Temperature characterizations of silica asymmetric Mach-Zehnder interferometer chip for quantum key distribution

Abstract Quantum key distribution (QKD) system based on passive silica planar lightwave circuit (PLC) asymmetric Mach-Zehnder interferometers (AMZI) is characterized with thermal stability, low loss and sufficient integration scalability. However, waveguide stresses, both intrinsic and temperature-induced stresses, have significant impacts on the stable operation of the system. We have designed silica AMZI chips of 400ps delay, with bend waveguides length equalized for both long and short arms to balance the stresses thereof. The temperature characteristics of silica PLC AMZI chip are studied. Interference visibilities at the single photon level is kept more than 95% over a wide temperature range of 12 ℃. The delay time change is 0.321 ps within a temperature change of 40 ℃. The spectral shift is 0.0011 nm/0.1 ℃. Temperature-induced delay time and peak wavelength variations do not affect interference visibility. The experiment results demonstrate the advantage of being tolerant to chip temperature fluctuations.