Browsing by Author "Liu, Jingbo"

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    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.
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    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.
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    Novel Devices for Terahertz Wave Imaging, Wave-guiding and Sensing
    (2013-09-16) Liu, Jingbo; Mittleman, Daniel M.; Kelly, Kevin F.; Kono, Junichiro
    Several novel optical devices, which were designed to manipulate terahertz waves for broadband near-field imaging, wave-guiding (invisible space), and sensing (resonator), are presented in this thesis. We developed the original working concepts of each device, and demonstrated the prototype experimentally in our lab. The working concepts of physics were investigated in experiment, in simulation and in theoretical analysis. We exploited a tapered parallel-plate waveguide (PPWG) as a novel probe for broadband near-field imaging. This imaging probe consists of two metal plates with the plate spacing gradually tapered from one end to the other. We proved that the space tapering enables this probe to propagate the broadband THz waves efficiently (with low-loss, no cut-off and nearly no dispersion) from the input end of large spacing into the narrow end of sub-wavelength spacing. Working in a reflection mode, this imaging probe is proved to be able to differentiate the dielectric features as well as topographic information on the sample. Combined with the methodology of filtered back projection, we reconstructed a two-dimensional image of a gold pattern on a GaAs chip by using this tapered PPWG probe. The smallest feature of ~100 µm is resolved by using the waves with average wavelength of 1.5 mm. We studied the phenomenon of surface plasmon-polariton in THz range on the platform of a parallel-plate waveguide (PPWG). In this thesis, we show the characterization of the waveguide mode of a finite-width parallel plate waveguide by using an improved scattering-probe technique. An abrupt waveguide mode transition was observed at a very narrow frequency range. We demonstrated that this transition frequency is determined by the material properties of the waveguide, the frequencies of the electromagnetic waves as well as the geometry of the waveguide. This result provides a good guidance for the waveguide design for THz transmission. We also exploited the capability of using the spoof surface plasmon to enhance the reflectivity of an interface between free space and a PPWG. We demonstrated that the reflection coefficient of this interface can be enhanced up to ~100 % at a designed frequency, by cutting a designed pattern of periodic rectangular groove on the output facet of the PPWG. A lateral shift and a phase shift of the reflected beam is observed in the experiment, which is a strong reminiscent of Goos-Hanchen shift. We carried out the experimental, simulation and theoretical characterizations of the lateral and phase shift. As an application, we designed and demonstrated a prototype of a band-pass THz resonator. We introduced the concept of a waveguide-based two-dimensional inhomogeneous artificial dielectric into THz range. This artificial dielectric is the space between the two metal plates of a PPWG working in TE1 mode. We designed a THz mirage device (or an invisible space device) by using ray-tracing and full-wave simulations, which contributed to the first experimental demonstration of such a device. A metal coin of size several times larger than the working wavelength can be hidden in the device without casting any shadow. This work is in collaboration with Dr. Rajind Mendis and the author of this thesis contributed to the design and characterization of the device in simulations.
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    The transition from a TEM-like mode to a plasmonic mode in finite-width THz parallel-plate waveguides
    (2011) Liu, Jingbo; Mittleman, Daniel M.
    By the near-field measurement of the electric field distribution inside the finite width THz parallel plate waveguide, we find the transition from conventional diffractive TEM-like mode to plasmonic mode. This mode transition depends on the geometry of the waveguide. The measurement is conducted on THz-TDS system with scattering probe-technique. We present the simulation which agrees with our experimental data