optocoupler only can use in dc signal.
...and transformer can't pass DC
Impossible to solve the problem if you don't know the problem. Does the 220V 50 Hz have a size/weight constraint? Reliability requirement? Failsafe?
As you can see, all you get is GUESSES
FWIW, CATV is analog RF (AC) on fiber...OPTO
Since you have a diode detector downstream AND an attenuator in your original posting, I'd say an LED+resistor and a photodiode/transistor type of optoisolator will do what you want quite nicely as it eliminates a lot of your downstream components that you've shown.