Localization of light in optical fibers: Cylinder, conical and bottle microresonators

A slightly nonuniform and even an ideally uniform optical fiber can perform as a high Q-factor optical microresonator which hosts different types of strongly localized states localized near the fiber surface. These states are usually excited by a transverse microfiber waveguide and can be classified into whispering gallery bottle, cylinder, and conical states. The whispering gallery bottle states can be excited in a fiber segment with tapered ends. The cylinder and conical states can be excited by a transverse microfiber in a uniform optical fiber and in a fiber having the shape of a cone with a small half-angle, respectively. In this paper, the theory and application of the whispering gallery bottle, cylindrical, and conical microresonators is reviewed.