Scaling laws for photonic bandgaps in photonic crystal fibres are described. Although only strictly valid for small refractive index contrast, they successfully identify corresponding features in structures with large index contrast. Furthermore, deviations from the scaling laws distinguish features that are vector phenomena unique to electromagnetic waves from those that would be expected for generic scalar waves.

We report a new type of photonic bandgap that becomes substantial at remarkably low air-filling fractions (~60%) in triangularlattice photonic crystal fibres (PCF) made from high index glass (n / 2.0). The ratio of inter-hole spacing to wavelength makes these new structures ideal for the experimental realisation of hollow-core PCF in the mid/farinfrared, where suitable glasses (e.g., tellurites and chalcogenides) tend to have high refractive indices.

To fully characterize photonic crystal guided wave optical devices, one needs to measure the spatial variation of both the phase and amplitude of the electromagnetic field. In this work, we simultaneously measure the intensity and phase in the near field of both propagating and evanescent fields by incorporating a scanning near-field optical microscope into one arm of a Mach–Zehnder interferometer. We demonstrate the technique by imaging the phase fronts of an evanescent wave formed by total internal reflection and by measuring the phase variation in the LP11 mode in an overmoded optical fiber.

It is shown that thin films of dielectric, etched through with a suitably chosen lattice of holes, can support surface-emitting vertical resonances with very-high-cavity Q factors (approximately 10(5) in the case of Al(x)GaAs(1-x) on oxidized AlyGaAs1-y). A Bloch-wave expansion is used to develop a complete vector-field analysis of these resonances and to reveal their underlying physics. Since they do not require multilayer mirrors, such resonators are a practical and simple replacement for conventional vertical-cavity surface-emitting laser structures. Other applications include wavelength-division-multiplexing components and highly sensitive gas detectors.

A major limitation to attaining low-loss single-mode guidance in hollow core photonic crystal fibre (PCF) is surface guided modes that are trapped in the core surround. This is particularly severe when high index (n > 2) glasses are used. By modelling a structure that has the characteristic features of a realistic fibre we show that, by tuning the thickness of the core wall, the influence of these 'surface' modes can be minimised. For a refractive index of 2.4 we predict power-in-air fractions of over 95% over a fractional bandwidth of ~ 5%, peaking at over 98%. The designs are appropriate for mid- to far-IR PCFs for which suitable glasses (e.g., tellurites and chalcogenides) have high refractive indices.