Assembly and testing of germanium/silica optical fibers for flexible endoscopic delivery of erbium:YAG laser radiation

Abstract

Endoscopic applications of the Erbium:YAG laser have been limited due to the lack of an optical fiber delivery system that is robust, flexible, and biocompatible. This study reports the assembly and testing of hybrid optical fibers consisting of 1-cm-length, 550-micron-core, silica fiber tips attached to either 350-micron or 425-micron germanium oxide “trunk” fibers. Er:YAG laser radiation with a wavelength of 2.94 microns, pulse lengths of 70 and 220 microseconds, repetition rates of 3-10 Hz, and laser output energies of up to 300 mJ was delivered through the fibers for testing. Maximum fiber output energies measured 180 ± 30 mJ and 82 ± 20 mJ (n=10) under straight and tight bending configurations, respectively, before fiber interface damage occurred. By comparison, the damage threshold for the germanium fibers without silica tips during contact soft tissue ablation was only 9 mJ (n=3). Studies using the hybrid fibers for lithotripsy also resulted in fiber damage thresholds (55-114 mJ) above the stone ablation threshold (15-23 mJ). Hybrid germanium / silica fibers represent a robust, flexible, and biocompatible method of delivering Er:YAG laser radiation during contact soft tissue ablation. Significant improvement in the hybrid fibers will be necessary before their use in Er:YAG laser lithotripsy.