We demonstrated that a high-sensitivity fiber sensor based on a superstructure fiber grating (SFG) can simultaneously measure the pressure and temperature by encapsulating the grating in a polymer-half-filled metal cylinder, in which there are two openings on opposite sides of the wall filled with the polymer to sense the pressure. The mechanism of sensing pressure is to transfer the pressure into the axial extended-strain. According to the optical characteristics of an SFG composed of a fiber Bragg grating (FBG) and long period grating (LPG), the various pressure and temperature will cause the variation of the center-wavelength and reflection simultaneously. Thus, the sensor can be used for the measurement both of the pressure and temperature. The pressure sensitivity of 2.28×10-2MPa-1 and the temperature sensitivity both of 0.015nm/°C and -0.143dB/°C are obtained.
The induced cladding-mode performance in a tilted superstructure fiber grating (SFG) is first experimentally demonstrated. As a slanted SFG is heated to shift wide-band loss dips for obtaining the multi-narrow-band reflection moved at various positions of the loss dip, the strength and central wavelength of the induced cladding-mode depend on the loss depth and the positive/negative sides of the dip, respectively. The characteristics may provide the third physical-parameter measurements in a simultaneous multi-parameters fiber sensor.
An all-fiber pressure sensor based on a fiber Bragg grating with the pressure sensitivity of 2.2x10-2 MPa-1 has been demonstrated. The physical configuration includes a FBG encapsulated in a polymer-half-filled metal cylinder with its end bonded to the central of a round plate attached to the surface of polymer, and the Young’s modulus of the polymer is four orders lower than FBG. This cylinder has two opening on opposite side of the wall at the polymer part. Under the pressure environment, the polymer can be pressurized along one radial direction only, and responds an axial force acting on the round plate, producing an axial strain on FBG. With a nice linearity, this sensor should be applied potentially for the measurement of mediums pressure, liquid level and depth underwater.