PHOTONIC CRYSTAL FIBERS : OPTIMIZATION FOR TELECOMMUNICATION PURPOSES

Photonic crystal bers are optical waveguides based on a periodic air-glass structure o ering higher design exibility compared to that of standard single-mode bers. On one hand, such bers allow for extremely tight mode con nement related to increased nonlinearity and better chromatic dispersion controllability. On the other hand, photonic crystal bers enable light guiding in very large cores keeping the single-mode regime of operation and low loss. This doctoral thesis deals with scienti c problems related to control of light propagation within photonic crystal bers and it contributes mainly to the areas of optics, photonics, telecommunication and sensing. The objective is to describe main design principles, nd their limitations and consequently optimize ber geometries. Until now, these limitations have not been investigated thoroughly and therefore became the central point for the doctoral thesis. The goal is not to present ber structures with novel geometries, but to investigate new limits in designing photonic crystal bers. One of the presented designs is a photonic crystal ber with a dispersion parameter as close as possible to zero value. Further e ort is applied on a hexagonal ber structure that is optimized to operate as a dispersion compensator of standard single-mode bers. The author predicts that the negative dispersion parameter cannot be higher in this structure operating over a bandwidth larger than that considered in this thesis. Another important part of the thesis aims to control of con nement loss, which is used to design a narrowband ber lter as well as an e ectively single-mode photonic crystal ber with large e ective mode area and chalcogenide background. Fiber designs were carried out by varying key geometrical parameters such as holeto- hole spacing, airhole diameters in selected rings and number of rings around the ber core. The in uence of each structural parameter on modal properties is examined and described in detail. Understanding the mechanism governing chromatic dispersion as well as con nement loss is necessary not only for the ber design, but also to predict the potential manufacturing tolerances. Last but not least, supercontinuum generation is investigated in the designed chalcogenide ber using the split-step Fourier method. The modal properties are calculated by the full-vectorial nite di erence frequency domain method. The simulation models of presented bers are veri ed by convergence testing.Katedra telekomunikační technik