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

Abstract

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.

Brillouin Dynamic Gratings – A Practical Form of Brillouin Enhanced Four Wave Mixing in Waveguides – The First Decade and Beyond

“…The phase of the reflections also plays an important role in BDG characterization. Interferometric measurements of temporally [95] or spectrally [24] spaced reflections have demonstrated superior sensitivity. The fact that the creation of BDG and its interrogation are separated, and that its reflections can be treated as a linear system (as manifested in Equation (5)), allows for the employment of long-known radar and optical signal processing techniques for the detection and processing of distributed reflections.…”

“…Distributed measurement of birefringence [17,95] and intermodal beat length [18,26], is the most natural application of BDG-based reflectometry, since by simply measuring the resonant frequency of the BDG readout along the fiber, ΔΩ ( ), the longitudinal variations of the fiber birefringence, Δ ( ), can be deduced, an accuracy of 10 -8 refractive index units with a spatial resolution of 30cm being the state of the art.…”

Brillouin Dynamic Gratings—A Practical Form of Brillouin Enhanced Four Wave Mixing in Waveguides: The First Decade and Beyond

“…The phase of the reflections also plays an important role in BDG characterization. Interferometric measurements of temporally [ 95 ] or spectrally [ 24 ] spaced reflections have demonstrated superior sensitivity.…”

“…Distributed measurement of birefringence [ 17 , 95 ] and intermodal beat length [ 18 , 26 ], is the most natural application of BDG-based reflectometry, since by simply measuring the resonant frequency of the BDG readout along the fiber, , the longitudinal variations of the fiber birefringence, , can be deduced, an accuracy of 10 −8 refractive index units with a spatial resolution of 30 cm being the state of the art.…”

Fast and direct measurement of the linear birefringence profile in standard single-mode optical fibers

“…Direct techniques, on the other hand, are capable of position-resolved measurements of the fiber birefringence. These implementations rely on either optical frequency domain reflectometry (OFDR) [8,9], dynamic Brillouin gratings (DBGs) [10,11], or phase-sensitive (φ) OTDR [12]. OFDR offers extremely high spatial resolutions, on the order of millimeters, but is limited to the characterization of short fiber lengths.…”