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/μϵ, 88.258 KHz/°C, and the sensitivity vs. temperature on FBG
₁
is 0.0016 dB/°C. The maximum measurement errors for temperature and strain are 3.8% and 5.01%, respectively.