Herein, a model is developed to study the polarization-selective light-coupling in quantum well infrared photodetector arrays with 15 and 30 μm pixel pitch. The polarization-selective light-coupling is achieved using 1D lamella gratings with varying grating orientation and studied through 2D and 3D finite-element method simulations. The extracted absorption quantum efficiency ηabs, derived from the field distribution, shows excellent agreement with experimental data in terms of absorption peak position for both pitch sizes. Several factors impacting the simulated absorptance level are discussed and a good agreement between the simulation and measured ηabs is achieved. Thanks to the developed 3D model, the polarization-selective light-coupling in pixels with 0° and 45° grating orientation is explored. The developed model paves the way for future studies on enhanced light-coupling in small pitch infrared detectors using resonance structures. © 2024 IRnova AB and The Author(s).