  Nontrivial properties of electronic states in topological insulators are
inherent not only to the surface and boundary states, but to bound states
localized at structure defects as well. We clarify how the unusual properties
of the defect-induced bound states are manifested in optical absorption spectra
in two-dimensional topological insulators. The calculations are carried out for
defects with short-range potential. We find that the defects give rise to the
appearance of specific features in the absorption spectrum, which are an
inherent property of topological insulators. They have the form of two or three
absorption peaks that are due to intracenter transitions between electron-like
and hole-like bound states.
