Phase-shifted Fiber Bragg Grating Based Humidity Sensor
In recent years, fiber Bragg grating sensors have been widely used because of their unique advantages, such as its multiplexing capability, remote monitoring capability, small size and immunity to electromagnetic. However, several challenges still need to be considered, one of which is the resolution and accuracy of measurements. In this thesis, a humidity fiber optic sensor based on phase-shifted (PS) fiber Bragg gratings (FBG) is demonstrated.
Compared to the standard fiber Bragg gratings, the peak of the PS-FBG slips into 2 peaks and forms a sharp peak in the middle. As a result, the resolution of the measurement will be higher. The sensors used in the experiments were fabricated by coating the PS-FBG surface with a moisture sensitive polyimide and is based on the strain effect caused by the swelling of the coating after moisture absorption. The same trend as standard fiber Bragg Grating sensor but with higher measurement resolution can be achieved in different humidity and temperature environments. This thesis presents the simulation and measurement results with suitability, including sensitivity and response time, of the phase-shifted FBG sensor approach for humidity sensing, as compared to the standard fiber Bragg Grating sensors. Besides, stability and hysteresis are also discussed.