Objective: To design a durable holmium laser fiber with high power, good transmission efficiency, flexible, and tight bend for holmium YAG laser lithotripsy. The new design has improved the common issues for existing Ho: YAG laser fibers including fiber fracture at bend, fiber burnt, and connector over heat.
Methods and Materials: We developed fiber modeling including ray-tracing optical simulation and CFD thermal modeling. Utilizing optical simulation, we find the over-fill and offset laser light leaking into the glass capillary was effectively absorbed by the fiber and SMA connector. The connector and fiber temperature increases were calculated using CFD thermal modeling based on the optical absorption from the ray-tracing. We introduced dimpled surfaces on the glass capillary tube to strip off the un-wanted rays to prevent the fiber from burning and the connector from overheating. We built and tested several small core (242 um) Super fiber samples for testing on different holmium laser systems (Lumenis P120H and VersaPulse® 100W). We evaluated the fiber durability under high power and tight bend conditions. The % transmission, fiber flexibility, and connector temperature were all measured under these conditions.
Results: We observed good agreement between our fiber test results and our optical and thermal modeling. These results help to illuminate the root cause of the holmium fiber failure modes. Indeed, the test results show the SuperFiber is very durable. For example, it delivered more than 1,000,000 joules under several stringent operating conditions including high power (50- 60W) in air, high frequency (25- 80 Hz), and 180° bend diameters from 16 mm down to 6 mm. One SuperFiber still survived after being tested at 60W (60Hz*1J) and 48W (80Hz*0.6J) while being bent to an 8 mm diameter for 30 minutes in air. This fiber has also showed a low transmission change after bending from 16mm down to 6 mm diameter (low bending induced loss).