G. Ravet

Polarization mode dispersion mapping in optical fibers with a polarization-OTDR

We describe a technique for the measurement of the polarization mode dispersion distribution along an optical fiber link based on a polarization optical time-domain reflectometer technique setup. This technique does not require the complete measurement of the polarization state of the backscattered signal. We report results performed on different types of fibers: standard step index, dispersion shifted, and dispersion compensating fibers.

Experimental demonstration of a passive all-fiber Q-switched erbium- and samarium-doped laser

Self-Q-switched operation of the all-fiber laser using erbium and samarium fibers in the cavity is realized experimentally. This passively Q-switched all-fiber laser produces very stable pulses with energy of 142 nJ and duration of 450 ns. The experimental results were well reproduced by the results obtained through the numerical integration of a rate-equations model.

Centralised Optical Monitoring of Tree-structured Passive Optical Networks using a Raman-assisted OTDR

Monitoring of tree-structured passive optical networks from a central office is difficult to achieve using a standard OTDR. Switchable reflective elements placed at the ONU can help to discriminate between the branches. In parallel, a Raman assisted OTDR is shown to increase the dynamic range of the reflectometry measurement, thus enabling to detect more faults in the network, and especially fibre breaks after the splitter.

Iterative method for Brillouin fiber ring resonator

The interest for Brillouin fiber ring lasers has significantly increased due to the large spectrum of their applications: the large scale of their peak power, the ultra-narrow linewidth and the low threshold power are the most exploited features. At the same time, their application is limited because of the important peak-power fluctuations which are mainly due to the stochastic nature of the Spontaneous Brillouin Scattering that initiates the Stimulated Brillouin Scattering (SBS). Therefore, it is of great interest to develop new models and methods for controlling these amplitude fluctuations. Several analytical and numerical solutions are often proposed to describe the steady state of the SBS in single mode optical fibers but, for instance, the general form of the non-linear equations system of the SBS is difficult to solve. Models start typically from the classical system [1] which couples the evolution of two optical fields with the acoustic field through the electrostriction process and propose several improvements to obtain a better agreement with experimental data or predict new behaviors.

Review of the Use of the Optical Fibers for Safety Applications in Tunnels and Car Parks: Pollution Monitoring, Fire and Explosive Gas Detection

Optical fiber sensors bring to measurement systems all the advantages offered by the optical fiber technology. The potential applications for these sensors are numerous and can spread from medical diagnosis to pipe line monitoring passing through geological measurements. This chapter will focus on the applications in road tunnels and undercroft car parks monitoring. It will detail the existing optical fiber sensor methods, commercially available or under development in the field of air quality monitoring, in particular NO2 that is representative of toxic automotive pollution, flaming fire detection and combustible gas leak detection (in particular methane and hydrogen).

Spectral broadening in Raman fiber amplifier pumped by partially coherent wave

In this paper, spectral broadening of the amplified signal in Raman fiber amplifiers is reported when a broadband continuous wave pump is used in a copropagating configuration. A Raman laser operating at 1455 nm is used as a pump. A wavelength division multiplexer (WDM) combines both waves for interaction in a 6 km long single dispersion shifted mode fiber. A scanning Fabry-Perot interferometer with a free spectral range of 15 GHz and a resolution (FWHM) of 100 MHz is used to analyze the signal spectrum. In addition, the numerical integration of the nonlinear Schrodinger equations was performed considering a CW signal and taking into account the partial coherence of the pump wave. The simulation result gives a good agreement with the experimental data confirming the mechanism of the spectrum broadening.

Multi-cascaded SBS in an optical fiber supported by Rayleigh backscattering

We performed numerical simulations in order to demonstrate that Rayleigh scattering - stimulated Brillouin scattering cooperative process (RS-SBS) can lead to generation of second-order SBS in standard telecom fibers. We give a clear physical insight into the RS-SBS mechanism and built 1-D model describing dynamics of first two SBS cascades. To our knowledge for the first time, we theoretically determine the threshold of the second-order SBS generation in the RS-SBS process and reveal how the SBS spectra, phase portraits and power distributions along the fiber evolve as the pump power grows leading to growth of the second-order SBS. Recently published experimental observations of low-threshold second order SBS in 4.4-km-long optical fiber [e.g., J.Opt.Soc.Am.B 19, 2341-2345 (2002)] are completely reproduced by our simulations.

Distributed measurement of modulation instability along optical fibers

We present an optical time domain reflectometry technique that allows characterizing the modulation instability along optical fibers. We can examine where the different frequencies are generated when high power pulses are launched in the fiber.

All-fiber passively Q-switched Erbium/Samarium laser

Q-switched fiber lasers operating at 1550nm are of great interest for various applications in medicine, aerial or space communications, optical time domain reflectometry, distributed fiber-optical sensing and investigation of nonlinear phenomena. The development of completely all-fiber passively Q-switched fiber lasers cavities is useful because of their high reliability, high damage threshold, device stability, the essential alignment of all the fibers. It also allows to reduce the cost for the laser realization because no external driver is needed.

Spectrum broadening in Raman fiber laser induced by cross-phase modulation

Raman fiber lasers (RFLs) are attractive laser sources providing almost any wavelength in the near infrared region. The RFL spectral performance is of great importance for their applications. At the same time, it is well known that the RFL radiation suffers from spectral broadening. Although a spectral broadening mechanism is not well justified yet, most of authors consider the four-wave mixing between Stokes wave longitudinal modes to be the main mechanism of the spectral broadening in the RFL. Here we show that it is not necessary the case. Comparing operations of the same RFL with co-and contra-propagating pumping we prove in a direct experiment that the modulation instability induced by cross-phase modulation of the broadband pump wave on the Stokes wave may significantly contribute to the RFL line. The ring Raman laser operates at 1550 nm. The laser is pumped at 1460 nm by another RFL emitting 6W. It is important for this experiment that the pump radiation exhibits rather broad spectral width of ~0.5 nm. The direction of the Stokes wave propagation in the ring cavity is determined by an optical circulator, so during the experiment we could easily invert this direction, other conditions being equal. The laser cavity comprises 200 m long Raman fiber with a Raman efficiency of 2.2/km/W and dispersion parameters of-29.6 and -18.5 ps/nm/km at 1460 and 1550 nm, respectively. The fiber Bragg grating (FBG) with a reflectivity of 20% is used to select the laser wavelength.