Optical crossconnects of reduced complexity for WDM networks with bidirectional symmetry

One promising approach to provisioning and restoration in long-haul wavelength-division-multiplexing (WDM) networks is to deploy a mesh of optical crossconnects that operate on individual wavelengths. As wavelength-count and traffic demand rapidly increase, however, this approach will likely require high-port-count optical crossconnects that severely strain the capabilities of known device technologies. Thus, it is critical to devise ways to build large crossconnects from a small number of constituent switches, each with reduced port count. We present a general means of accomplishing this for networks, such as current long-haul networks, that demonstrate bidirectional symmetry. We describe a broad class of symmetry-exploiting architectures that yield N x N crossconnects, both rearrangeably nonblocking and strictly nonblocking, using constituent switch fabrics no larger than N/2 x N/2. By exploiting connection-symmetry, these architectures reduce the number of such N/2 x N/2 fabrics by 30%-50% compared with corresponding fully connected three-stage Benes and Clos switch structures.