Polarization‐dependent photoluminescence (PL) and optical absorption spectra of (AlAs)1/2(GaAs)1/2and (Al0.5Ga0.5As)1/2(GaAs)1/2fractional layer superlattices (FLSs) were measured at room temperature. For the first time, it was observed that the spectra are dependent on their polarizations. The anisotropies in the PL and absorption spectra show that quantum confinement unambiguously occurs in the direction parallel to the surface, i.e.,lateralquantum carrier confinement effect appears. This finding proves that FLSs are promising for novel optical devices.