Cascaded downconversion interface to convert single-photon-level signals at 650  nm to the telecom band

• Published in: Optics letters Vol. 43; no. 22; p. 5655
• Main Authors: Esfandyarpour, Vahid, Langrock, Carsten, Fejer, Martin
• Format: Journal Article
• Language: English
• Published: United States 15.11.2018
• ISSN: 1539-4794
• DOI: 10.1364/OL.43.005655

We present a device designed for two-step downconversion of single-photon-level signals at 650 nm to the 1.5-μm band with low excess noise and low required pump power as a quantum interface between matter-qubit-based nodes and low-loss photonic channels for quantum communication networks. The required pump power for this interface is around 60% of that for a comparable conventional single-pass device, which reduces the demand on the pump laser and yields a corresponding reduction in dark counts due to inelastic pump scattering. The single-photon-level signal at 649.7 nm is downconverted to the telecom band using a fiber-coupled reverse proton exchange periodically poled lithium niobate waveguide and a 2.19-μm pump laser. By testing the device in the linear regime with a classical input, we achieved 99% depletion efficiency for each stage, corresponding to an internal quantum efficiency of 63% at the optimum pump power for the complete cascaded process.