We present the optical analysis of spatial single-mode monolithic quantum cascade laser arrays in the mid-IR. Subwavelength parallel microstripe waveguides are buried into InP:Fe and phase locked by evanescent coupling. Lasing at room temperature is obtained at λ=8.4 μm. We describe the near- and far-field of stripe arrays comprising up to 32 emitters. One hundred percent coherent emission is shown experimentally and well accounted for by a standard optical simulation.