Characterization of evanescent wave coupling in side-polished hollow optical fiber and its application as a broadband coupler

We have investigated side-polished fiber coupler made of a hollow optical fiber (HOF) with a ring core. It is theoretically shown that the large mode size and the weakly guiding property of the HOF makes it easy to excite the evanescent field by the side-polishing technique. Analytic equation to calculate the remaining cladding thickness of the side-polished HOF is presented and a novel technique to couple the conventional single mode fiber is also experimentally demonstrated.