Optics Optik Optik Optik 116 (2005) 527–541 Investigation of SOA-assisted Sagnac recirculating shift register switching characteristics K.E. Zoiros à , J. Vardakas, T. Houbavlis, M. Moyssidis Lightwave Communications Research Group, Department of Electrical and Computer Engineering, Democritus University of Thrace, 12 Vas. Sofias Street, GR 671 00, Xanthi, Greece Received 28 December 2004; accepted 30 March 2005 Abstract The switching characteristics of a Semiconductor Optical Amplifier (SOA)-assisted Sagnac recirculating shift register with an inverter are investigated by undertaking a numerical analysis that describes the dynamic gain response of the SOA to high speed and strong feedback optical pulses. The key performance parameters are identified and their role in the formation of the switching window is analyzed. The optimum values of these parameters are not unique and must be adapted to the specific all-optical shift register network application. For this reason, they must be properly selected and combined so as to ensure the satisfaction of the desired operating conditions. The technical restrictions that the derived values may impose on the state-of-the-art photonics technology are also discussed and efficient ways of overcoming them are proposed. r 2005 Elsevier GmbH. All rights reserved. Keywords: All-optical recirculating shift register; All-optical signal processing; Semiconductor optical amplifier (SOA); SOA- assisted Sagnac switch; Switching window 1. Introduction The unceasing bandwidth demand that is fuelled by the massive use of Internet and multimedia applications has spurred the development of ultrafast all-optical networks capable of offering large traffic capacities and supporting high-quality integrated services [1]. The main characteristic of these networks is that information remains exclusively in the optical domain along the communications path without opto-electrical (O/E) and electro-optical (E/O) conversions but only inevitably at the receiver nodes, thus eliminating the problem of electronic bottleneck [2] and opening the road for the performance of all-optical packet switching functions with the inherent advantages of bandwidth use on demand, flexibility and granularity [3]. A fundamental and indispensable building module for the implementa- tion of such networks is an all-optical memory [3,4], which is essentially a shift register that can perform several critical network processing tasks. More specifi- cally, it can be employed at the interface between users nodes and the optical backbone to store either low-rate multiplexed data packets until bandwidth on the network becomes available or high bit rate received data packets while they are rate converted so that they can be further processed by the available lower-speed ARTICLE IN PRESS www.elsevier.de/ijleo 0030-4026/$-see front matter r 2005 Elsevier GmbH. All rights reserved. doi:10.1016/j.ijleo.2005.03.005 à Corresponding author. Tel.: +302541079975; fax: +302541079595. E-mail address: kzoiros@ee.duth.gr (K.E. Zoiros).