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Optical Engineering

Spiral phase plates with radial discontinuities for the generation of multiring orbital angular momentum beams: fabrication, characterization, and application
Author(s): Gianluca Ruffato; Michele Massari; Marta Carli; Filippo Romanato
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Paper Abstract

A design of spiral phase plates for the generation of multiring beams carrying orbital angular momentum (OAM) is presented. Besides the usual helical profile, these phase plates present radial π-discontinuities in correspondence of the zeros of the associated Laguerre polynomials. Samples were fabricated by electron beam lithography over glass substrates coated with a polymethylmethacrylate resist layer. The optical response was analyzed and the purity of the generated beams was investigated in terms of Laguerre-Gaussian modes contributions. The far-field intensity pattern was compared with theoretical models and numerical simulations, while the expected phase features were confirmed by interferometric analysis with a Mach-Zehnder setup. The high quality of the output beams confirms the applicability of these phase plates for the generation of high-order OAM beams with nonzero radial index. An application consisting of the design of computer-generated holograms encoding information for light beams carrying phase singularities is presented and described. A numerical code based on an iterative Fourier transform algorithm has been developed for the computation of phase-only diffractive optical element for illumination under OAM beams. Numerical analysis and preliminary experimental results confirm the applicability of these devices as high-security optical elements for anticounterfeiting applications.

Paper Details

Date Published: 13 August 2015
PDF: 8 pages
Opt. Eng. 54(11) 111307 doi: 10.1117/1.OE.54.11.111307
Published in: Optical Engineering Volume 54, Issue 11
Show Author Affiliations
Gianluca Ruffato, Univ. degli Studi di Padova (Italy)
Michele Massari, Veneto Nanotech s.c.p.a. (Italy)
Marta Carli, Univ. degli Studi di Padova (Italy)
Filippo Romanato, Univ. degli Studi di Padova (Italy)
CNR-INFM TASC IOM National Laboratory (Italy)

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