Aberration-Correcting Diffraction Grating for Wavelength Selective Switches
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Solution Overview
Problem
Optical systems, particularly wavelength selective switch devices, face significant challenges with optical aberrations such as coma and spherical aberration due to the asymmetric nature of beams, which limit their performance and require costly and complex two-mirror designs for correction.
Innovation Solution
A diffraction grating with a variable line spacing and curvature is used to impart a predefined phase change to optical beams, correcting for aberrations by modeling and optimizing the phase profile to minimize M2 values and achieve a Gaussian beam shape, thereby reducing aberrations without the need for additional mirrors or complex alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a two-mirror Czerny-Turner system is used to correct optical aberrations, then aberration correction is achieved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the aberration correction function from the complex two-mirror system and implements it within a single diffraction grating element. The grating equation is modified to include an aberration correction term, allowing one element to perform both wavelength separation and aberration correction that previously required multiple components.
Solution Approach 2:
The patent combines multiple functions (wavelength dispersion and aberration correction) into a single diffraction grating element. By modifying the grating equation to include both the standard diffraction term and an aberration correction term, the system merges what were previously separate functions into one integrated component, reducing overall system complexity.
2Measurement precision
If beam spot size is reduced to achieve sharper channels, then channel resolution is improved, but optical aberrations increase
Solution Approach 1:
The patent changes the parameters of the diffraction grating (line spacing, curvature) to optimize the balance between beam spot size and aberration. By adjusting these grating parameters according to the modified grating equation, the system achieves smaller effective beam spots for sharper channels while the aberration correction term compensates for increased optical aberrations.
Solution Approach 2:
The patent applies preliminary anti-action by pre-correcting for aberrations in the grating design before the beam propagation occurs. The modified grating equation includes an aberration correction term that anticipates and counteracts the aberrations that will occur during beam propagation, allowing the system to use smaller beam spots without suffering from excessive aberrations.
3Productivity
If asymmetric beam profiles are used for efficient wavelength channel switching, then switching efficiency is improved, but optical aberrations increase
Solution Approach 1:
The patent applies local quality by making the diffraction grating properties spatially varying. The grating line spacing and curvature are adjusted locally across different regions of the grating surface according to the modified grating equation, allowing asymmetric beam profiles to be efficiently switched while local variations in grating structure compensate for position-dependent aberrations.
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 solution effectively corrects optical aberrations in single-mirror WSS systems, improving beam symmetry and filter shape, reducing the need for complex designs and additional components, while maintaining performance comparable to two-mirror systems.
Implementation Method 1
an array of spaced-apart diffraction lines configured to spatially separate wavelength channels within incident optical beams
Implementation Method 2
impart a predefined phase change to the optical beams to at least partially correct the beams for optical aberrations present in the optical system
Data Source
AI summary
Described herein is a diffraction grating (1) for use in an optical system. The diffraction grating includes a substrate (2) and an array of elongate diffracting elements (3) arranged in a grating profile across the substrate. The grating profile imparts a predefined phase change to optical beams to at least partially correct the beams for optical aberrations present in the optical system.