Abstract
We experimentally and theoretically demonstrate a class of narrowband transmissive filters in the terahertz spectrum. Their operation is based on the excitation of guided-mode resonances in thin films of the low-loss cyclo-olefin polymer Zeonor, upon which aluminum stripe and patch arrays are patterned via standard photolithography. The filters are engineered to operate in low atmospheric loss THz spectral windows, they exhibit very high transmittance and quality factors, compact thickness, and mechanical stability. The dependence of their filtering properties on the geometrical parameters, the substrate thickness and the angle of incidence is investigated, discussing the physical limitations in their performance. This class of filters provides a cost-effective solution for broadband source or channel filtering in view of emerging terahertz wireless communication systems.
Highlights
Terahertz (THz) frequencies are increasingly capturing the attention of the scientific community, as they represent the less exploited region of the electromagnetic spectrum and they bridge the gap between optics and radiofrequency science and technology
High transmittance and narrow-linewidth THz transmissive filters have been demonstrated based on interfering metasurfaces, which result in a bandpass frequency comb and as such do not allow for out-of-band rejection[40]
Contrary to the frequency-selective surfaces (FSS)-based established THz filters that typically transmit the THz wave through subwavelength apertures in a free-standing configuration, the operation of the proposed filters relies on the excitation of guided mode resonances (GMR) stemming from the coupling between waves on periodic structures with modes guided in a dielectric substrate
Summary
Superscripts (Teig), (Tfw), and (ETDS) stand for “Theoretical/eigenfrequency analysis”, “Theoretical/full-wave analysis” and “Experimental TDS measurements” respectively. Since material dispersion cannot be incorporated in a straightforward manner, in each studied case the Al permittivity was taken equal to the value given by the Drude model at the resonant frequency observed in the corresponding transmittance spectra This analysis provides additional evidence that the resonant behaviour of the proposed filters stems from the excitation of guided-modes in the substrate. For the cross-polarization the Al grating acts as a nearly ideal mirror Such polarization-sensitive behavior was investigated in the case of chip #2, which is based on Al-stripe lattice, and designed to have a resonant frequency at 850 GHz. In order to elucidate more on the physics behind the observed resonance in the transmittance spectrum of the device, we have calculated the profiles of the electric field components via FEM full-wave simulations off- and on-resonance, at the frequency of 600 and 667 GHz, respectively.
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