The terahertz (THz) region occupies a large portion of the electromagnetic spectrum, located between the microwave and
optical frequencies and normally is defined as the band ranging from 0.1 to 10 THz. In recent years, this intermediate
THz radiation band has attracted considerable interest, because it offers significant scientific and technological potential
for applications in many fields, such as sensing [1], imaging [2] and spectroscopy [3]. However, waveguiding in this
intermediate spectral region is a major challenge and strong dielectric and conductive losses in the terahertz frequency
range have been a major problem for waveguiding. The conventional guiding structures exemplified by microstrips,
coplanar striplines and coplanar waveguides [4] are highly lossy and dispersive. However, so far the most promising
dielectric waveguides have been the use of photonic crystal fibers at terahertz frequencies [5, 6] and metal coated guides
[7] at terahertz frequencies. In this paper, various types of practical dielectric and metal coated waveguides are evaluated
and design optimization of Quantum Cascade Lasers, MMI-based power splitters and narrow-band filters are presented,
by using full-vectorial finite element method [8].
The evolution of surface plasmon supermodes through the effective coupling of isolated surface plasmon modes in a
semi-insulating quantum cascade laser (QCL) waveguide is thoroughly discussed here. The effect of varying the material
and geometric parameters of GaSb/AlGaSb QCL operating at 3.0 THz are thoroughly studied using a full-vectorial finite
element method.
Vectorial modal field profiles and the complex propagation characteristics of Surface Plasmon modes in optical and THz
guided wave structures are presented by using a H-field based finite element method. It is shown here that by
engineering the metal electrode mode selectivity in a Quantum cascade laser can be enhanced. Additionally, it is also
shown that by introducing Teflon coating, the propagation loss of a hollow-core rectangular waveguide can be
significantly reduced.
When the cross-section of an optical waveguide is much smaller than the operating wavelength, unique materials and
structural dependent properties can be observed. In this regard silicon has been particularly attractive as the low-cost and
mature CMOS fabrication technology widely used in the electronics industry can be exploited. The high index contrast
of silicon allows light confinement in submicron size waveguides, along with the creation of very compact bends, to
allow increased functionality of photonic integrated circuits. A rigorously H-field based vectorial modal analysis has
been carried out, which can more accurately characterize the abrupt dielectric discontinuity of a high index contrast
optical waveguide. As a result, the full-vectorial H and E-field and the Poynting vector profiles are shown in detail. The
work done and reported reveals that the mode profile of a circular silicon nanowire is not circular and also has a strong
axial field component. Arising from the results of the analysis, the characteristics of single mode operation, the vector
field profiles, the modal ellipticity and the group velocity dispersion of this silicon nanowire both circular and planar are
presented. The modal hybridness and birefringence of rectangular silicon nanowires and slot-type waveguides are also
presented.
Surface plasmons are confined to the surfaces which interact strongly with the electromagnetic waves.
They occur at the interfaces where the relative permittivities of the bounding materials are of opposite
sign. It is well know that some metals and highly doped semiconductor shows highly negative
relative permittivity and such a structure with a dielectric cladding can support surface plasmon
modes. These modes decay exponentially, they can be highly localised and can also be confined
inside a sub-wavelength size guided wave structure. A rigorous full vectorial finite element-based
approach has been developed to characterize a wide range of plasmonic devices, both at optical and
terahertz frequencies. Results for wave confinement in quantum cascaded lasers for terahertz (THz)
frequencies and metal coated photonic crystal fibres are presented.
Compact Quantum Cascade Laser waveguides have been analyzed using the full-vectorial finite element method. Modal
intensity profiles, detailed power confinements and loss factors have been characterized for waveguides based on
GaSb/AlGaSb multiple quantum well structures. Variations in these key parameters were also further investigated whilst
varying the semiconductor doping concentration. Higher order modes having a low propagation loss were also shown.
The emergence of terahertz (THz) technology has opened up a new frontier of fundamental research with many novel
applications, such as in imaging and spectroscopy. For these fibers, the waveguiding parameters are easily controllable,
when compared to conventional all silica optical fibers and recently there has been an initiative to use such waveguides
for guiding THz frequencies. In this context, A rigorous full-vectorial finite element method has been used to obtain the
modal solutions of simple, high-density polystyrene dielectric waveguides along with their propagation constants,
attenuation characteristics, vectorial modal field profiles, the spot-size and the modal hybridness.
Finite element analysis, based on the vector H-field formulation and incorporating the perturbation technique, is used to
calculate the complex propagation characteristics of silver/polystyrene (PS) coated hollow glass waveguides for terahertz
(THz) frequency radiation. The mode profiles, which after emerging from the waveguide travel through either a
horizontal or vertical polarizer are also presented and camera images of these profiles are compared to numerically
simulated results. The effect of the polystyrene coating thickness on the attenuation characteristics of these waveguides
has also been investigated and is shown to be critical to their design optimization.
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