  Adiabatic following has been an widely-employed technique for achieving
near-complete population transfer in a `two-level' quantum mechanical system.
The theoretical basis, however, could be generalized to a broad class of
systems exhibiting SU(2) symmetry. In the present work, we present an analogy
of population transfer dynamics of two level atomic system with that of light
propagation in a classical `one-dimensional' photonic crystal, commonly known
as distributed-Bragg-reflector (DBR). This formalism facilitates in adapting
the idea of adiabatic following, more precisely the rapid adiabatic passage
(RAP) which is usually encountered in a broad class of quantum-mechanical
systems. We present a chirped DBR configuration in which the adiabatic
constraints are satisfied by virtue of optimally chirping the DBR. The
reflection spectrum of the configuration exhibit broadening of photonic bandgap
(PBG) in addition to a varying degree of suppression of sharp reflection peaks
in the transmission band. The intermodal coupling between counter-propagating
modes as well as their phase-mismatch, for the DBR configuration, exhibits a
longitudinal variation which is usually observed in `Allen-Eberly' scheme of
adiabatic population transfer in two-level atomic systems.

Optics;Quantum Physics