We consider a two-level atom driven by modulated light and find that complete population
inversion can be induced by light without any resonant frequency component. This
is in contrast to the familiar case of monochromatic driving in which complete population
inversion is only possible with resonant light. This result concerns experimentally
realizable systems and hence the effect of spontaneous emission is also considered. We
also relate our work to other recent works on quantum double-well. Analogies with the
suppression of quantum tunneling and with the low-frequency radiation generation are
discussed.
By translating the results from the study of the two-level atom to the theory of optical
waveguides, we introduce a new geometric representation for analysing the optical state
of a single-mode optical coupler. We find that an optical coupler with out-of-phase
index modulations can control and suppress the evanescent power transfer between
cores. A new type of optical band-pass filter based on the modulated index coupler is
proposed
