Scanning OCT endoscope with 2-axis magnetic micromirror

Abstract

Micromirrors used to steer optical beams at the tip of an endoscope are an active area of research. MEMS mirrors with various actuation mechanisms have been reported including rotating micromotors, parallel plate electrostatic drive, electrothermal and electrostatic comb drive. This paper presents a two-axis magnetically actuated micromirror designed for an OCT (Optical Coherence Tomography) endoscope. Magnetic actuation allows large angular deflections at low voltage (1-3 V), a significant advantage for patient safety relative to the high voltages used for electrostatic mirrors. Actuation is accomplished with small coils in proximity to the moving mirror, which contains a small permanent magnet. The endoscope scan engine is contained in a 2.8 mm ID plastic tube. The MEMS scan mirror was fabricated by a simple process using an SOI wafer and only 2 photo-steps. The mirror is supported by silicon springs on both axes, and can scan to +/- 20 degrees mechanical on both axes. Both time domain and spectral domain OCT have been used to take cross-sectional tissue images. By operating the 2-axis mirror in a raster scan, a sequence of cross-sections is taken to form a 3-D image. Details of the endoscope design, MEMS fabrication, and sample OCT images are presented.