Adiabatic microring modulators

In this work, we demonstrate and experimentally characterize a new class of high-performance silicon photonic modulators-the adiabatic microring modulator. The adiabatic microring modulator utilizes a vertical PN junction and interior electrical contacts, leveraging all the advantages of previously-demonstrated microdisk modulators. However, this device also incorporates an adiabatic transition from the wide, multimode contact region, to a narrow, single-mode coupling region, eliminating unwanted spatial modes common to microdisks. As a result, the adiabatic microring modulator demonstrated in this work is the smallest microring modulator demonstrated to date, with a diameter of only 4 μm, yielding a 6.92-THz uncorrupted free spectral range. Here, we perform an experimental comparative analysis between silicon adiabatic microring modulators, silicon microdisk modulators, and a commercial lithium-niobate Mach-Zehnder modulator. We show that the silicon adiabatic microring modulator using partial doping is capable of operating at 12.5-Gb/s data rates and beyond. This device combines the best of all modulator designs, leveraging the depletion-based method to maximize the speed, utilizing the vertical-junction configuration to minimize the power consumption, employing a unique adiabatic design to eliminate higher-order modes, and using partial doping to reduce resistance, further enhancing the speed of the device.