Transverse localization of light in one-dimensional waveguide arrays with width disorder has been studied in
both linear and nonlinear regimes. Defect mode is generated in the bandgap of the disordered waveguide array
when introducing refractive index modulation into a single waveguide, and its localization strength depends on
the width disorder level of the waveguide array. The evolution of the nonlinear disordered modes with either the
self-focusing or the self-defocusing optical nonlinearities has been studied. The results show that the nonlinear
disordered modes may be delocalized significantly due to the resonant interaction with the nearby eigen modes
in the width-disordered waveguide array.
In this paper, we reviewed the theoretical and experimental studies on the manipulation of the group delay of
light based on the transverse phase modulation effect induced by a Gaussian beam. We introduced the basic
theory of slow and fast lights in a thin nonlinear material based on the transverse phase modulation effect.
We introduced a simple but effective technique to actively and chromatically control the group velocity of light
at arbitrary wavelength, therefore, eliminating the requirements on the optical nonlinearity and the photonic
resonance at the signal wavelength. Furthermore, a technique to improve the transverse-modulation-induced
relative delay of light in nonlinear media through the combination of an optical nonlinearity and a resonant
Fabry-Perot cavity was introduced and theoretically demonstrated in ruby as an example. The introduction of
a resonant Fabry-Perot cavity can improve the relative delay by orders of magnitude. The techniques of active
chromatic manipulation and resonant improvement of the group delay of light may have potential applications
in optical information processing and optical communication network.