A Fabry–Pérot laser diode (FP laser diode) is the most common type of laser diode, having a laser resonator which is a Fabry–Pérot interferometer. This means that substantial light reflections occur at both ends, but not within the gain medium. FP laser cavity functions as a Fabry-Perot interferometer, which is based on the fundamental principle of multiple beam. A Fabry‑Perot (FP) laser is a common, cost‑efficient light source used within optical transceiver modules, particularly SFP modules. Its primary application is in low-data-rate short-distance transmission over distances of up to 20 kilometers.