K-space design of terahertz plasmonic filters

Abstract

Wireless communication systems in the terahertz (THz) frequency range promise to dramatically increase available bandwidth in the electromagnetic spectrum. These wireless systems will require filtering techniques capable of operating in this relatively unused part of the spectrum. Here, we report a versatile technique for designing different classes of THz plasmonic filters based on a k-space methodology, in which the desired frequency response is mapped into two-dimensional (2D) k-space and then inverse Fourier transformed into the spatial domain. We use a recently developed inkjet printing technique to fabricate the spatial patterns allowing for grayscale conductivity variation. In general, any technique that allows for high-fidelity reproduction of the real-space grayscale variation in the fabricated plasmonic structure can be used. We demonstrate the flexibility of this approach by creating several classes of filters that allow for changes in the relative magnitudes in multiresonant filters; the polarization dependence, where the anisotropy can be carefully controlled; and the resonance bandwidth. We further demonstrate that, by cascading or adding filter functions together, even more complex filter designs can be achieved. We expect this approach to dramatically expand the design capabilities for filter technology for THz systems applications, such as THz wireless communications as well as applications in other spectral regions.