Ultra-Long Subwavelength Micro/Nanofibers with Low Loss

Subwavelength diameter micro/nanofiber (MNF) provides excellent platform for many applications. In this work, we fabricate subwavelength diameter MNFs with ultra-long waist and analyze the propagation loss origin for such fibers. Transmittance as high as 99.4% is measured for MNF with a waist length of 10 cm and diameter of $1.2\mu \text{m}$ , and the loss is mainly resulted from the modal leakage of the taper. However, when the MNF is getting longer and thinner, the intrinsic surface roughness induced during the fabrication process overrides the modal leakage and plays a major role in the propagation loss. Our study reveals existence of an ultimate transmission limitation for ultra-long MNFs.