Cascaded versus parallel architectures of two‐stage optical crossbar switches with an extra set of inputs and outputs

Abstract

Two principal two-stage switch architectures (cascaded and parallel), both of which are composed of two identical optical crossbar switches with an extra set of inputs and outputs, are compared in terms of their number of crosspoints, switch control complexities, and key optical performances, such as insertion loss and crosstalk power, through theoretical analysis. The authors begin by briefly introducing a known N × N cascaded optical crossbar switch with N 2/2 crosspoints, where N is the switch size, and present a new functional perspective based on quasi-bitonic sorting. Subsequently, the authors derive two types of two-stage parallel optical crossbar switches with reduced crosspoints from a conventional single-stage parallel crossbar switch with N 2 + 2N crosspoints. The first type uses two N/2 × N asymmetric switches in parallel, both of which are embedded in a single N/2 × N/2 crossbar switch. It has (N 2 + 2N)/2 crosspoints and suffers from a complex switch control of O(N 2). The second type is equivalent to a three-stage Benes network and exploits bidirectional transmission to reduce the number of switching stages. It requires (N 2 + 3N)/2 crosspoints, but has a dramatically reduced switch control complexity of O(N), and significantly improved optical performance.