THERMO-REFRACTOMETER SENSOR BASED ON A SEMI-DISTRIBUTED CAVITY USING CHIRPED FIBER BRAGG GRATINGS

Abstract

Thermo-refractometer is a sensing technology that enables measurements of Refractive Index (RI) and temperature that has found applications in various scientific and industrial areas. Determining RI values allows the detection of concentration of specific analytes, crack location in buildings, or assessment of power transformer’s operating conditions. Meanwhile, the temperature detection can compensate for undesired thermal effects from the environment or the medium in which the sensor is used which in turn can affect the determination of accurate RI readings. The work presented in this thesis is carried out to develop and fabricate an efficient thermorefractometer with simple design and fabrication made of a single Chirped Fiber Bragg Grating (CFBG). Three sensors are fabricated by creating a semi-distributed cavity on the grating using fiber cleaver along the grating. The sensors are first calibrated for temperature by measuring the spectral response in water with increasing temperature from 25 ºC to 80 ºC. RI calibration is conducted in sucrose solutions with concentrations from 10% to 15%. Sensitivities to temperature and RI are encoded in the wavelength shift of the main-band and power change of the sidelobes’ spectrum, respectively. The sensor with highest performance demonstrates a temperature sensitivity of 11.03 pm/°C and RI sensitivity of -230.3 dB/RIU.