Fractional Vortex Beam Charge Measurement Under Low Coherence
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Solution Overview
Problem
Current methods for measuring the topological charge of fractional vortex beams, particularly those with non-integer values, suffer from low accuracy and fail to provide quantitative characterization when coherence degrades, especially for partially coherent beams.
Innovation Solution
A method involving irradiation of a partially coherent fractional vortex beam onto a scattering sample, followed by horizontal and vertical overlap scans, and using a detector to acquire diffraction light intensity, coupled with a multimode stacked diffraction algorithm to iteratively update the electric field and reconstruct the cross-spectral density function, allowing for reverse transmission calculation to determine the topological charge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional measurement methods are used for fractional vortex beams, then the measurement process is simple, but the measurement precision deteriorates significantly for partially coherent beams
Solution Approach 1:
The patent introduces a scattering sample as an intermediary element that converts the partially coherent fractional vortex beam into a diffraction pattern. This intermediary enables the complex measurement of topological charge to be transformed into a measurable intensity distribution, solving the precision problem while maintaining operational simplicity through the standard scattering-measurement framework.
Solution Approach 2:
The patent replaces complex optical measurement systems with a computational approach. By using the multimode stacked diffraction algorithm to iteratively update the electric field and reconstruct the cross-spectral density function, the system substitutes mechanical/optical complexity with computational algorithms, achieving high precision measurement without additional optical devices.
2Measurement precision
If additional optical devices are added to improve measurement accuracy, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent eliminates the need for additional optical devices by substituting them with computational algorithms. The multimode stacked diffraction algorithm performs the measurement function that would otherwise require complex optical systems, achieving high precision through software-based processing rather than hardware complexity.
Solution Approach 2:
The scattering sample, which is already present in the measurement setup, serves dual purposes: it enables the measurement process and provides the necessary diffraction information for topological charge determination. The system uses the existing scattering mechanism to achieve measurement goals without requiring additional specialized optical components.
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
Enables accurate and precise measurement of the topological charge of partially coherent fractional vortex beams, even under conditions of low coherence, with high optical efficiency and no additional optical devices, enhancing applications in optical communication and imaging.
Implementation Method 1
irradiating a to-be-measured fractional vortex beam to a scattering sample
Implementation Method 2
acquiring diffraction light intensity by using a detector placed in a diffraction area
Data Source
AI summary
A to-be-measured partially coherent fractional vortex beam passes through a scattering object, an error between measurable information and to-be-measured information is minimized by using an optimization algorithm, and a main electric field mode and a weight of a to-be-measured fractional vortex beam are reconstructed by using a multimode stacked diffraction algorithm. A cross-spectral density function of the partially coherent fractional vortex beam is calculated, a cross-spectral density of a partially coherent fractional vortex optical field is reconstructed, and complete information including light intensity, a light intensity association, an electric field association, a phase, and the like of the partially coherent fractional vortex optical field is obtained. After the complete information of the partially coherent fractional vortex optical field is obtained, reverse transmission calculation is performed to obtain a source field vortex phase distribution, thereby implementing accurate topological charge measurement of the fractional vortex beam under low coherence conditions.