Abstract

In recent years, multiple optical fibers are installed on each optical link to deal with the surge of Internet traffic, which calls for large-scale reconfigurable optical add/drop multiplexers (ROADMs). However, the scalability of the standard optical cross-connect (OXC), the key component of ROADM, is limited by the port count of commercial wavelength selective switches (WSSs). The theory of Clos network could be used to design a scalable OXC, but it will lead to a large insertion loss (∼30 dB). To address this issue, we propose a three-phase approach to construct a modular OXC network. Starting from a classical OXC, phase 1 decomposes each WSS in the input and output stages into a two-stage cascaded structure of WSSs, based on which phase 2 factorizes the shuffle network between the inputs and the outputs of the original OXC into the interconnection of small-size shuffle networks. Phase 3 combines the small-size shuffle networks together with the small-size WSSs to form small-size OXC modules. As a result, we obtain a modular OXC network, which is an interconnection of small-size OXCs. The modular OXC network is a strictly nonblocking and flex-grid optical switching fabric and has ∼20-dB insertion loss. At last, we experimentally evaluate the transmission performance of modular OXC network and discuss the related issues when it is deployed in a ROADM.