Supercontinuum generation using picosecond pulses pumped into cobweb photonic crystal fibres is investigated. Dispersion profiles are calculated for several fibre designs. The influence of the fibre structural parameters on the location of the Stokes/anti-Stokes peaks and gain bandwidth is investigated. We find that four-wave mixing is the dominant physical mechanism for the pumping scheme considered here, and that there is a tradeoff between the spectral width and the spectral flatness. The balance of this tradeoff is determined by nanometer-scale design of the fibre structural parameters.
Photonic crystal materials and waveguides have since their appearance in 1987 attracted very much attention from the scientific community. From being a more academia discipline, new components and functionalities have emerged, and photonic crystals have today started to enter the field of commercial devices. Especially the photonic crystal fiber (PCF) with its lattice of air holes running along the length of the fiber has matured, and the technology provides a large variety of novel optical properties and improvements compared to standard optical fibers. With respect to optical sensors, the photonic crystal structures have several important properties. First of all the wavelength-scale periodically-arranged material structures provide completely new means of fabricating tailored optical properties either using modified total internal reflection or the photonic bandgap effect. Secondly, the new materials with numerous micro- or even nano-scale structures and voids allow for superior mode control, use of polarization properties, and even more a the potential of close interaction between optical field and the material under test. The present paper will be using the example of the relatively mature photonic crystal fiber to discuss the fundamental optical properties of the photonic crystals, and recent examples of their use as optical sensors will be reviewed.
Photonic crystal fibers (PCF) exhibit many challenges with respect to production. One property of such fibers that make them more complicated than standard fibers is their cladding structure that consists of air holes. These holes are typically arranged in a periodic pattern formation. We propose a novel monitoring method for non-destructive and non-invasive characterization of hole diameter and hole spacing of such photonic cladding structures. This method is applicable simultaneously to drawing a fiber but also as an off-line non-destructive characterisation method. By transversal illumination of a crystal fiber with a white light source, a colourful diffraction pattern can be observed. Hue, saturation and intensity (HSI) analysis of this diffraction pattern reveals information about 1) density of the number of cladding holes present, 2) air hole diameter, and 3) air hole spacing. This HSI based measurement method does not give absolute values for the fiber parameters but is very applicable as a differential measurement technique sensitive to even minor changes in the cladding structure, and may, therefore, potentially serve as a sensitive monitoring method during fabcication of PCFs. We will present comparative results for various types of photonic crystal fibers.