Electrostatic MEMS resonating micro-polygonal scanner for circumferential endoscopic bio-imaging

Abstract

An electrostatically-driven microelectromechanical systems (MEMS) based pyramidal-polygonal micro-scanner is developed for circumferential-scanning endoscopic probes. In this paper, an endoscopic optical coherence tomography (OCT) probe is proposed, which utilizes multiple parallel incident light beams to drastically reduce the required mechanical rotation angle to achieve near 360-degree circumferential scanning. Manual assembly is employed to construct this micro scanner, which combines a silicon micromachined MEMS actuator with four sets of electrostatic comb-drives and a polymer-based pyramidal-polygonal micro-reflector. The pyramidal-polygonal micro-reflector is developed using a combination of high-precision diamond turning and soft lithography molding technologies. The measured average surface roughness and root-mean-square roughness of the diamond turned mold are 7.02 nm and 9.02 nm respectively, and those of the PDMS casted polygon micro-reflector with an Au coating are 48.95 nm and 61.90 nm respectively. Since near-infrared light sources with wavelengths ranging from 930 nm to 1550 nm are typically utilized for OCT applications, the surface roughness of the polygon reflector is better than λ/10 of the operating wavelength indicating that its quality meets the requirement of the OCT bio-imaging applications. An overall optical scan angle of near-360 degrees is demonstrated experimentally at a resonant frequency of 180 Hz with 80 Vpp ac driving voltage. The proposed MEMS scanner offers an alternative solution for circumferential scanning in endoscopic OCT probes owing to its advantages of compact design, fast scanning speed and low operational power consumption.