Design and fabrication of micromirrors for optical applications

The research presented in this thesis concentrates on the design and development of electrostatically actuated micromachined mirrors for fiber-optic cross-connects (OXCs), optical phased arrays and single-mirror scanners.; System design parameters, scalability limitations and loss mechanisms in beam-steering OXC switches are analyzed to determine micromirror device specifications. A large-angle model of the beam-steering OXC switch fabric shows us that network crosstalk and insertion losses limit scalability of 1-dimensional switches to ∼100 x 100, and 2-dimensional switches to ∼10000 x 10000. Results from a successful implementation of a low crosstalk, low insertion loss microelectromechanical (MEM) 2 x 2 beam-steering OXC switch using surface-micromachined mirrors are presented to demonstrate viability of micromirrors in optical switching applications. These micromirrors require large deflection angles, optically flat surfaces, high resonant frequencies and large-force stable actuators for reliable switch operation within network switching specifications.; Dual-mode Vertically Staggered Combdrive (VSC) actuators were developed to improve actuator stability and device functionality. These large-force actuators allow independent control of torsional motion and piston motion of the device. This provides both directional control and optical phase correction for optical beams in precision spatial scanning applications. Surface-micromachined proof-of-concept dual-mode micromirrors were designed and characterized to successfully demonstrate a phased array application.; Surface-micromachined mirrors were replaced with single-crystal-silicon-based micromirrors to improve surface quality, increase deflection ranges and increase device speed. A self-alignment technique was developed to fabricate these VSC actuated silicon micromirrors. This thesis presents details on design and fabrication of self-aligned micromirrors based on Deep Reactive Ion Etching (DRIE) of Silicon-On-Insulator (SOI) wafers. Analytical arguments are outlined to establish the importance of alignment accuracies in VSC actuator designs to prevent side-snap device failure modes. Device characterization results are provided to emphasize the validity of this process and to show process related advantages in device characteristics. This simple self-alignment process allows fabrication of narrow-gap, high-force actuators with good yield.; The dual-mode actuator design along with the self-aligned fabrication process are enabling technologies for new optical applications such as pulse shaping and optical filtering while significantly contributing to the improvement of micromirror designs in a wide range of conventional optical applications.