We present a detailed investigation on the optical properties of a 30-layer, strain-coupled InAs/GaAs quantum dot heterostructure. Using a combination of thin In0.15Ga0.85As and GaAs capping layers, we studied the effects of varying their thicknesses on the photoluminescence emission spectrum. From the photoluminescence peak multimodal distribution of the quantum dots is observed. The emission peaks exhibit an initial red-shift; further increasing the thickness of the GaAs spacer produces a continuous blue-shift, and increasing the In0.15Ga0.85As spacer thickness produces a red-shift. The FWHM increases (from a minimum of 22 nm) and activation energy decreases (with maximum of 377 meV) with an increase in the thickness of either spacer, starting from a combination of 2-nm In0.15Ga0.85As and 10-nm GaAs capping layers. The inter-subband spectral responses obtained from the fabricated single-pixel detectors are in the mid infrared range. © 2014 Elsevier B.V. All rights reserved.