Recommendation ITU-T G.9804.3 describes a 50-Gigabit-capable passive optical network (50G PON) system in an optical access network for residential, business, mobile backhaul and other applications. This system operates over a point-to-multipoint optical access infrastructure at the nominal line rate of 50 Gbit/s in the downstream direction. In the upstream direction, 25 Gbit/s and 50 Gbit/s nominal line rates are defined. This Recommendation contains the references, the common definitions, acronyms, abbreviations and the specifications of the physical media dependent layer of the 50G-PON system. Amendment 1 defines a third upstream wavelength "option 3" to support triple WDM coexistence with both GPON and XG(S)-PON, optical interface parameters of 50 Gbit/s upstream direction, optical interface parameters for non-MPM use cases, and the ONU out-of-band power spectral density requirements. Amendment 2 defines the optical interface parameters of 50 Gbit/s upstream direction on further power budget classes besides N1 class. Amendment 3 deprecates 12.44Gbit/s upstream line rate, defines several more power budgets specifications for the non-MPM use cases, applies narrow band wavelength option for 50G upstream in Option 2, and updates the OPL encoding.