CUDOS@USyd Research

Microstructured and tapered fibre devices ...

Martijn de Sterke, Benjamin Eggleton, Boris Kuhlmey, Eric Magi, Ross McPhedran, Hong Nguyen, Cameron Smith, Michael Lamont, Chunle Xiong

Photonic crystal fiber
Photonic crystal fiber or microstructured optical fibres (MOFs) are optical fibres with holes running along their length, have attracted considerable interest in the last ten years for their extraordinary guidance properties. Depending on their geometry, MOFs can guide light through modified total internal reflection, photonic bandgap effects or, when the holes are infiltrated by high index fluids, through antiresonant backscattering from the holes (so called ARROW fibres).

Interesting properties
The different guidance mechanisms give MOF structures the ability to guide light in hollow cores, remain single-moded over an infinite wavelength range, confine light in very small cores with associated non-linear coefficients orders of magnitude higher than in standard fibres or have exceptional group velocity dispersion. Among these properties the latter two are in fact mainly due to the strong refractive index contrast between the silica core and the holes, and narrow silica rods, called microfibres, can exhibit very similar properties. Microfibres typically have diameters of the order of a micrometre, and could be used for microphotonic integration.

Nonlinear properties
Because they can have large non-linear coefficients and almost arbitrary group velocity dispersion, ARROW MOFs are an excellent
platform for the demonstration of non-linear processes and soliton physics. Further, the fluid's refractive index in the holes responds differently from the refractive index of the silica background, so that dispersion and confinement properties can be tuned to a large extend by controlling the temperature.

Using temperature gradients, dispersion properties can be varied along the fibre, giving a useful additional degree of freedom for non-linear processes. We are also extending the ARROW picture of the guidance mechanism, with which important physical insight on guidance properties of the overall complex structure can be extracted from the knowledge of resonances of single inclusions. We have started using the ARROW model to design novel MOF devices, but the extended ARROW picture is not restricted to MOFs and is also useful for the understanding of planar photonic crystal structures.

Fibre Tapers
Through tapering, even conventional fibres can get access to strongly modified waveguiding properties. The tapering of microstructured fibres therefore provides a particularly exciting platform for photonic micro-devices, sensing and enhanced nonlinear optics. The fibre taper rig is a computer controlled machine which heats and stretches optical fibre to produce a fibre taper. The taper profiles are tailored by the appropriate choice of flame brushing profile, elongation and rate of elongation. The taper rig is used to modify the physical properties of both conventional as well as microstructured fibers. These include shifting the fundamental band gap of photonic crystal fibre, micro-pipettes for micro-fluidic experiments, nano-wires for photonic circuits and super-continuum generation. We have used our taper rig facility to demonstrate fundamental effects and important new applications in these microstructured fibre tapers.

Recently we have used the taper rig to create localised sensing regions in tapered microstructured fiber photonic wires, in which the guided mode is protected from the external environment, even at 10µm diameter. We have also demonstrated microcoils using such fibre tapers, which can be bent into a loop as tight as 100µm, and yet exhibit low bend-loss (below 0.1 dB). Since the guided mode is embedded within the taper, no resonant effects are observed in the microcoils, contrary to microcoils of conventional step-index fibers with similar dimensions.

Authorised by: Prof. Ben Eggleton
Maintained by: Bill Corcoran
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