Characterization of novel designs of Terahertz fibers

Abstract

This thesis characterizes a range of novel designs of Terahertz (THz) fibers fabricated from photonic crystal fiber’s fabrication techniques. These fibers are characterized using a highly versatile THz time-domain spectroscopy (THz TDS) setup. The coherent THz TDS setup produces a broadband pulse of THz radiation from 0.2 to 1.5 THz frequency range, and measures the electric field of the THz pulse. This allows for direct extraction of amplitude and phase details via Fourier transform of the measured temporal waveform. For all of the fibers, we present, for the first time, the experimentally determined values for the group velocity dispersion β2 parameter in the THz region. We experimentally observed propagation of an HE11 mode in the THz high-index guiding microstructured fiber with a single layer of air-holes as its cladding. The fibers are made of a low loss and a very low dispersion polymer known as Zeonex in the THz spectral range. The fibers are shown to exhibit negligible waveguide loss. We have achieved a high coupling efficiency, close to 80%, using the specially designed symmetric-pass lenses. Our measurements show that low dispersion over a wide range of THz frequencies can be achieved in these fibers. These measured data are in good agreement with the simulation results obtained from the effective index method and the finite-difference frequency domain (FDFD) method. Wideband THz guidance in air-core all-dielectric kagome microstructured fibers is demonstrated in this work. High loss peaks identified in the fibers’ loss spectra are associated with the resonance condition related to the core and cladding modes overlap. The fundamental mode propagated in the fibers shows close-to-zero dispersion characteristic in the THz frequencies. We observed good agreement between our measured data and the results from the simulations using FDFD method. THz propagation in a hollow core fiber with wire inclusions is also investigated. The modes’ evolution in the two- and four-wire configurations are characterized. The two-wire configuration is measured to have lower propagation loss than the four-wire configuration. Close-to-zero dispersion propagation is observed in THz frequencies, and the experimental results are in good agreement with the results from the FDFD simulations.