Design, Fabrication, and Characterization of a High Q Silica Nanobeam Cavity With Orthogonal Resonant Modes

We design and fabricate a high
$Q$
silica nanobeam cavity that supports both transverse electric (TE) and transverse magnetic modes in the 1.55 
$\mathrm{\mu }$
m wavelength range. The
$Q$
values obtained for both modes exceed
$10^4$
and are the highest reported values for photonic crystal (PhC) nanocavities made of silica. We also investigate the optimum conditions for coupling with the cavity in a side-coupled configuration. We achieve a coupling efficiency of 87% with the TE mode while maintaining a loaded
$Q$
of more than
$10^4$
. We also found that the presence of a coupled waveguide reduces the intrinsic
$Q$
of the cavity, depending on the gap distance. This provides useful quantitative information for establishing an efficient scheme for coupling with low-index PhC nanocavities.