Double Anticrossing Coupling in a Single Metal-Clad Microcapillary

Mode coupling is studied comprehensively in a proposed metal-clad microcapillary cavity, which is an optofluidic capillary with two silver films coated on both surfaces of the silica wall. The dispersion relations of resonant wavelength dependencies on wall thickness of silica microcapillary and surrounding medium index are calculated, and different types of mode coupling are observed clearly. Besides the reported traditional mode coupling, double anticrossing coupling involving two plasmonic modes and one photonic mode is achieved in a single cavity for the first time. Also, Q factors and field distributions of coupled modes are calculated, manifesting that the coupled modes are the high Q factor hybrid modes. The field evolutions of coupled modes are interpreted well by the effective potential approach. The coupled modes in such a metal-clad microcapillary could find some interesting applications requiring both the high Q factor and the high field enhancement factor.