A system includes a substrate. The system also includes a detector array disposed over the substrate, where the detector array includes multiple detector pixels. The system further includes multiple plasmonic gratings disposed over top surfaces of the detector pixels, where each plasmonic grating includes multiple convex polyhedrons separated by valleys. Each detector pixel may have a mesa shape, and the convex polyhedrons of the plasmonic gratings may have a smaller size than the mesa shape of the detector pixels. A dimension across a base of each convex polyhedron of the plasmonic gratings may be selected based on a desired resonance wavelength of the plasmonic gratings.