Coherent frequency bridge between visible and telecommunications band for vortex light

In quantum communications, vortex photons can encode higher-dimensional quantum states and build high-dimensional communication networks(HDCNs). The interfaces that connect different wavelengths are significant in HDCNs. We construct a coherent orbital angular momentum (OAM) frequency bridge via difference frequency conversion in a nonlinear bulk crystal for HDCNs. Using a single resonant cavity, maximum quantum conversion efficiencies

from visible to infrared are 36%, 15%, and 7.8% for topological charges of 0,1, and 2, respectively. The average fidelity obtained using quantum state tomography for the down-converted infrared OAM-state of topological charge 1 is 96.51%. We also prove that the OAM is conserved in this process by measuring visible and infrared interference patterns. This coherent

OAM frequency-down conversion bridge represents a basis for an interface between two highdimensional quantum systems operating with different spectra.

Fig. 1: The experimental setups.

Fig. 2:The main results of OAM-frequency bridge.

Article: Opt. Express 25 (20) (2017) 24290–24298.