Localized high-Q modes in conical microcavities

•Localized high-Q modes on a conical surface were realized.•Effective radius was introduced to analyze optical mode profile.•Criterion of the existence of mode localization was presented.

We carry out three-dimensional (3D) numerical simulation on a conical microcavity with a half-angle of 11 degree, where there exists high-Q modes by introducing a thin high refractive index film on a conical surface. Our study reveals that, rather than the surface profile of the microcavity, the effective radius plays crucial role in whether the cavity may support localized modes. Specifically, the change of high refractive index film thickness creates an additional angular momentum barrier, so that the conical microcavity may sustain localized high-Q modes. Our study offers a new degree of freedom to control the properties of 3D microcavities, which is useful for microlaser or sensor applications.