Fiber coupled single photon receivers based on superconducting detectors for quantum communications and quantum cryptography

摘要

At present superconducting detectors become increasingly attractive for various practical applications. In this paper we present results on the depelopment of fiber coupled receiver systems for the registration of IR single photons, optimized for telecommunication and quantum-cryptography. These receiver systems were developed on the basis of superconducting single photon detectors (SSPD) of VIS and IR wavelength ranges. The core of the SSPD is a narrow (～100 nm) and long (-0,5 mm) strip in the form of a meander which is patterned from a 4-nm-thick NbN film (T_c=10-11 K, j_c=～5-7·10~6 A/cm~2); the sensitive area dimensions are 10×10 μm~2. The main problem to be solved while the receiver system development was optical coupling of a single-mode fiber (9 microns in diameter) with the SSPD sensitive area. Characteristics of the developed system at the optical input are as follows: quantum efficiency >10 % (at 1.3 μm), >4 % (at 1.55 μm); dark counts rate ≤ s~(-1); duration of voltage pulse ≤5 ns; jitter ≤40 ps. The receiver systems have either one or two identical channels (for the case of carrying out correlation measurements) and are made as an insert in a helium storage Dewar.