Integrated flexible-grid WDM transmitter using an optical frequency comb in microring modulators.

Advanced optical interconnects require high-speed links, which can be achieved by combining high channel rates with wavelength-division multiplexing (WDM). We report a multi-channel transmitter using cascaded microring modulators (MRMs) in silicon photonics. One MRM works as a flexible-grid optical comb generator, while the others work as channel modulators. With a single-wavelength laser input, we achieve flexible channel spacing (up to 25 GHz) with a tone-to-noise ratio above 54 dB at low power consumption of less than 4.6 mW. We examine experimentally multi-channel transmission modulating data onto adjacent comb lines without significant signal crosstalk. This single-laser, flexible-grid WDM transmitter is a scalable solution: more comb lines can be obtained using uncoupled MRMs in a series. To the best of our knowledge, this is the first demonstration of monolithic integration of a comb generator and multi-channel modulators for ultra-compact, power-efficient WDM photonic interconnects.