Temporal characteristics and scaling considerations of multimode interference couplers

A mode propagation model is used to analyze the temporal response of a multimode interference (MMI) coupler. The response is characterized as a function of the splitting ratio so that the effects of architectural scaling can be predicted. Results are presented for a specific coupler design. The results indicate that an increase in aggregate bandwidth, defined as the combined bandwidth of the parallel output channels of the coupler, is accompanied by a decrease in coupled power and energy. The loss in efficiency is shown to be independent of whether the increase in aggregate bandwidth is produced by an increase in the splitting ratio or the signal bandwidth.