Browsing by Author "Guo, Q"

Now showing 1 - 4 of 4

Does the phenomenological approach contradict the quantum theory of exciton-polariton spatial dispersion?
(2005-05-01)
Guo, Q
;
Chi, S
;
光電工程學系
;
Department of Photonics
This paper clarifies the controversial issue over 40 years between the quantum approach by Pekar and the phenomenological approach by Ginzburg about the exciton-polariton spatial dispersion theory. For an isotropic nongyrotropic medium, the analytical explicit function of the impermeability tensor eta(ij)(omega, (k) over right arrow) (the inverse of the permittivity tensor) is obtained from the anisotropic undamped-wave harmonic oscillator model. After expanding eta(ij)(omega, (k) over right arrow) with respect to small parameters within it rather than to wavevector (k) over right arrow, the approximate refractive indices can be determined from the eigenvalue equation. By this treatment, the phenomenological approach is proved to be the approximation of the quantum approach near the resonance frequency. The condition for the approximation is discussed.
Large phase shift of nonlocal optical spatial solitons
(2004-01-01)
Guo, Q
;
Luo, B
;
Yi, FH
;
Chi, S
;
Xie, YQ
In this paper, we discuss the evolution of the optical beam in nonlocal cubic nonlinear media, modeled by the nonlocal nonlinear Schrodinger equation (NNLSE). A different approximate model to the NNLSE is presented for the strongly nonlocal media with arbitrary response functions. An exact analytical solution of the model is obtained, and a spatial soliton is found to exist. A different phenomenon is revealed that the phase shift of such a nonlocal optical spatial soliton can be very large comparable to its local counterpart. The stability of the solution is rigorously proved. The comparisons of our analytical solution with the numerical simulation of the NNLSE, as well as with Snyder-Mitchell (linear) model [A. W. Snyder and D. J. Mitchell, Science 276, 1538 (1997)] are given.
Nonlinear light beam propagation in uniaxial crystals: nonlinear refractive index, self-trapping and self-focusing
(2000-01-01)
Guo, Q
;
Chi, S
;
光電工程學系
;
Department of Photonics
We derive the nonlinear paraxial wave equation for the propagation of an optical beam in nonlinear anisotropic media with centrosymmetry. As an application of the equation, we obtain the nonlinear refractive index (NRI) in three uniaxial crystals belonging to the symmetry classes 6/mmm of the hexagonal system, 4/mmm of the tetragonal system, and (3) over bar m of the trigonal system, respectively, and consider the self-trapping and self-focusing of the beam propagating in any direction in these crystals. We conclude that NRI, critical power and self-focusing length are all anisotropic (dependent upon the propagation direction) for an extraordinary light but isotropic for an ordinary light, and that there exists an elliptical self-trapping beam for the extraordinary light.
Optical beams in sub-strongly non-local nonlinear media: A variational solution
(2006-03-01)
Guo, Q
;
Luo, B
;
Chi, S
;
光電工程學系
;
Department of Photonics
Discussed is the propagation of optical beams in non-local nonlinear media modelled by 1 + 1D non-local nonlinear Schrodinger equation (NNLSE). In the sub-strongly non-local case, an approximate analytical solution is obtained for an arbitrary response function by a variational approach. Described by a combination of the Jacobian elliptic functions, the solution is periodic, and its period depends on not only the input power but also the initial beam width, which is confirmed by the numerical simulation of the NNLSE. (c) 2005 Elsevier B.V. All rights reserved.