MEMS based Two dimensional lens scanning module for forward endoscopic imaging

Abstract

This research presents a MEMS based two-dimensional lens scanning module for forward endoscopic imaging. Two-dimensional forward scanning with high resolution is demonstrated implementing MEMS scannersof an x-scanner (in-plane comb drive) and y-scanner (vertical comb drive) together with a millimeter aspheric glass lens. A light delivered from an optical fiber is coupled with a collimating lens and scanned with two scanning lenses, which has diameter of 1mm. Then it focuses to the image plan using an objective lens. To identify the feasibility of high resolution, optical simulations with a commercialized ray tracing program $ASAP^{TM}$ for beam divergence are performed. Simulation results present no significant change of the beam spot size until the light goes through inside of the ideal optical surface region of the objective lens. This represents about 3 degree of the scanning angle with an objective lens, which has 2mm diameter. The operation of each scanning lens is achieved by electrostatic MEMS actuators integrated on a chip with specially designed lens holders to grab lenses. Each scanner is designed to have maximum scan length of $\pm$40$\mum$ with considerations of simulation results. Designed two-dimensional MEMS scanners are integrated to a micro optical bench with a special groove for optical fiber, considering both optical and mechanical requirements. Micro optical bench is fabricated by standard SOI (Silicon on Insulator) wafer process, and then released with vapor phase HF gases so that the batch process at a wafer level is achieved. Fabricated device is separated from wafer using specially designed fused tether technique due to the complex geometry of the micro optical bench. Then, the device eventually packaged on the Printed Circuit Board and glass lenses are mounted using UV curable epoxy resins. Resonant frequency of the device is 2.1kHz before the lens mounting, however, decreases to 276.5Hz due to the heavy mass of the lens whi...