Theis P. Hansen

Highly birefringent index-guiding photonic crystal fibers

Photonic crystal fibers (PCFs) offer new possibilities of realizing highly birefringent fibers due to a higher intrinsic index contrast compared to conventional fibers. In this letter, we analyze theoretically the levels of birefringence that can be expected using relatively simple PCF designs. While extremely high degrees of birefringence may be obtained for the fibers, we demonstrate that careful design with respect to multimode behavior must be performed. We further discuss the cutoff properties of birefringent PCFs and present experimental results in agreement with theoretical predictions on both single- and multimode behavior and on levels of birefringence.

Gas sensing using air-guiding photonic bandgap fibers

We report on experimental studies of gas sensing using air-guiding photonic bandgap fibers. The photonic bandgap fibers have at one end been spliced to standard single mode fibers for ease of use and improved stability

Photonic crystal fiber based evanescent-wave sensor for detection of biomolecules in aqueous solutions

We demonstrate highly efficient evanescent-wave detection of fluorophore-labeled biomolecules in aqueous solutions positioned in the air holes of the microstructured part of a photonic crystal fiber. The air-suspended silica structures located between three neighboring air holes in the cladding crystal guide light with a large fraction of the optical field penetrating into the sample even at wavelengths in the visible range. An effective interaction length of several centimeters is obtained when a sample volume of less than 1 microL is used.

Selective filling of photonic crystal fibres

A model for calculating the time necessary for filling one or more specific holes in a photonic crystal fibre is made. This model is verified for water, and its enabling potential is illustrated by a polymer application. Selective filling of the core in an air-guide photonic crystal fibre is demonstrated for a polymer and for water. Launching light into such a hybrid-material core proves to be very easily done. Finally, a scheme for enabling access to the core alone, by use of a fusion splicer, is presented.

Photonic crystal fibers

Photonic crystal fibers having a complex microstructure in the transverse plane constitute a new and promising class of optical fibers. Such fibers can either guide light through total internal reflection or the photonic bandgap effect, In this paper, we review the different types and applications of photonic crystal fibers with particular emphasis on recent advances in the field.

Ultra-large bandwidth hollow-core guiding in all-silica bragg fibers with nano-supports

We demonstrate a new class of hollow-core Bragg fibers that are composed of concentric cylindrical silica rings separated by nanoscale support bridges. We theoretically predict and experimentally observe hollow-core confinement over an octave frequency range. The bandwidth of bandgap guiding in this new class of Bragg fibers exceeds that of other hollow-core fibers reported in the literature. With only three rings of silica cladding layers, these Bragg fibers achieve propagation loss of the order of 1 dB/m.

Experimental investigation of the polarization properties of a hollow core photonic bandgap fiber for 1550 nm.

The properties of a hollow core photonic bandgap fiber designed for 1.55 um transmission are investigated with special emphasis on polarization issues. Large and strongly wavelength dependent phase and group delays are found. At the same time the principle states of polarization move strongly and erratically as a function of wavelength, leading to strong mode coupling. Wavelength regions with high polarization dependent loss coincide with depolarization due to a polarization dependent coupling to surface modes at these wavelengths.

Experimental investigation of cutoff phenomena in nonlinear photonic crystal fibers

Modal cutoff is investigated experimentally in a series of high-quality nonlinear photonic crystal fibers. We demonstrate a suitable measurement technique with which to determine the cutoff wavelength and verify the technique by inspecting the near field of the modes that may be excited below and above the cutoff. We observe a double-peak structure in the cutoff spectra, which is attributed to splitting of the higher-order modes. The cutoff is measured for seven different fiber geometries with different pitches and relative hole sizes, and very good agreement with recent theoretical work is found.

Dispersion Properties of Photonic Crystal Fibers - Issues and Opportunities

The dispersion, which expresses the variation with wavelength of the guided-mode group velocity, is one of the most important properties of optical fibers. Photonic crystal fibers (PCFs) offer much larger flexibility than conventional fibers with respect to tailoring of the dispersion curve. This is partly due to the large refractive-index contrast available in silica/air microstructures, and partly due to the possibility of making complex refractive-index structures over the fiber cross section. We discuss the fundamental physical mechanisms determining the dispersion properties of PCFs guiding by either total internal reflection or photonic bandgap effects, and use these insights to outline design principles and generic behaviours of various types of PCFs. A number of examples from recent modeling and experimental work serve to illustrate our general conclusions.

Solid-core photonic bandgap fiber with large anomalous dispersion

For the first time, a theoretical investigation is performed for a novel solid-core photonic band-gap fiber design. The design features large positive waveguide dispersion, which enables an anomalous dispersion of up to D=600 ps/km/nm at /spl lambda/=1.55 /spl mu/m.