Augmentation of Sensitivity of FBG Sensor Using Microwave Photonics and Nonlinear Effect

A simple and unique scheme of high-sensitive fiber Bragg grating (FBG) interrogation system based on microwave signal measurement utilizing the concept of microwave photonics and nonlinear four-wave mixing (FWM) is proposed. The concept of FWM process is combined with microwave photonics to enhance the sensitivity of FBG sensor. The strain-induced wavelength shift of the sensing FBG is translated to a higher wavelength shift of the corresponding higher order FWM signals on either side of FBG sensor wavelength in opposite directions. Thus, the wavelength separation between the FWM signals increases with a small increase in strain. Utilizing the FWM effect and microwave photonics technique, the microwave phase difference is altered, which is ultimately converted to a significant change in RF intensity. A novel mathematical relationship relating FWM, applied strain, and the microwave power of the proposed scheme is established. A high strain sensitivity of $36.52 ~\mu \text{V}/\mu \varepsilon $ ( $26.67 ~\mu \text{W}/\mu \varepsilon {)}$ is attained using the proposed FWM and microwave photonics technique against the initial sensitivity of $4.9 ~\mu \text{V}/\mu \varepsilon $ ( $0.48 ~\mu \text{W}/\mu \varepsilon {)}$ using only microwave photonics technique. The proposed scheme automatically compensates the temperature variations and eliminates the requirement of high dispersive component to enhance the sensitivity.