  We present a comparative study of the optical properties - reflectance,
transmission and optical conductivity - and Raman spectra of two layered
bismuth-tellurohalides BiTeBr and BiTeCl at 300 K and 5 K, for light polarized
in the a-b planes. Despite different space groups, the optical properties of
the two compounds are very similar. Both materials are doped semiconductors,
with the absorption edge above the optical gap which is lower in BiTeBr (0.62
eV) than in BiTeCl (0.77 eV). The same Rashba splitting is observed in the two
materials. A non-Drude free carrier contribution in the optical conductivity,
as well as three Raman and two infrared phonon modes, are observed in each
compound. There is a dramatic difference in the highest infrared phonon
intensity for the two compounds, and a difference in the doping levels. Aspects
of the strong electron-phonon interaction are identified. Several interband
transitions are assigned, among them the low-lying absorption $\beta$ which has
the same value 0.25 eV in both compounds, and is caused by the Rashba spin
splitting of the conduction band. An additional weak transition is found in
BiTeCl, caused by the lower crystal symmetry.
