  We experimentally realized Floquet topological photonic insulators using a
square lattice of direct-coupled octagonal resonators. Unlike previously
reported topological insulator systems based on microring lattices, the
nontrivial topological behaviors of our system arise directly from the periodic
evolution of light around each octagon to emulate a periodically-driven system.
By exploiting asynchronism in the evanescent coupling between adjacent
octagonal resonators, we could achieve strong and asymmetric couplings in each
unit cell, which are necessary for observing Anomalous Floquet Insulator
behaviors. Direct imaging of scattered light from fabricated samples confirmed
the existence of chiral edge states as predicted by the topological phase map
of the lattice. In addition, by exploiting the frequency dispersion of the
coupling coefficients, we could also observe topological phase changes of the
lattice from normal insulator to Chern and Floquet insulators. Our lattice thus
provides a versatile nanophotonic system for investigating 2D Floquet
topological insulators.
