Theoretical Analysis and Preparation of Tapered Suspended Core Microstructure Fibers

Suspended core microstructured optical fibers (SC-MOFs) represent a special kind of microstructured fibers which can be employed for optical sensing. In this article one experimental SC-MOF and its tapers were numerically analyzed in order to determine if the overlap of evanescent waves with the fiber cladding holes can be increased by tapering. Power distributions of fundamental modes in the SC-MOF and its tapers were calculated by using a vectorial finite element method. The calculations have shown that the evanescent wave overlap (at a wavelength of 1550 nm) can be increased from 0.75% up to 26% by tapering of a section of the SC-MOF from an original diameter of 125 µm down to 31.25 µm. Fiber tapers designed on the basis of the numerical analysis were prepared by so-called ‘flame brush technique’ employing a fiber puller of own construction. Experiments with the prepared tapers have proved that the cladding holes remain sufficiently large for passing liquid and gas analytes through and that the core diameter of the untapered pigtails is large enough for low-loss coupling of optical beams into the tapered fiber.