Fiber sensors based on fiber gratings

In this paper, we present two different types of pressure sensors including a high-sensitivity lateral pressure sensor and a temperature-independent differential pressure sensor by using fiber Bragg gratings to be encapsulated in a polymer-half-filled metal cylinder. The schematic diagram of lateral pressure sensor is shown in Fig.1 which operating mechanism is based on transferring radial pressure into axial strain to induce Bragg wavelength shift with the sensitivity of 2.2×10^-2Mpa^-1, which is 10900 times higher than that of using a bare FBG.. For being used in water-level measurement, a sensitivity of 1.526×10^-5 cm^-1 is experimentally obtained with a very nice linear relationship between the center-wavelength shift and water level. For a temperature-independent differential pressure sensor, by extending the previous packaged-structure design, a temperature independent differential pressure sensor as shown in Fig.2 is based on two fiber Bragg gratings with the sensitivity of the differential pressure of 5.27×10^-1 Mpa^-1. This device can also be used measuring differential pressure and temperature simultaneously for applying in liquid level, liquid density or specific gravity detection.