Determining the non-separability of vector modes with digital micromirror devices

Abstract

The non-separability between the spatial and polarization Degrees of Freedom (DoF) of complex vector light fields has drawn significant attention in recent times. Key to this is its remarkable similarities with quantum entanglement, with quantum-like effects observed at the classical level. Crucially, this parallelism enables the use of quantum tools to quantify the coupling between the spatial and polarization DoFs, usually implemented with polarization-dependent spatial light modulators, which requires the splitting of the vector mode into two orthogonal polarization components. Here, we put forward an alternative approach that relies on the use of Digital Micromirror Devices (DMDs) for a fast, cheap, and robust measurement, while the polarization-independent nature of DMDs enables a reduction in the number of required measurements by 25%. We tested our approach experimentally on cylindrical vector modes with arbitrary degrees of non-separability, of great relevance in a wide variety of applications. Our technique provides a reliable way to measure in real time the purity of vector modes, paving the way for a wide variety of applications where the degree of non-separability can be used as an optical sensor.