Nanogap Enabled Trajectory Splitting and 3D Optical Coupling in Self-Assembled Microtubular Cavities.

We report the generation of multiple sets of 3D confined resonant modes in a single microtube cavity owing to nanogap induced resonant trajectory splits. The optical field largely overlaps in the split resonant trajectories, enabling strong optical coupling of 3D confined resonant light. The anticrossing feature and modes changing-over were demonstrated as direct evidence of strong coupling. In such an optical coupling system, the spatial optical field distribution of 3D coupling modes was experimentally mapped under the strong coupling regime, which allows direct observation of the energy transfer process between two hybrid states. Numerical calculations based on a quasi-potential model and the mode detuning process are in excellent agreement with the experimental results. The generation of multiple sets of 3D confined resonant modes and their efficient coupling in a single microcavity are of high interest for directional coupling with a higher degree of freedom to realize on-chip integration with elevated functionalities such as multiplexing, 3D lasing, and signal processing.