Comparison of Silicon Ring Modulators With Interdigitated and Lateral p-n Junctions

We present a rigorous comparison between Si ring modulators based on interdigitated and lateral p-n junctions. A detailed Si ring modulator model is derived, which is used to fit and benchmark the measured modulation performance of both ring modulators. At 10 Gb/s and 1 V_pp drive swing, the interdigitated ring modulator is found to exhibit a superior extinction ratio at low insertion loss as compared to the lateral ring modulator, at the expense of a higher capacitive load. Design improvements are proposed to obtain 25-Gb/s operation with similar extinction ratio and low insertion loss in future devices. Such devices are attractive to enable power-efficient scaling of optical interconnects to 400 Gb/s and beyond.