Broadband orbital angular momentum manipulation using liquid crystal thin-films

We introduce two high efficiency thin-film optical elements, operating over a wide spectral range, to generate and control the Orbital Angular Momentum (OAM) of various light sources: a broadband q-plate and a broadband Forked Polarization Grating (FPG). The broadband OAM manipulation is achieved by thin liquid crystal polymer layers that are aligned to provide the required spatially varying anisotropy. These elements operate using geometric phase principles to generate raised and lowered OAM modes whose efficiencies are sensitive to the polarization state of the incident light. We discuss the design principles involved and experimentally demonstrate broadband q-plates and FPGs that are highly efficient (> 90%) in the visible wavelength range. These thin film elements enable easy integration into various optical systems requiring broadband OAM manipulation such as optical trapping and high capacity information.