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Cross-sections of (a) standard PPWG with cylindrical silicon lenses for coupling. (b) two-cylinder waveguide coupler for which adiabatic wave compression is used for coupling through the subwavelength gap.
Amplitude transmission of the two-cylinder coupler with TM-polarization for different gap widths. For clarity some of the curves have been lifted as follows: curve , curve , curve , and curve . For small gaps single TEM-mode propagation is observed, while for larger gaps propagation also occurs above the indicated cut-off frequencies.
Amplitude transmission of the two-cylinder coupler for TE-polarization and different gap widths. For clarity the curves have been lifted as follows: curve , curve , and curve . The transmission turns on sharply at the cut-off frequencies. Also higher TE-modes are observed.
Comparison of the transmitted terahertz pulses for the silicon lens coupled PPWG (lower trace) and the two-cylinder coupler (upper trace), both with gaps and mode propagation. Inset: corresponding spectral amplitudes.
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