A Dielectric Guided-Wave Device Platform for Terahertz/Sub-Millimeter Wave Applications


Student thesis: Doctoral Thesis

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  • Peng ZHOU


Awarding Institution
Award date19 Jul 2016


The field of Terahertz/sub-millimetre (THz/Sub-mm) wave has attracted great attention because this slice of the electromagnetic spectrum that lies between the microwave and the optical regimes has unique attributes that not only allows it to propagate into a variety of substances, such as textiles, synthetics and paper but also features characteristic absorption lines for biomolecules, proteins, and explosives. These unique features make these electromagnetic waves ideal to be exploited in potential applications in areas such as medicine, communication and in particular security.
As the operating frequency of these applications keeps increasing and moving further away from the microwave frequency regime, conventional metallic based guided-wave components will need to be scaled smaller and smaller to satisfy the required single mode operation condition. Thus, it becomes more challenging and expensive to design and build these components with the fabrication precision that they require. One method to overcome this fabrication precision challenge is to adopt techniques from the optics regimes of using dielectric waveguide structures. A number of dielectric waveguide structures based on a variety of material systems and configurations have been proposed and demonstrated in THz/Sub-mm wave, with various degrees of success in terms of performance and manufacturability. The aims of this study were to design and demonstrate a low cost dielectric guide-wave device platform for THz/Sub-mm wave application based on common commercial material platform that is suitable for mass production.
In this study, absorption properties in the THz band of common industrial thermoplastics were first investigated with THz time-domain spectroscopy to determine if they are suitable for operation in the THz regime. It was found that a relatively low absorption of less than 1 per centimeter was observed for most of the commercial thermoplastics. The result shows that they are potentially suitable for operation in the lower THz range and Sub-mm wave regime. Furthermore, these thermoplastics are compatible with the various moulding processes in the industry making them mass producible.
Using these thermoplastics and the industrial injection moulding process, we designed and demonstrated transition adaptors that effectively transfer signal between the conventional metallic waveguide systems, such as the input/output ports of network analyzers, to both the rectangular and circular dielectric waveguide structures. The measured throughput loss results of approximately 1 dB per transition in frequency range of 160 GHz to 220 GHz agree well with the simulation results.
To show the viability of the proposed device platform, we have designed and demonstrated a variety of power splitting components, including Y-junction-based 1 by 2 power splitter and Multi-mode Interference (MMI)-based 1 by N power splitters. The result of Y-junctions shows that broadband and even power splitting of within 0.5 dB between all output ports can be achieved with an adiabatic design; for the 1 by N MMIs, although the power can almost be equally distributed to all output ports, they have a limited operation range due to the total output power becoming lower at higher frequency due to the shallow focal spot. These measured results reveal that these structures can potentially be used in practical THz/Sub-mm wave functional devices.
We believe that the proposed dielectric guided-wave platform with the power adaptors and power splitting devices have shown a viable path to lower the manufacturing cost of THz components, in particular in the lower THz and Sub-mm wave regime. Furthermore, nano-particles and/or desired elements with various properties can be mixed into the thermoplastics and lead to future advanced devices based on the demonstrated platform.