A comparison of microresonator devices for WDM-compatible mode-division multiplexing

For next-generation on-chip optical communications, the combination of wavelength- and mode-division multi-plexing has been proposed as way to achieve high aggregate bandwidth on a single multimode silicon bus waveguide. In this application, microring resonators are used to multiplex and demultiplex the different wavelength and mode channels. The designs of the microrings ultimately determine the throughput and power consumption of the circuit. In this work, we perform a comprehensive numerical comparison of the two designs that have already been demonstrated (the point-coupled and racetrack microring resonators) with a new, waveguide-wrapped design. The proposed design reduces the size of the microring cavity, which reduces the spatial footprint and increases the free spectral range (bandwidth), without heavily increasing loss and intermodal crosstalk (power budget). We believe that efficiency improvements to next-generation optical communications circuits like these can help meet the growing global demand for bandwidth without adding to the growing cost of operating them.