide systems face challenges in providing improved performance across a wide wavelength range due to the trade-off between wavelength bandwidth, expansion ratio, and field of view, particularly in designing gratings for color displays.
Innovation Solution
The use of two separate waveguides, each optimized for specific wavelength ranges, with offset input coupling gratings and overlapping output coupling gratings, allows for independent grating design and improved optical performance without stray light paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single waveguide is used to guide all wavelengths, then the device complexity is reduced, but the wavelength bandwidth performance deteriorates due to trade-offs in grating design
Solution Approach 1:
The system divides the broadband wavelength range into multiple subsets, with each waveguide optimized for a specific subset. This segmentation allows each grating to be designed for optimal performance in its designated wavelength range, resolving the trade-off between device complexity and wavelength bandwidth performance.
2Ease of operation
If the exit pupil is made larger to accommodate eye alignment flexibility, then the ease of operation improves, but the device complexity increases due to pupil replication requirements
Solution Approach 1:
The pupil expansion function is segmented across multiple waveguides, where each waveguide contributes to the overall exit pupil. This distributed approach achieves large exit pupil for eye alignment flexibility while managing device complexity through modular waveguide units.
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 approach enables larger exit pupils, reduced stray light, and enhanced color performance by optimizing gratings for individual wavelength sets, resulting in a more efficient and flexible waveguide system.
Implementation Method 1
Each waveguide comprises: an input coupling grating configured to receive image light of a respective subset of optical wavelengths and diffract the image light at specific angles to couple the image light into the waveguide
Implementation Method 2
The waveguide body is optically transmissive such that the user views the real world through the waveguide and the image from the projection system is overlaid onto that view
Implementation Method 3
an output coupling grating configured to diffract image light from the waveguide at specific angles to direct image light to a display exit pupil
Data Source
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AI summary
An optical system for a colour head up display, the optical system being for guiding image light from an image projection system to an exit pupil. First and second waveguides are utilised, each waveguide guiding a predetermined set of wavelengths.