title: All-fiber anamorphic core-shape transitions.
abstract: We demonstrate low-loss anamorphic transitions between circular and rectangular fiber cores with aspect ratios up to 5:1, and hence improved coupling from a diode laser by using only a spherical lens. Differential hole pressurization and localized heating of a stock photonic crystal fiber inflates the holes at different rates. Some holes are plugged in the fiber end face where pressure is applied, so they remain at ambient pressure. Alternatively, holes of different sizes expand at different rates because the effective pressure due to surface tension differs.
authors.affiliation: Department of Physics, Unviersity of Bath, Claverton Down, Bath, UK.
authors.forename: A
authors.initials: A
authors.lastname: Witkowska
authors.forename: K
authors.initials: K
authors.lastname: Lai
authors.forename: S G
authors.initials: SG
authors.lastname: Leon-Saval
authors.forename: W J
authors.initials: WJ
authors.lastname: Wadsworth
authors.forename: T A
authors.initials: TA
authors.lastname: Birks