Whispering Gallery Mode Enhanced Broadband and High-Speed Silicon Microring Modulator

Silicon microring modulators have a compact footprint, low power consumption, and are intrinsically compatible with wavelength-division multiplexing (WDM) techniques, facilitating the integration of multiple ring cavities at different resonant wavelengths to achieve a high aggregated data communication capacity. However, the limited free spectral range (FSR) of a ring resonator restricts the number of usable wavelength channels and the corresponding total data rate capacity using a shared bus waveguide. In this work, we design and demonstrate a novel silicon microring modulator enabled by whispering gallery mode (WGM) to achieve a large FSR and high-speed operation simultaneously. An ultra-wide and uncorrupted FSR of 4.5 THz can be obtained in our experiment while supporting an electro-optical 3-dB bandwidth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&gt;$</tex-math></inline-formula> 110 GHz. Using our proposed microring modulator with 4-level pulse amplitude modulation (PAM-4), a single-lane data rate of 256 Gbps and 300 Gbps can be realized with measured bit error rate below the 7% hard-decision (HD) forward error correction (FEC) threshold and 20% soft-decision (SD) FEC limit, respectively. Compared with the prior arts, our proposed microring modulator represents a compelling candidate for the next generation of high-capacity, short-reach optical communication systems.