Interrogation of Ultra-Weak FBG Array Using Double-Pulse and Heterodyne Detection

Abstract

A high performance interrogation method for ultra-weak FBG (UWFBG) using double-pulse and heterodyne detection method is proposed. The perturbation along the UWFBG array is located quickly through the use of double-pulsed optical input waveform. Then the perturbation of fiber is quantified precisely by demodulating the phase of differential signals from a heterodyne configuration. The efficiency of measuring the perturbation is improved by more than 20 times than that of using single probe pulse. In comparison with conventional Rayleigh scattering based approach, the proposed method is supreme in signal-to-noise ratio (SNR), approximately 18 dB higher. The use of differential signaling method can effectively remove the influence from frequency drift of the laser source, making this proposed method capable of measuring low frequency vibration. In our experiment, perturbations with both sinusoidal and triangle waveform were generated to quantitatively evaluate the performance of the proposed method. The minimum detectable fiber length variation is 14.85 nm, and the sensing frequency can be as low as 0.2 Hz.

Corrosion Behavior Evaluation of Coated Steel Using Fiber Bragg Grating Sensors

“…Among all fiber optic sensors, fiber Bragg grating (FBG) sensors are well-known for its reliability, high sensitivity, and the ease in installation [38,39]. The relatively low cost of FBG sensors made large-scale application practical [38,[40][41][42][43] and the chemical inertness of the FBG sensors made them great candidates in corrosion monitoring systems. A few recent attempts to apply FBG sensors in corrosion monitoring of steel rebar in reinforced concrete had shown the possibility of FBG sensors in corrosion monitoring [36,[44][45][46][47].…”

FBG Arrays for Quasi-Distributed Sensing: A Review

“…Heterodyne detection could provide gain to the photoelectric conversion process and improve the receiving sensitivity, which results in longer sensing distance. Liu et al [55] reported a high performance interrogation system for the UWFBG array using the double-pulse and a heterodyne detection method.…”

The Sensitivity Improvement Characterization of Distributed Strain Sensors Due to Weak Fiber Bragg Gratings

“…It can achieve a fiber length variation sensitivity of 117 pm/√Hz with a distance between WFBGs equal to 99 m [ 38 ]. Investigations of vast arrays of WFBG were carried out in a laboratory: setup with 964 WFBGs for nε-scale deformation measurements [ 40 ], 90 WFBGs helped to detect 14.63 nm deformations of 50 m fiber between neighboring reflectors [ 41 ]. Parallel measurements using traditional sensors were carried out: phi-OTDR system with 660 WFBGs was compared to geophones and showed good agreement in signal shape [ 42 ].…”