Low-loss terahertz ribbon waveguides

Abstract

The submillimeter wave or terahertz (THz) band (1 mm-100 microm) is one of the last unexplored frontiers in the electromagnetic spectrum. A major stumbling block hampering instrument deployment in this frequency regime is the lack of a low-loss guiding structure equivalent to the optical fiber that is so prevalent at the visible wavelengths. The presence of strong inherent vibrational absorption bands in solids and the high skin-depth losses of conductors make the traditional microstripline circuits, conventional dielectric lines, or metallic waveguides, which are common at microwave frequencies, much too lossy to be used in the THz bands. Even the modern surface plasmon polariton waveguides are much too lossy for long-distance transmission in the THz bands. We describe a concept for overcoming this drawback and describe a new family of ultra-low-loss ribbon-based guide structures and matching components for propagating single-mode THz signals. For straight runs this ribbon-based waveguide can provide an attenuation constant that is more than 100 times less than that of a conventional dielectric or metallic waveguide. Problems dealing with efficient coupling of power into and out of the ribbon guide, achieving low-loss bends and branches, and forming THz circuit elements are discussed in detail. One notes that active circuit elements can be integrated directly onto the ribbon structure (when it is made with semiconductor material) and that the absence of metallic structures in the ribbon guide provides the possibility of high-power carrying capability. It thus appears that this ribbon-based dielectric waveguide and associated components can be used as fundamental building blocks for a new generation of ultra-high-speed electronic integrated circuits or THz interconnects.

Design of a Low Loss Metallo-Dielectric EBG Waveguide at Submillimeter Wavelengths

“…However, this implies that many modes are above the cut-off and they are readily excited at bends or small discontinuities. Similarly, to avoid the high dielectric losses, guides structured such that most of the propagating field lies outside the dielectric region (ribbon guides [3]) have been constructed, but here the mode confinement is not very strong and there is significant mode conversion around bends.…”

Optimization of the E-Plane Loaded Rectangular Waveguide for Low-Loss Propagation

“…E-plane loaded rectangular waveguide fabricated in the Ka-band. (b) (a) (b) (a) 29 and dielectrics have a high power absorption [11], which increases the attenuation of any waveguide [12]. This makes common waveguides, e.g., the metallic rectangular or circular waveguides, impractical.…”

“…This makes common waveguides, e.g., the metallic rectangular or circular waveguides, impractical. Several low-loss waveguides have been proposed to solve this problem, e.g., the dielectric circular waveguide [27], the elliptical polymer tube [28], the Ribbon waveguide [29] or the single-wire waveguide [30]. All these waveguides present low attenuation at high frequencies, but are affected by high losses on bends and discontinuities.…”

Cylindrically periodic dielectric waveguide at submillimeter waves

“…However this implies that many modes are above cut-off and they may easily be excited, as in case of bends. Another viable candidate to accomplish such a low propagation loss is the high dielectric constant ribbon waveguide [1] [2]. Ribbon guide works by maintaining a large ratio between its lateral dimensions (width-to-height) in such a way that the mode propagates on the interface between the dielectric and the air instead of in the material, as in traditional dielectric waveguides.…”

“…Ribbon guide works by maintaining a large ratio between its lateral dimensions (width-to-height) in such a way that the mode propagates on the interface between the dielectric and the air instead of in the material, as in traditional dielectric waveguides. This dramatically lowers the propagation loss of such a mode, however this waveguide has substantial radiation losses at any sharp bends if no coating is used [2]. Waveguides that are cylindrically periodic (CPWG), see Fig.…”