Ultra-thin Fiber Distance Sensors for Robotic Microsurgery

In microsurgical procedures, including retinal surgery, precise localization of the tool tip with respect to the tissue would be beneficial for safety, surgical guidance and for closed-loop control. To this end, it has been proposed that fiber-optic distance sensors be integrated into robotic surgical devices [1, 2]. For high-resolution position sensing over distances of a few millimeters, low coherence interferometry (LCI) is a particularly promising technology. LCI is the basis of Optical Coherence Tomography (OCT), an imaging technique widely used for ophthalmic diagnostics as well as for other emerging applications. An LCI based distance sensor essentially collects one depth resolved column (an A-scan) of an OCT image. This A-scan records the intensity of light reflected as a function of the distance of the reflecting tissue layers from the probe. Hence, by identifying the first reflection corresponding to the surface of the tissue, the distance to the tissue is obtained. The tip of the probe requires only a single lens, which can be fabricated directly onto the tip of the fiber, resulting in a probe that can be as narrow as 125 μm in its diameter and flexible along its entire length, suitable for integration into highly miniaturized tools. In this paper, we describe the fabrication of lensed LCI fiber distance sensing probes and demonstrate their ability to track distance to the surface of the tissue.