The current study aimed to develop surface modifications of a capillary ferrule to avoid misalignment-related thermal damage in the fiber connector and the eventual fiber failure during high-power laser lithotripsy. Numerical analysis showed that the modified surface diffused leaking rays (high-order modes) from the misalignment. The light diffusion subsequently confined absorption-induced heat accumulation to the stainless steel connector tip (used as heat sink). Light-offset experiments validated minimal transient and steady-state heating of the modified connector surface with no thermal damage in the connector due to diffusive optical-thermal transport. The ferrule surface modifications may prevent fiber failure during the lithotripsy.