Impact of Joint and Independent Switching Paradigms on Switching Capacity of Contention/-Less SDM-ROADM Designs

We evaluate the switching capacity of reconfigurable optical add/drop multiplexer (ROADM) nodes for space division multiplexed (SDM) networks considering the joint and independent switching of spatial channels. We discuss different switching strategies for independent switching of spatial channels: (a) add/drop transceivers serving channels from all directions, (b) serving a specific spatial channel from all directions (c) serving all spatial channels from a specific direction, and (d) bound to a specific spatial channel and direction. We account for total switching functions (routing and add/drop) and quantify the impact of wavelength contention in add/drop port aggregators. We evaluate the possible ways add/drop transceivers serve all nodal directions, spatial and wavelength channels per SDM-ROADM architecture. Our analysis indicates that common transceivers serving adds/drops to/from every direction shared among spatial channels performs the best among all independent switching architectures at smaller number of spatial channels as compared to nodal directions. However, at equal number of spatial channels and nodal directions, SDM-ROADM architecture with common transceivers to serve adds/drops to/from every spatial channel shared among all directions performs the best. We also observe that performance penalty of contentional SDM-ROADM is lower in all independent switching architecture as compared to joint switching due to the larger addressable directions and spatial counts leading to greater flexibility. Our observations suggest the use of a transceivers to serve all spatial channels for individual directions with partial wavelength contention features at lower number of transceivers and spatial-directional SDM-ROADM at higher number of transceivers or a combination of both.