Localization of light on a cone: theoretical evidence and experimental demonstration for an optical fiber

The classical rays propagating along a conical surface are bounded on the narrower side of the cone and unbounded on its wider side. In contrast, it is shown here that a dielectric cone with a small half-angle γ can perform as a high Q-factor optical microresonator which completely confines light. The theory of the discovered localized conical states is confirmed by the experimental demonstration, providing a unique approach for accurate local characterization of optical fibers (which usually have γ ~ 10(-5) or less) and a new paradigm in the field of high Q-factor resonators.