An Interior-Ridge Silicon Microring Modulator

We design and demonstrate a new microring modulator geometry utilizing low-resistance interior ridge contacts and a hard outer waveguide wall to achieve high-speed operation in a device with a large free spectral range (FSR). The depletion-mode silicon microring modulator utilizes a hybrid vertical-horizontal junction to maximize the frequency response for a given voltage within a compact 2.5 μm radius. The 2.5-μm radius microring modulator demonstrates low energy (4.5 fJ/bit) error-free (bit error rate <;10 ^-12) operation for 30 Gb/s nonreturn-to-zero data transmission without utilizing preemphasis or equalization. The modulator exhibits single mode operation over a wide, uncorrupted FSR of 5.3 THz, the largest reported in a high-speed (>25 Gb/s) modulator. The resulting combination of high-speed, low-energy operation, and a wide FSR offers the potential for very high bandwidth densities in future femtojoule-class communication links.