Abstract
We propose a simple geometric criterion based on the size of the core relative to the photonic crystal to quickly determine whether an air-core photonic-bandgap fiber with a given geometry supports surface modes. Comparison to computer simulations show that when applied to fibers with a triangular-pattern cladding and a circular air core, this criterion accurately predicts the existence of a finite number of discrete ranges of core radii that support no surface modes. This valuable tool obviates the need for time-consuming and costly simulations, and it can be easily applied to fibers with an arbitrary photonic-crystal structure and core profile.
Highlights
In recent months there has been mounting evidence that surface modes impose serious limitations in air-core photonic-bandgap fibers (PBFs) [1,2,3,4]
This mode was calculated for a triangular-pattern air-core PBF made of silica, with a core radius R = 1.15Λ and air holes of radius ρ = 0.47Λ, where Λ is the period of the photonic crystal
We propose a fast and simple geometric criterion to evaluate whether a particular fiber design supports surface modes
Summary
In recent months there has been mounting evidence that surface modes impose serious limitations in air-core photonic-bandgap fibers (PBFs) [1,2,3,4]. A typical surface mode is displayed in Fig. 1(a) for the purpose of illustration This mode was calculated for a triangular-pattern air-core PBF made of silica, with a core radius R = 1.15Λ and air holes of radius ρ = 0.47Λ, where Λ is the period of the photonic crystal. We show that surface modes are created when the surface of the core intersects one or more of the dielectric corners of the photonic crystal Based on this observation, we propose a fast and simple geometric criterion to evaluate whether a particular fiber design supports surface modes. We propose a fast and simple geometric criterion to evaluate whether a particular fiber design supports surface modes We apply this criterion to triangular-pattern PBFs with a circular air core and find that in spite of its simplicity, this approximate model yields quantitative predictions in remarkable agreement with computer simulations
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