Special Section on Complex Light

Spiral phase plates with radial discontinuities for the generation of multiring orbital angular momentum beams: fabrication, characterization, and application

[+] Author Affiliations
Gianluca Ruffato, Marta Carli

University of Padova, Department of Physics and Astronomy “G. Galilei,” via Marzolo 8, 35131 Padova, Italy

Michele Massari

Veneto Nanotech, Laboratory for Nanofabrication of Nanodevices, Corso Stati Uniti 4, 35129 Padova, Italy

Filippo Romanato

University of Padova, Department of Physics and Astronomy “G. Galilei,” via Marzolo 8, 35131 Padova, Italy

CNR-INFM TASC IOM National Laboratory, S.S. 14 Km 163.5, 34012 Basovizza, Trieste, Italy

Opt. Eng. 54(11), 111307 (Aug 13, 2015). doi:10.1117/1.OE.54.11.111307
History: Received March 13, 2015; Accepted July 8, 2015
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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.

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© 2015 Society of Photo-Optical Instrumentation Engineers

Citation

Gianluca Ruffato ; Michele Massari ; Marta Carli and Filippo Romanato
"Spiral phase plates with radial discontinuities for the generation of multiring orbital angular momentum beams: fabrication, characterization, and application", Opt. Eng. 54(11), 111307 (Aug 13, 2015). ; http://dx.doi.org/10.1117/1.OE.54.11.111307


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