Chemical Wet Etching of an Optical Fiber Using a Hydrogen Fluoride-Free Solution for a Saturable Absorber Based on the Evanescent Field Interaction

We propose a chemical wet etching technique that does not make use of toxic Hydrofluoric solution to produce cladding-etched optical fiber intended for use as a platform for a fiberized saturable absorber. The wet etching technique is based on the use of a mixed solution of NH4F and (NH4)2SO4, which is not toxic, and a small, specially-devised etching cradle to achieve precise control of the etched fiber length. A fiberized saturable absorber was implemented by depositing the graphene oxide particles on top of the residual cladding for our cladding-etched fiber by using the drop & dry method. The saturable absorber was incorporated into an erbium-doped fiber ring cavity to test its suitability as a mode-locker with a modulation depth larger than 4.3%. Femtosecond pulses with a temporal width of ~615 fs were readily obtained at a repetition rate of ~17.09 MHz. The saturable absorption and laser performance of our saturable absorber were compared to those of an absorber on a core-etched fiber platform prepared through the formation of microdroplets of HF and surface tension-driven flow, as in [57].