Hybrid germanium/silica optical fibers for endoscopic delivery of erbium:YAG laser radiation

BACKGROUND AND OBJECTIVES: Endoscopic applications of the erbium (Er):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 testing of a hybrid germanium/silica fiber capable of delivering Er:YAG laser radiation through a flexible endoscope. STUDY DESIGN/MATERIALS AND METHODS: Hybrid optical fibers were assembled from 1-cm length, 550-microm core, silica fiber tips attached to either 350- or 425-microm germanium oxide "trunk" fibers. Er:YAG laser radiation (lambda = 2.94 microm) with laser pulse lengths of 70 and 220 microseconds, pulse repetition rates of 3-10 Hz, and laser output energies of up to 300 mJ was delivered through the fibers for testing. RESULTS: Maximum fiber output energies measured 180+/-30 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). CONCLUSIONS: Hybrid germanium/silica fibers represent a robust, flexible, and biocompatible method of delivering Er:YAG laser radiation during contact soft tissue ablation. However, significant improvement in the hybrid fibers will be necessary before they can be used for efficient Er:YAG laser lithotripsy.