Multispectral electro-optical/infrared payloads are being developed for a variety of defence and commercial system applications. Many applications depend on their ability to detect and recognize low-contrast and distant targets in a complex environment. The development of such systems necessitates the use of specialized optical filters capable of separating different spectral bands. To separate the bands from visible to mid-wave infrared (MWIR), a dichroic beam splitter is used. We have designed and simulated these two beam splitters with a 45-deg angle of incidence that will be used to separate the bands from visible to MWIR. The beam splitter in such an optical system must separate visible, short-wave infrared (SWIR), and MWIR. We present the thin-film coating design and simulation of these two beam splitters. The first beam splitter separates MWIR from visible and SWIR. The second beam splitter separates the remaining two bands: visible and SWIR.