Ultrahigh-Q one-dimensional photonic crystal nanocavities with modulated mode-gap barriers on SiO₂ claddings and on air claddings

We report designs for a silicon-on-insulator (SOI) onedimensional (ID) photonic crystal (PhC) nanocavity with modulated modegap barriers based on the lowest dielectric band. These cavities have an ultrahigh theoretical quality factor (Q) of 10⁷-10⁸ while maintaining a very small modal volume of 0.6-2.0 (λ/n)³, which are the highest Q for any nanocavities with SiO₂ under-cladding. We have fabricated these SOI 1DPhC cavities and confirmed that they exhibited a Q of 3.6×10 ⁵, which is also the highest measured Q for SOI-type PhC nanocavities. We have also applied the same design to ID PhC cavities with air claddings, and found that they exhibit a theoretical quality factor higher than 10⁹. The fabricated air-cladding ID Si PhC cavities have showed a quality factor of 7.2×10⁵, which is close to the highest Q value for ID PhC cavities.