[AFMUG] fiber signaling

[Adam Moffett via Af]

Something came up in fiber training that I attended recently that I 
found hard to believe.

The instructor said that the signaling was simply on/off.  I.E.: light 
on = 1 and light off = 0.

I would have /assumed/ they would use some sort of more advanced 
modulation than that.  In fact, I'm sure I've read about creating an 
optical carrier wave and modulating it.

Was the instructor correct?  Is it just blinky blinky on/off and that's 
it?  If so, then why the hell would they do that?  Wouldn't they get 
another order of magnitude of capacity by applying a more advanced 
modulation scheme?