Understanding formation of photonic bandgap edge for maximum propagation angle in all-solid photonic bandgap fibers

Abstract

We propose a simple formula that gives the effective refractive index of the first-order photonic bandgap (PBG) edge for the maximum propagation angle, which corresponds to the PBG floor in all-solid photonic bandgap fibers (PBGFs). In particular, based on an antiresonant reflecting optical waveguide (ARROW) theory incorporating a phase relation between resonant modes in low-index regions for perpendicular direction of the light propagation, we show that the effective index of the PBG edge at a wavelength does not depend on the diameter and refractive index of high-index rods, and is largely determined only by the pitch when normalized rod diameters are small. In other words, it has a constant value for the structural parameters with which the PBG emerges at the same wavelength normalized by the pitch. Moreover, the source of rod-diameter and refractive-index dependences on the condition for the formation of the PBG edge is demonstrated when the diameter and the refractive index of high-index rods are effectively large. Finally, the validity of the proposed simple formula, which can be applied for any structural parameters, is verified with the vectorial solver based on the finite-element method (FEM).

Design of Single-Band Bandpass Filter Using Photonic Bandgap Fiber by Suppressing Core Modes in Higher Order Bandgaps

“…In the latter, the periodic cladding structure gives rise to certain photonic bandgaps (PBGs) in which light is not able to penetrate through the cladding region, thus confined in the core. All-solid PBGF consists of silica background with a periodic structure of cylindrical high index inclusions which leads to the formation of the bandgaps of the photonic crystal cladding [1], [2], [3], [4]. These bandgaps, exhibit wavelengths selective guiding in the core, therefore enable optical filter engineering.…”

Large-mode-area neodymium-doped all-solid double-cladding silicate photonic bandgap fiber with an index step of ～0.5%

“…Although light guidance based on photonic bandgaps at low-index contrast have been demonstrated by passive AS-PBGFs [27,28] , cladding with low-index difference will lead to shallow bandgaps [29] , thus decreasing the effective numerical aperture (NA) of the fiber core [30] . To our knowledge, the rare-earth-doped AS-PBGFs with low-index contrast have not been well studied, and it is not known whether laser emission can be generated in such fibers.…”