  Artificial gauge fields enable the intriguing possibility to manipulate the
propagation of light as if it were under the influence of a magnetic field even
though photons possess no intrinsic electric charge. Typically, such fields are
engineered via periodic modulations of photonic lattices such that the
effective coupling coefficients after one period become complex-valued. In this
work, we investigate the possibility to introduce randomness into artificial
gauge fields by applying local random phase shifts in the modulation of
lattices of optical waveguides. We first study the elemental unit consisting of
two coupled single-mode waveguides and determine the effective complex-valued
coupling coefficient after one period of the modulation as a function of the
phase shift, the modulation amplitude and the modulation frequency. Thereby we
identify the regime where varying the modulation phase yields sufficiently
large changes of the effective coupling coefficient to induce Anderson
localization. Using these results, we demonstrate numerically the onset of
Anderson localization in 1D- and 2D-lattices of x-, and helically-modulated
waveguides via randomly choosing the modulation phases of the individual
waveguides. Besides further fundamental investigations of wave propagation in
the presence of random gauge fields, our findings enable the engineering of the
coupling coefficients without changing the footprint of the overall lattice. As
a proof of concept, we demonstrate how to engineer out-of-phase modulated
lattices which exhibit dynamic localization and defect-free surface states.
Therefore, we anticipate that the modulation phase will play an important role
in the judicious design of functional waveguide lattices.

Optics;Quantum Physics