Subwavelength-engineered O-band silicon nitride photonic metacrystal cavities with large Q/V

Silicon nitride is emerging as a leading material platform for next-generation photonics due to its wide transparency window and foundry compatibility. As this platform matures, it is imperative to develop photonic structures that increase light-matter interactions to reduce the footprint and power requirements for on-chip applications, including data communication and quantum information systems. We report on two subwavelength-engineered photonic metacrystal nanobeam cavities with high Q designed for O-band telecommunications wavelengths: a bowtie unit cell (loaded Q_L=5×10⁴, fabricated critical dimension of 22 nm) and an antislot unit cell (loaded Q_L=1×10⁴, fabricated critical dimension of 55 nm). These unit cells are designed to better confine light and reduce mode volume by geometrically exploiting electromagnetic boundary conditions. We also demonstrate that further reducing the critical feature size or suspending the photonic metacrystals could produce a figure-of-merit Q/V greater than 10⁶.