Anisotropic Diffraction Grating for Rainbow Suppression
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Solution Overview
Problem
Compact planar optical components in wearable displays, such as diffraction gratings, often suffer from rainbow effects due to angular dispersion of external light, which can be distracting and affect image quality, and manufacturing these components with high yield is challenging, especially at duty cycles outside the typical range of 0.3 to 0.7.
Innovation Solution
A method of manufacturing diffraction gratings with triangular ridges and grating lines of different refractive indices, where the grating lines are selectively deposited on one side of the ridges, and an overcoat layer is used to reduce the refractive index difference, allowing for a broader range of duty cycles and minimizing rainbow effects by optimizing the refractive indices, thickness, tilt angle, and duty cycle to achieve destructive interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If compact planar optical components are used to reduce size and weight, then weight and size are reduced, but image quality deteriorates due to rainbow effects and visual artifacts
Solution Approach 1:
The patent modifies the physical parameters of the diffraction grating, specifically the duty cycle (ratio of grating line width to pitch) and refractive index contrast between grating lines and surrounding material. By operating outside the conventional duty cycle range of 0.3-0.7 and optimizing refractive index differences, the design achieves rainbow suppression while maintaining compact form factor and acceptable image quality
Solution Approach 2:
The patent employs composite material structures with different refractive indices arranged in specific patterns. The diffraction grating uses materials with contrasting refractive indices to create controlled optical interference that suppresses rainbow effects. This composite approach allows simultaneous achievement of compact size, weight reduction, and improved image quality through optical interference management
2Adaptability or versatility
If diffraction gratings are manufactured with duty cycles outside the typical range of 0.3 to 0.7, then adaptability and design flexibility are improved, but manufacturing precision and yield deteriorate
Solution Approach 1:
The patent deliberately extends the duty cycle parameter beyond conventional limits (0.3-0.7) to achieve specific optical performance characteristics. By combining extreme duty cycle values with optimized refractive index contrasts, the design achieves rainbow suppression functionality that is not attainable within conventional parameter ranges, while the manufacturing process is adapted to accommodate these non-standard parameters
3Object-affected harmful factors
If angular dispersion of external light is reduced to suppress rainbow effects, then harmful factors are reduced, but image quality and brightness may deteriorate
Solution Approach 1:
The patent converts the harmful angular dispersion effect into a beneficial one by using controlled optical interference. The diffraction grating structure is designed to create destructive interference specifically for rainbow-causing wavelengths and angles, while constructive interference maintains brightness for the desired image wavelengths. This transforms the potentially harmful dispersion effect into a mechanism for selective wavelength filtering that suppresses rainbows while preserving image quality and brightness
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 effectively suppresses rainbow effects while maintaining the pupil-replicating function, enabling a more comfortable and immersive viewing experience by reducing optical power of rainbow beams and optimizing image distribution across the replicated pupil.
Implementation Method 1
A diffraction grating includes a substrate and an array of ridges extending from the substrate... An array of grating lines... each grating line comprising a slab of transparent material supported by the first side of a corresponding ridge
Implementation Method 2
an overcoat layer is formed over the array of grating lines... optimizing the refractive indices, thickness, tilt angle, and duty cycle to achieve destructive interference
Implementation Method 3
A refractive index of the array of grating lines is different from a refractive index of the array of ridges... optimizing the refractive indices
Data Source
AI summary
A diffraction grating includes a substrate and an array of triangular ridges extending from the substrate. The ridges run parallel to one another and have triangular cross-sections such that first sides of the ridges face in a first direction and adjacent second sides of the ridges face in a second, different direction. An array of grating lines is disposed over the first sides of the array of ridges, each grating line of the array of grating lines comprising a slab of transparent material supported by the first side of a corresponding ridge of the array of ridges. A refractive index of the array of grating lines is different from a refractive index of the array of ridges.