Optical Data Encoding through Spatiotemporal Orbital Angular Momentum Spectral Engineering

Optical vortices are associated with photons carrying orbital angular momentum (OAM). Orthogonal OAM states constitute a spectrum that can be utilized for precision measurement, optical transmission, and quantum entanglement. Traditional OAM spectrum is confined to weighted superposition of spatial optical vortices with longitudinal OAM oriented in the direction of beam propagation. To fully exploit the vector nature of OAM spectrum, this work demonstrates a scheme for the generation and characterization of a spatiotemporal OAM spectrum that consists of weighted spatiotemporal optical vortices with OAM perpendicular to the propagation direction. The weight and topological charge of individual spatiotemporal vortices are accurately controlled. Spatiotemporal OAM spectra ranging from −12th to +12th orders are experimentally achieved. Subsequently, grayscale image coding and decoding are demonstrated using 8-bit spatiotemporal OAM spectra. The spatiotemporal OAM spectrum provides additional dimension of information and can be combined with conventional spatial OAM spectrum to achieve high-dimensional optical information processing.