Single-stage spin-orbit Laguerre-Gaussian modal beam shaping from silica optics

We report on the design, fabrication and performance of novel flat-optical spin-orbit modal beam shapers made from silica glass by femtosecond laser nanostructuring technology, choosing the Laguerre-Gauss basis as a case study. The basic design principle involves endowing a transparent dielectric material, initially isotropic and homogeneous, with doubly inhomogeneous anisotropic characteristics (optical axis orientation and birefringence). The quantitative structural characterization of the fabricated devices is achieved by Stokes polarimetric analysis and the modal beam shaping performance is assessed via modal decomposition. The modal beam shaping capabilities obtained outperform those of previously produced spin-orbit beam shapers based on the same fabrication technology. Also, current challenges and perspectives associated with high-order and spectrally broadband modal beam shaping are discussed. More generally, the proposed approach extends the scope of spin-orbit optical elements to any situation where complex field amplitude shaping is required in a single stage.