Generation of optical vortex beams with bandwidth exceeding 550 nm using a helical fiber needle exhibiting strong mode coupling

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Abstract
A strong-coupling helical fiber needle (HFN) is proposed and demonstrated for the realization of bandwidth-enhanced broadband optical vortex beam (OVB) generation. The HFN is based on a single mode fiber and operates at the dispersion-turning-point (DTP) of the lowest radial order of the cladding mode (i.e., LP11) but with a remarkably high mode coupling efficiency. By utilizing this novel, to the best of our knowledge, HFN, successful generation of the first-order OVB with an impressive bandwidth up to 556 nm at −10 dB and a center wavelength of ∼1570 nm has been achieved. This represents the broadest bandwidth demonstrated among all fiber grating-based OVB generators to date. The proposed HFN-based OVB generator exhibits a relatively compact size, ultra-wide bandwidth, and customizable center wavelength, making it highly promising for applications in optical vortex-based endoscopic imaging as well as particle detection and manipulation.
Funding Information
  • National Natural Science Foundation of China (62003081, U22A2021)
  • Natural Science Foundation of Hebei Province (F2020501003, F2020501040)
  • Scientific and Technical Research Project in Colleges and Universities of Hebei Province (BJ2021101)
  • Fundamental Research Funds for the Central Universities (N2223030)

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