| Summary: | 碩士 === 國立雲林科技大學 === 電子工程系 === 102 === Low-cost and low-loss terahertz (THz) waveguide is essential for integrating and minimizing terahertz systems. To achieve low loss, it is important to investigate how to couple terahertz wave into waveguide effectively to enhance system performance. In this work, coupling efficiencies of terahertz pipe waveguides and subwavelength fibers are numerically studied. For the pipe waveguides, influences of operating frequency, waveguide shape, and polarization on coupling efficiency are examined. For the subwavelength fibers, the relationship between operating frequencies and electric field confinement and the factor for optimizing Gaussian beam waist are investigated.
We first take the slab type hollow waveguide, which can be treated as the one-dimensional version of the pipe waveguide, into consideration. Numerical results show that, owing to the mismatch between field distributions of waveguide mode and THz source, the coupling efficiency is relatively low at resonant frequencies. However, at antiresonant frequencies, the coupling efficiency can be well above 90%. Moreover, TE mode is higher than TM mode in coupling efficiency. While for the two-dimensional pipe waveguide, the coupling efficiency has the same trend in frequency which is similar to that shown in the 1D case. For the case of direct coupling between two pipe waveguides, the coupling efficiency for waveguides with the same shape is higher than the coupling efficiency for waveguides with the different shape. Moreover, when shapes of the two connecting pipe waveguides are the same, coupling efficiency for circular shape is higher than that for square shape.
For the terahertz subwavelength fibers, it is found that coupling efficiency from the source to the subwavelength THz fiber can be above 90%. However, if the operating frequency decreases, the coupling efficiency will become a little bit lower because the field is less confined.
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