Femtosecond-Laser Written Universal Photonic Processors

Universal photonic processors (UPPs) are programmable photonic integrated circuits (PICs) that are attracting increasing attention from both the industry and the academic world in applications as diverse as quantum information processing, neuromorphic computing and 3D imaging [1]. Differently from application-specific PICs, UPPs can implement any arbitrary linear optical transformation, providing the possibility of reconfiguring the circuit operation even at run-time. Today the most common UPP architectures rely on interferometric meshes, whose operation is set through thermo-optic phase shifters. UPPs have been demonstrated in different waveguide fabrication platforms and materials, but the state of the art in terms of complexity is currently set by the silicon nitride. The best in class device operates at 1550 nm wavelength and features 20 photonic modes, insertion losses around 2.9 dB and an average fidelity of 97.4%, at the cost of a large power budget of hundreds of mW per shifter that hinders a further scaling [2].