| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 93 === In the electromagnetic spectrum, terahertz frequencies, which usually defined as those in the range of 100 GHz – 10 THz, form a significant region that connects the microwave and optical-wave bands. Since various important physical phenomena happened in this region, more and more attention had been paid to the investigations of terahertz science in recent years. Many different techniques regarding the generation and detection of terahertz wave were also proposed one after another. However, for the reason that most of the materials have a great absorption constant in the terahertz frequency, the propagation of terahertz wave is usually controlled by metallic reflectors in almost all the applications, which makes the terahertz systems not only vulnerable to environmental disturbance but also inflexible in the construction of application setups. Hence, there will be a lot of difficulties in the future applications of terahertz system for lack of a reliable and low-loss guiding method. In view of this, we proposed and demonstrated a terahertz subwavelength fiber with a very low attenuation constant (~0.01 cm-1) for guiding terahertz wave.
In our design, the sub-wavelength fiber core is made of polyethylene wires or tubes that surrounded by the air serving as the cladding. Due to the sub-wavelength characteristic of the fiber core, the only sustained mode is HE11 which delivers most of the fields in the air cladding, which enormously reduces the degree of core absorption in the propagation. In addition, as polyethylene has a lower absorption constant in the terahertz region, the power delivered in the core will be attenuated less than the cores made of other materials. By adopting above structure, we successfully reduce the loss in terahertz wave guiding which can make the terahertz systems compact and less complex. We believe that it will be very helpful to the realization of terahertz applications such as fiber sensing, biomedical-imaging, and so on.
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