Abstract
Abstract As an indispensable complement to an integer vortex beam, the fractional vortex beam has unique physical properties such as radially notched intensity distribution, complex phase structure consisting of alternating charge vortex chains, and more sophisticated orbital angular momentum modulation dimension. In recent years, we have noticed that the fractional vortex beam was widely used for complex micro-particle manipulation in optical tweezers, improving communication capacity, controllable edge enhancement of image and quantum entanglement. Moreover, this has stimulated extensive research interest, including the deep digging of the phenomenon and physics based on different advanced beam sources and has led to a new research boom in micro/nano-optical devices. Here, we review the recent advances leading to theoretical models, propagation, generation, measurement, and applications of fractional vortex beams and consider the possible directions and challenges in the future.
Highlights
Vortex beam refers to a type of beam carrying helical phase [1,2,3] that is formed by the spiral rotation of theIn most studies related to vortices, the value of topological charge (TC) is merely restricted as an integer where the helical phase has a 2lπ step
As an indispensable complement to an integer vortex beam, the fractional vortex beam has unique physical properties such as radially notched intensity distribution, complex phase structure consisting of alternating charge vortex chains, and more sophisticated orbital angular momentum modulation dimension
In contrast to the integer-order vortex beam, the phase appears as a discontinuity along the phase step, and the annular intensity ring is broken as a radial dark opening
Summary
Vortex beam refers to a type of beam carrying helical phase [1,2,3] that is formed by the spiral rotation of the. In optical communication systems, the fractional vortex beam with continuous integer and noninteger OAM states [47, 48] can overcome the limitation of aperture size and expand the communication capacity [66, 67] Another practical application of fractional vortex beam is optical imaging. This review includes a general introduction (Section 1), the theoretical models of six categories of fractional vortex beams ranging from fully coherent to partially coherent (Section 2), propagation properties (Section 3), classical experimental generation methods of different categories of fractional vortex beams (Section 4), measurement of the TC and OAM (Section 5), and applications in optical manipulation, optical communication, optical imaging, and quantum entanglement (Section 6). We summarize the research on fractional vortex beam and its future development
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