The nonlinearity in optical fibres can be enhanced significantly by reducing the effective mode area or by using materials
with higher nonlinear-index coefficient (<i>n<sub>2</sub></i>). In this paper we combine these two concepts and experimentally
demonstrate enhanced Kerr nonlinear effects in tapered highly nonlinear As<sub>2</sub>Se<sub>3</sub> chalcogenide fibre. We taper the fibre to sub-wavelength waist diameter of 1.2 μm and observe enhanced nonlinearity of 63,600 W<sup>-1</sup>km<sup>-1</sup>. This is 40,000 times larger than in silica single-mode fibre, owing to the 400 times larger <i>n<sub>2</sub></i> and almost 100 times smaller effective mode area. We also discuss the role of group velocity dispersion in these highly nonlinear fibre tapers.
Chalcogenide glass based optical waveguides offer many attractive properties in all-optical signal processing because of the large Kerr nonlinearity (up to 420 × silica glass), the associated intrinsic response time of less than 100 fs and low two-photon absorption. These properties together with the convenience of a fiber format allow us to achieve all-optical signal processing at low peak power and in a very compact form. In this talk, a number of non-linear processing tasks will be demonstrated including all-optical regeneration, wavelength conversion and femtosecond pedestal-free pulse compression. In all-optical regeneration, we generate a near step-like power transfer function using only 2.8 m of fiber. Wavelength conversion is demonstrated over a range of 10 nm using 1 m of fiber with 7 ps pulses, peak power of 2.1 W, and 1.4 dB additional penalty. Finally, we will show efficient compression of low-power 6 ps pulses to 420 fs around 1550 nm in a compact all-fiber scheme.
These applications show chalcogenide glass fibers are very promising candidate materials for nonlinear all-optic signal processing.
In this paper we review the fabrication and characterisation techniques of m icrostructured optical fibre (M OF) tapers, their fundam ental waveguiding properties and potential applications. W e fabricate photonic crystal fibre tapers without collapsing the air-holes, and confirm this along the taper with a non-invasive probing technique. We then describe the fundam ental property of such tapers associated with the leakage of the core m ode that leads to long wavelength loss. We also revisit the waveguiding properties in another form of tapered MOF photonic wires, which transition through waveguiding regimes associated with how strongly the mode is isolated from the external environment. We explore these regimes as a potential basis for evanescent field sensing applications, in which we can take advantage of controlled airhole collapse as an extra dimension to these photonic wires.