Detection of chemicals using a novel fiber-optic sensor element built in fiber loop ring-resonators

We developed an evanescent field access block (EAB) sensor with an etched single mode fiber, fabricated with a core diameter of 8 ?m and reduced cladding diameter down to 11 ?m by hydrofluoric acid (HF) etching technique. Here, we describe the manufacturing process of the packaged sensor block and demonstrate that the sensor is able to detect sample absorption and refractive index (RI) changes. The sensor is tested with different chemical solutions such as ethylenediamine (EDA), dimethyl sulfoxide (DMSO) and ethanol (C2H5OH). At the same time, we fabricated (at CSIR-CGCRI) high quality optical fiber couplers having low splitting ratios (99.5:0.5%), which we used to build a 4 m long optical evanescent-wave fiber ring cavity with an embedded EAB. After a careful analysis of the fiber loop characteristics, we performed cavity ring-down measurements in order to detect the presence of liquid samples on the EAB.