High- $Q$ and High-Order Side-Coupled Air-Mode Nanobeam Photonic Crystal Cavities in Silicon

We demonstrate the design, fabrication, and characterization of side-coupled airmode nanobeam photonic crystal cavities in silicon-on-insulator platform. Results show that repeatable devices achieve similar high loaded quality factors (>10
⁴
) and large optical energy ratio in low refractive region. The unload Q-factors of the fabricated cavities are estimated to exceed 10
⁵
. With side-coupled configuration, high transmission of through port is achieved with typical insertion loss less than 0.5 dB. Wavelength shifts of the measured resonances with respect to the designed values are observed and well explained by considering the fluctuation of etching depth. The demonstrated side-coupled airmode nanobeam photonic crystal cavities may find their applications in ultracompact integrated photonics, especially for on-chip photonic sensor, notch filter, or optical switch.