An improved surface-plasmonic nanobeam cavity for higher Q and smaller V

We demonstrate a high-Q hybrid surface-plasmon-polariton-photonic crystal （SP3C） nanobeam cavity. The proposed cavities are analyzed numerically using the three-dimensional finite difference time domain （3D-FDTD） method. The results show that a Q-factor of 2076 and a modal volume V of 0.16（λ/2n）^3 can be achieved in a 50 nm silica-gap hybrid SP3C nanobeam cavity when it operates at telecommunications wavelengths and at room temperature. V can be further reduced to 0.02（λ/2n）^3 when the silica thickness decreases to 10 nm, which leads to a Q/V ratio that is 11 times that of the corresponding plasmonic-photonic nanobeam cavity （without silica）. The ultrahigh Q/V ratio originates from the low-loss nature and deep sub-wavelength confinement of the hybrid plasmonic waveguide, as well as the mode gap effect used to reduce the radiation loss. The proposed structure is fully compatible with semiconductor fabrication techniques and could lead to a wide range of applications.