InAs/InP multiwavelength quantum dash lasers are promising solutions to rising data loads in our telecommunications systems, as one laser chip can replace many lasers operating at a single wavelength. Quantum dashes are quasi-one-dimensional nanoparticles that offer equal or increased performance as laser gain media when compared to equivalent quantum well devices. InAs/InP quantum dashes are ideal for laser devices emitting in the C-band region, centred around 1550 nm. The quantum dashes in this thesis are epitaxially grown via the self assembled Stranski-Krastanow mode. Characterizing how structure and composition of these quantum dashes affect the energy level spacing and emission wavelengths is crucial for designing better performing telecommunications lasers. In this thesis a method for determining the average heights and widths of these nanoparticles from atomic force microscopy measurements of uncapped InAs/InGaAsP/InP quantum dashes is developed. Single quantum dash simulations are built in Crosslight Photonic Integrated Circuit Simulator (PICS3D) with the lowest energy transition tuned to photoluminescence peak wavelengths provided by National Research Council Canada. These simulations are used to determine the impact of quantum dash dimensions, compositions, and heterostructure changes to the overlap integrals and emission energies. Phosphorus concentration within the quantum dash and wetting layer can modify the predicted emission wavelength by ∼200 nm, and increasing quantum dash lengths beyond 200 nm has negligible effect on emission energy and energy level spacing. The sublayer thickness is increased from 0.1 to 1 nm, and shows that emission energy will increase for GaP sublayers and decrease for GaAs sublayers by up to 30 meV. The role of the wetting layer on energy level spacing is discussed and determined to increase the emission energy by ∼15 meV when the 0.5 nm wetting layer is removed for a 2 nm quantum dash. The role of As/P intermixing is investigated in three ways: by incorporating phosphorus concentration in (1) the quantum dash and wetting layer, (2) the wetting layer, and (3) the lower portion of the quantum dash without a wetting layer. There is negligible change in the overlap integral for these three cases with all other variables held constant, and the trends between each case remain the same. Further experimental analysis of buried InAs quantum dashes is recommended for compositional information. The implementation of variable strain profiles in this model is also recommended, in addition to developing vertically coupled quantum dash simulations. Finally, performing these simulations at varying temperatures will better represent the operating conditions of quantum dash lasers.