  Polarization-sensitive devices rely on meta-materials to exhibit varying
degrees of absorption of light of a given handedness. The chiral surface states
of a topological insulator(TI) selectively absorb right and left circularly
polarized light in the vicinity of the Dirac cone reaching its maximum of unity
at the $ \Gamma $ point. In this letter, we demonstrate that a band gap open TI
with C$_{2v}$ symmetry which is represented through a combination of Rashba and
Dresselhaus Hamiltonians alters the preferential absorption of left and right
circularly polarized light allowing a smooth variation of the circular
dichroism(CD). This variation in CD, reflected in a range of positive and
negative values is shown to be a function of the Rashba and Dresselhaus
coupling parameters. Additionally, we draw a parallel between the varying CD
and the emerging field of valley-electronics in transition metal
dichalcogenides and note the possibility of the chiral states as a basis toward
quantum information processing.
