The objective of this SBIR proposal is to improve the efficacy of optical lithotrypsy by developing an Er:YAG laser system for urinary stone ablation. Current treatment usually involves fragmenting the stones in the patient's body. In some cases, optical ablation is used, and the most common optical ablation method employs Ho:YAG lasers. Recent research suggests that Er:YAG lasers are better suited to the task. Using an Er:YAG laser, urinary stones can be ablated 2.4 times faster than using a Ho:YAG laser, under otherwise identical conditions. Patient time under anesthesia and operating room usage could be significantly reduced when performing lithotripsy using an Er:YAG laser system. Suitable Er:YAG lasers exist and could be modified for lithotripsy. The missing enabler is a fiber that is capable of delivering the Er:YAG light through a flexible endoscope to the urinary stone in the patient's body. While several different fibers have been tried for this application, including sapphire, chalcogenide and hollow-core metal-coated fibers, none of them have been able to fulfill the entire set of specifications for this application. OmniGuide Communications has developed a new approach for the fabrication of photonic bandgap fibers, based on technology it has exclusively licensed from MIT. In this Project (Phase I and II) OGCI will leverage its unique technology to develop a fiber for guiding Er:YAG laser beams. Phase I will focus on the development of a prototype fiber. Phase II will focus on system integration. The final goal of this Project is to bring an Er:YAG laser system for lithotripsy to market.