Two-dimensional Forward Optical Scanner using Glass Microlens Pre-assembled Substrate

Abstract

A miniaturized two-dimensional forward optical scanner is designed and fabricated in 2.26×1.97×0.62 mm3-size for endoscopic imaging through MEMS technology. Firstly, glass microlens pre-assembled substrate is newly proposed to address the long-time-period bottleneck in microlens-integrated devices, that is, the complicated manual assembly process. It is a silicon substrate with embedded microlens array fabricated via twice of thermal reflows at 850 ˚C. As with a silicon-on-insulator (SOI) substrate, it can be utilized as the base substrate for implementing various microlens-optical components including actuators and collimator array. As a fundamental experiment, microlenses with diameter range from 30 μm to 50 μm are successfully fabricated within less than 1% error with the designed radius of curvature. Dual-axis lateral resonator is designed with single-layer stage-in-the-stage structure and isolated electrodes via glass isolation blocks. Six isolation blocks are integrated in the inner frame structure through thermal reflow process, simultaneously with the fabrication of microlens. Glass microlens of 400 μm-diameter is successfully fabricated for forward optical scanner. The microlens have high consistent with the expected surface profile. Average roughness of the microlens surface is measured 22 nm. Dynamic characteristics are measured in atmospheric pressure. Resonant frequency of the stage in X and Y axis are 3.238 kHz and 2.198 kHz, respectively. Relevant quality factor is 168 and 69.1, respectively. More than 40 μm lateral displacements are achieved in both axes, when 21 V is applied, in resonant mode. Demonstration of beam steering has successfully proven the applicability of the proposed microlens fabrication and assembly method. Measured tilting angle of the beam in X and Y direction are approximately ±4.9˚ and ±4.7˚ at resonance, at a beam diameter of 2.0 mm.