LVD micromirror for rapid reference scanning in optical coherence tomography

A translationally-scanning mirror is always desired for the axial scanning in optical coherence tomography (OCT), but conventional scanners are bulky and have relatively slow scanning speed. This paper reports a micromirror that has the potential to achieve both the scanning speed and range required by OCT. The large piston motion of the micromirror is obtained using a large-vertical- displacemcnt (LVD) microactuator. The device is fabricated using a deep-reactive-ion-etch (DRIE) CMOS-MEMS process. A pair of electrothermal bimorph actuators is employed to achieve tilt-free mirror plate and large piston motion. A linear voltage divider with a voltage ratio of 1:2.3 between the two electrothermal actuators has been used to obtain static displacements up to 200 μm. The frequency response of this device was obtained using a laser Doppler vibrometer, and resonant peaks were observed at 1.18 and 2.62 kHz. AC signals at 50 Hz with a voltage ratio of 1:1.2 were supplied to the actuators, and the maximum dynamic piston motion was measured to be 26 μm. The decreasing amplitude over increasing frequency was caused by the heat-sink effect of the mirror plate. A phase delay between the two actuators was also observed.