A split-ring-resonator-based polarization-insensitive ultra broadband filter in terahertz range
Split-ring-resonators (SRRs) are one of the most common unit cell designs for metamaterials. Though extensively studied and well understood, such devices are often used as narrow-band filters due to SRRs’ sharp resonance to electromagnetic wave. In this work, based on the idea of patterning metal SRRs on both sides of a dielectric substrate while rotating patterns on one side 90o to the other, we show that simple circular SRR can be a building block for broadband filters in terahertz (THz) range. The design principle is detailed with simulation results, showing that such fabricated devices essentially equates to two narrow-band filters on both sides of the substrate connected in series. By changing the unit cell from single SRR to double SRR, we effectively expanded the stop band width of the broadband filter. Devices were created on two types of substrates, 1 mm thick quartz and 100 µm thick polyethylene terephthalate (PET), demonstrating the ease and wide applicability of the fabrication process, while a bandwidth of as large as 1.40 THz has been achieved.