Andrey Denisov

Going beyond 1000000 resolved points in a Brillouin distributed fiber sensor: theoretical analysis and experimental demonstration

Distributed fiber sensing possesses the unique ability to measure the distributed profile of an environmental quantity along many tens of kilometers with spatial resolutions in the meter or even centimeter scale. This feature enables distributed sensors to provide a large number of resolved points using a single optical fiber. However, in current systems, this number has remained constrained to a few hundreds of thousands due to the finite signal-to-noise ratio (SNR) of the measurements, which imposes significant challenges in the development of more performing sensors. Here, we propose and experimentally demonstrate an ultimately optimized distributed fiber sensor capable of resolving 2100000 independent points, which corresponds to a one-order-of-magnitude improvement compared to the state-of-the-art. Using a Brillouin distributed fiber sensor based on phase-modulation correlation-domain analysis combined with temporal gating of the pump and time-domain acquisition, a spatial resolution of 8.3 mm is demonstrated over a distance of 17.5 km. The sensor design addresses the most relevant factors impacting the SNR and the performance of medium-to-long range sensors as well as of sub-meter spatial resolution schemes. This step record in the number of resolved points could be reached due to two theoretical models proposed and experimentally validated in this study: one model describes the spatial resolution of the system and its relation with the sampling interval, and the other describes the amplitude response of the sensor, providing an accurate estimation of the SNR of the measurements.

1’000’000 resolved points along a Brillouin distributed fibre sensor

The challenge to resolve a record of one million points along a single optical fibre is demonstrated using a Brillouin distributed fibre sensor. The proposed system is based on a phase-correlation technique combined with a temporal pump gating, making possible to detect a 14 mm-long hot-spot located at the end of a 17.5 km-long fibre. This corresponds to an increase by one order of magnitude in the number of points that a single system has resolved, representing a major breakthrough in the field. Specific issues arising when resolving such a large number of points are discussed.

Time gated phase-correlation distributed Brillouin fibre sensor

A random access distributed Brillouin fibre sensor is presented, based on phase modulation using a pseudo-random bit sequence (PRBS) together with time gating. The standard phase-correlation technique is known to show a noise level increasing linearly with the number of measured points due to weak gratings generated randomly along the whole sensing fibre. Here we show how intensity modulated pump and time gated detection significantly improve the signal-tonoise ratio (SNR) of the system with no impact on the spatial resolution. A measurement with 1.1 cm spatial resolution over 3.3 km is demonstrated, representing 300’000 equivalent points. The limitations of the proposed technique are discussed through the paper.

Power evolution along phase-sensitive parametric amplifiers: an experimental survey

We propose and experimentally demonstrate a method based on Brillouin optical time-domain analysis to measure the longitudinal signal power distribution along phase-sensitive fiber-optical parametric amplifiers (PS-FOPAs). Experimental results show that the amplification of a PS-FOPA could go through different longitudinal profiles and yet finish with the same overall gain. This behavior is in sheer contrast with theoretical expectations, according to which longitudinal gain distribution should follow certain profiles determined by the initial relative phase difference but can never end up in the same overall gain. The gap between theory and experiment only becomes evident when the pump wavelength is within the fluctuation range of the zero dispersion wavelength (ZDW) of the PS-FOPA.

Mapping dispersion fluctuations along optical fibers using brillouin probing and a fast analytic calculation

A simple analytic formula is derived to extract tiny dispersion fluctuations along highly nonlinear fibers from distributed measurements of parametric gain. A refined BOTDA scheme, suitable to track Kerr processes, enables low noise measurements.

All-optical storage and processing in optical fibers

The recent possibility to generate and read dynamic Bragg gratings in optical fibers by the interaction of multiple optical waves through stimulated Brillouin scattering has opened a new field to realize all-optical fiber-based functions.

Mapping the Uniformity of Optical Microwires Using Phase-Correlation Brillouin Distributed Measurements

The distributed Brillouin gain profile of an ultrathin optical microwire made of chalcogenide-glass is characterized using a phase-modulated correlation-domain measurement technique. Method resolves variations of uniformity below 5% along a 13 cm-long microwire.

Highly sensitive dispersion map extraction from highly nonlinear fibers using BOTDA probing of parametric amplification

In this paper, by improving the experimental scheme, we have been able to measure the fiber optical parametric amplifier (FOPA) gain along the fiber with low noise, which enabled us to derive zero dispersion wavelength (ZDW) fluctuations as low as 0.02 nm along highly nonlinear fibers (HNLFs) with 2 meters longitudinal resolution.

Kerr effect in structured superluminal media

Kerr effect accounts for the change in refractive index of a material with the light intensity and appears in all known optical materials. In this work we analyze Kerr effect in structured superluminal media (e.g some specific types of resonators). We show that Kerr effect in these structures can be cancelled or even reversed (in comparison with the Kerr effect of the material composing the structure) depending on the group index of the structure. We also discuss some possible realizations of structured superluminal media.

Highly-sensitive distributed birefringence measurements based on a two-pulse interrogation of a dynamic Brillouin grating

A method for distributed birefringence measurements is proposed based on the interference pattern generated by the interrogation of a dynamic Brillouin grating (DBG) using two short consecutive optical pulses. Compared to existing DBG interrogation techniques, the method here offers an improved sensitivity to birefringence changes thanks to the interferometric effect generated by the reflections of the two pulses. Experimental results demonstrate the possibility to obtain the longitudinal birefringence profile of a 20 m-long Panda fibre with an accuracy of ∼10−8 using 16 averages and 30 cm spatial resolution. The method enables sub-metric and highly-accurate distributed temperature and strain sensing.