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Investigation of Operation Principles and Design of the Terahertz Oscillators and Detectors Based on Intrinsic Josephson Junctions in Layered Superconductors

Kokabi, Alireza | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43219 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Fardmanesh, Mehdi
  7. Abstract:
  8. Trahertz gap science and technology is becoming more and more attractive due to the wide range of applications in medical science, communications and security. In addition, this band connect the optical and microwave devices. In this thesis, special optical structures composed of superconducting nanostructure based on the elemental type-II and layered high-Tc superconductors are proposed. The photonic band structure and the optical S-matrix are calculated for these proposed structures for different geometrical values. Such structures produce terahertz (THz) photonic band gap, which is controlled by the temperature and geometrical parameters. In addition, the proposed structures show controllable optical reflectance and transmittance in the considered terahertz range. The calculations are performed in a special frequency range in which the refractive index of the layered superconductors has negative value according to the previous analyses. At the second part, terahertz radiation of the stack of intrinsic Josephson junctions in the mesa structure of the layered high-Tc superconductors is analyzed and presented. The dependency of the radiated power to the geometrical parameters, cavity-waveguide boundaries, and magnetic and electric bias has been investigated. This has been done by numerical calculation of the previously proposed coupled sine-Gordon equations, which characterize the electromagnetic dynamics of the stack of the intrinsic Josephson junctions. Using the obtained numerical results from these coupled equations, the effect of the design parameters such as dimensions of the mesa structure and the magnitude of the applied magnetic field and the dc current on the enhancement of the radiated power is studied. Thus, the radiated power is optimized with respect to these considered parameters. By variation of the number of layers, we also investigate the effect of the number of intrinsic Josephson junctions on the total radiated power. The results from this part are also compared with the previous analytical models. At the third part, the possibility of enhancing the radiation power and monochromaticity by optically induced photonic crystal in the superconducting cavity is proposed and investigated. In such a structure, by periodically irradiating the stacked Josephson junctions and consequently partially suppression of the superconductivity in the irradiated positions due to depairing, a periodic optical configuration is formed. This leads to photonic band gap opening in the range of the terahertz radiation emitted from the layered superconductor. We show that such a photonic band gap significantly enhances the impedance matching at the boundary of the cavity and the waveguide. Since the weak optical coupling of the outer and inner space of layered superconductor samples is a serious reason of reducing radiated power especially in the experiments, the proposed configuration is capable of extremely enhancement in the emitted power along with attenuation of the undesired harmonics
  9. Keywords:
  10. Layered Superconductors ; Josephson Vortices ; Terahertz Trancievers ; Josephson Plasma

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