Deep subwavelength plasmonic whispering-gallery-mode cavity.

We propose a plasmonic whispering-gallery-mode cavity comprising of a dielectric disk with sub-hundred nanometer thickness sandwiched by two silver disks. By reducing radius and thickness carefully based on the investigated resonant wavelength dependencies, the surface-plasmon-polariton cavity mode with a resonant wavelength of 1550 nm can be confined in a disk with a radius of 88 nm and a thickness of 10 nm, where the physical size of the cavity is 0.000064 λ(0) <(3) (λ(0): free space wavelength). The cavity mode has a deep subwavelength mode volume of 0.010 (λ/2n)(3) and a high quality factor of 1900 at 40K, consequently, a large Purcell factor of 1.1 x 10(5).