IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 10, NO. 3, MAY/JUNE 2004 545 Electromagnetic 2 2 MEMS Optical Switch Chang-Hyeon Ji, Youngjoo Yee, Junghoon Choi, Seong-Hyok Kim, and Jong-Uk Bu, Member, IEEE Abstract—This paper presents the design, fabrication, and measurement results of a 2 2 microelectromechanical systems optical switch. The switch comprises an electromagnet and lensed fibers assembled with a micromachined movable vertical micromirror. The optical switch utilizes the out-of-plane motion of the vertical micromirror actuated by electromagnetic force compared to the comb-driven linear actuation achieved by the electrostatic force. At a wavelength of 1550 nm, the insertion loss of 0.2–0.8 dB and the polarization-dependent loss of 0.02–0.2 dB are measured. The switching time is 1 ms. A novel method of realizing a latchable optical switch using an electromagnetic actuator is also provided and verified. The latch mechanism is based on the latchability of the electropermanent magnet instead of the mechanical one using conventional arch-shaped leaf springs. Index Terms—Electromagnetic actuation, micromirror, optical switch . I. INTRODUCTION T HE electromagnetic microactuator has been a promising candidate in the field of optical switching and other microphotonic applications. Instead of using the conventional electrostatic actuation, everal research groups have success- fully demonstrated the magnetic actuation of various types of micromirrors for such applications as optical switching and holographic data storage [1]–[8]. In the case of using the plane parallel to the substrate as the reflective surface, large angular deflection of the micromirror is required, and optical fiber integration process adds more complexity [5]–[7]. For optical switching devices, the latch capability results in a dramatic decrease in power consumption. Therefore, the latchability is one of the most important factors characterizing the overall performance of the device. Dellmann et al. used mechanical latch mechanism of arch-shaped leaf springs actu- ated by electrostatic comb-drive actuators [2]. Behin et al.used electrostatic force between the electromagnetic actuator and the vertical sidewall to obtain the latch operation [5]. Toshiyoshi et al.proposed a magnetic latch mechanism using a micromirror coated with a hard magnetic material and magnetization of a soft magnetic material core [6]. In this research, we designed, fabricated, and measured basic characteristics of a 2 2 microelectromechanical systems (MEMS) optical switch by combining an electromagnetic vertical micromirror and an electromagnet. By utilizing the vertical sidewall of the out-of-plane motion electromagnetic actuator as the reflective surface, optical switching is attained with less than 10 of angular deflection. Single-crystal silicon is used as the mechanical microstructure, including the torsional Manuscript received October 18, 2003; revised February 5, 2004. The authors are with the Devices and Materials Laboratory, LG Electronics Institute of Technology, Seoul 137-724, Korea (e-mail: maserati@lge.com). Digital Object Identifier 10.1109/JSTQE.2004.829199 Fig. 1. Schematic drawings of the 2 2 MEMS optical switch. springs and the vertical micromirror. The electroplating of soft magnetic material and the deep silicon etch process are used in the fabrication. Moreover, a new concept of a latchable switching device utilizing the electropermanent magnet is proposed and experimented. The electropermanent magnet is fabricated with a permanent magnet core, an iron yoke, and a coil. II. DESIGN A. Micromirror A schematic view of the switch is illustrated in Fig. 1. The device consists of a 2- m-wide vertical micromirror formed at one end of the out-of-plane motion electromagnetic actuator. The other end of the actuator is connected to the substrate via the torsion beams. The reflective metal (gold) is coated on the sidewall of the micromirror, which rotates up and down to alter- nate the input beam path. As depicted in Fig. 1(b), the vertical micromirror reflects the input beam and maintains the bar state while no input current is applied to the electromagnet. The tran- sition from the bar state to the cross state is implemented by the actuation of the vertical micromirror. The micromirror is actuated by the interaction between the soft magnetic material formed on top of the actuator and the vertical magnetic field in- duced by the external electromagnet [3]. B. Electromagnet The electromagnet is fabricated with an iron yoke and a self-wound coil. The outer diameter and the height of the 1077-260X/04$20.00 © 2004 IEEE