Re: broken glass
Unfortunately I don't think POF will offer any enhanced robustness over glass fibre: If you bend it past the recommended bend radius then you will still encounter reflection issues. Also, whilst it might not snap as catastrophically as glass, accidentally crushing, bending, treading on a plastic fibre may result in stressing of the plastic which will make the plastic go "cloudy" in the stress area and stop it working.
Tricky: You could use QAM on fibres in general, but there's not a lot of point as in practice it would increase noise in other modulation techniques and thus not offer any benefit.
Frequency Division Multiplexing is generally used when sending lots of data over a single-mode fibre, which means that you divide the frequencies available on the fibre into many channels and send data along each one. It's analagous to how they can send several TV channels over the same bit of space between the transmitter and your TV. You have a different data stream on each channel.