Design and optimization of terahertz waveguides with low loss and dispersion




Shiran, Vahid

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Electromagnetic waves in the terahertz spectral range have gained significant research focus due to their applications in various fields of science. To effectively generate and integrate terahertz waves in systems, appropriate waveguide design is critical. Conventionally waveguides have been used to control the propagation of electromagnetic waves. A waveguide with low loss and dispersion is always preferred. But achieving these characteristics is quite challenging especially if operating in the terahertz spectral range. There are inherent material and geometric limitations that exist for terahertz waveguides. It is therefore important to optimize the design to enable their use in applications efficiently. This thesis investigates the characteristics of three primary terahertz waveguides based on the underlying theory and results obtained from simulations. The three waveguides are parallel-plate waveguides, two-wire waveguides, and coplanar striplines. The work in this thesis mostly focuses on coplanar striplines, optimal for building a highly efficient commercial and portable terahertz system-on-chip (TSOC). The contribution of the thesis is around the use of different types of passive components mounted on a thin commercial Silicon Nitride membrane. A bias tee is introduced which is a combination of interdigitated electrodes and a meander inductor. The length of the interdigitated electrodes and the gap between them are 55 um and 5 um, respectively. The S21 parameter for this structure ranges from -24 dB/mm at near-zero frequencies to -0.8 dB/mm at 1 THz. This indicates that the designed bias tee can appropriately block low frequencies. Split-ring resonators are also used to act as band-stop filters. The resonant frequency of the resonator depends on the radii of the split-rings. In the optimized design, the internal radius of the outer ring is 25 um and the external radius of the inner ring is 20 um. This results in a narrowband band-stop filter with its resonant frequency centered at 701 GHz. The optimized final TSOC design discussed in this work uses these passive components placed on the Silicon Nitride membrane and is shown to have a total loss that is 3 dB/mm less than any of the previous work for terahertz frequencies.



Terahertz waveguide, On-chip-system, Low loss