Visible and Online Detection of Near‐Infrared Optical Vortices via Nonlinear Photonic Crystals

Abstract Near‐infrared (NIR) optical vortices (OVs), which carry specific orbital angular momentum, are believed to greatly increase the capacity of conventional optical communication systems. However, due to the equipment limits in invisible wavelengths, NIR OVs detection remains a great difficulty. Here, the up‐conversion imaging technology is exploited to circumvent using NIR detectors. A lithium niobate crystal with its quadratic susceptibility modulated by a specially designed Dammann vortex grating is fabricated to realize the frequency conversion—from NIR to the visible region—while converting multiplexed OVs to Gaussian modes in specific multichannels. During the detection process, the most of energies of the detected OVs are preserved, which can be considered as online detection. Additionally, at least 400 nm applicable wavelength range of this method is experimentally demonstrated, as well as up to 25 independent detection channels. Compared with existing solutions, this scheme enables a large‐broadband wavelength, low energy loss, and multiprocessing channels platform for visible detection of NIR OVs, showing great potential to be applied in optical communication systems.