Distributed birefringence measurement with beat period detection of homodyne Brillouin optical time-domain reflectometry

Abstract

We report a distributed optical fiber birefringence measurement method based on homodyne Brillouin optical time-domain reflectometry (BOTDR). Unlike conventional BOTDR, which requires scanning of the local oscillator to get the Brillouin spectrum, instead we propose the beat period measurement of fast and slow components of the backscattered Brillouin signal in single-mode fibers using homodyne detection. The beat period is measured by detecting the envelope of the Brillouin beat signal, which gives the beat length at different fiber locations, so that birefringence can be calculated accordingly. The distributed birefringence of a 1.7 km SMF-28 and a 4.3 km large-effective-area fiber were measured with 0.6 m spatial resolution without frequency scanning of the Brillouin spectrum.

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

“…While a high birefringence is intentionally imposed during the fabrication of polarisation-maintaining fibres (PMF), birefringence can also be highly affected by external environmental perturbations, thus giving the possibility to perform sensing of quantities such as temperature, strain, electric current, hydrostatic pressure, and others [1][2][3][4][5][6][7][8][9][10] . Although there exist several techniques for birefringence measurement, most of them can only measure the average birefringence value, thus limiting those methods only to discrete sensing applications.…”

“…For birefringence-based distributed sensing, several techniques based on reflectometry have been proposed in the literature: e.g. phase-or polarisation-sensitive Rayleigh based reflectometry in time or frequency domain (OTDR, OFRD, POTDR, POFDR) [1][2][3][4] , Brillouin optical timedomain reflectometry (BOTDR) 5 , and dynamic Brillouin gratings (DBG) 6 . Those methods provide either direct or indirect measurements of the local fibre birefringence.…”

Distributed phase birefringence measurements based on polarization correlation in phase-sensitive optical time-domain reflectometers

“…Only a limited amount of techniques that allow for distributed birefringence measurements have been proposed in the state-of-the-art [7][8][9][10][11][12][13][14][15][16][17][18][19]. Considering that the fiber birefringence is affected by external factors, many of those techniques have been exploited for distributed optical fiber sensing in order to detect changes of environmental quantities of interest, such as strain & temperature [6], electric current [13], and external physical perturbations for intrusion detection [19].…”

“…Considering that the fiber birefringence is affected by external factors, many of those techniques have been exploited for distributed optical fiber sensing in order to detect changes of environmental quantities of interest, such as strain & temperature [6], electric current [13], and external physical perturbations for intrusion detection [19]. These techniques retrieve the information using very diverse approaches, such as polarization-sensitive optical time-domain reflectometry (POTDR) [7][8][9][10][11], polarizationsensitive optical frequency-domain reflectometry (POFDR) [12,13], Brillouin optical timedomain reflectometry (BOTDR) [14], optical frequency-domain reflectometry (OFDR) [15,16], and dynamic Brillouin gratings (DBG) [6,17]. From all these techniques, POTDR and BOTDR are indirect measurement methods, in which the evolution of the state of polarization of the backscattered signal and respective beat length are measured and then used to calculate the local birefringence information based on given mathematical models.…”

Polarization Beat Length Estimation Based on the Statistical Properties of Brillouin Gain in SMF

“…Due to the intrinsic polarization dependence properties of SBS gain, the birefringence measurement systems based on SBS can be much faster and without the need of expensive polarization optics. Till now, besides the complicated approach of DBG (dynamical Brillouin grating) technique [12], all Brillouinbased birefringence measurements are based on FFT (fast Fourier transform) algorithm of Brillouin gain signal along the fiber [11], [13], [14].…”