Two-dimensional electrothermal MEMS fiber scanner for forward-viewing endomicroscopic applications

Abstract

Optical endomicroscopy holds a great promise for clinical applications such as optical biopsy or im-age guided surgery. Forward-viewing catheters have been interested in endomicroscopic applications, because forward-viewing imaging can provide a same viewing direction as conventional endoscope through the acces-sory channel. There are various catheter for forward-viewing catheter, and resonant fiber scanners using a piezoelectric tube (PZT) actuator have been widely used for forward-viewing imaging due to simple, compact and robust packaging. Resonant PZT fiber scanner also gives large field-of-view (FOV) with low operation voltage. Nevertheless, it has limits for miniaturization and high price. In this research, we report a novel two dimensional electrothermal MEMS fiber scanner for forward-viewing endomicroscopy. The assembled MEMS fiber scanner consists of double hot arm structures, cold arm structure, and a directly mounted 125 μm single mode optical fiber. Lateral motion is induced by thermal expansion of hot arm structures by Joule heating, and vertical motion is induced by bimorph structures by heated MEMS fiber scanner and the mounted single mode fiber. MEMS fiber scanner is operated at resonance frequency to amplify the scanning amplitude of the op-tical fiber at low operating voltage. The Top silicon cantilever of the MEMS fiber scanner has different spring constant in x and y directions, especially, spring constants of the cantilever in x-direction is stiffer than spring constant of the cantilever in y-direction. It makes resonance frequencies separation of the mounted optical fiber with x, y direction, and it allows two-dimensional scanning with voltage which contains x and y reso-nance frequencies. Lissajous pattern was successfully demonstrated by using the MEMS fiber scanner within 18 V. The proposed MEMS fiber scanner was fabricated by using deep reactive ion etching (DRIE) process on a heavily doped 6 inch silicon SOI wafer with good electrical conductivity, and its physical dimensions are smaller than conventional quadratic PZT tube. This MEMS fiber scanner can provide a new direction for compact and cost-effective forward-viewing endomicroscopic applications.