Electrothermal micromirror with dual-reflective surfaces for circumferential scanning endoscopic imaging

We report the design, fabrication, and measurements of a dual-reflective, single-crystal silicon-based micromirror that can perform circumferential scanning for endoscopic optical coherence tomography (EOCT). Full 360-deg optical scan angle (OSA) can be achieved by using a dual-reflective mirror with ±45-deg (or 90-deg) mechanical scan angle (MSA), where each reflective mirror surface contributes a 180-deg optical scanning. A novel surface- and bulk-combined micromachining process based on silicon on insulator (SOI) wafers is developed for fabricating the dual-reflective micromirror. The mirror flatness is maintained by the single-crystal-silicon device layer of SOI wafers, and aluminum is coated on both sides for reflection. A fabricated device demonstrated about half circumferential scanning range at resonance of 425 Hz. Other measured data include the radii of curvature, -129 mm (front surface) and 132 mm (back surface), and the reflectance, 86.3% (front surface) and 84.2% (back surface). This micromirror has the potential to realize full-circumferential-scanning EOCT imaging.