Cubic-wavelength mode volume photonic crystal nanobeam cavities in a monolithic CMOS platform

We report on the design, fabrication, and experimental characterization of photonic crystal (PhC) nanobeam cav-ities with the smallest footprint, largest intrinsic quality factor, and smallest mode volume to be demonstrated to date in a monolithic CMOS platform. Two types of cavi-ties were designed, with opposite spatial mode symmetries. The opposite mode symmetry, combined with evanescent coupling, allows the nanobeam cavities to be used in reflec-tionless topologies, desirable in complex photonic integrated circuits (PICs). The devices were implemented and fabri-cated in a 45 nm monolithic electronics-photonics CMOS platform optimized for silicon photonics (GlobalFoundries 45CLO) and do not require any post-processing. Quality fac-tors exceeding 100 000 were measured for both devices, the highest, to the best of our knowledge, among fully cladded PhC nanobeam cavities in any silicon-on-insulator (SOI) platform. Additionally, the ability of the cavities to confine light into small mode volumes, of the order of (lambda/n)3, was confirmed experimentally using near-field scanning optical microscopy (NSOM). These types of cavities are an impor-tant step toward realizing ultra-low energy active devices required for the next generation of integrated optical links beyond the current microring resonator-based links and other CMOS PICs. (c) 2023 Optica Publishing Group