Controlled-chemical etching of the cladding in optical fibers for the design of analytical sensors

•An optimized chemical method is developed for etching the cladding of an optical fiber without degrading its core.•This technique consists of attacking the cladding with a buffer solution of fluorinated salts with 3 concentrations.•Two different etching kinetics are observed corresponding to the attack of the cladding and the core.•With increased buffer concentration, the etching time is decreased.•The evolution of a transmitted signal in the fiber shows the transition zone where the cladding is removed.