An open and low-cost optical-fiber measurement system for the optical detection of oxygen using a multifrequency phase-resolved method

In this paper we present an open and low-cost optical-fiber measurement system for the optical detection of oxygen. A multifrequency phase-resolved method is proposed as the measurement technique in order to evaluate the oxygen-concentration-dependent phase-shift (or luminescence lifetime). Such evaluation is based on the operating principles of quadrature detection (also known as I/Q method), which may be entirely performed by digital signal processing. Theoretical aspects of the proposed methodology as well as the design and construction of the measurement system are discussed in this work. The system performance is assessed by characterization and evaluation of an oxygen-sensitive film (an oxygen-sensitive luminescent dye [Pt(II) meso-Tetra(pentafluorophenyl)porphine (PtTFPP)] immobilized into an oxygen-permeable polymeric matrix). These results are compared successfully with reference measurements obtained on the same sample using a conventional experimental setup based on a commercial lock-in amplifier. In this case, a measurement accuracy of <0.2 kPa oxygen partial pressure has been obtained over the measurement range of 0–20 kPa, for short periods of continuous measurement (<2 min), and at a room temperature of 21 °C.