1038 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 16, NO. 4, APRIL 2004 Carrier Injection-Based Digital Optical Switch With Reconfigurable Output Waveguide Arms S. Abdalla, S. Ng, P. Barrios, D. Celo, A. Delâge, S. El-Mougy, I. Golub, J.-J. He, S. Janz, R. McKinnon, P. Poole, S. Raymond, T. J. Smy, and B. Syrett Abstract—A compact 1 2 waveguide digital optical switch (DOS) with electrically reconfigurable output waveguide arms is proposed and demonstrated. Calculations show that this switch can be much shorter and consume less power than previous DOS designs. An InGaAsP–InP waveguide device based on carrier in- jection was designed and fabricated and exhibits a 20-dB switching contrast ratio. The device length is 1400 m. Index Terms—Integrated optoelectronics, optical switching, op- tical waveguide components. I. INTRODUCTION F AST OPTICAL switching is a cornerstone in future optical networks and other telecommunications applica- tions. Optical switches with a digital response remain in the switched state at any bias above a given threshold. Compared to switches that rely on interference or absorption, such digital optical switches (DOSs) are of particular interest since they are wavelength independent and have relaxed bias tolerances. It is, therefore, important to find improved DOS designs and to optimize their performance. Moreover, the integration of DOS in switching networks and with optical add–drop multiplexers for optical cross-connects also dictates the requirement for miniaturization of these components. Previous DOS devices based on adiabatic modal evolution are long and require high driving voltages. While improvements can be made by shaping the branches [1], [2], tapering elec- trodes and waveguides [3], and using double-etched waveguides with variable height and width [4], low crosstalk and compact- ness are difficult to achieve simultaneously. For devices to have better than 20-dB crosstalk, the electrodes had to be several mil- limeters long and the total device length was on the order of 1 cm [3], [4]. In addition to high power consumption, the ca- pacitance of such long electrodes can limit the switching speed even though the switching mechanism itself can be intrinsically fast. DOS designs employing total internal reflection (TIR) have larger branching angles and shorter electrodes. However, even with improvements such as bow-tie electrodes [5], the smallest Manuscript received November 3, 2003. This work was supported in part by the National Capital Institute of Telecommunications (NCIT) under Research Project “High Speed Reconfigurable Optical Router and its Application to Op- tical Switching in IP Networks.” S. Abdalla, S. Ng, D. Cello, S. El-Mougy, T. J. Smy, and B. Syrett are with the Department of Electronics, Carleton University, Ottawa, ON K1S 5B6, Canada. P. Barrios, A. Delâge, I. Golub, J.-J. He, S. Janz, R. McKinnon, P. Poole, and S. Raymond are with the Institute for Microstructural Sciences, National Research Council, Ottawa, ON K1A 0R6, Canada (e-mail: Ilya.Golub@nrc- cnrc.gc.ca). Digital Object Identifier 10.1109/LPT.2004.824984 Fig. 1. (a) Configuration of the DOS Y-junction switch, and (b) effective waveguide configuration when the index under the biased electrode matches the refractive index of the surrounding slab region. The shaded areas indicate high effective index, while the clear areas indicate low effective index. reported electrode length was 0.6 mm with an overall device length of 5 mm. In this letter, we describe and implement an InGaAsP–InP Y-junction waveguide switch based on the electrical recon- figuration of the branch waveguides. The required index modulation is achieved using carrier injection. Beam prop- agation method (BPM) simulations predict that this switch can achieve switching contrast ratios better than 40 dB. The fabricated switch has a measured contrast ratio of better than 20 dB, with an electrode length of 300 m and a Y-branch angle of 0.9 . The overall switch length is 1400 m. II. THEORY AND DESIGN The switch consists of a Y-junction waveguide splitter formed by rib waveguides etched in a InP–InGaAsP–InP p-i-n diode waveguide structure, with two electrodes arranged as shown in Fig. 1(a). Carrier injection is used as the switching mechanism. Note that the electrodes are only in electrical contact with the device where they overlap the waveguide ridges. The inner edge of each electrode is a continuation of an arc formed by inner edge of the complementary Y-junction 1041-1135/04$20.00 © 2004 IEEE