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ABSTRACT: Subpeaks in the Brillouin loss spectra of distributed fiber-optic sensors were observed for what is believed to be the first time and studied. We discovered that the Fourier spectrum of the pulsed signal and the off-resonance oscillation both contributed to subpeaks. The off-resonance oscillation at frequency /v - vB/ is the oscillation in the Brillouin time domain when beat frequency v of the two counterpropagating laser beams does not match local Brillouin frequency vB. This study is important in differentiating the subpeaks from actual strain-temperature peaks.
Optics Letters 06/2005; 30(10):1099-101. · 3.40 Impact Factor
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17th International Conference on Optical Fibre Sensors; 05/2005
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ABSTRACT: Because of the power imbalance between the two arms of an interferometer in an electro-optic modulator (EOM), the output of the EOM is combined amplitude modulation (AM) and phase modulation (PM) for the probe signal consisting of the pulse and the dc component. Because of this PM, the Brillouin gain-loss spectrum becomes asymmetric. The central Brillouin frequency is shifted from that of an AM pulse. The maximum extinction ratio of the EOM is limited to approximately 29 dB for a power-splitting ratio of 51% to 49%. The asymmetric property induced by PM is not pulse shape dependent; for both Gaussian- and super-Gaussian-shaped pulses the Brillouin loss spectrum is symmetric for AM and asymmetric for combined AM and PM (power imbalance).
Optics Letters 05/2005; 30(8):827-9. · 3.40 Impact Factor
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ABSTRACT: We provide a theoretical explanation for a coherent probe-pump-based Brillouin sensor system that achieves centimeter spatial resolution with high-frequency resolution. It was recently discovered that, when a combination of cw and pulsed light (the probe beam) interacts with a cw laser (the pump beam), centimeter spatial resolution with high-frequency resolution can be achieved even though the probe-pulse duration is 1.5 ns [Opt. Lett. 29, 1485 (2004)]. Our study reveals that the coherent portion inside the pulse length of these two interactions caused by the same phase is responsible for this behavior. It allows us to detect 1.5-cm outer-layer cracks on an optical ground-wire cable.
Optics Letters 03/2005; 30(4):370-2. · 3.40 Impact Factor
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Photonics North 2004: Photonic Applications in Telecommunications, Sensors, Software, and Lasers; 11/2004
