Opto Coupler for RF application

I am looking for an isolation as high as 100dB between two stages.
(VCO and modulator at 4GHz)

I have heard of opto-coupler providing very high isolation,How do they work?
Can it be used in above application?

I request forum guys to suggest a few such parts ,which can provide isolation at 4GHz and above
and some application note.

no such part.

but you could moldulate a laser diode, run a few inches of fiberoptic cable, and hit a photo detector. that would be over 100 dB of isolation if you packaged it properly, but you would have linearity, noise, and signal level issues to fight.

Hi biff44,
As always,you are among the first to answer my RF related queries.
I admire your depth of knowledge and always look forward for solutions
from you.

Could you direct me to some reference materials,which addresses similar isolation issue.

I remember a senior Professor telling me that,its all about |S21*S12| value which decides ,how much isolation you
require at VCO output? Can somebody explain this?

Also,it is often suggested that there is simple mathematical calculation,to find out,how much isolation is required between VCO o/p
and mixer or modulator i/p.Can somebody tell,how its to be calculated? I have been doing this practically till now.