Determining the topological charge of optical vortex by intensity distribution of a quasi-Airy vortex beam

This work explains diffraction of Laguerre-Gaussian (LG) beams having non-zero radial indices from one dimensional (1D) periodic structures and their transformation into Hermite-Gaussian (HG) modes, theoretically, verifies using simulations and demonstrates the phenomenon experimentally. We first report a general theoretical formulation for such diffraction schemes, and then use it to investigate the near-field diffraction patterns from a binary grating having a small opening ratio (OR) by providing numerous examples. Results show that for OR≲ 0.1, at the Talbot planes, mainly at the first Talbot image, the images of individual lines of the grating obtain HG modes’ intensity patterns. Therefore, the topological charge (TC) of the incident beam and its radial index can be determined from the observed HG mode. In this study, the effects of the OR of the grating and the number of Talbot plane on the quality of the generated 1D array of HG modes are also investigated. The optimum beam radius for a given grating is also determined. The theoretical predictions, are well confirmed by a number of simulations based on the free space transfer function and fast Fourier transform approach, and by experiments. The observed phenomenon, the transformation of LG beams into 1D array of HG modes under the Talbot effect, in addition of providing a way for characterization of LG beams with non-zero radial indices, itself is interesting and may be used in other fields of wave physics, especially for long-wavelength waves.

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Transformation of Laguerre-Gaussian beams into 1D array of Hermite-Gaussian modes under the Talbot effect

Rasouli

Amiri

Hebri

2023

Opt. Express

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Crosstalk mitigation of a controllable annular auto-focusing vortex beam array in a turbulent atmosphere

Ge,

Shang,

et al. 2024

Opt. Express

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In this paper, we introduce a new type of controllable auto-focusing vortex beam array named annular quasi-Airy vortex beam array (QAVBA), which can reduce the crosstalk among different orbital angular momentum (OAM) modes of optical vortex. The effects of initial beam parameters of annular QAVBA and propagation conditions on the OAM mode propagation performance are investigated. The results indicate that the topological angle θ, the topological charge m, and the decay parameter α could manipulate the auto-focusing characteristics of annular QAVBA and regulate the crosstalk of OAM modes. The crosstalk among OAM modes increases with the turbulence strength. Interestingly, the annular QAVBA with obtuse topological angle is favorable for the OAM mode transmitting at far propagation distance or in strong atmospheric turbulence when the decay parameter α is large enough for the energy of annular QAVBA mainly concentrating on the main light ring. Our research provides a reference for optimizing the design of light sources and free-space optical communication system with annular QAVBA.

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Determining the topological charge of optical vortex by intensity distribution of a quasi-Airy vortex beam

Cited by 2 publications

References 41 publications

Transformation of Laguerre-Gaussian beams into 1D array of Hermite-Gaussian modes under the Talbot effect

Transformation of Laguerre-Gaussian beams into 1D array of Hermite-Gaussian modes under the Talbot effect

Crosstalk mitigation of a controllable annular auto-focusing vortex beam array in a turbulent atmosphere

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