Why optical fibre discks should be keep away from magnate?

Permanent magnets and strong electromagnets may damage data that has been recorded on the computers diskettes and on the video cassettes, because the information is on these in a magnetic form.
Source (in Finnish): http://www.edu.helsinki.fi/astel-ope/sahko/magneettinen_tiedon_tallennu…

Fiber Optic Cables are immunity to electromagnetic disturbance and its signal transmission characteristics make it the ideal support for high-speed data transmission. There occurs no electromagnetic radiation.
The light waves travel along the optical core which is made from silica, melted quartz or plastic.
Sources:
http://www.cablofil.com/content.aspx?page=123&section=60
http://www.patentstorm.us/patents/7241954-description.html

Find more about the subject:
http://www.ieee.org/portal/site/iportals >
Find an article in the IEEE Xplore digital library
http://www.iec.ch/zone/emc/