Fabry-Pérot based refractive index optical fiber sensor for measurement of oxygen concentration levels in hypoxic tumors during radiotherapy treatment

An optical fiber sensor based on Fabry-Pérot interferometer to measure the refractive index changes due to oxygenation level changes in hypoxic tumors for radiotherapy treatments is proposed. The sensors have an outer diameter of 220μm with a 20-30μm length air-cavity and a 30μm thickness end cap located at the tip of the sensor. The sensors are used to measure the phase change in the received optical spectrum when there is a change in refractive index using a Fast Fourier Transform based analysis method. The refractive index change is measured in order to determine the oxygenation level in hypoxic tumors. In this paper, different concentrations of iso-propanol solution are prepared to produce refractive index values between 1.3438 and 1.3655 in order to mimic the refractive index of hemoglobin. The sensors are coated with a 100 nm thick gold layer and a comparison is made with non-coated sensors. The coated sensors have a resolution in order of 10^-3 RIU.