Amendment 1 to Recommendation ITU-T G.984.5 defines the specifications for the "WDM1r" and "WDM1rn" devices, and also provides some direction regarding the deployment of such filters.
ITU-T G.984.5 AMD 1-2009 history
2014ITU-T G.984.5-2014 Gigabit-capable passive optical networks (G-PON): Enhancement band
2009ITU-T G.984.5 AMD 1-2009 Gigabit-capable passive optical networks (G-PON): Enhancement band Amendment 1 Study Group 15