Jean Pierre von der Weid

Phase measurement in frequency-doubling fibers

Fibers were prepared for second-harmonic generation by injecting a frequency-doubled (seed) signal with the fundamental light from a Nd:YAG laser. The relative phase shift between the seed and the second-harmonic light generated by the fiber was measured to be close to 90 degrees ( approximately 99 +/- 9.2 degrees ). A water cell was used to sweep the relative phase of the waves with interferometric precision. Some physical consequences of a pi/2 phase shift are pointed out.

Real-time monitoring of single-photon detectors against eavesdropping in quantum key distribution systems

By employing real-time monitoring of single-photon avalanche photodiodes we demonstrate how two types of practical eavesdropping strategies, the after-gate and time-shift attacks, may be detected. Both attacks are identified with the detectors operating without any special modifications, making this proposal well suited for real-world applications. The monitoring system is based on accumulating statistics of the times between consecutive detection events, and extracting the afterpulse and overall efficiency of the detectors in real-time using mathematical models fit to the measured data. We are able to directly observe changes in the afterpulse probabilities generated from the after-gate and faint after-gate attacks, as well as different timing signatures in the time-shift attack. We also discuss the applicability of our scheme to other general blinding attacks.

Statistics of polarization mode dispersion-induced gain fluctuations in Raman amplified optical transmissions

A systematic experimental evaluation of polarization mode dispersion (PMD–) –induced polarization-dependent gain (PDG) in forward pumped Raman amplification in dispersion-shifted and in dispersion-compensating fiber was performed. Good agreement was obtained between the measured statistical parameters and the current analytical model for PDG fluctuation statistics. The probability distribution of the PDG was approximately Maxwellian within the range PMD >0.05 ps/km1/2. The interplay between PMD and gain fluctuations is discussed; random birefringence strongly reduces PDG fluctuations. However, the trade-off between reduction of the power penalties for PDG and increase of the penalties for PMD distortion precludes the use of PMD instead of source depolarization techniques for reduction of PDG.

Automatic Fault Detection in WDM-PON With Tunable Photon Counting OTDR

An automatic fiber-optical fault analysis system making use of a tunable photon counting optical time-domain reflectometry (OTDR) (ν-OTDR) is proposed and demonstrated in a passive optical network testbed. The employment of the ℓ trend filter as a signal processing tool enables the minimization of the intrinsic coherent random noise impact on the acquired data and also an automatic identification of fiber faults. A feedback loop between an FPGA-based acquisition unit and the filters selections yields highly accurate automatic results and minute monitoring periods with ITU-T grid DWDM tunability, spatial resolution of 6 m and a measured 32 dB dynamic range.

Spectral characterization of weak coherent state sources based on two-photon interference

We demonstrate a method for characterizing the coherence function of coherent states based on two-photon interference. Two states from frequency mismatched faint laser sources are fed into a Hong–Ou–Mandel interferometer, and the interference pattern is fitted with the presented theoretical model for the quantum beat. The fitting parameters are compared to the classical optical beat when bright versions of the sources are used. The results show the equivalence between both techniques.

A robot for offshore pipeline inspection

The robot presented in this paper was designed to find damages to the external sheath of offshore pipelines. The pipeline section subject to inspection is known as “riser” and connects the pipe running on the seabed to the production facility at the platform or “floating production, storage and offloading” ship (FPSO). When compared to the current tools used to perform this work, the main advantage of this robot is to be able to execute the inspection without umbilical cable or operator assistance. The vehicle, called Autonomous Underwater Riser Inspection robot (AURI), uses the pipeline for guidance. A closed feedback loop control system is used to maintain constant speed during the mission. Several sensors provides multiple return conditions for safe operation, such as maximum depth, maximum time or maximum distance. The robot is suited to carry different inspection devices (payloads). The payload for the first prototype consists of four cameras which provide 100% coverage of the external pipe surface. All robot vessels were designed to support up to 100 Bar of pressure, allowing the vehicle to reach a maximum depth of one thousand meters. This paper presents the general concepts of the robot as well as results from the tests in a pool, including some hydrodynamic parameters of the vehicle.

Fiber Monitoring Using a Sub-Carrier Band in a Sub-Carrier Multiplexed Radio-Over-Fiber Transmission System for Applications in Analog Mobile Fronthaul

In this paper, we describe an efficient method for monitoring fiber links utilizing sub-carrier multiplexing. By assigning a void sub-carrier frequency band for monitoring purposes, the method reuses the data transmitter without any impact on data transmission and provides capability of in-service reflectometry measurements of fiber optic lines with 10-m spatial resolution and 1.0-dB fault detection sensitivity. Its promising properties and performance enable potential application in emerging networks such as relatively short distance analogue mobile fronthaul.

Adaptive Filter for Automatic Identification of Multiple Faults in a Noisy OTDR Profile

We present a novel methodology that is able to distinguish meaningful level shifts from typical signal fluctuations which, in a fiber monitoring context, is associated with the problem of identifying small losses within a noisy optical time-domain reflectometer (OTDR) profile. A two-stage regularization filtering can accurately identify the location of the significant level shifts with an efficient parameter-free algorithm. The developed methodology demands low computational effort and can easily be embedded in a dedicated processing unit. Our case studies compare the new methodology with the current available ones and show that it is the most adequate technique for fast detection of multiple unknown level shifts in a noisy OTDR profile.

Impact of Raman Scattered Noise from Multiple Telecom Channels on Fiber-Optic Quantum Key Distribution Systems

In this paper, we analyze the impact of the spontaneous Raman scattered noise generated from multiple optical classical channels on a single quantum key distribution channel, all within the telecom C-band. We experimentally measure the noise generated from up to 14 continuous-wave laser sources with different wavelengths using the dense wavelength division multiplexing (DWDM) standard, in both propagation directions in respect to the QKD channel, over different standard SMF-28 fiber lengths. We then simulate the expected secure key generation rate for a decoy-states-based system as a function of distance under the presence of simultaneous telecom traffic with different modulation techniques, and show a severe penalty growing with the number of classical channels present. Our results show that, for in-band coexistence, the telecom channels should be distributed as close as possible from the quantum channel to avoid the Raman noise peaks. Operation far from the zero dispersion wavelength of the fiber is also beneficial as it greatly reduces the generation of four-wave mixing inside the quantum channel. Furthermore, narrow spectral filtering on the quantum channels is required due to the harsh limitations of performing QKD under real telecom environments, with the quantum and several classical channels coexisting in the same ITU-T C-band.

Long-Distance Bell-State Analysis of Fully Independent Polarization Weak Coherent States

Here we report the experimental implementation of a linear-optics partial Bell-state analyzer following the propagation of single-photons through long telecommunication optical fibers. Polarization encoded weak coherent states were sent from independent remote continuous wave faint laser sources over two 8.5 km long optical fiber spools. Automatic polarization stabilization systems were used in each spool to compensate the random polarization drift. We demonstrate stable two-photon interference with a dip visibility of 47.8% over a 40 minute time-interval, close to the theoretical maximum of 50% for weak coherent states. We successfully show that it is possible to carry out remote long-distance Bell-state analysis of polarization weak coherent states in spite of random residual birefringence fluctuations in optical fibers. These results pave the way for important applications in quantum communications with polarization qubits such as measurement device-independent quantum key distribution and quantum repeaters.