Retaining and characterising nano-structure within tapered air-silica structured optical fibers

Critical phenomenon in tapered dielectric structures

We demonstrate the existence of a critical behavior of a single electromagnetic mode propagating in a tapered dielectric structure. This behavior is described in terms of a critical phase velocity in the case of an adiabatic tapering. In the vicinity of this critical phase velocity, the tapered structure no longer confines the radiation and a significant fraction of the power escapes transversely.

Enhanced method for determining the optical response of highly complex biological photonic structures

We present a set of techniques that enhances a previously developed time domain simulation of wave propagation and allows the study of the optical response of a broad range of dielectric photonic structures. This method is particularly suitable for dealing with complex biological structures, especially due to the simple and intuitive way of defining the setup and the photonic structure to be simulated, which can be done via a digital image of the structure. The presented techniques include a direction filter that permits the decoupling of waves traveling simultaneously in different directions, a dynamic differential absorber to cancel the waves reflected at the edges of the simulation space, and a multifrequency excitation scheme. We also show how the simulation can be adapted to apply a near to far field method in order to evaluate the resulting wavefield outside the simulation domain. We validate these techniques, and, as an example, we apply the method to the complex structure of a microorganism called Diachea leucopoda, which exhibits a multicolor iridescent appearance.

Characterization of nanoscale features in tapered fractal and photonic crystal fibers

The internal structure of nanostructured air-silica fiber probes have been characterized using a combined focused ion beam and scanning electron microscopy technique. The collapse rate of the air-holes is shown to differ substantially between a regular photonic crystal fiber (PCF) and the quasi-periodic Fractal fiber. The integrity of the Fractal fiber structure is maintained down to an outer diameter as small as 120 nm, whereas the air-holes of the regular PCF begin to collapse when the outer diameter is approximately 820 nm. The observed smallest hole diameter of 10 nm is suggested to be due to physical limits imposed by the molecular structure of silica. These results confirm structural inferences made in previous publications.

Manipulation of spontaneous emission in a tapered photonic crystal fibre

We characterize the spontaneous emission of dye that is introduced into the central core of a tapered photonic crystal fiber. Since the photonic crystal period in the fibre cladding varies along the taper, the transmission and spontaneous emission spectra over a wide range of relative frequencies can be observed. The spontaneous emission spectra of the fibre transverse to the fiber axis show suppression due to partial band-gaps of the structure, and also enhancement of spontaneous emission near the band edges. We associate these with van Hove features, as well as finite cluster size effects.

Exposure and characterization of nano-structured hole arrays in tapered photonic crystal fibers using a combined FIB/SEM technique

This paper presents a technique to expose and characterize nano-structured hole arrays in tapered photonic crystal fibers. Hole array structures are examined with taper outer diameters ranging from 12.9 microm to 1.6 microm. A combined focused ion beam milling and scanning electron microscope system was used to expose and characterize the arrayed air-silica structures. Results from this combined technique are presented which resolve hole-to-hole pitch sizes and hole diameters in the order of 120 nm and 60 nm, respectively.

Tapered photonic crystal fibers

We demonstrate the tapering of a photonic crystal fiber to achieve a microstructure pitch of less than 300 nm. We probe the tapered fiber in the transverse geometry to demonstrate the scaling of the photonic bandgaps associated with the microstructure. We show that the fundamental gap can be shifted down to the communications wavelengths, or even further to the visible spectrum. Our optical measurements are correlated with band structure calculations.