Multi-Point Fiber-Optic Distance Sensor for Endoscopic Surgery Monitoring

We present a sub-mm diameter multi-point endoscopic sensor for simultaneous measurement of the minimum distance and orientation of the sensor head with respect to a flat tissue surface. The approach is based on frequency modulated continuous wave (FMCW) LIDAR, which is a coherent measurement method immune to stray light interference. As a swept source, a commercially available 850 nm VCSEL is wavelength modulated by self-heating to achieve a tuning range of 4.1 nm at up to 10 kHz repetition rate. The resulting interferograms are calibrated in k- space using a reference Mach-Zender interferometer. Multiple measurement beams are split at the sensor tip using a 3D nano-printed microprism array, which achieves this refractively for higher collection efficiency and a larger measurement range compared to a diffractive element. Preliminary experiments under controlled conditions validate the sensor performance.