Whispering gallery mode nanodisk resonator based on layered metal-dielectric waveguide

This paper proposes a layered metal-dielectric waveguide consisting of a stack of alternating metal and dielectric films which enables an ultracompact mode confinement. The properties of whispering gallery modes supported by disk resonators based on such waveguides are investigated for achieving a large Purcell factor. We show that by stacking three layers of 10 nm thick silver with two layers of 50 nm dielectric layers (of refractive index n) in sequence, the disk radius can be as small as 61 nm ∼λ(0)/(7n) and the mode volume is only 0.0175(λ(0)/(2n))(3). When operating at 40 K, the cavity's Q-factor can be ~670; Purcell factor can be as large as 2.3×10(4), which is more than five times larger than that achievable in a metal-dielectric-metal disk cavity in the same condition. When more dielectric layers with smaller thicknesses are used, even more compact confinement can be achieved. For example, the radius of a cavity consisting of seven dielectric-layer waveguide can be shrunk down to λ(0)/(13.5n), corresponding to a mode volume of 0.005λ(0)/(2n))(3), and Purcell factor can be enhanced to 7.3×10(4) at 40 K. The influence of parameters like thicknesses of dielectric and metal films, cavity size, and number of dielectric layers is also comprehensively studied. The proposed waveguide and nanodisk cavity provide an alternative for ultracompact light confinement, and can find applications where a strong light-matter interaction is necessary.