title: Cross-correlated imaging of single-mode photonic crystal rod fiber with distributed mode filtering.
abstract: Photonic crystal bandgap fibers employing distributed mode filtering design provide near diffraction-limited light outputs, a critical property of fiber-based high-power lasers. Microstructure of the fibers is tailored to achieve single-mode operation at specific wavelength by resonant mode coupling of higher-order modes. We analyze the modal regimes of the fibers having a mode field diameter of 60 µm by the cross-correlated (C(2)) imaging method in different wavelength ranges and evaluate the sensitivity of the modal content to various input-coupling conditions. As a result, we experimentally identify regimes of resonant coupling between higher-order core modes and cladding band. We demonstrate a passive fiber design in which the higher-order modal content inside the single-mode guiding regime is suppressed by at least 20 dB even for significantly misaligned input-coupling configurations.
authors.affiliation: DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark. malau@fotonik.dtu.dk
authors.forename: Marko
authors.initials: M
authors.lastname: Laurila
authors.forename: Roman
authors.initials: R
authors.lastname: Barankov
authors.forename: Mette M
authors.initials: MM
authors.lastname: Jørgensen
authors.forename: Thomas T
authors.initials: TT
authors.lastname: Alkeskjold
authors.forename: Jes
authors.initials: J
authors.lastname: Broeng
authors.forename: Jesper
authors.initials: J
authors.lastname: Lægsgaard
authors.forename: Siddharth
authors.initials: S
authors.lastname: Ramachandran
mesh_terms: D017076:Computer-Aided Design; D003460:Crystallization; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005336:Fiber Optic Technology / Q000295:instrumentation*; D057139:Nanofibers / Q000737:chemistry* / Q000648:ultrastructure*