High-Efficiency Characterization of Optical Vortices with Arbitrary State of Polarization Using Straight-Line and Parabolic-Line Polarization Gratings

An optical system consisting of a straight-line polarization grating (SPG) and two parabolic-line polarization gratings (PPGs) is presented for the characterization of optical vortices (OVs) with arbitrary states of polarization (SoPs). The PPG is capable of converting an OV with a specific SoP into a bright bar-like spot with 100% efficiency. The number of dark lines and their orientation respectively correspond to the magnitude and sign of topological charge (TC) of the incident OV, thereby enabling characterization of OVs with high efficiency. Furthermore, on combining an SPG with PPGs, the present system can characterize the TC of incident OVs regardless of their SoP. The feasibility of the system was demonstrated in experiments using gratings fabricated by applying the photoalignment method and employing films of a photo-crosslinkable polymer liquid crystal. The experimentally obtained efficiency is 70.2%. We furthermore demonstrate the system’s capability to characterize polarization vortices.