Taper-assisted coupling between two optical cavities at exceptional point and bound state in the continuum

Long-distance coupling between two optical cavities is enabled through a taper fiber. Phase shift and loss induced by the taper lead to complex coupling strength and hence observation of various distinctive coupling conditions like exceptional points, bound state in the continuum, and dissipative coupling with optothermal effect. Large tunability of coupling conditions is demonstrated via controlling the translation stage, as manifested in the transmission spectrum. Theoretical prediction and simulation coincide well with experimental measurement. Lastly, we propose to advance the role of taper for application in taper-based sensing and optomechanics.