Macro Duty Cycle Gratings for Waveguide Manufacturing
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Solution Overview
Problem
The manufacturing of diffraction gratings for waveguides in HUDs and HMDs is challenging due to the need for modulating feature sizes that are difficult to achieve as they decrease to tens of nanometers, leading to non-manufacturable aspect ratios and inefficiencies.
Innovation Solution
A waveguide with a grating structure featuring discontinuous regions of diffraction interleaved with regions of no diffraction, where the size of each successive diffraction region increases, allowing for varying periods and macro duty cycles that can be modulated to maintain manufacturability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the duty cycle of the grating is modulated to improve image uniformity and efficiency, then the manufacturing precision deteriorates due to feature sizes decreasing to tens of nanometers
Solution Approach 1:
The grating structure is divided into multiple discrete regions with different duty cycles rather than using a continuously modulated grating. Each region maintains manufacturable feature sizes while collectively achieving the desired optical performance through the combination of discrete segments.
Solution Approach 2:
Different regions of the grating are assigned different duty cycle values tailored to local optical requirements. This allows optimization of image uniformity and efficiency in specific areas without compromising the manufacturability of individual grating features, as each local region uses appropriate feature dimensions.
2Manufacturing precision
If the depth of the gratings is modulated to improve diffraction efficiency, then the aspect ratio grows to non-manufacturable levels
Solution Approach 1:
Instead of modulating grating depth to achieve desired optical effects, the patent changes the duty cycle parameter across different regions. This parameter substitution allows achieving similar optical performance without creating excessively deep gratings that would have non-manufacturable aspect ratios.
3Use of energy by moving object
If traditional gratings completely fill the aperture to maximize light utilization, then the device complexity increases due to untenable manufacturing processes
Solution Approach 1:
Rather than completely filling the aperture with a continuously modulated grating that would require complex manufacturing, the patent uses partial action by implementing discrete grating regions. These regions collectively utilize light effectively while maintaining simpler, more manufacturable structures with clear boundaries between regions.
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 high-yield manufacturability while maintaining image uniformity and efficiency, with feature sizes remaining above manufacturing limits and user visibility unaffected by the modulation of blank periods.
Implementation Method 1
Waveguides in head-up displays (HUDs) and helmet mounted displays (HMDs) utilize diffraction gratings
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A waveguide includes a grating structure with discontinuous regions of diffraction; regions of diffraction are interleaved with regions of no diffraction. The regions of diffraction and no diffraction may vary in size such that the width of each successive region of diffraction increases across the face of the waveguide. Neighboring regions of diffraction, separated by regions of non-diffraction, may define different periods.