A Scanning Micro-Mirror with an Adjustable Focal Length for Endoscope Applications

In this work, we report design, fabrication and characterization of a 3-D scanning micro-mirror device that combines 2-D beam scanning with focus control in the same device using micro-electro-mechanical-systems (MEMS) technology. The micro-mirror consists of a biaxial gimbal structure for 2-D beam scanning, and a deformable mirror membrane surface to achieve focus control. The micro-mirror with 800 micrometer diameter is designed to be sufficiently compact and efficient so that it can be incorporated into an endoscopic imaging probe. Using the focus-tracking MEMS scanning mirror, we achieved an optical scanning range of >16 degrees with <;40 V actuation voltage at resonance and a tunable focal length between infinity and 25 mm with <;100 V applied bias. We have also obtained imaging results using a micro-mirror with beam scanning-only function in both time-domain and spectral-domain optical coherence tomography systems.