Switching the sign of the topological charge of vortex beams via changing the fork grating resolution

Mohagheghian, Maryam; Sabouri, Saeed Ghavami

doi:10.1016/j.optlastec.2022.108641

Cited by 7 publications

(5 citation statements)

References 36 publications

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“…For instance, a superposition of three basis modes As can be seen, four reconstructed intensities are different in distribution and rotation as a result of different measured amplitudes and phase values using four sampling methods. The similarity between the simulation and reconstructed intensities is investigated by the fidelity parameter [34] which is to be 0.97, 0.76, 0.73, and 0.07 related to random squares, random circles, sectors, and shifted concentric circles sampling methods, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…In this work, as a consequence of using a DMD with 800 × 600 resolution, superposed vortex beams consisting of two basis modes can be generated and measured with high accuracy. More research has also demonstrated that DMD resolution has a considerable effect on the beam quality and the intensity distribution [34,35], and on the modal content of a superposition of LG modes [36].…”

Section: Resultsmentioning

confidence: 99%

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The measurement of complex modal coefficients of a superposed vortex beam based on intensity sampling methods

Mohagheghian,

Ghavami Sabouri

2024

J. Opt.

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In recent years, extracting information from superposed vortex beams has been a topic of intense study. In this paper, complex coefficients of various superpositions are measured in both simulation and experiment by proposing and implementing four different sampling methods. Superposed vortex beams are experimentally generated using a digital micromirror device, and recorded on a 2 f optical imaging setup. To extract both amplitude and phase values of modal coefficients, a single intensity frame of the beam is sampled in the form of concentric circles, sectors, random circles, and random squares. Considering just specified parts of the intensity instead of the whole to sample the pattern increases the speed of the modal coefficient extraction. Besides, a linear set of coherent equations is solved, and achievements are compared together. As a consequence, measuring both the amplitude and phase values of coefficients simultaneously can pave the way to enable high-capacity optical communication which is carried out in this research with better than 99% and 96% accuracy, respectively.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

The measurement of complex modal coefficients of a superposed vortex beam based on intensity sampling methods

Mohagheghian,

Ghavami Sabouri

2024

J. Opt.

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“…The general shape of a forked grating results from the interference of a helical wave with that of an inclined plane wave. The general form of the forked grating can be expressed as follows [38]:…”

Section: Designing the Gratingmentioning

confidence: 99%

Generation of vortex beams with nonuniform phase jumps in azimuthal locations

Sabouri

2023

J. Opt.

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The phase angle of the vortex beam along a closed loop centered on the optical singularity changes 2πℓ where ℓ is the number of phase jumps (PJs) from 0 to 2 and indicates the topological charge (TC) of the vortex beam. In this paper, generation and specification of a new type of vortex beams that their PJs are asymmetrically embedded in the phase pattern are reported. In contrast to Laguerre-Gaussian (LG) vortex beams, where PJs are equally spaced azimuthally around the optical singularity, the presented vortex beams have PJs embedded at arbitrary azimuthal angles. By designing a particular forked grating and displaying it on a spatial light modulator, this type of vortex beam is experimentally generated. As with conventional forked grating, the designed grating produces vortex beams with opposite orbital angular momentum (OAM) sign in the first diffraction order. By measuring the relative orientation of the intensity profile of these OAM beams in the first diffraction order, the position of the PJs on the wavefront of a vortex beam with ℓ =2 can be determined. This type of vortex beam could have potential applications in various fields of photonics, especially in optical communications based on optical vortices.

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“…According to the holographic emersion, this kind of structure can diffract the Gauss beam and generate multiple vortex beams. 20,[36][37][38][39] On the basis of the previous report, fork gratings have been applied to generate vortex beams in crystals through the FLDW, and the filaments forming the grating are all belong to the type-II modification. 40,41 In the reported previous work, the researchers always focused on the design of fork-grating structures or researching the vortex beam by fork grating, but how to improve the diffraction efficiency of fork grating with the same period was neglected.…”

Section: Introductionmentioning

confidence: 99%

“…It is a result of interference by a plane and Laguerre–Gauss beam. According to the holographic emersion, this kind of structure can diffract the Gauss beam and generate multiple vortex beams 20,36–39 …”

Section: Introductionmentioning

confidence: 99%

Femtosecond‐laser micromachining fork gratings in LN crystal with different mechanisms

Liu,

Zhang,

et al. 2023

Micro & Optical Tech Letters

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In this work, we used femtosecond‐laser direct writing to fabricate two kinds of modified structures with opposite refractive‐index changes to build fork‐grating configurations in z‐cut LiNbO3 (LN) crystals. Experimental and simulation results indicate that the fork grating combined with the modified area of the refractive index increased and refractive index decreased produces a more effective diffraction effect at 532 nm. The diffraction results of these fork gratings have been investigated. Compared with the fork grating only with the refractive‐index‐decreased filaments, when the incident beam is at transverse magnetic, transverse electric, and circular polarizations, the diffraction efficiency is improved by 5.3%, 4.3%, and 9.6%, respectively. Our work provides a new perspective for improving the diffraction efficiency of fork gratings in LN crystals.

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Switching the sign of the topological charge of vortex beams via changing the fork grating resolution

Cited by 7 publications

References 36 publications

The measurement of complex modal coefficients of a superposed vortex beam based on intensity sampling methods

The measurement of complex modal coefficients of a superposed vortex beam based on intensity sampling methods

Generation of vortex beams with nonuniform phase jumps in azimuthal locations

Femtosecond‐laser micromachining fork gratings in LN crystal with different mechanisms

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