Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.Includes bibliographical references (p. 243-260).Integrated optical circuits have the potential to lower manufacturing and operating costs and enhance the functionality of optical systems in a manner similar to what has been achieved by integrating electronic circuits. One of the basic optical elements required to enable integrated optical circuits is an integrated optical switch, analogous to transistor switches used in integrated electronic circuits. An ideal switch for integrated optical circuits would provide wavelength-selective switching. Wavelength- selective behavior is an important characteristic for devices intended for networking applications as wavelength division multiplexing (WDM) of optical signals has become the accepted standard. A major contribution of this thesis is the design, fabrication, and experimental demonstration of a wavelength-selective, integrated optical switch. This switch operates by combining a microring resonator filter with a microelectromechanical system (MEMS) device that allows the normally static ring resonator filter to be switched on and off. This represents the first demonstration of a wavelength-selective integrated optical MEMS switch. Additional contributions of this work include a new study of dielectric charging, analysis of the use of titanium nitride as structural material for MEMS, two new MEMS actuation techniques that lead to higher speed and/or lower actuation volt- age, and a feasibility analysis for wavelength tuning using a generalized version of the switch design. A model for the evolution of dielectric charging during the actuation of MEMS devices was developed to address a deviation of the experimentally fabricated devices from the theoretical predictions according to older models.(cont.) The new model predicts the experimental voltage versus displacement behavior of the wave-length selective switch accurately, and offers new insights into the physics of dielectric charging. The use of titanium nitride as a MEMS material was conceived as a solution to residual stress problems that are common in cantilever-type of actuators in general, including the wavelength-selective switch. Specific details on MEMS implementation using titanium nitride are discussed in the thesis. To address CMOS compatibility and speed challenges, two new complementary MEMS switch actuation techniques were developed. The new methods require less voltage and energy for actuation while at the same time reducing the switching time of the device to levels unachievable with current MEMS actuation techniques. Preliminary theoretical and experimental results are presented and discussed. Finally, the thesis covers the feasibility analysis of a version of the switch design where the motion is analog and, hence, can be used for tuning of resonant integrated optical structures. The analysis shows that the required positional accuracy is achievable with on-chip capacitive position sensing and feedback control, and points to a promising new direction for mechanically tunable integrated photonics. While these contributions are all outgrowths of work directed towards realizing an integrated optical circuit, they are also significant for applications such as radio- frequency (RF) MEMS switching and free-space optical MEMS devices (i.e. micro- mirror arrays for projection displays).by Gregory Nolan Nielson.Ph.D
