Interferometric detection of OAM-carrying Helico-conical beams

Helico-conical beams (HCBs) are a class of orbital angular momentum (OAM)-carrying beams with spiral phase and intensity profiles. In this communication, we demonstrate the use of a common path interferometer (CPI) to phase-image incoming HCBs and directly detect their OAM-associated properties. The output intensity of the CPI is a direct mapping of the HCB's phase, hence both the topological charge value and sign manifest in the output intensity distribution. The topological charge value is calculated by fringe counting, while the helicity is determined by observing the intensity along the phi = 0 region. With our current CPI setup, we can firmly detect up to l = +/- 20. Higher values of l lead to a decrease in the fringe visibility, but this can in principle be improved by tailoring the parameters of the phase contrast filter (PCF) employed in the CPI. We present analytical expressions to optimize the CPI for HCB charge detection.