Rodrigo Kendy Yamashita

Measurement Range Elongation Based on Temporal Gating in Brillouin Optical Correlation Domain Distributed Simultaneous Sensing of Strain and Temperature

We had earlier demonstrated the distributed discrimination of strain and temperature by localizing and scanning both the stimulated Brillouin scattering and the Brillouin dynamic grating along a polarization-maintaining fiber. The localization and scanning were performed by a correlation domain technique, whose measurement range was restricted by the distance between consecutive correlation peaks. To overcome this restriction, in this letter, we apply a temporal gating scheme to the system by enlarging the measurement range from ~25 to ~500 m. We report the results confirming the effectiveness of this scheme in a system operated by a single laser source, and demonstrate the strain-temperature discrimination when strain or temperature is applied to segments on the 500-m-long fiber under test.

Spatial Resolution Improvement in Correlation Domain Distributed Measurement of Brillouin Grating

We have demonstrated that intensity modulation enhances the spatial resolution in the distributed measurement of Brillouin dynamic grating (BDG) spectrum by the Brillouin optical correlation domain analysis. According to the correlation domain principle, the stimulated Brillouin scattering is localized in so-called correlation peaks, but these peaks actually have side lobes, which excite the BDG out of the peak region, compromising the spatial resolution in the BDG spectrum measurement. To solve this, we applied intensity modulation to apodize the optical power spectrum of the input lightwave to the system, suppressing the side lobes. We experimentally confirmed about 4.5 times improvement in the spatial resolution. A 25-cm-long stressed segment in a 500-m-long fiber was successfully recognized in the proposed system, which could not be achieved by a system without the intensity modulation.

Simulation for estimating spatial resolution in distributed measurement of Brillouin dynamic grating by correlation domain technique

We propose a simulation method to calculate reflection spectra of Brillouin dynamic grating localized by the correlation domain technique. Simulation results match with experiments and the spatial localization of the dynamic grating can be estimated.

Spatial resolution improvement based on intensity modulation in measurement of Brillouin dynamic grating localized by correlation domain technique

We demonstrated that intensity modulation synchronized with laser frequency modulation enhances the spatial resolution in the measurement of Brillouin dynamic grating (BDG) spectrum localized by the correlation domain technique. Following the correlation domain principle, the stimulated Brillouin scattering is localized in so-called correlation peak, but the peak actually has side lobes which excite the BDG out of the peak region. To overcome this, we applied intensity modulation and apodize the optical spectrum of the participating waves to suppress the side lobes. We confirmed spatial resolution improvement from 75 cm to 17 cm in a measurement fiber of 500 m.

Measurement range elongation based on a temporal gating scheme in Brillouin correlation domain distributed discrimination system for strain and temperature operated by a single laser

We have demonstrated distributed discrimination of strain and temperature by localizing and scanning both the Stimulated Brillouin scattering (SBS) and the Brillouin dynamic grating (BDG) along a polarization maintaining fiber, with elongated measurement range. The localization and scanning is performed by a correlation domain technique, whose measurement range is restricted by the distance between consecutive correlation peaks. To overcome this restriction, we applied a temporal gating scheme to the system, enlarging the measurement range from ~8 m to ~500 m. Here, we report the results confirming the effectiveness of this scheme in a system operated by a single laser source and demonstrate strain-temperature discrimination when strain or temperature is applied to segments on the 500-m-long fiber under test.

Theoretical evaluation of Brillouin dynamic grating length localized by optical correlation domain technique through reflection spectrum simulation

We derive formulae based on Fourier transformation to calculate the reflection spectrum of a Brillouin dynamic grating (BDG), which is localized along an optical fiber by an optical correlation domain technique. First, we calculate the typical reflection spectra of the BDG localized by the technique and confirm the validity of the formulae by showing coincidence with previous theoretical or experimental works. Next, we evaluate theoretically the spatial resolution in the BDG distributed measurement by the technique, through simulations considering different strained fiber lengths. It is confirmed theoretically, for the first time, that the resolution in the BDG measurement is worse than that for the Brillouin gain spectrum.

Effect of pump-read optical path difference on the measurement of Brillouin dynamic grating spectra localized bythe correlation domain technique with a single laser setup

In correlation domain distributed measurement of Brillouin dynamic grating (BDG) in polarization maintaining fiber, adjustment of the frequency modulation (FM) phase between the pump and read lightwaves is essential. We experimentally evaluated the phase difference impact on the measurement. A single laser setup can acquire the BDG spectra with higher stability, but the FM phase relation is fixed. Therefore the FM synchronization is not guaranteed for all points of the fiber under test due to the birefringence of the fiber. In this report, we varied the optical path difference between the pump and the read lightwaves, showing the spectrum degradation.

Determination of Brillouin Dynamic Grating Spectrum Localized by the Correlation Domain Technique through Fourier Transformation

We propose a Fourier transformation based method to calculate the shape of Brillouin dynamic grating spectrum, when the grating is localized by the correlation domain technique. The simulation results match with experimental data reported previously.

Numerical simulation for optimization of temporal gatings in Brillouin optical correlation domain analysis

Brillouin sensors have the potential to measure strain or temperature distribution along the optical fiber, by determination of the Brillouin frequency shift (BFS). The Brillouin optical correlation domain analysis (BOCDA) is an important technique in Brillouin sensors, having great spatial resolution over a restricted measurement range, comparing to other systems, such as the Brillouin optical time domain analysis (BOTDA). To elongate the restricted measurement range, temporal gating techniques have been proposed and demonstrated, but the influence of these techniques on the performance of the BOCDA system or the parameter requirement for system optimization have not been investigated. In this report, we first determine a simulation method to calculate the BOCDA output with temporal gatings and find out that the phase relation between the gating pulses and the sinusoidal frequency modulation (FM) may change the system output. Although that influence can be neglected for most cases, the phase optimization can make the system output approach the ideal case that the temporal gating is not being applied. Finally, calculations of system output for different gating pulse lengths are held, showing that the pulse length does not have to strictly match one period of the sinusoidal FM of the laser source.