Spectral Properties of the Signal in Phase-Sensitive Optical Time-Domain Reflectometry With Direct Detection

Abstract

The spectral properties of the Rayleigh backscattered traces measured by a phase-sensitive optical time-domain reflectometer (φOTDR) with direct detection are theoretically and experimentally analyzed. The spectrum of the measured φOTDR signal is found to be strictly dependent on the spectral shape of the probing optical pulse. Furthermore, the visibility, spatial resolution, fading rate, and correlation spectrum of the traces are analyzed using different detection bandwidths. Results point out that the quality of φOTDR traces and target spatial resolution are secured only if the electrical bandwidth of the photodetector is broad enough to cover at least 80% of the total power contained in the electrical spectral density function of the measured trace. This means that in the case of using direct detection of the Rayleigh backscattered light induced by rectangular-shaped optical pulses, the minimum bandwidth required for a proper detection of the traces is equal to the reciprocal of the pulse temporal width (which is larger than the pulse spectral width). Although the theoretical analysis and numerical simulations are here experimentally validated for rectangular and sinc-shaped optical pulses, the results and methodology presented in this article can be applied to optimize the direct-detection bandwidth of φOTDR sensors using any optical pulse shape.

Dual functionality of wavelength scanning coherent optical time domain reflectometer

“…About 7 m fiber of the second fiber section is wrapped around a PZT tube and subject to a sinusoid vibration at 2 Hz. The bandwidth of the photodetector is 125 MHz, enough to guarantee the spatial resolution of the sensing system 8 . The analog signal from the photodetector is sampled at a rate of 250 MS/s and the digitized signal is processed by a computer.…”

Phase Error Evaluation via Differentiation and Cross-Multiplication Demodulation in Phase-Sensitive Optical Time-Domain Reflectometry

“…Finally, the electrical signal was digitized and processed with the DCM algorithm and I/Q demodulation scheme using a personal computer. The width of the optical pulse was set to 10 ns, and the 3 dB width of the backscattered light was in a frequency domain of about 60 MHz [24]. The bandwidth of the photodetectors was 125 MHz, which is larger than the 3 dB width of the spectrum, so the required spatial resolution could be achieved [24].…”

Distributed Acoustic Sensing to Monitor Ground Motion/Movement at Multi-Frequency Bands

“…One arm of the IMZI is 2 m longer than the other, determining the gauge length. The bandwidth of the photodetector is 125 MHz, which is large enough to faithfully acquire the backscattered light [30]. The analog signal from the photodetectors is digitalized at a rate of 250 MS/s.…”