@melm
i must admit i have not used fmc modules just by themselves... in my setup i went to a sonore optical rendu on the receiving end... on the sending end i use an uptone etherregen unit which conveniently has an optical module slot built into it
i also used, prior to that, a quite economical trendnet unmanaged switch with a built-in optical slot in it as well, on the sending side (the trendnet is recommended by andrew gillis at small green computer, from which i bought the optical rendu) - that switch uses a 5v dc feed, so it is easy to also use a quiet lps or filtered swps just ’to be safe’, although in theory noise can exist on that end upstream of the optical conversion
TrendNet Simple Switch with SFP slot
hope that helps