Side-polished Optical Fiber Structure for Sodium Nitrate Sensor

Side-polished optical fiber has long been used to build fiber sensors in a range of applications. In this work, we demonstrate a biochemical sensor application leading to sodium nitrate solutions enhanced by the interaction of multi-walled carbon nanotubes (MWCNTs) with evanescent field of propagating light in a side-polished optical fiber. Insertion loss of this sensor was estimated to be around 5 dB, which is quite high and close to the core index of the polished fiber. The influence of MWCNTs film, particularly on its sensitivity to sodium nitrate, was investigated by coating single drop of MWCNTs on a side-polished single mode fiber. It is observed the improvement of sensitivity with MWCNTs coated side-polished optical fiber has reached 0.125 dBm/°C near the resonant wavelength of 1550 nm. The experimental results clearly verify the present of MWCNTs on side-polished optical fiber has slightly influence the performance of the fiber. The output power values and shifting of the spectral positions were observed during the sensor tests by exposure of the sodium nitrate solutions with increasing concentration from 1 to 7%.