Low-Energy Optical-to-Electrical Converters Based on Superconducting Nanowire for Single-Flux-Quantum Circuits

Kemmei KAJINO  Shigehito MIKI  Taro YAMASHITA  Hirotaka TERAI  

IEICE TRANSACTIONS on Electronics   Vol.E98-C   No.3   pp.227-231
Publication Date: 2015/03/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E98.C.227
Type of Manuscript: INVITED PAPER (Special Section on Leading-Edge Applications and Fundamentals of Superconducting Sensors and Detectors)
superconductor,  single photon detector,  single-flux-quantum circuit,  optical interface,  cryocooler implementation,  

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We report the energy-efficient optical input interface using NbN superconducting nanowire-based optical-to-electrical (SN-OE) converters for a single-flux-quantum (SFQ) data processing system. The SN-OE converters with small active areas ranging from 1×1 to 10×10 μm2 were fabricated to improve the recovery time by reducing the kinetic inductance of the nanowire. The SN-OE with the smallest area of 1×1 μm2 showed the recovery time of around 0.3 ns, while its detection efficiency for a single photon was reduced below 0.1% due to insufficient coupling efficiency with a single-mode optical fiber. However, the optical power dependence of the error rate of this device showed that the required optical power to achieve the error rate below 10-12 at 10 GHz operation is as large as 70 μW, which is still one order of magnitude lower than semiconductor photo diodes. We also demonstrated the operation of the SN-OE converters combined with the SFQ readout circuit and confirmed the operating speed up to 77 MHz.