A novel and simple analytical expression to describe the Brillouin gain spectral broadening as a function of the spatial resolution in time-domain Brillouin distributed fiber sensors is deduced. The proposed model is experimentally validated using a pump-probe Brillouin sensing setup and also compared with numerical and approximate results. In addition, a compact mathematical form is presented for the peak gain reduction resulting from incomplete acoustic-wave activation in Brillouin sensors with short spatial resolution. Both mathematical expressions can be used together to quantitatively predict the impact of the spatial resolution on the signal-to-noise ratio and frequency uncertainty of the sensor.
A technique based on the use of orthogonally-polarized pulses is proposed to mitigate the detrimental impact of modulation instability on Brillouin distributed fiber sensors. While the theoretical underpinnings of the method are described by introducing a detailed model for the vector modulation instability, the technique is experimentally validated in a 25-km sensing link. Numerical and experimental results demonstrate that the use of orthogonally-polarized pulses not only mitigates the impact of modulation instability, but also the four-wave mixing occurring in systems using pumps with parallel polarization; thus, providing an important sensing range enhancement with a reduced pump depletion.
KEYWORDS: Modulation, Sensors, Optical fibers, Monte Carlo methods, Fiber optics sensors, Single mode fibers, Modeling, Fiber Bragg gratings, Signal attenuation, Signal detection
An analytical model for the depletion length of modulation instability in single-mode optical fibres is proposed. The
model gives the possibility to determine the maximum sensing distance that distributed optical fibre sensors can reach
before being limited by the pump depletion induced by modulation instability. The important role of the noise level in
the evolution of both modulation instability and the respective power depletion is clarified. The model gives a closedform
expression helpful for a predictive design and is validated comparing the analytical results obtained by the model
with measurements in a 25 km long Brillouin fibre sensor.
A thorough study of the generation of modulation instability (MI) in distributed Brillouin fibre sensors is presented. ASE noise co-propagating with the pump pulses within the MI gain spectrum has been identified to be an important factor seeding modulation instability and reducing its power threshold. The paper describes how optical narrowband filtering reduces the pump depletion resulting from MI, allowing pump pulses to propagate through longer distances in standard optical single-mode fibres.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.