Fano Resonances in Location-Dependent Terahertz Stub Waveguide

The quest for simpler structures that do not require the use of nanofabrication techniques and exhibit high Q Fano resonances has attracted growing interest in the past decade. Here, we study an arrangement of coupled resonator waveguides that can excite Fano resonances. The results show that an odd mode, except for the usual even mode, is excited due to the symmetry breaking of the position stub intersection. The superposition of the even and odd modes generates a Fano-shaped spectrum with a very narrow linewidth. Coupled mode theory is used to analyze these waveguide-based Fano resonances. Experimental results obtained using VNA and VDI show good agreement with theory and simulations. Such waveguide-based Fano resonances can be tailored and are simple in structure and have potential applications in narrowband filtering, sensing, lasing, and nonlinearity enhancement.