title: As₂S₃-silica double-nanospike waveguide for mid-infrared supercontinuum generation.
abstract: A double-nanospike As2S3-silica hybrid waveguide structure is reported. The structure comprises nanotapers at input and output ends of a step-index waveguide with a subwavelength core (1 μm in diameter), with the aim of increasing the in-coupling and out-coupling efficiency. The design of the input nanospike is numerically optimized to match both the diameter and divergence of the input beam, resulting in efficient excitation of the fundamental mode of the waveguide. The output nanospike is introduced to reduce the output beam divergence and the strong endface Fresnel reflection. The insertion loss of the waveguide is measured to be ∼2  dB at 1550 nm in the case of free-space in-coupling, which is ∼7  dB lower than the previously reported single-nanospike waveguide. By pumping a 3-mm-long waveguide at 1550 nm using a 60-fs fiber laser, an octave-spanning supercontinuum (from 0.8 to beyond 2.5 μm) is generated at 38 pJ input energy.
authors.forename: Shangran
authors.initials: S
authors.lastname: Xie
authors.forename: Francesco
authors.initials: F
authors.lastname: Tani
authors.forename: John C
authors.initials: JC
authors.lastname: Travers
authors.forename: Patrick
authors.initials: P
authors.lastname: Uebel
authors.forename: Celine
authors.initials: C
authors.lastname: Caillaud
authors.forename: Johann
authors.initials: J
authors.lastname: Troles
authors.forename: Markus A
authors.initials: MA
authors.lastname: Schmidt
authors.forename: Philip St J
authors.initials: PS
authors.lastname: Russell