Temperature-Compensated Fiber Bragg Grating Strain Sensor Based on a Two-Tap Microwave Photonic Filter

A temperature-compensated microwave photonic filter (MPF) based fiber Bragg grating (FBG) strain interrogation system is proposed and experimentally validated. This technique uses two FBGs: one acts as the reference FBG(1) to measure temperature and the other is employed as the sensing FBG(2) to detect temperature and strain. The reflected signals of two FBGs propagate in two different paths to form a two-tap MPF. Functioning as an edge filter, the amplified spontaneous emission (ASE) offers a wavelength-depended loss for FBG(1), leading to the peak-to-bottom (PBR) of the S-21 curve varying with the applied temperature. With the help of a roll of dispersion compensate fiber (DCF), the wavelength shift of FBG(2) is converted to the frequency change of the S-21 curve. Therefore, the temperature applied on FBG(1) can be recovered by recording the PBR change, and the temperature and strain applied on FBG(2) can be interrogated by tracking the frequency change. As a result, the temperature applied on FBG(2) can be eliminated by solving the cross-sensitivity equation. The experimental results show that the sensitivities vs. strain and temperature on FBG(2) are 9.288 KHz/mu epsilon, 88.258 KHz/C-o, and the sensitivity vs. temperature on FBG(1) is 0.0016 dB/C-o. The maximum measurement errors for temperature and strain are 3.8% and 5.01%, respectively.