Design of photonic band gap fibers with suppressed higher-order modes: Towards the development of effectively single mode large hollow-core fiber platforms

Kunimasa Saitoh,Tadashi Murao,Masanori Koshiba,Nikolaos J Florous

doi:10.1364/oe.14.007342

Abstract

The objective of the present investigation is to propose and theoretically demonstrate the effective suppression of higher-order modes in large-hollow-core photonic band gap fibers (PBGFs), mainly for low-loss data transmission platforms and/or high power delivery systems. The proposed design strategy is based on the index-matching mechanism of central air-core modes with defected outer core modes. By incorporating several air-cores in the cladding of the PBGF with 6-fold symmetry it is possible to resonantly couple the light corresponding to higher-order modes into the outer core, thus significantly increasing the leakage losses of the higher-order modes in comparison to the fundamental mode, thus making our proposed design to operate in an effectively single mode fashion with polarization independent propagation characteristics. The validation of the procedure is ensured with a detailed PBGF analysis based on an accurate finite element modal solver. Extensive numerical results show that the leakage losses of the higher-order modes can be enhanced in a level of at least 2 orders of magnitude in comparison to those of the fundamental mode. Our investigation is expected to remove an essential obstacle in the development of large-core single-mode hollow-core fibers, thus enabling them to surpass the attenuation of conventional fibers.

Highlights

Microstructured optical fibers (MOFs) [1], known as photonic crystal fibers (PCFs) or holey fibers (HFs), have stimulated much research and have shown great potentials in telecommunications and other applications [1, 2]
The proposed design strategy is based on the index-matching mechanism of central air-core modes
The validation of the procedure is ensured with a detailed photonic band gap fibers (PBGFs) analysis based on an accurate finite

Summary

Introduction

Microstructured optical fibers (MOFs) [1], known as photonic crystal fibers (PCFs) or holey fibers (HFs), have stimulated much research and have shown great potentials in telecommunications and other applications [1, 2]. MOFs [9]-[11].We take this intuitive mechanism and we propose a general methodology for designing PBGFs with suppressed HOMs. The basic design tradeoff between large effective mode areas and HOM suppression is explored for several structural parameters of PBGFs. We perform numerical simulations using an accurate and robust modal solver based on the finite element method (FEM) [12, 13], and we show that the presence of several hollow-cores in the cladding of the PBGF, gives rise to resonant light-wave coupling between higher-order central core-modes and outer core-modes. This fact can enable the index-matching mechanism to take place by bringing the two cores (large-central-core and outer-core) close to each other, enabling resonant coupling over a certain wavelength regime. By a judicious choice of the design parameters, this mechanism is expected to enhance the leakage losses of the higher-order modes, enabling effectively single-mode operation

Derivation of the optimized structural parameters

Feasibility and compatibility of the proposed large-hollow-core PBGF

Conclusions