  The light absorption due to the transitions between the edge and
two-dimensional (2D) states of a 2D topological insulator (TI) is considered in
the Volkov-Pankratov model. It is shown that the transitions are allowed only
for the in-plane electric field orthogonal to the edge of the TI. It is found
that the absorption is accompanied by the pure spin photocurrent along the TI
edge. The possibility of the spin current measurement using polarized
luminescence from 2D TI quantum dots is discussed.
