Ultra-Dense Wavelength-Division Multiplexing With Microring Modulator

Silicon photonics can be used to increase the versatility of wavelength division multiplexing (WDM). Ultra-dense wavelength division multiplexing (uDWDM) shrinks channel spacing between WDM channels to decrease guard bands and increase spectral efficiency. Microring modulators (MRMs) provide a simple solution for uDWDM transmitters - they require no multiplexer/demultiplexer. When used with comb lasers, MRMs provide extremely compact and low power solutions. The spectral efficiency is limited by interchannel interference (ICI) from incomplete isolation of channels. We report an MRM-uDWDM transmitter achieving channel spacing comparable to the symbol rate in each WDM channel, reaching a spectrum occupation of 80%. By choosing the correct operating point, we demonstrate experimentally our fabricated MRM chip design causes no discernable ICI power penalty. To the best of our knowledge, this is the first demonstration of MRM-uDWDM to support such dense channel spacing.