Identification and Investigation of the Various Contributions to Confinement Loss in Hollow-Core Tube Lattice Fibers

Hollow Core Inhibited Coupling Fibers have experienced a huge investigation in recent years with the result of a rapid reduction in the propagation loss [1], [2]. Despite the great advances both from theoretical and manufacturing point of view, there are still many aspects to be clarified. From a theoretical point of view, there is a lack of tools to identify and possibly separate the contributions of the different loss mechanisms contributing to the confinement loss (CL). The goal of the present work is to gain insight in the various loss mechanisms occurring in ideal fibers. The followed approach has allowed to identify two different loss contributions to the confinement loss: The Core Modes-Dielectric Modes Coupling Loss (CDCL) related to the coupling between the Fundamental Core Mode (FCM) and the Dielectric Modes confined in the cladding tube membranes; The Tube Tunneling Loss (TTL) related to the evanescent decay and the consequent power tunneling of the Core Mode field inside the tubes. CDCL depends on the overlap integral between core and dielectric modes which can be effectively estimated by the core mode azimuthal Fourier spectrum [3]: