Optical bottle microresonators with axially uniform eigenmode field distribution.

We show that the fundamental eigenmode of a shallow optical bottle microresonator (also called a SNAP microresonator) can be made exceptionally uniform along its axial length. The introduced microresonator has effective radius variation resembling the contour of a bat with ears and wings. Remarkably, reduction of the axial size of this microresonator achieved by cutting the wings does not alter the uniformity of its fundamental eigenmode. Being of general interest, our findings pave a way for improving the perceptibility of micro/nanoparticle sensing. These results also suggest a bottle microresonator suitable for accurate assembling of quantum emitters near the maximum of its eigenmode to be important in cavity quantum electrodynamics.