3D micro-optical elements for generation of tightly focused vortex beams

¹ Centre for Micro-Photonics, Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
² Institute of Physics, Center for Physical Sciences and Technology, 231 Savanoriu Avenue, LT-02300 Vilnius, Lithuania
³ University of Bordeaux, CNRS, Laboratoire Ondes et Matière d’Aquitaine, 351 cours de la libération, F-33400 Talence, France
⁴ Department of Quantum Electronics, Physics Faculty, Vilnius University, Saulėtekio Ave. 10, LT-10223 Vilnius, Lithuania
⁵ Melbourne Centre for Nanofabrication, 151 Wellington Road, Clayton, VIC 3168, Australia

^a e-mail: abalcytis@swin.edu.au

Abstract

Orbital angular momentum carrying light beams are usedfor optical trapping and manipulation. This emerging trend provides new challenges involving device miniaturization for improved performance and enhanced functionality at the microscale. Here we discus a new fabrication method based on combining the additive 3D structuring capability laser photopolymerization and the substractive sub-wavelength resolution patterning of focused ion beam lithography to produce micro-optical elements capable of compound functionality. As a case in point of this approach binary spiral zone pattern based high numerical aperture micro-lenses capable of generating topological charge carrying tightly focused vortex beams in a single wavefront transformation step are presented. The devices were modelled using finite-difference time-domain simulations, and the theoretical predictions were verified by optically characterizing the propagation properties of light transmitted through the fabricated structures. The resulting devices had focal lengths close to the predicted values of f = 18 µm and f = 13 µm as well as topological charge ℓ dependent vortex focal spot sizes of ~ 1:3 µm and ~ 2:0 µm for ℓ = 1 and ℓ = 2 respectively.