Three-beam Interferometric Based Hydrogen Sensors

Hydrogen is a new energy sources of abundant, high calorific value, non-polluting,and it is an important way to solve the short of energy shortage in China. Liquidhydrogen has become one of the main fuel for the space shuttle and the launch vehicle,also plays an important role in many areas of new energy vehicles, petrochemical, foodprocessing, defense and military. But there are security risks about the attendant,hydrogen production, storage, transport and use of hydrogen.In this paper, a three-beam interferometric fiber-optic hydrogen sensor based on thecorrosion graded-index multimode fiber has been studied:（1） The first, we fabricate more than210sensors to study. Though the analysis ofthe maximum fringe contrast and the spot size, we find that, with the increase of theGI-MMF length, the maximum fringe contrast of reflect spectra and the spot sizechange periodically. The period of the spot size is about520μm, which is matched withthe result of Rsoft simulation, while the period the maximum fringe contrast is half ofit.（2） The second, we study the characteristics of the three-beam interferometerfiber-optic sensor to detect of liquid refractive index. By single sensor tests andmultiplexed experiments, we find that the spectrum of such a sensor drift as thetemperature rises, and the relationship between them meets a quadratic function, thevalue of curve fitting reached0.99977, and the wavelength drift reached5180pm from14°C to500°C. But by the FFT, we find that the peak value of the correspondingsensor did not change significantly.（3） The third, we study multiplexing characteristics of the sensors as refractiveindex sensors. The refractive index multiplexed experiment of four sensors shows thatsuch a sensor can satisfy the multiplexing of at least10sensors, and the peak value ofFFT transform spectrum change significantly. The refractive index and the peak value ofthe FFT spectrum is fitted linear:V0.18578-0.14036n0, with a refractive indexcoefficient of about-0.14036/RIU, and the value of curve fitting is-0.99634. While wedo the temperature test below100°C, we find that the FFT transform spectra peak of the selected sensor don’t change significantly, the change of the peak value is0.00068,the sensitivity is8.5×10^-6/°C. Thus the temperature cross sensitivity is6.0×10^-5RIU/°C,so that the sensor can be considered temperature-insensitive.（4） At last, we plate with a hydrogen sensitive film sensor. The sensors coated withPd and Pd-Y are both sensitive to hydrogen, it maximum fringe contrast is decreasing asthe increase of hydrogen concentration, but we can see from the experiment, the sensorcoated with Pd-Y has less response time and could use longer. From the test oftemperature, if the temperature changes in a limited range, the maximum fringe contrastof sensor almost remain the same.