Studies on the readability and on the detection rate in a Mach-Zehnder interferometer-based implementation for high-rate, long-distance QKD protocols

We study the way that chromatic dispersion affects the visibility and the synchronization on Quantum Key Distribution (QKD) protocols in a widely-used setup based on the use of two fiber-based Mach-Zehnder (MZ) interferometers at transmitter/receiver stations. We identify the necessary conditions for the path length difference between the two arms of the interferometers for achieving the desired visibility given the transmission distance -- where the form of the detector's window can be considered. We also associate the above limitations with the maximum detection rate that can be recorded in our setup, including the quantum non-linearity phenomenon, and to the maximum time window of the detector's gate. Exploiting our results we provide two methods, depending on the clock rate of the setup, to perform chromatic dispersion compensation techniques to the signal for keeping the correct order of the transmitted symbols. At the end, we apply our theoretical outcomes in a more realistic QKD deployment, considering the case of phase-encoding BB84 QKD protocol, which is widely used. Our proposed methods, depending on the transmission distance and on the photon emission rate at transmitter station, can be easily generalized to every fiber-optic QKD protocol, for which the discrimination of each symbol is crucial.Comment: 14 pages, 12 figure

Multi-Rate and Multi-Channel Optical Equalizer Based on Photonic Integration

We propose and experimentally demonstrate a photonic integrated circuit (PIC) that operates as an optical equalizer (OE) with multi-rate and multi-channel capability. The OE has the structure of a 3-tap direct form finite impulse response (FIR) filter and is based on the use of micro-ring resonators (MRRs) for the tuning of its delay lines. The PIC is fabricated on TriPleX platform and has 17 reconfigurable elements in total including nine MRRs, five optical couplers and three standalone phase shifters. Using this OE in an on-off keying system with bandwidth limitations we achieve an eye-diagram opening improvement more than 14 dB working with signals at 4.67 and 5.84 Gbaud both in single- and dual-channel operation. Extension to higher modulation formats is direct. Extension to higher symbol rates is also possible via the use of smaller MRRs

Integrated heterodyne laser Doppler vibrometer based on stress-optic frequency shift in silicon nitride

Abstract We demonstrate a compact heterodyne Laser Doppler Vibrometer (LDV) based on the realization of optical frequency shift in the silicon nitride photonic integration platform (TriPleX). We theoretically study, and experimentally evaluate two different photonic integrated optical frequency shifters (OFSs), utilizing serrodyne and single-sideband (SSB) modulation. Both OFSs employ stress-optic modulators (SOMs) based on the non-resonant piezoelectrical actuation of lead zirconate titanate (PZT) thin-films, deposited on top of the silicon nitride waveguides with a wafer-scale process. To improve the modulation bandwidth of the SOMs we investigate a novel configuration of the electrodes used for the actuation, where both electrodes are placed on top of the PZT layer. Using this top-top electrode configuration we report frequency shift of 100 kHz and 2.5 MHz, and suppression ratio of the unwanted sidebands of 22.1 dB and 39 dB, using the serrodyne and the SSB OFS, respectively. The best performing SOM structure induces 0.25π peak-to-peak sinusoidal phase-shift with 156 mW power dissipation at 2.5 MHz. We use the SSB-OFS in our compact LDV system to demonstrate vibration measurements in the kHz regime. The system comprises a dual-polarization coherent detector built in the PolyBoard platform, utilizing hybrid integration of InP photodiodes (PDs). High quality LDV performance with measurement of vibration frequencies up to several hundreds of kHz and displacement resolution of 10 pm are supported with our system