Optical fiber oxygen sensor utilizing a robust phase demodulator

Measuring the phase shift of luminescence is always used to achieve oxygen concentration detection. A robust phase demodulator is proposed in this paper to measure luminescent phase, overcoming common faults of bad SNR in optical fiber oxygen sensor. Its phase detection linearity of 0.99999 R-square is calibrated by a commercial lock-in amplifier (Model 7230). Modulation frequency of 16 kHz is used in the oxygen measurements and a phase resolution of 0.02° is achieved by the demodulator. Phase noises of 0.03, 0.06, 0.08 and 0.1° were measured in different oxygen levels of 0.99%, 3%, 5% and 8% in experiments. A resolution of better than ±0.005% in 0.99% O2 is realized. In addition, the demodulator which is simple but robust can be used in many luminescence phase based applications.