a week ago
Correct. When talking about GPON it's common only to mention the 1310nm upstream signal strength.
It's the signal coming out of the OLT and it's the one you might measure with your OPM.
The 1490nm downstream signal is the one coming out of your ONU. It's much harder to measure with your OPM as most ONU's don't spit out signal unless they also receive. In normal daily operatrions nobody checks the downstream signal strength.