Interferometric, fiber-based, real-time distance sensor for endoscopic applications

Abstract

A miniaturized non-contact laser ranging sensor for endoscopic inspection and surgery tools is demonstrated. The sensor can measure the absolute distance between the endoscopic tool and the tissue in the 0-20 mm range with an axial resolution of 5 µm based on frequency-modulated continuous wave interferometry. As a tunable laser source, a commercially available 850 nm VCSEL is wavelength-modulated via self-heating, achieving a tuning range of 2.5 nm at 2.9 kHz repetition rate. Once coupled into a single-mode fiber, the laser light is projected onto the tissue using a loosely-focusing, Φ350 μm GRIN lens located at the distal end of the probe. The spectrum of the light collected by the same GRIN lens on the return path, which encodes the tissue distance in a well-defined modulation frequency, is detected by a silicon photodetector. Due to its low-cost, small diameter, flexibility and simplicity this sensor can be integrated monolithically into an endoscope or employed as a stand-alone sensor operating through the working channel.