The core modes of all solid photonic band gap fibers as bound states in the continuum

In this paper we propose a new hypothesis of out of plane band gap formation in all solid photonic band gap (PBG) fibers. At first, one considers the process of the core modes formation as a result of excitation of continuous mode spectrum of single dielectric rod of the cladding. It is shown that the core modes can be considered as transverse resonance of a set of the radiation modes decoupled from the continuum provided that the phase matching condition for the propagation constants are fulfilled. An analogy between the core mode formation in all solid PBG fibers and formation of bound states in the continuum in photonics are drawn. Based on these conclusions, the light guiding in all solid PBG fiber with disordered cladding structure and quasi 3D photonic band gap formation in all solid PBG fibers with a small index (1%) can be explained.