Browsing by Author "Mendis, Rajind"

Now showing 1 - 8 of 8
  • Thumbnail Image
    Item
    A terahertz band-pass resonator based on enhanced reflectivity using spoof surface plasmons
    (IOP Publishing, 2013) Liu, Jingbo; Mendis, Rajind; Mittleman, Daniel M.
    We demonstrate a band-pass resonator in the terahertz (THz) range, based on a frequency-selective designer reflector. The resonator consists of a parallel-plate waveguide, a designed groove pattern cut into the output facet of each plate, and a reflecting mirror. The patterned facet supports a spoof surface plasmon mode, which modifies the reflectivity at the waveguide output facet by interacting with the waveguide mode. By tuning the geometrical parameters of the groove pattern, the reflectivity at the patterned output facet can be increased up to ~100% for a selected frequency. Broadband THz waves are quasi-optically coupled into this resonator and reflected multiple times from the patterned facet. This leads to a narrowing of the spectrum at the selected frequency. The Q value of the resonator increases as the number of reflections on the patterned facet increases, reaching ~25 when the THz wave has experienced 12 reflections.
  • Thumbnail Image
    Item
    Focused terahertz waves generated by a phase velocity gradient in a parallel-plate waveguide
    (Optical Society of America, 2015) McKinney, Robert W.; Monnai, Yasuaki; Mendis, Rajind; Mittleman, Daniel
    We demonstrate the focusing of a free-space THz beam emerging from a leaky parallel-plate waveguide (PPWG). Focusing is accomplished by grading the launch angle of the leaky wave using a PPWG with gradient plate separation. Inside the PPWG, the phase velocity of the guided TE1ﾠmode exceeds the vacuum light speed, allowing the wave to leak into free space from a slit cut along the top plate. Since the leaky wave angle changes as the plate separation decreases, the beam divergence can be controlled by grading the plate separation along the propagation axis. We experimentally demonstrate focusing of the leaky wave at a selected location at frequencies of 100 GHz and 170 GHz, and compare our measurements with numerical simulations. The proposed concept can be valuable for implementing a flat and wide-aperture beam-former for THz communications systems.
  • Thumbnail Image
    Item
    A Maxwell’s fish eye lens for the terahertz region
    (American Institute of Physics, 2013-07-15) Liu, Jingbo; Mendis, Rajind; Mittleman, Daniel M.
    We implement a two-dimensional Maxwell’s fish eye lens using a waveguide-based artificial dielectric. The Maxwell’s fish eye lens consists of two metallic cylindrical plates sandwiching a free-space region, with the inner surface of one plate shaped into a hollow conical form. This lens has the capability to image terahertz beams from a source located at the edge (between the plates) to the diametrically opposite point on the edge, independent of the incident angle.
  • Thumbnail Image
    Item
    A mode-matching analysis of dielectric-filled resonant cavities coupled to terahertz parallelplate waveguides
    (Optical Society of America, 2012-09-07) Astley, Victoria; Reichel, Kimberly S.; Jones, Jonathan; Mendis, Rajind; Mittleman, Daniel M.
    We use the mode-matching technique to study parallel-plate waveguide resonant cavities that are filled with a dielectric. We apply the generalized scattering matrix theory to calculate the power transmission through the waveguide-cavities. We compare the analytical results to experimental data to confirm the validity of this approach.
  • Thumbnail Image
    Item
    Resonant cavity integrated into a waveguide for terahertz sensing
    (2012-11-13) Mendis, Rajind; Mittleman, Daniel M.; Rice University; United States Patent and Trademark Office
    A method comprising polarizing and coupling an electromagnetic beam to a first-order transverse electric (TE1) mode with respect to a parallel plate waveguide (PPWG) integrated resonator comprising two plates and a cavity, sending the electromagnetic beam into the PPWG integrated resonator to excite the cavity by the TE1 mode and cause a resonance response, and obtaining wave amplitude data that comprises a resonant frequency, and obtaining the refractive index of fluids filling the cavity via the shift in resonant frequency.
  • 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.
  • Thumbnail Image
    Item
    Terahertz Microfluidic Sensing Using a Parallel-plate Waveguide Sensor
    (JoVE, 2012) Astley, Victoria; Reichel, Kimberly; Mendis, Rajind; Mittleman, Daniel M.
    Refractive index (RI) sensing is a powerful noninvasive and label-free sensing technique for the identification, detection and monitoring of microfluidic samples with a wide range of possible sensor designs such as interferometers and resonators [1,2]. Most of the existing RI sensing applications focus on biological materials in aqueous solutions in visible and IR frequencies, such as DNA hybridization and genome sequencing. At terahertz frequencies, applications include quality control, monitoring of industrial processes and sensing and detection applications involving nonpolar materials. Several potential designs for refractive index sensors in the terahertz regime exist, including photonic crystal waveguides [3], asymmetric splitring resonators [4], and photonic band gap structures integrated into parallel-plate waveguides [5]. Many of these designs are based on optical resonators such as rings or cavities. The resonant frequencies of these structures are dependent on the refractive index of the material in or around the resonator. By monitoring the shifts in resonant frequency the refractive index of a sample can be accurately measured and this in turn can be used to identify a material, monitor contamination or dilution, etc. The sensor design we use here is based on a simple parallel-plate waveguide [6,7]. A rectangular groove machined into one face acts as a resonant cavity (Figures 1 and 2). When terahertz radiation is coupled into the waveguide and propagates in the lowest-order transverse-electric (TE1) mode, the result is a single strong resonant feature with a tunable resonant frequency that is dependent on the geometry of the groove [6,8]. This groove can be filled with nonpolar liquid microfluidic samples which cause a shift in the observed resonant frequency that depends on the amount of liquid in the groove and its refractive index [9]. Our technique has an advantage over other terahertz techniques in its simplicity, both in fabrication and implementation, since the procedure can be accomplished with standard laboratory equipment without the need for a clean room or any special fabrication or experimental techniques. It can also be easily expanded to multichannel operation by the incorporation of multiple grooves [10]. In this video we will describe our complete experimental procedure, from the design of the sensor to the data analysis and determination of the sample refractive index.
  • Thumbnail Image
    Item
    Ultra low loss waveguide for broadband Terahertz radiation
    (2012-09-04) Mendis, Rajind; Mittleman, Daniel M.; Rice University; United States Patent and Trademark Office
    An apparatus comprising a parallel plate waveguide (PPWG) comprising two plates separated by a distance that supports a multimode wave, and a transmitter configured to emit a wave having a frequency from about one hundred Gigahertz (GHz) to about ten terahertz (THz) and to couple to one mode of the PPWG. Also disclosed is an apparatus comprising two plates substantially parallel to one another and separated by at least about five millimeters (mm), and an antenna coupled to the two plates and configured to transmit or receive a wave having a frequency from about one hundred GHz to about ten THz. Disclosed is a method comprising polarizing an electromagnetic beam in the first transverse electric (TE1) mode with respect to a PPWG comprising two plates, adjusting the diameter of the electromagnetic beam based on the separation between the plates, and sending the electromagnetic beam into the PPWG.