This work systematically investigated the optical and structural properties of multilayer electronic vertically coupled InAs/GaAs quantum dot (QDs) structures grown by molecular beam epitaxy for long-wavelength applications. A significant energy blue-shift in the photoluminescence (PL) spectra from 30-period InAs/GaAs QDs structures was observed as the GaAs spacer thickness was decreased. Transmission electron microscopy (TEM) and PL measurements indicated that the abnormal blue-shift can be attributed to the strain-driven In/Ga intermixing between QDs and spacer layers, which overcompensates for the effects of electronic and structural couplings between QD layers. Moreover, this study demonstrates that increasing the growth rate of InAs QDs can prevent intermixing. A PL emission wavelength of 1320nm with strong luminescence at room temperature, which corresponds to an energy red-shift of 50meV from that of the single QD layer sample, was achieved in a 10-period InAs/GaAs QD superlattice with a spacer thickness of 16nm.