METHOD AND SYSTEM FOR MEASURING PHOTON ORBITAL ANGULAR MOMENTUM MODE BASED ON SPIRAL TRANSFORMATION

A method and a system for measuring photon orbital angular momentum mode based on spiral transformation: by means of a phase plate (1) positioned on an input plane, mapping an incident light field along a helical path on the input plane to a straight line on an output plane; a phase plate (2) positioned on the output plane compensates the phase of the light field accumulated when propagating from the input plane to the output plane during the transformation process, thereby implementing transformation of the photon orbital angular momentum mode to be measured at the input plane to a plane wave mode having a specific oblique wavefront at the output plane; by means of a convex lens, focusing plane wave modes having a different oblique wavefront to different positions on a focal plane, thereby implementing the one-to-one correspondence and detection of the photon orbital angular momentum mode to be measured and the spatial position. The problem of the crosstalk of adjacent modes caused by demodulation spot broadening is effectively overcome, further implementing high resolution photon orbital angular momentum mode measurements whilst maintaining high demodulation efficiency.