Abstract

Ultra-low loss fiber design seeks an attention towards all the possible source of losses such as confinement loss (CL), macro-bending loss (BL), Rayleigh scattering loss (RSL), surfaces scattering loss (SSL), and fabrication loss [1,2]. It is found that hollow core anti-resonant fiber (ARF) with nodeless structure does not have SSL due to non-touching tubes and RSL is ignored due to less interaction of light in hollow air core with surrounding silica tubes [3]. Fabrication tolerances should be worked out while choosing the fiber design parameters. CL becomes the dominating loss in these fibers and it can be lowered by optimizing the fiber design. In field applications, bending of these fibers become a major source of loss. One needs to work on the fiber structure/design to reduce its loss under bending conditions – bending axes and bending radii. Under bend conditions, the core modes and cladding modes start leaking and coupling with each ither which results in the loss of core modes and coupling of cladding modes into the core. The fiber design is optimized such that the higher order modes (HOM) are avoided/suppressed and fundamental modes (FM) are confined inside the core having lowest possible CL using mode analysis based on Finite element method in COMSOL [4].

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