Olivier Guinnard

Quantum key distribution over 67 km with a plug&play system

We present a fibre-optical quantum key distribution system. It works at 1550nm and is based on the plug & play setup. We tested the stability under field conditions using aerial and terrestrial cables and performed a key exchange over 67 km between Geneva and Lausanne.

Photon counting at telecom wavelengths with commercial InGaAs/InP avalanche photodiodes: current performance

Abstract InGaAs/InP avalanche photodiodes operated in the so-called Geiger mode currently represent the best solution to detect single-photon beyond 900nm. They cover the 1100–1650nm wavelength interval, which includes in particular the two windows used for optical communications (1310 and 1550nm). A detection efficiency at 1550nm of 10% with a dark count probability of 10−5 ns−1 is common, although significant variations can be encountered. At this efficiency, a FWHM temporal response of 300 ps can be achieved. Afterpulses caused by charges trapped by defects in the high field region of the junction constitute the main performance impairment phenomenon. They enhance the dark count probability and reduce out-of-gate detector blindness. These photon counting detectors can be used in optical time-domain reflectometry to improve the spatial resolution and reduce dead-zone effects. Quantum key distribution over metropolitan area networks also constitutes an important application.

Fast and user-friendly quantum key distribution

Abstract Some guidelines for the comparison of different quantum key distribution experiments are proposed. An improved ‘plug & play’ interferometric system allowing fast key exchange is introduced. Self-alignment and compensation of birefringence remain. Original electronics implementing the BB84 protocol and allowing user-friendly operation is presented. Key creation with 0.1 photon per pulse at a rate of 486 Hz with a 5.4% QBER, corresponding to a net rate of 210Hz, over a 23 Km installed cable was performed.

A fast and versatile quantum key distribution system with hardware key distillation and wavelength multiplexing

We present a compactly integrated, 625 MHz clocked coherent one-way quantum key distribution system which continuously distributes secret keys over an optical fibre link. To support high secret key rates, we implemented a fast hardware key distillation engine which allows for key distillation rates up to 4 Mbps in real time. The system employs wavelength multiplexing in order to run over only a single optical fibre. Using fast gated InGaAs single photon detectors, we reliably distribute secret keys with a rate above 21 kbps over 25 km of optical fibre. We optimized the system considering a security analysis that respects finite-key-size effects, authentication costs and system errors for a security parameter of eQKD = 4 × 10−9.

Optical frequency domain reflectometry with a narrow linewidth fiber laser

The present a new optical frequency domain reflectometer based on a tunable fiber laser with a very narrow linewidth (about 10 kHz). This instrument performs reflectivity measurements with -110 dB sensitivity and 80 dB dynamic range. The narrow linewidth allows long-range measurements, at 150 m, with a spatial resolution of 16 cm. At short range, about 5 m, the resolution increases to subcentimeter.

Distributed gain measurements in Er-doped fibers with high resolution and accuracy using an optical frequency domain reflectometer

For critical erbium-doped fiber amplifier (EDFA) design, e.g., gain tilt optimization in WDM booster amplifiers, knowledge of the gain distribution within the active fiber can present a valuable information. Among the different techniques to evaluate the distributed gain in active fibers, the technique of optical frequency domain reflectometry seems most promising as it is a non-destructive measurement method well matched to the task due to its dynamic range, resolution, and range. Moreover, background light from ASE or residual pump light is strongly rejected due to the coherent detection scheme employed. Using different erbium-doped fibers with strongly varying doping levels and confinements, we demonstrate the excellent accuracy and reproducibility of the technique.

Sine gating detector with simple filtering for low-noise infra-red single photon detection at room temperature

We present and analyze a gated single photon avalanche detector using a sine gating scheme with a simple but effective low-pass filtering technique for fast low-noise single photon detection at telecom wavelength. The detector is characterized by 130 ps short gates applied with a frequency of 1.25 GHz, yields only 70 ps timing jitter and noise probabilities as low as 7·10−7 per gate at 10% detection efficiency. We show that the detector is suitable for high rate quantum key distribution (QKD) and even at room temperature it could allow for QKD over distances larger than 25u2009km.

Free-running single-photon detection based on a negative feedback InGaAs APD

InGaAs/InP-based semiconductor avalanche photodiodes are usually employed for single-photon counting at telecom wavelength. However they are affected by afterpulsing which limits the diode performance. Recently, Princeton Lightwave has commercialized a diode integrating monolithically a feedback resistor. This solution effectively quenches the avalanche and drastically reduces afterpulsing. Here, we report the development and characterization of a detector module based on this diode, implementing an active hold-off circuit which further reduces the afterpulsing and notably improves the detector performances. We demonstrate free-running operation with 600u2009Hz dark count rate at 10% detection efficiency. We also improved the standard double-window technique for the afterpulsing characterization. Our algorithm implemented by a FPGA allows one to put the APD in a well-defined initial condition and to measure the impact of the higher order afterpulses.

Analysis of the polarization evolution in a ribbon cable using high-resolution coherent OFDR

Exploiting the inherent polarization dependence and good spatial resolution of optical frequency domain reflectometry (OFDR), the beatlength in a ribbon fiber can be straightforwardly measured. The results clearly show the different amount of polarization ordering for inner and outer ribbon fibers due to the stress-induced birefringence from the common outer coating.

Continuous QKD and high speed data encryption

We present the results of a Swiss project dedicated to the development of high speed quantum key distribution and data encryption. The QKD engine features fully automated key exchange, hardware key distillation based on finite key security analysis, efficient authentication and wavelength division multiplexing of the quantum and the classical channel and one-time pas encryption. The encryption device allows authenticated symmetric key encryption (e.g AES) at rates of up to 100 Gb/s. A new quantum key can uploaded up to 1000 times second from the QKD engine.