Optical fiber evanescent wave sensor for oxygen deficiency detection

We have designed and developed an optical fiber based evanescent sensor for oxygen deficiency detection. The sensing dye, methylene blue, was immobilized in the substitutional cladding using sol–gel process. The sensing properties of the optical sensor to gaseous oxygen at room temperature were characterized. The response of the sensor is logarithmic linear within the oxygen concentration range between 0.6% and 20.9%. This newly developed oxygen deficiency sensor has significant advantages over the currently available oxygen sensors such as fast response and recovery, good reversibility and repeatability, and minimal temperature influence. The change of temperature from 21 to 35 °C seems not affecting the system sensing properties such as response and recovery time. Particularly, even though the spectrum intensities at the fixed wavelength 636 nm shifted with the temperature increase from 21 to 35 °C, the degree of the relative evanescent absorbance originated from oxygen kept unchanged. Compared with the optical oxygen sensors based on dynamic luminescence quenching, the optical fiber oxygen sensor we developed here is based on the evanescent field absorption and should be more straightforwardly responding to the change of oxygen concentrations.