  Manipulating the topological properties of insulators, encoded in invariants
such as the Chern number and its generalizations, is now a major issue for
realizing novel charge/spin responses in electron systems. We propose that a
simple optical means --subjecting to a driving laser field with circular
polarization, can be fruitfully incorporated to this end. Taking as a
prototypical example the two-band insulator first considered by Haldane, we
show how the electron system can be tuned through phases associated with
different Chern numbers as the laser intensity is adiabatically swept; i.e., a
photo-induced analog of the quantum Hall plateau transition. The implications
of our findings includes the possibility of laser-tuning a conventional
insulator into a quantum spin Hall system.
