Flow cell for strain- and temperature-compensated refractive index measurements by means of cascaded optical fibre long period and Bragg gratings

An optical fibre sensing system based on a hybrid cascaded long period grating (LPG) andfibre Bragg grating configuration and a thermo-stabilized flow cell for refractometricmeasurements is proposed. The system makes it possible to measure, and thus to cancel, theLPG cross-sensitivities to strain, temperature and fibre bending. The experimental resultsshow that the proposed system provides satisfactory performances as far as the refractive indexsensitivity and resolution are concerned. The maximum sensor sensitivity and resolution are3120 nm/RIU and 2 × 10-5 RIU, respectively. The whole system with its flow cell and thegratings fabrication are extensively described, together with the acquisition and dataprocessing. The stability of the sensor for several hours was also tested. We believe that theproposed system can be successfully used for label-free chemical/biochemical sensing.