[Show abstract][Hide abstract] ABSTRACT: The real remoteness of a distributed optical fiber sensor based on Brillouin optical time-domain analysis is considerably extended in this paper using seeded second-order Raman amplification and optical pulse coding. The presented analysis and the experimental results demonstrate that a proper optimization of both methods combined with a well-equalized two-sideband probe wave provide a suitable solution to enhance the signal-to-noise ratio of the measurements when an ultra-long sensing fiber is used. In particular, the implemented system is based on an extended optical fiber length, in which half of the fiber is used for sensing purposes, and the other half is used to carry the optical signals to the most distant sensing point, providing also a long fiber for distributed Raman amplification. Power levels of all signals launched into the fiber are properly optimized in order to avoid nonlinear effects, pump depletion, and especially any power imbalance between the two sidebands of the probe wave. This last issue turns out to be extremely important in ultra-long Brillouin sensing to provide strong robustness of the system against pump depletion. This way, by employing a 240 km-long optical fiber-loop, sensing from the interrogation unit up to a 120 km remote position (i.e., corresponding to the real sensing distance away from the sensor unit) is experimentally demonstrated with a spatial resolution of 5 m. Furthermore, this implementation requires no powered element in the whole 240 km fiber loop, providing considerable advantages in situations where the sensing cable crosses large unmanned areas.
Journal of Lightwave Technology 01/2014; 32(1):152-162. · 2.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: Slow light systems are particularly attractive for analog signal processing, since their inherent limitation to a delay-bandwidth product of 1 is less critical for analog systems such as those used in microwave photonics. We present here the implementation of two basic functions - phase shifting and true time delaying - fully optically controlled using stimulated Brillouin scattering in optical fibers. The combination of these two functions makes possible the implementation of true time delays without limitation on the microwave carrier frequency using the separate carrier tuning technique. This is illustrated by the implementation of the delaying system for the realization of a microwave tunable notch filter.
[Show abstract][Hide abstract] ABSTRACT: Optical fibre sensors based on stimulated Brillouin scattering have now clearly demonstrated their excellent capability for long-range distributed strain and temperature measurements. The fibre is used as sensing element and a value for temperature and/or strain can be obtained from any point along the fibre. While classical configurations have practically a spatial resolution limited by the phonon lifetime to 1 meter, novel approaches have been demonstrated these past years that can overcome this limit. This can be achieved either by the prior activation of the acoustic wave by a long lasting pre-pumping signal, leading to the optimized configuration using Brillouin echoes, or by probing a classically generated steady acoustic wave using a ultra-short pulse propagating in the orthogonal polarization of a highly birefringent fibre. These novel configurations can offer spatial resolutions in the centimetre range, while preserving the full accuracy on the determination of temperature and strain.
[Show abstract][Hide abstract] ABSTRACT: A novel technique to realize true time reversal of an optical signal, using dynamic Brillouin gratings in high-birefringence fibers, is proposed. A data sequence of optical pulses with 2-ns duration was efficiently time-reversed.
[Show abstract][Hide abstract] ABSTRACT: We experimentally demonstrate a novel technique to realize a tunable delay line based on dynamic Brillouin gratings in a high birefringence fiber. A 8ns pulse signal is continuously delayed up to 184ns with minor distortion.
[Show abstract][Hide abstract] ABSTRACT: The ubiquitous role of optical fibers in modern photonic systems has stimulated research to realize slow and fast light devices directly in this close-to-perfect transmission line. Recent progress in developing optically-controlled delays in optical fibers, operating under normal environmental conditions and at telecommunications wavelengths, has paved the way towards real applications for slow and fast light. Advanced schemes can be realized thanks to the extremely flexible possibility to shape the gain spectrum to make it optimized for applications. Ultra wide bandwidth, delaying with flat amplitude response and lower distortion were successfully demonstrated this way.
[Show abstract][Hide abstract] ABSTRACT: This paper reviews the major advances in Brillouin slow light devices along the last two years. We also focus on the positive and negative implications of this effect in the development of fiber sensors.
[Show abstract][Hide abstract] ABSTRACT: Generation of optical delays with minor amplitude change are realized through the superposition of gain and loss profiles generated by stimulated Brillouin scattering. It results in synthesized spectral profiles identical to an ideal electromagnetically-induced transparency.