Browsing by Author "Karl, Nicholas"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Electrically Driven Terahertz Metamaterial Diffractive Modulator
    (2014-09-19) Karl, Nicholas; Mittleman, Daniel M.; Natelson, Doug; Kono, Jun
    This thesis describes a method for terahertz (THz) modulation using active metamaterials. At optical and telecom frequencies, modulation of freely propagating and guided signals is an important concept that is fundamental to key technologies and applications such as communications and imaging. At THz frequencies, the ability to modulate these signals at the capacity necessary to realize these applications effectively does not exist. In order to remedy this, we investigate the use of metamaterials to modulate free space propagating waves at THz frequencies. Metamaterials are an ideal modulation platform for use in the THz frequency range because they avoid many issues that have challenged traditional THz modulators. Furthermore, the ability of metamaterials to function as artificial media holds considerable potential in the THz frequency range because it allows for a wide range of tunable material parameters extending beyond natural THz material responses. We develop and demonstrate a switchable diffractive modulator using an electrically driven metamaterial to tune transmission in real-time via voltage application. The metamaterial elements are grouped giving rise to the grating structure. We observe that the device operates as a relatively high-speed, wide-bandwidth, high-contrast modulator, with more than 20 dB of dynamic range.
  • Thumbnail Image
    Item
    Terahertz Artificial Dielectric Lens
    (Springer Nature, 2016) Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M.
    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices.