77 zyxwvu I zyxwvutsrq A Novel AOTF-Based Multichannel Add-Drop Node and its Cascadability in WDM Ring Networks I Roberto Gaudhot and Daniel J. Blumenthal" 'Dipartimento di Elettronica, Politecnico di Torino, Corso Duca degli Abruzzi, 24, 10 129 Torino, Italy e-mail: gaudino@polito.it "Optical Communications and Photonic Networks (OCPN) Laboratory School of Electrical and Computer Engineering Georgia Institute of Technology, Atlanta, GA 30332-0250 e-mail zyxwvu : danb@ee.gatech.edu zyxw Abstract A novel AOTF multichannel add/drop node is demonstrated and its cascadability in a ring network is evaluated. It is shown that an alternate channel spacing scheme produces acceptable power penalties for up to 7 cascaded nodes with channel rates of 2.5 Gbps. Introduction: Acousto-optic tunable filter (AOTF) technology has greatly evolved over the last several years and research grade products are available for wavelength division multiplexed (WDM) applications [l]. These devices still have limitations in dense WDM systems, particularly when several zyxwv RF frequencies are applied for multichannel adding/dropping functions [2, 31. Techniques like spatial and/or wavelength dilation have been utilized to overcome these limitations [4]. In this paper, we present a novel add-drop node architecture based on two cascaded AOTFs. This node is particularly suited for circuit switched all-optical ring networks. We experimentally measure the node performance in several worst case situations in a 400 GHz (3.2 nm) spaced WDM network. Node cascadability is investigated using a recirculating loop. It is shown that the power penalty per node due to AOTF related impailments is less than 1 dB provided that adjacent channels are not simultaneously droppedadded in the same node. This constraint && must be dealt with using a proper medium- access protocol (MAC) at the network management level. This architecture employs a much simpler hardware implementation compared to standard spatial or wavelength dilated architectures. From Ring I RF generators I *Ow I T hi ,.., hj zyxw 1 I ,.., hn EE!3 LOCAL HOST Multichannel Add-drop Node Architecture: The Multichannel AOTF add-drop node is shown in Fig. 1. The first AOTF acts as a dropping filter for wavelengths, zyxwvu [hi,. .. ,Aj] when the appropriate set of RF frequencies V;, .. .21;1 are applied. The second improves the extinction ratio on the dropped channels and allows new wavelengths [A,, .. .,A,,,] to be added. Figure 1: Add-drop node architecture To Ring zy ECOC 97, 22-25 September 1997, Conference Publication No. 448, 0 zyxwv IEE, 1997