2D Output Grating Asymmetry for First-Order Diffraction Suppression
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Solution Overview
Problem
The use of a two-dimensional grating in near-eye displays for augmented reality systems results in a line of bright spots due to the (1, 1) diffraction order, which degrades the display quality.
Innovation Solution
A grating design with two materials of different refractive indices, periodically repeated in two dimensions, is used to suppress the (1, 1) diffraction order by reducing its Fourier coefficient to less than half the (1, 0) and (0, 1) coefficients, with a thickness of 300 nm or less, and a spatially nonsymmetrical pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a two-dimensional grating is used in near-eye displays, then the display functionality is achieved, but a line of bright spots appears due to the (1, 1) diffraction order degrading display quality
Solution Approach 1:
The patent modifies the grating structure parameters by introducing a spatially nonsymmetrical pattern with specific geometric configurations. This changes the diffraction characteristics to suppress the (1, 1) order while maintaining the necessary display functionality. The nonsymmetrical design alters the Fourier coefficients to reduce the harmful diffraction order intensity.
Solution Approach 2:
The patent employs spatially nonsymmetrical patterns in the grating design to suppress the (1, 1) diffraction order. By breaking the symmetry of the conventional periodic structure, the diffraction efficiency into the harmful (1, 1) order is reduced, thereby eliminating the line of bright spots while preserving the display function.
2Object-affected harmful factors
If the grating layer thickness is reduced to 300 nm or less, then the (1, 1) diffraction order is suppressed, but manufacturing precision requirements increase
Solution Approach 1:
The patent specifies a thickness parameter of 300 nm or less for the grating layer to achieve suppression of the (1, 1) diffraction order. This thin-film parameter change enables the desired optical effect while the nonsymmetrical pattern design compensates for potential manufacturing variations.
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 the (1, 1) diffraction order, enhancing the quality of the two-dimensional grating as an output coupler for waveguides in near-eye displays.
Implementation Method 1
a grating configured to couple light out of the waveguide, wherein: the grating comprises a design of two or more materials having different refractive indices; the design is repeated periodically in a first dimension and repeated periodically in a second dimension to form a two-dimensional pattern
Implementation Method 2
a waveguide configured to guide light received from the projector
Data Source
AI summary
An output grating for waveguide of a head-mounted display is configured to suppress the (1, 1) diffraction order of the output grating. The grating has a design of two or more materials having different refractive indices. The design is repeated periodically in a first dimension and repeated periodically in a second dimension, to form a two-dimensional pattern. A refractive index of the two-dimensional pattern is approximated by a two-dimensional Fourier series comprising a first coefficient of order (1, 0), a second coefficient of order (0, 1), and a third coefficient of order (1, 1). The third coefficient is less than half the first coefficient and less than half the second coefficient, such that light from the (1, 1) diffraction order of the grating is suppressed.