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Light propagation and Localization in Inhomogeneous and Random Optical Waveguide Lattices

Khazaei Nezhad Gharehtekan, Mehdi | 2014

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 45555 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Mahdavi, Mohammad; Bahrampour, Ali Reza
  7. Abstract:
  8. Photonic lattices can provide an inexpensive and fine tools to investigate some common phenomena in condensed matter physics, quantum optics, relativistic mechanics,atomic and molecular physics. These phenomena contain Anderson localization,Bloch oscillation, Dynamic localization, coherent and squeezed states, Relativistic Dirac equation, Rabi oscillation, ... .In this thesis, it was investigated three worthy phenomena of them, which at first are introduced in condensed matter physics for electronic systems, in photonic lattices. These phenomena are as follow: Transverse localization of light wave, Bloch oscillation and dynamic localization of light. It was also simulate classically, the photon number distribution function of squeezed states in quantum optics, by light intensity distribution in special photonic lattices.In part one of this thesis, the effects of Kerr-type nonlinearity, surface effects and long-range correlation in disorder have been studied numerically on the transverse localization of light in 1D array of optical waveguides. The Kerr-type nonlinearity causes the self-trapping effect and enhances the transverse localization of light.The probability of self-trapping is decreased by increasing the strength of disorder in system. Therefore, unlike the linear systems, the long-range correlated disorder enhances the transverse localization of light in high nonlinear arrays. Moreover, the surface modes are more localized than the bulk modes in high nonlinear parameters.In part two, it was introduced a semi-infinite photonic lattices including two separated arrays of coupled optical waveguides with inhomogeneous coupling coefficients in each array. we called this lattices as squeezed phonic lattices, since the light intensity distribution along the propagation distance, in each guide, remind the time evolution of photon number distribution function in squeezed states in quantum optics.The propagation distance plays the role of time in optical lattices. The light intensity distribution in each guide is obtained by operator methods.In optical lattices, the linear transverse gradient on propagation constants and the curvature of guides play the role of fixed and alternative external forces in electronic super lattices, respectively. At the next step in this part, it was also investigated the possibility of spatial Bloch oscillation in squeezed lattices by introducing the linear transverse gradient on propagation constants of each guide (). Our analytical results show that the Bloch-like oscillations appear above a critical value for the linear gradient of propagation constant ( > c). The phase transition (in the propagation properties of the waveguide) is a result of competition between discrete and Bragg diffraction. Moreover, the light intensity decays algebraically along each waveguide at the critical point while it falls off exponentially below the critical point (
  9. Keywords:
  10. Anderson Localization ; Kerr Nonlinearity Effect ; Transverse Localization ; Lang Range Correlation ; Bloch Oscillations ; Dynamic Localization ; Squeezed Lattices

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