We investigated the electronic subband structure of an InAs quantum-dot infrared photodetector (QDIP) structure utilizing photoluminescence (PL) and PL excitation (PLE) spectroscopy. At 10 K, the PLE spectrum of the PL maximum (1.046 eV) shows an absorption peak associated with InAs quantum dots in an asymmetric well (DASWELL). The strongest transitions in the PLE spectrum are at $sim$85 and $sim$160 meV above the ground-state transition, and weaker transitions occur at $sim$63 and $sim$130 meV. Another peak at $sim$30 meV is a phonon-assisted peak, and the peaks observed above 300 meV are related to quantum wells formed by InGaAs regions between island QDs. From these data, we construct the electronic subband structure of the active region in an InAs QDIP with a DASWELL structure and a AlGaAs/GaAs superlattice barrier.