Strained-layer superlattices (SLS) composed of a sequence of ultrathin Si and Ge layers are grown on Ge(110) buffer layers by MBE. Crystalline quality, relaxation of asymmetrically SLS, and interdiffusion are studied in situ by LEED and AES. New optical transitions in the range of 0.7 to 0.8 eV are observed with photoluminescence experiments