Photonic crystal fibres (PCFs)—thin strands of glass with an intricate array of hollow channels running along their length—offer both hollow and solid glass cores, and allow unprecedented control over dispersion and birefringence, ushering in a new era of linear and nonlinear fibre optics, for example: chiral PCF is circularly and topologically birefringent, supporting optical vortices and in some cases strong circular dichroism; through pressure-adjustable dispersion, gas-filled hollow-core PCF provides an elegant means of compressing pulses to single-cycle durations, as well as underpinning a range of unique sources of tunable deep and vacuum ultraviolet light; microparticles optically trapped inside hollow core PCF van be used to sense physical quantities with high spatial resolution; and strong optomechanical effects in solid-core PCF permit stable timing-modulated high harmonic mode-locking at few-GHz repetition rates.
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