Large-Period Grating Waveguide Display for FOV and Color Control
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Solution Overview
Problem
Existing waveguide displays face limitations in field-of-view (FOV) expansion and color control, necessitating improved design freedoms and achromatic capabilities.
Innovation Solution
Employing gratings with a period significantly larger than visible light wavelengths, typically 5 µm or more, featuring a one- or two-dimensional non-periodic microstructure pattern, allowing for multiple diffraction orders and finer angular division, enabling achromatic behavior and enhanced FOV.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional small-period gratings are used, then the grating structure is simple and easy to manufacture, but the field-of-view is limited and color control is poor
Solution Approach 1:
The patent fundamentally changes the period parameter of the grating from conventional small periods (comparable to wavelength) to large periods (at least fivefold the maximum visible light wavelength, typically 5 µm or more). This parameter change enables multiple diffraction orders and finer angular division, thereby expanding the field-of-view and improving color control without excessive complexity increase
Solution Approach 2:
The grating structure is segmented into multiple periods, where each period contains a non-periodic microstructure pattern. This segmentation approach allows the large-period grating to achieve achromatic behavior by distributing diffraction across multiple orders while maintaining manufacturability through repetitive unit structures
2Reliability
If conventional gratings are used, then the manufacturing process is simple, but achromatic capability is not achieved
Solution Approach 1:
By changing the period parameter to be at least fivefold the maximum visible light wavelength, the grating achieves achromatic capability through multiple diffraction orders. The large period allows different wavelengths to be diffracted into different orders that can be controlled to achieve wavelength-independent output angles
Solution Approach 2:
The grating is divided into multiple periods with non-periodic microstructure patterns within each period. This segmentation enables the achievement of achromatic behavior through the collective effect of multiple periods while maintaining ease of manufacture through the repetitive nature of the unit structure
3Adaptability or versatility
If large-period gratings are used, then design freedom and FOV are increased, but the grating period becomes much larger than conventional gratings
Solution Approach 1:
The patent deliberately changes the period parameter to large values (at least fivefold the maximum visible light wavelength) to increase design freedom. This parameter change enables the grating to support multiple diffraction orders and achieve finer angular division, providing greater versatility in display design despite the larger physical dimensions
Solution Approach 2:
The large-period grating is segmented into multiple identical periods, each containing a non-periodic microstructure pattern. This segmentation allows the large overall period to be achieved while maintaining manufacturing feasibility through the repetition of smaller unit structures, effectively managing the scale increase
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 provides increased design freedoms, allowing for achromatic operation and improved FOV by utilizing multiple diffraction orders and finer angular division, enhancing user experience in HMDs and HUDs.
Implementation Method 1
light is directed from a projector to a one-dimensional in-coupling grating, which diffracts the wavelengths of the incoming light into the waveguide
Implementation Method 2
The gratings have periods which are in the order of wavelength of visible light
Implementation Method 3
where they propagate via total internal reflections towards an out-coupling grating
Data Source
Figure 1A~1D
Figure 2~3B
AI summary
The invention concerns a waveguide display and display element therefor, and a method of designing a waveguide element. The element comprises a waveguide and at least one grating arranged on or within the waveguide, the at least one grating being arranged to couple visible light into, within, and/or out of the waveguide. According to the invention, the period of the grating is in the range of 5 μm or more. The invention increases freedoms of design of grating-based display elements and allows for better color and FOV control.