  Topological insulators have attracted abundant attention for a variety of
reasons -- notably, the possibility for lossless energy transport through edge
states `protected' against disorder. Topological effects like the Quantum Hall
state can be induced through a gauge field, which is however hard to create in
practice, especially for charge-neutral particles. One way to induce an
effective gauge potential is through a dynamic, time-periodic modulation of the
lattice confining such particles. In this way, the Haldane Quantum Hall effect
was recently observed in a cold atom system. Here, we show how this same effect
can be induced for light confined to a lattice of identical optical resonators,
using an on-site modulation of the resonant frequencies. We further demonstrate
the existence of one-directional edge states immune to back-scattering losses,
and discuss the possibilities for a practical implementation, which would
enable slow-light devices of unprecedented quality.
