A new design approach to large input/output-number multimode interference (MMI) couplers and its WDM applications

Abstract

Photonic integrated circuits based on MMI couplers have been implemented for a variety of optical signal processing functions. However, it is difficult to obtain high-performance for N/spl times/N MMI couplers with large N due to the modal phase errors in self-imaging. For example, MMI-based phased-array (PHASAR) demultiplexers are of interest because of their application to WDM systems. One important factor that limits the crosstalk of these MMI-PHASARs is the performance degradation of N/spl times/N MMI couplers due to modal phase errors. In this study, a new design approach by optimizing the index-contrast to reduce phase error is described which yields a device design with extremely low imbalance and insertion loss.