A Design of Terahertz Broadband Filters and its Effect in Eliminating Asymmetric Characteristics in Device Structures

We report a straightforward way to design polarization-insensitive broadband bandstop filters in terahertz range by fabricating identical metal patterns on both sides of a dielectric substrate with one layer rotated 90° to the other. The unit cells used in such designs are the well-studied split-ring-resonators, hence the frequency range of the stop band can be easily tuned by varying the dimensions of the unit cell structures. Through simulation analysis, we show that such fabrication method requires no alignment in lithography step and works with common dielectric substrates. Two types of substrates, 1-mm-thick quartz and 100-μm-thick polyethylene terephthalate, were used as a demonstration. The transmission level stayed below 12% for a stopband of 0.42-THz frequency range. Lastly, we reasoned with simulation results that the proposed broadband filters give consistent performance regardless of the gap location in the unit cell, which will further extend their use in practical applications.