Design and Fabrication of Microstructured Optical Fibers With Optimized Core Suspension for Enhanced Supercontinuum Generation

Nonlinear microstructured optical fibers (MOFs) offer better prospects in various interdisciplinary fields than conventional nonlinear fibers. High air filling fraction and small core are necessary to ensure high nonlinearity of MOFs. The air holes adjacent to the core can be elongated and tapered into the core in a controlled way during fiber drawing so that the solid core seems to be suspended in air with very thin silica struts connecting it to the matrix. This reduces the effective core area thereby increasing nonlinearity. In this study, the effect of core suspension on the nonlinearity and dispersion of MOFs are systematically investigated on the basis of a geometrical design parameter called suspension factor (SF). Detailed study reveals that MOF designs with enhanced nonlinearity can be obtained even with larger pitch and such MOF structures are easier to fabricate. Fiber drawing parameters which control the SF are precisely identified and optimized. Several fiber samples were drawn at different drawing conditions under constant monitoring and it was observed that high furnace temperature and high drawing speed are the two key parameters that ensure high SF. Further, the role of SF on nonlinear spectral broadening was experimentally investigated and it was found that MOF having high SF offers almost two octave-spanning supercontinuum.