Free-spectral-range-free microring-based coupling modulator with integrated contra-directional-couplers

In this work, we experimentally demonstrate a FSR-free, MRR-based, coupling modulator that integrates a bent, grating-based contra-directional-coupler (contra-DC) into a microring cavity to achieve an FSR-free response at its through port. Our modulator suppresses the amplitude response at all but one resonance, operating mode (hence, has an FSR-free response). In our modulator, coupling modulation is used and is achieved by modulating a relatively short, 210 μm long, p-n junction phase-shifter in a two-point coupler (which forms the drop-port coupler of the MRR). We demonstrate open eyes at 2.5 Gbps and discuss how the effects of DUV lithography on the contra-DC limited the electro-optic bandwidth of the fabricated modulator to 2.6 GHz. In these proceedings, we also cover details of the device design and the small and large signal characterization of the device, including an analysis of the effect of lithography on the “as-fabricated" device performance. We also discuss how to significantly improve the electro-optic bandwidth in future implementations by accounting for these lithographic effects in the device design flow and layout.