Smart optical fiber probes for precise tissue treatment

Optical features of a novel technique for fiber-optic-based laser delivery into a precise tissue area are investigated. As a key optical element, the technique includes a single delivery fiber with a specially angle shaped tip. Because of the frustrated-total-internal-reflectance caused by the refractive-index change of the surrounding medium, the angled fiber tip acts as a smart, tissue-activated probe. It provides a safe way for laser delivery that includes only two states of tissue illumination: (1) off-state (no tissue illumination), when the fiber tip is out of the tissue area and the laser emission is backreflected due to total-internal-reflection; and (2) on-state (maximum tissue illumination), when the fiber tip is on the absorbing tissue area and becomes "transparent" because of the frustrated-total-internal-reflectance and the laser energy is coupled into the absorber. Here, optical properties of tissue-activated fiber probes used for precise laser delivery are investigated both experimentally and theoretically by analyzing the backreflectance signal power. Optical fibers with various geometrical parameters are used and a spatial resolution of 2 mum is achieved when the fiber tip is moved toward the absorption tissue surface. The results confirm the system potential for on-the-spot laser delivery applicable to precise laser treatment, tissue diagnostics, and micro-scale surgical procedures.