Optical Insanity

neilgregge

Hello,

I have been given an assignment to design an optical communication system. A 12 MHz LED (laser diode would be too easy) signal has to be sent 45km via optic fibre and read at the other end. Simple enough, you may think. however I have been told that I have to use multimodal cable, and all I have read has said that there are insane signal losses associated with multimode (one place, i read there was 2dB loss for every km, whicc was about 90% after 10km), hence its use primarily for internal networks. As repeater stations along the way are prohibited, I am at a loss (much like my signal) as to how to go about this.

Any help would be appreciated,

Neil

Averagesupernova

Treat the system as an FM radio system. Think about it. How much loss do we have between a transmitting antenna and a receiving antenna which are seperated by 45 Km?

Edit: 2 db per Km is 90 db total. This has an input to output ratio (in power) of 1 billion to one.