Fiber optic chemical sensors for water testing by using fiber loop ringdown spectroscopy technique

Real-time response, low cost, sensitive and easy setup fiber optic chemical sensors were fabricated by etching a part of single mode fiber in hydrofluoric (HF) acid solution and tested in different water samples such as tap water, DI water, salty and sugar water with different concentrations to record ringdown time (RDT) differences between media due to refractive index differences by employing the fiber loop ringdown (FLRD) spectroscopy technique. Baseline stability of 0.63% and the minimum detectable RDT of 5.05 mu s for this kind of fiber optic chemical sensors were obtained. Fabricated sensors were coated with N,N-Diethyl-p-phenylenediamine for the first time and tested in several water solutions. Afterwards, the sensors were immersed into salty and sugar water solutions in different concentrations. The results showed that this kind of FLRDS fiber optic chemical sensors can be applicable to trace chemicals in water solutions. Moreover, fiber optic sensors can be specially modified to trace specifically any target chemicals in solutions for the special purpose and the early detection.