BACKGROUND
A broadband, wireless terahertz signal is comprised of a multitude of individual frequency components. These frequencies travel at different speeds through the atmosphere, which causes the composite signal to spread out in time, as some frequency components arrive later than others. This is an undesirable effect known as “group delay dispersion” (GDD). Positive GDD occurs when terahertz waves propagate through the atmosphere, and this indicates that high frequencies arrive later than low frequencies. The resulting temporal broadening due to GDD distorts the received signals, reduces the achievable data rate, and may prevent bitstream resolution entirely under serve conditions. Thus, a mechanism to compensate for atmospheric dispersion before a terahertz signal is resolved is necessary.
SUMMARY OF TECHNOLOGY
The invention disclosed in this document provides such a mechanism. Generally speaking, the invention is realized as a stratified structure of transparent, dielectric layers and/or frequency-selective surfaces and/or structured dielectrics and/or artificial dielectrics backed by a highly reflective surface (which may or may not be frequency selective). Specific structures (embodiments) of the invention are described later in this disclosure. When the structure is illuminated by an incident terahertz signal, multiple reflections off the material boundaries and resonances between the layers cause the signal to experience frequency-dependent interference with itself. As some frequencies will penetrate deeper into the structure and resonate between layers for a longer period of time, this interference is manifested as frequency-selective surfaces are tuned such that the group delay of the structure as a whole produces GDD of approximately the same frequency-dependent magnitude as that introduced by propagation through the atmosphere, except of the opposite (negative) sing, thus eliminating GDD as a whole. Multiple such structures may be used in concert to achieve better compensation of the signal. The parameters of the device as a whole (such as layer thicknesses and/or frequency-selective surface geometries and/or polarization and/or layer spacing and/or number of bounces off of a single structure and/or the inclusion or prevention of bounces from a multiplicity of structures with either equal or differently tuned responses) may be dynamically adjusted to match changing atmospheric conditions and signal ranges.
POTENTIAL AREAS OF APPLICATION
MAIND ADVANTAGES
STAGE OF DEVELOPMENT