Sources of noise in Brillouin optical time-domain analyzers

This paper presents a thorough study of the different sources of noise affecting Brillouin optical time-domain analyzers (BOTDA), providing a deep insight into the understanding of the fundamental limitations of this kind of sensors. Analytical and experimental results indicate that the noise source ultimately fixing the sensor performance depends basically on the fiber length and the input pump-probe powers. Thus, while the phase-to-intensity noise conversion induced by stimulated Brillouin scattering can have a dominating effect at short distances, a combination of sources determines the noise in long-range sensing, basically dominated by probe double Rayleigh scattering.J. Urricelqui acknowledges the support from the Spanish Ministerio de Economia y Competitividad through the project TEC2013-47264-C2-2-R, FEDER funds, the COST action TD1001 and Universidad Pública de Navarra

Going beyond limits in Brillouin distributed fibre sensors: Challenges and possible approaches

Brillouin distributed optical fibre sensing has been a subject of intense research and industrial development for more than twenty years, demonstrating its capabilities to be an effective and powerful measurement tool for a wide range of applications. Making use of sophisticated implementations, remarkable progresses on the sensing performance have been reported in the last decade, allowing significant improvements in spatial resolution and sensing range. However, the demand for distributed sensors with more performing features is steadily growing, imposing new and more challenging requirements to the sensor design. This paper presents a brief overview of the fundamentals of Brillouin distributed fibre sensing and reviews the main current limitations and challenges faced when the sensing capabilities are pushed beyond the state-of-the-art. Different possible approaches and methods to enhance and compare the sensing performance are also discussed

Four wave mixing effects in gain-equalized distributed fiber raman amplifiers

The degradation of the performance of distributed fiber Raman amplifiers (DFRAs) is shown to be dependent on the interaction between pump-pump four-wave mixing (FWM) and stimulated Raman scattering (SRS), by means of numerical simulations. We verify that FWM processes, including depletion and parametric gain, generate new sources of SRS and a redistribution of the pump power along the fiber. Results show impairments on the performance of DFRAs such as loss of flatness on the spectral gain and reduction on the Raman gain and presence of FWM products within the transmission band

Redistribution of pump power and impairments in gain-equalized distributed fiber Raman amplifiers due to four-wave mixing and parametric amplification

In this work, by using a comprehensive numerical model which rigorously describes the interaction between stimulated Raman scattering (SRS) and four-wave mixing (FWM), we verify that FWM processes, including depletion and parametric gain, generate a redistribution of pump power in distributed fiber Raman amplifiers (DFRAs). As a consequence of pump–pump FWM, several FWM components can be generated, which act as new sources of SRS for Raman pumping. Due to new SRS–FWM interactions, a redistribution and exchange of pump power along the fiber also occurs, producing degradation in the performance of the amplifier. Numerical results show impairments in distributed amplified systems due to these interactions, such as loss of flatness on the spectral gain, reduction on the net Raman gain, and the presence of strong FWM products within the transmission band. We note that the localization of the zero dispersion wavelength (λZD) of the fiber is a critical factor in the occurrence of these impairments. A reduction of net Raman gain up to 3 dB and tilt up to 7 dB in the spectral gain profile have been found in different amplified systems as consequence of pump–pump FWM and parametric gain of Raman pumps

Modeling and evaluating the performance of Brillouin distributed optical fiber sensors

A thorough analysis of the key factors impacting on the performance of Brillouin distributed optical fiber sensors is presented. An analytical expression is derived to estimate the error on the determination of the Brillouin peak gain frequency, based for the first time on real experimental conditions. This expression is experimentally validated, and describes how this frequency uncertainty depends on measurement parameters, such as Brillouin gain linewidth, frequency scanning step and signal-to-noise ratio. Based on the model leading to this expression and considering the limitations imposed by nonlinear effects and pump depletion, a figure-of-merit is proposed to fairly compare the performance of Brillouin distributed sensing systems. This figure-of-merit offers to the research community and to potential users the possibility to evaluate with an objective metric the real performance gain resulting from any proposed configuration

Impairments in Gain-Equalized Distributed Fiber Raman Amplifiers due to Four-Wave Mixing and Parametric Amplification Processes

In this work, by means of numerical simulations, we verify that four‐wave mixing (FWM) processes, including depletion and parametric gain, generate a redistribution of pump power in distributed fiber Raman amplifiers (DFRAs). As a consequence of pump‐pump FWM, FWM products are generated, as well as a power exchange between pumps, which produces degradation in the performance of the amplifier due to new SRS‐FWM interactions. Numerical results show impairments in distributed amplified systems due to these interactions, such as loss of flatness on the spectral gain, reduction on the net Raman gain, and presence of strong FWM products within the transmission band

Brillouin distributed fiber sensors: Practical limitations and guidelines for the making of a good sensor

By analyzing the fundamentals of the operation of Brillouin sensors it will be shown that all efforts must be focused on obtaining the largest signal-to-noise ratio on the raw optical signal, which ultimately scales all performance of the sensor. Guidelines will be presented, together with recent research efforts to find out smart solutions pushing further the limits

Towards 1’000’000 resolved points in a distributed optical fibre sensor

Increasing the number of resolved points, by either improving the spatial resolution or extending the measurement range, is one of the main challenges being currently faced in distributed optical fibre sensing. This paper explores the main parameters affecting the performance of Brillouin distributed fibre sensors and analyses potential configurations and directions to reach one million equivalent resolved points

Optical process and optical device, allowing to avoid unwanted nonlinear effects in an optical fiber

The invention concerns a process comprising the following steps: injecting, in an optical fiber, N time limited replica optical signals at distinct frequencies, each replica signal being temporally shifted relative to the other replica signals; then propagating the temporally shifted replica signals along the optical fiber; then receiving, at an output of the optical fiber, N output time-limited optical signals at distinct frequencies resulting from the replica signals, each output signal being temporally shifted relative to the other output signals; and constructing a useful signal by temporally superimposing the N output signals, such that the useful signal comprises a combination of the N output signals that are not temporally shifted anymore. Application to distributed sensors