Fiber Bragg grating in single-multi-single mode fiber structure (FBG-in-SMS) is proposed to be used as a sensor. It could realize temperature and strain measurement simultaneously because of the different responses of the different parts of the FBG-in-SMS transmission spectrum. The temperature response is decided by the thermo-optic coefficient of the multimode fiber mainly, which is focused on especially in order to optimize its performance.
We propose a simultaneous demodulation scheme of polarization mode coupling and fiber Bragg grating in a polarization maintaining fiber based on a white light interferometer. A polarization maintaining fiber with two inscribed fiber Bragg gratings is used to demonstrate the feasibility.
A <i>C</i><sub>2</sub><i>H</i><sub>5</sub><i>OH</i> gas sensor based on a LPFG coated with the T<sub>i</sub><i>O</i><sub>2</sub> nano-film is presented.Based on LPmodes,the four-layer
model is studied the change of the effective refractive indics and the resonance wavelength of cladding modes as the
thickness of overlay increased.The elementary experimental results show that the wavelength of the LPFG loss peak is
shifted by ~1.7nm for the case of the T<sub>i</sub><i>O</i><sub>2</sub> nano-film of ~80nm in thickness when the concentration of
surrounding <i>C</i><sub>2</sub><i>H</i><sub>5</sub><i>OH</i> gas is 1000ppm. And the sensitivity is 1.7 10<sup>-3</sup> nm/ppm. The results indicate that the LPFG sensor is highly sensitive to <i>C</i><sub>2</sub><i>H</i><sub>5</sub><i>OH</i> gas and the sensing scheme is feasible.