Ultra-Wide Free-Spectral-Range Silicon Microring Modulator for High Capacity WDM

Silicon microring modulators (MRM) are a promising technology for next generation datacenter interconnects, where migration to higher data capacities will require the increasing use of wavelength division multiplexing (WDM). However the periodic repetition of wavelength resonances, and the limited free-spectral range (FSR) of MRMs, can limit the number of WDM channels when we use the wavelength selectivity of the MRM to modulate a particular wavelength from frequency comb sources or other multi-wavelength sources propagating in the bus waveguide. In this paper, we realize an ultra-compact, high bandwidth, CMOS compatible MRM which has an ultra-wide FSR of 4 THz, 3-dB electro-optic (EO) bandwidth of >67 GHz and which can operate at high datarates for standard single mode fiber transmission in the C-band. Using the modulator, we demonstrate 100 Gbaud PAM-4 intensity modulation-direct detection (IM-DD) with 4 wavelengths within a single FSR in the wavelength range of 1540 nm–1570 nm. The bit-error-rate (BER) of the transmission was below the general 7% hard-decision forward-error correction (HD-FEC) of 3.8 × 10−3.