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Fabrication of a tellurite hollow core optical fiber for mid-infrared transmission

Due to the air-guiding characteristics of the air-core, hollow-core optical fibers (HCOFs) can give rise to many potential applications including optical data transmission, terahertz propagation, power beam delivery for industrial applications such as cutting, welding, and engraving, medical applications and chemical sensing. In this work, tellurite HCOFs which have 6 air holes in the cladding and a large hollow core in the center are studied. By numerical analysis, it was realized that the confinement loss in the core will be high when the gap between two nearby cladding air -holes is large or when they connect to each other. The light propagation and transmission properties were demonstrated experimentally from 0.4 to 4.0 μm. By carefully controlling the coupling conditions, lights were coupled successfully into the air core by the fundamental mode. The transmission spectrum included high transmission bands and low transmission bands alternately due to the effect of resonant reflection and anti-resonant reflection. Due to the current operating range of the laser source, the transmission spectrum was measured up to 3.9 μm. But, it is expected to extend to the mid-IR range around 6 μm as shown in the calculation. When the input light at 2.1 μm was linearly polarized, the polarization was maintained in the fiber because the fundamental mode was dominant and the coupling efficiency of the 1st order mode was very weak.