Light Localization In Disordered Microstructures And Its Applications

The flow of light can be delicately molded with photonic lattices, due to the rich-ness of the associated band structure and diffraction relation when compared to the homogenous bulk media. When introducing structure disorder into such systems, the transverse Anderson localization of light occurs. For light propagating in disordered random medium, the weak localization effect——coherent backscattering of light can be observed in the backscattering direction due to multiple scattering. Taking the one-dimensional waveguide array as an example, the thesis focuses on the transverse An-derson localization and refractive behaviors of light propagating in disordered photonic lattices. We have also studied one of the applications of coherent backscattering of light——the lensless imaging based on coherent backscattering in random medium both the-oretically and experimentally.In Chapter1, we give a brief introduction on the related background. The progress and mechanism of Anderson localization has been presented. Then, we show the light propagation behavior in photonic lattice. Furthermore, we give a short review on the coherent backscattering of light in random media, and the related application——lens-less imaging technique in random meida. The research content and significance are also given.In Chapter2, the evolution of linear and nonlinear eigen modes in the disordered one-dimensional waveguide arrays has been studied. More and more eigen modes will become localized near the band edges of the arrays with increasing disorder level. When taking the optical nonlinearity into consideration, the evolution of nonlinear disordered modes originating from different eigen modes in the band will be very different from each other. This is mainly because of the joint effects of the diffraction in the band structure and the resonant interaction between the nonlinear disordered modes and the eigen modes in the bands.In Chapter3, by introducing a refractive index defect into a single waveguide of the disordered waveguide array, defect mode will be generated in the bandgap. Further- more, we find that the influence of disorder level on the defect mode is much different from that on the Anderson mode. The evolution of nonlinear defect mode is similar to that of nonlinear disordered mode. The nonlinear defect modes may be delocalized significantly due to the resonant interaction with the nearby eigen modes in the bands of the array.In Chapter4, we have studied the light refractive behavior at the entrance surface of the disordered one-dimensional waveguide array. Anomalous refractive behaviors can be observed for the eigen modes in the first band, which is much different form the case in a uniform periodic waveguide array. The transverse propagation velocities of the eigen modes in the first band are dramatically suppressed and the correspond-ing light is tightly confined and propagates around the initially exciting waveguides. These anomalous refractive behaviors of light in disordered photonic lattices provide an effective method for beam coupling and collimation.In Chapter5, we study the lensless imaging technique based on coherent backscat-tering in random medium both theoretically and experimentally. The corresponding point spread function of such system has been deduced. By optimizing various param-eters, such as the solid content of the suspension, the size of the scatterer, the distance between the random medium and the object to be imaged, the image contrast and res-olution can be improved. Moreover, for complicated objects, the contrast and quality of the image can be improved dramatically using the photon correlation measurement, which promotes the practical use of this image technique.In Chapter6, the summary and prospects of this thesis are made.