Characterization of Orbital Angular Momentum Beams by Polar Mapping and Fourier Transform

Abstract

The recognition, decoding and tracking of vortex patterns is of increasing importance in many fields, ranging from the astronomical observations of distant galaxies to turbulence phenomena in liquids or gases. Currently, coherent light beams with orbital angular momentum (OAM) are of particular interest for optical communication, metrology, micro-machining or particle manipulation. One common task is to identify characteristic spiral patterns in pixelated intensity maps at real-world signal-to-noise ratios. A recently introduced combination of polar mapping and Fast Fourier Transform (FFT) was extended to novel sampling configurations and applied to the quantitative analysis of the spiral interference patterns of OAM beams. It is demonstrated that specific information on topological parameters in non-uniform arrays of OAM beams can be obtained from significantly distorted and noisy intensity maps by extracting one- or two-dimensional angular frequency spectra from single or concatenated circular cuts in either spatially fixed or scanning mode. The method also enables the evaluation of the quality of beam shaping and optical transmission. Results of proof-of-principle experiments are presented, resolution limits are discussed, and the potential for applications is addressed.

Generation of Propagation-Dependent OAM Self-Torque with Chirped Spiral Gratings

“…To characterize twist and self-torque phenomena of OAM beams, the spectral Gouy rotation [22][23][24] was exploited. The approach enables a direct visualization of spectrally resolved internal vortex structures instead of analyzing complex spiral interference patterns [64]. In contrast to timeconsuming fiber-scanning techniques [25], single-shot detection of propagation-dependent azimuthal angles of spectral eyes with a matrix camera works much faster.…”

Generation of Propagation-Dependent OAM Self-Torque with Chirped Spiral Gratings

“…To characterize the twist and self-torque phenomena of OAM beams, the spectral Gouy rotation [22][23][24] was exploited. The approach enables a direct visualization of spectrally resolved internal vortex structures instead of analyzing complex spiral interference patterns [63]. In contrast to time-consuming fiber-scanning techniques [25], the single-shot detection of propagation-dependent azimuthal angles of spectral eyes with a matrix camera works much faster.…”

Study on the Imaging Interference of a Vortex-Light-Modulated Gaussian Beam

“…In 2014, García-García, J et al proposed a method for generating perfect vortex light, and the results were obtained using SLM [1]. In 2024, Ruediger Grunwald et al used SLM to generate a vortex beam and extracted the parameters of a single or a group of distorted non-uniform vortex images by Fixed Circle Fourier Transform and Scanning Circle Fourier Transform [11].…”