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We have demonstrated a quasi-distributed sensor using an active mode-locking (AML) laser with multiple fiber Bragg grating (FBG) reflections of the same center wavelength. We found that variations in the multiple cavity segment lengths between FBGs can be measured by simply sweeping the modulation frequency, because the modulation frequency of the AML laser is proportionally affected by cavity length.
The frequency division multiplexing (FDM) technique is firstly introduced into a direct-detection phase-sensitive OTDR to improve the distributed fiber acoustic sensing performance by using a frequency step sweeping laser source and a dual probe pulse scheme. By using FDM technique, a 40 kHz sampling rate to vibration is realized with a 10 km measurement range, which implies the tradeoff between the...
Brillouin optical time domain analysis (BOTDA) enhanced by the tailored compensation for the propagation loss of a pump pulse is experimentally demonstrated for long-distance and high-resolution distributed sensing. Distributed Brillouin amplification (DBA) of the pump pulse is applied in addition to an ordinary BOTDA configuration, where the frequency modulation with time-dependent amplitude variation...
We demonstrate a high spatial resolution multiplexing scheme for fiber Bragg grating (FBG) sensors based on single-arm frequency-shifted interferometry (SA-FSI). The SA-FSI system uses an incoherent broadband source, a slow detector, and an electro-optic modulator (EOM). By sweeping the frequency of EOM and taking the fast Fourier transform (FFT) of the interference signal, we resolved the locations...
Pound-Drever-Hall (PDH) technique has been widely adopted for ultrahigh resolution fiber-optic sensors, but its performance degenerates seriously as the light power drops. To solve this problem, we developed a coherent PDH technique for weak optical signal detection, with which the signal-to-noise ratio (SNR) of demodulated PDH signal is dramatically improved. In the demonstrational experiments, a...
We have demonstrated enhancement of measurement function in Brillouin Optical Correlation Domain Reflectometry (BOCDR) by totally combining, for the first time, four performance improvement schemes, which are double modulation scheme, temporal gating scheme, intensity modulation scheme, and phase modulation scheme. We have achieved distributed strain measurement with 10.1cm spatial resolution, over...
We propose a novel method to increase sensing points of Brillouin optical correlation domain analysis (BOCDA) by utilizing degenerated four-wave-mixing (FWM) process. A sinusoidally frequency-modulated lightwave is used as the pump of FWM, and the generated idlers have a broadened frequency modulation span. The idlers produced by FWM are used in BOCDA system to increase the sensing points of BOCDA...
A novel setup for coherent-detection-assisted Brillouin optical time domain analysis (BOTDA) is proposed and demonstrated. Performance enhancement is enabled by a power-controllable local oscillator (LO) generated using single-side-band (SSB) modulation. Through employing a commercial coherent receiver and polarization diversity scheme, the Brillouin gain traces carried on a stable intermediate frequency...
We present an enhanced performance Brillouin optical time-domain analysis sensor that uses dual probes waves with optical frequency modulation and cyclic coding. The frequency modulation serves to increase the probe power that can be injected in the fiber before the onset of non-local effects and noise generated by spontaneous Brillouin scattering. This leads to higher detected signal-to-noise ratio...
A dynamic distributed Brillouin optical fiber sensor based on dual-modulation is proposed, in which the scanning of the Brillouin gain spectrum (BGS) is implemented by the combination of a single-frequency modulation and a frequency-agility modulation. The frequency of the single-frequency modulation is slightly lower than the Brillouin frequency shift of the fiber (∼10.8 GHz for silica fibers), while...
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