Differential Frequency Exploration of Vortex Light in Lithium Niobate Crystals

Abstract

In recent years, Orbital Angular Momentum (OAM) beams have been applied in optical communications to improve channel capacity and spectral efficiency. However, in practical applications, OAM information is often imprinted on short-wavelength light beams. How to completely transfer this information to the O-band to achieve long-distance transmission has not been conveniently achieved through most traditional methods. We studied the differential frequency experiment of OAM-carrying beams from both theoretical and experimental facets. In the periodic polarization 0 class matched lithium niobate crystal, the difference in frequency between the incident 1950 nm strong pump light and the 780 nm weak input light is achieved, resulting in output light in the O band. The polarization period of the crystal is 20 μm, and the best phase matching is achieved when the temperature is maintained at 41.2 °C. At this time, 780 nm vortex light produces 1300 nm vortex light, and the nonlinear conversion efficiency reaches 0.1387% (topological charge number l = 5). During the experiment, momentum, energy, and topological charge are all conserved. Our experiment successfully converted vortex light at 780 nm into vortex light at 1300 nm, paving the way for the subsequent conversion of 780 nm single photons generated by quantum dots carrying OAM into OAM photons in the communication band.