Kerr Switching for Temporal Noise Filtering in Optical Telecom Quantum Communication

Abstract

Implementing quantum key distribution in existing optical telecommunication infrastructure requires the employment of appropriate spatial, spectral, and temporal filtering to achieve high tolerance to noise from classical optical signals present in fibre networks. Electronic temporal filtering may be limited by the nanosecond-scale timing jitter of typical single-photon detectors; this requires us to use faster physical processes to rapidly gate the desired optical signal, while rejecting random noise photons arriving outside of a narrow passing window.

In this work, we use ultrashort optical pulses to implement a Kerr switch in a 1-metre length of single-mode fibre to perform all-optical temporal filtering of noise in a telecom-wavelength quantum channel. Using our switch, we demonstrate 2.4-ps temporal gating of 1.3 µm-wavelength signal photons with a near-unity switching efficiency of 98.77 ± 0.01%. We also show that our switch can be used as an effective ultrafast temporal filter capable of reducing noise introduced into a quantum channel by up to 18.2 dB.