Optical conductivity of the non-superconducting cuprate, La8-x Srx Cu8O20

La8-xSrxCu8O20 is a nonsuperconducting cuprate which exhibits a doubling of the elementary cell along the c axis. Its optical conductivity has been first measured here, down to 20 K, in two single crystals with x = 1.56 and x = 2.24. Along c, bands are observed in both samples which correspond to strongly bound charges and confirm that the cell doubling is due to charge ordering. In the ab plane, in addition to the Drude term one observes an infrared peak at similar to0.1 eV and a midinfrared band at 0.7 eV. The 0.1-eV peak, is found at higher frequencies below 200 K, in correspondence with an anomalous increase in the dc resistivity and consistently with its assignment to localized charges. These results point out similarities and differences with respect to the optical properties of superconducting cuprates.