Compact, low-voltage, high-performance modulator based on micro-resonators far off critical coupling

Micro-resonator modulators working in the critical coupling mode is usually sensitive to fabrication variation. We employ two modulated racetrack-resonators symmetrically coupled to a waveguide on two sides on a silicon-on-insulator wafer. The structure in the strong-coupling regime can perform modulation function stably through the interference of two racetracks. Fabrication variation (30~50%) of coupling constant or quality factor can be compensated by static voltage bias applied on the diode-embedded resonators. Detailed working principle and fabrication-variation compensation will be presented. Experimentally, we demonstrate 50 ~ 56 Gb/s modulation with high extinction ratio of 7.9 ~ 9.4 dB and high signal-to-noise ratio of 6~7, while maintaining low driving voltage (<2.5 Vpp) and small size (tens of microns).