RT info:eu-repo/semantics/preprint T1 Chirped-pulse Phase-sensitive Reflectometer Assisted by First Order Raman Amplification A1 Pastor Graells, Juan A1 García Ruiz, Andrés A1 Martín López, Sonia A1 González Herráez, Miguel A1 Nuño del Campo, Javier A1 Fernández Ruiz, María del Rosario A1 Fidalgo Martins, Hugo K1 Acoustic sensor K1 Chirp modulation K1 Distributed sensor K1 Rayleigh scattering K1 Raman amplification K1 Electrónica K1 Electronics AB The use of linearly chirped probe pulses in phase sensitive-(Phi)OTDR technology has been recently demonstrated to allow for high-resolution, quantitative and dynamic temperature or strain variation measurements in a simple and very robust manner. This new sensing technology, known as chirped-pulse PhiOTDR, had a maximum reported sensing range of 11 km. In this paper, a 75 km sensing range with 10 m spatial resolution is demonstrated by using bidirectional first order Raman amplification. The system is capable of performing truly linear, single-shot measurements of strain perturbations with an update rate of 1 kHz and 1 nepsilon resolution. The time-domain trace of the sensor exhibits a signal to noise ratio (SNR) in the worst point of >3 dB, allowing to monitor vibrations up to 500 Hz with remarkable accuracy. To demonstrate the capabilities of the proposed system, we apply 20 dB (with only 300 ms analysis window and no post-processing) and no evidence of nonlinearity in the acoustic response. The optical nonlinear effects that the probe pulse could suffer along the sensing fiber are thoroughly studied, paying special attention to potential distortions of the pulse shape, particularly in its instantaneous frequency profile. Our analysis reveals that, for proper values of peak power, the pulse does not suffer any major distortion and therefore the system performance is not compromised. SN 0733-8724 YR 2017 FD 2017-09-26 LK http://hdl.handle.net/10017/30640 UL http://hdl.handle.net/10017/30640 LA eng NO European Commission DS MINDS@UW RD 29-mar-2024