Abstract
Materials with a periodic structure have photonic bandgaps (PBGs), in which light can not be guided within certain wavelength ranges; thus light can be confined within a low-index region by the bandgap effect. In this paper, rectangular-shaped hollow waveguides having waveguide-walls (claddings) using the PBG have been discussed. The design principle for HE modes of hollow-core rectangular PBG waveguides with a Bragg cladding consisting of alternating high- and low-index layers, based on a 1D periodic multilayer approximation for the Bragg cladding, is established and then a novel single-polarization hollow-core square PBG waveguide using the bandgap difference between two polarized waves is proposed. Our results demonstrated that a single-polarization guiding can be achieved by using the square Bragg cladding structure with different layer thickness ratios in the mutually orthogonal directions and the transmission loss of the guided mode in a designed hollow-core square PBG waveguide is numerically estimated to be 0.04 dB/cm.
Highlights
Photonic crystal waveguides with periodic structures in the cladding and/or core regions have the potential of achieving various novel properties that are quite impossible in conventional waveguides, and have been studied actively from the mid 1990s.1 In particular, photonic bandgap (PBG) effects caused by a periodic modulation of refractive index prohibit the propagation of light of certain frequencies, and photonic bandgaps (PBGs) fibers/waveguides based on the PBG confinement[2] can open up a possibility for trapping light in low-index regions and enable air-guiding that is impossible in conventional waveguides relying on index guiding
Our results demonstrated that a single-polarization guiding can be achieved by using the square Bragg cladding structure with different layer thickness ratios in the mutually orthogonal directions and the transmission loss of the guided mode in a designed hollow-core square PBG waveguide is numerically estimated to be 0.04 dB/cm
We first present the design principle for HE modes of hollow-core rectangular PBG waveguides with a Bragg cladding, based on a 1D periodic multilayer approximation for the Bragg cladding, and attempt to design a hollow-core rectangular PBG waveguide using the omnidirectional Bragg reflection caused by its cladding
Summary
Photonic crystal waveguides with periodic structures in the cladding and/or core regions have the potential of achieving various novel properties that are quite impossible in conventional waveguides, and have been studied actively from the mid 1990s.1 In particular, photonic bandgap (PBG) effects caused by a periodic modulation of refractive index prohibit the propagation of light of certain frequencies, and PBG fibers/waveguides based on the PBG confinement[2] can open up a possibility for trapping light in low-index regions and enable air-guiding that is impossible in conventional waveguides relying on index guiding. Because of the high heat resistance and extremely low nonlinearity of the core material (i.e., air), the PBG waveguides are suitable for high power delivery. The hollow waveguides presented in Ref. have a hollow core, to be sure, but they have a Bragg confinement structure only in the vertical direction and not in the horizontal direction, and seem to be close to slab waveguides in terms of spatial light confinement. In order to obtain the PBG guidance of the HE modes of hollow-core rectangular PBG waveguides with a Bragg stack cladding, we devise the design principle based on the bandgap estimation of their rectangular Bragg claddings using the approximated 1D periodic dielectric films. A hollow-core rectangular PBG waveguide using the omnidirectional Bragg reflection caused by the multilayer cladding wall is designed based on the results. By using the polarization anisotropy in the PBG of periodic multilayers, a novel single-polarization hollow-core square PBG waveguide with relatively low loss that supports only one polarization state is designed
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