Perex
Abstrakt: The talk would present work on a new class of terahertz (THz)
waveguides based on structured metal geometries. The waveguides are
designed with the core idea that adoption of planar layout in
fabrication can lead to exponential growth in device capabilities,
analogous to the growth in device capabilities based in electronics.
From a functional point of view, the waveguides rely upon propagation
of surface waves along the surface of metals.
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This approach is
preferred, since dielectrics tend to be lossy at THz and the loss
parameters scales almost quadratically with frequency for most
dielectrics. The loss in propagating wave is minimized by utilizing
metals, which are highly conducting at THz frequencies. Structuring the
metal surface with periodic array of apertures of sub-wavelength
dimension allows bound surface wave to propagate as the wave can
evanescently decay into the metal. This phenomenon is referred as the
coupling of propagating wave to surface plasmon polariton (SPP) like
mode at the interface of structured metal surface and air. Thus, these
propagating THz waves are simply surface plasmon-polaritons (SPPs).
Similarly, complimentary structures that do not perforate the metal, but
rather stand on the metal surface also support SPPs. The wavelength of
SPPs can be controlled by changing the dimension of these
apertures/structures, since the dispersion relationship of the medium
depends on the geometrical size. This engineering capability has been
exploited in creating all the waveguides presented in this thesis. The
devices presented are categorized based on the fabrication technique.
Each technique is unique in its own regard and can be selected based on
functional needs. A commonly adopted process of laser ablation covers a
wide set of waveguides presented here. In one of the waveguides
fabricated using ablation technique, the role of disorder is discussed.
The waveguide with introduction leads to observance of localized mode
with spectral and spatial feature like Anderson localized modes of
photons. It is the first report of localized mode at THz frequency. 3D
rapid prototyping involving 3D printer is used to create waveguides with
complex layout that can allow for multi-plane signal routing. This also
is the first demonstration of 3D printing in the development of THz
devices. In another approach a unique fabrication technique had to be
developed to create waveguides mediums with negative index of refraction
(NIM) as they require feature sizes which cannot easily be attained
using conventional clean room techniques and 3D printing. This new
fabrication approach uses a sacrificial layer technique that is used
create an effective medium with negative index of refraction and length
on the order of tens of wavelength.