A chirped photonic-crystal fibre

Photonic crystals have widely increased the facility to guide and confine light at wavelengths close to the optical wavelength(1-3). Because they can include extremely sharp bends, photonic-crystal waveguides are a key element in future integrated optical devices(4). Moreover, they enable the manipulation of the spontaneous emission properties of luminescent devices(5), the localization of light in microcavities(6), and they may serve to generate negative refraction(7,8). A special class of these devices are the hollow-core photonic-crystal fibres(9-11), which confine the light by means of a periodic cladding, consisting of several layers of identical cells. This design resonantly decreases the transmission losses of such fibres to values of a few dB km(-1) in a narrow wavelength range. However, the rather narrowband transmission bands and the detrimental third-order dispersion characteristics of this single-cell design generally render application of such hollow-core fibres difficult in the femtosecond range(12). Therefore, no fibre-based concept can currently provide guiding of sub-100 fs pulses over extended distances. By introducing a radial chirp into the photonic crystal, we here demonstrate a novel concept for photonic-crystal fibres that breaks with the paradigm of lattice homogeneity and enables a new degree of freedom in photonic-crystal-fibre design, eliminating much of the pulse duration restriction of earlier approaches.