Open AccessMethod for increasing coupling efficiency between helical-core and standard single-mode fibers
Author(s) -
Gabriela Statkiewicz-Barabach,
Maciej Napiórkowski,
Marta Bernas,
Lidia Czyżewska,
Paweł Mergo,
Wacław Urbańczyk
Publication year - 2021
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.413358
Subject(s) - optics , coupling (piping) , cladding (metalworking) , excitation , core (optical fiber) , wavelength , modal , transfer efficiency , materials science , physics , mode coupling , quantum mechanics , polymer chemistry , biochemical engineering , metallurgy , engineering
Helical core fibers (HCFs) suffer from low coupling efficiency and unavoidable excitation of higher order modes below the cutoff wavelength because of a core tilt with respect to the symmetry axis of the cladding. We propose an effective way of increasing the coupling efficiency to a HCF by untwisting its beginning section in a hydrogen ame. The proposed solution provides also a control over the excitation of higher order modes in HCFs and can be applied in splicing as well as in a free-space launching configuration. We experimentally demonstrate that by using the proposed method, the coupling efficiency between a SMF-28 and HCF can be increased to the level reachable for straight fibers, which is limited only by a modal fields mismatch. We also present detailed numerical and analytical studies of the coupling efficiency between a HCF and SMF versus the pitch distance in the partially untwisted input section of the HCF, which takes into account fundamental and higher-order modes.