Fiber Optic Communication System

[CUTigers]

I was wondering if anyone here has a good understanding of either building such a system or the parts contained in one. Frequency division multiplexing will be used during the process. More information can be posted if someone feels the urge to assist.

[oberon]

You mean DWDM (dense wave division multiplexing)? I've used gigabit Ethernet over fiber (continuous multimode cables between switches, no patch panels) but never even seen a system that uses DWDM in person. I suspect only telcos or large corporations have any use for DWDM. So, why are you asking?

[goddfather40]

Frequency Division multiplexing is simply assigning each signal a certain frequency range (or wavelength range in fiber terminology) just like the FM spectrum, AM spectrum, etc. in the RF world. Go ahead and post some more details, I am an EE and took an upper-division Fiber Optics class my senior year about a year ago.

[CUTigers]

System is to utilize FDM of FSK digital signals to transmit and receive signals from various nodes (100 nodes). 5 km of fiber optic cable to be used and at each node, there is to be a transmitter/receiver pair. Transmitter should use LED with peak emission in the range of 800 to 950 nm while the output power of the transmitter should be in range of 5 to 10 mW. Carrier frequencies are 100 Khz to 900 Khz with 8 Khz spacing. Band limited at each node to achieve -40 dB of attenuation. When Master transmitter is ON, node transmitters should be off, wwhile aslo, when the Master Transmitter is turned off, node transmitters should be set to TRANSMIT and send their information back to Master Receiver.

That is the system specs. Any ideas for designing such a system, such as components, would be appreciated. Thanks.

[goddfather40]

What kind of data rate is required, and is 10^-9 an acceptable BER? Is there any cost restrictions?

By the way, the book I used when I took my fiber class was 'Intro to Fiber Optic Systems' by Powers, and it was pretty good for a systems level book without going into the very detailed electromagnetic response of fibers.

[CUTigers]

Cost restriction is relatively vague, described as being "reasonable". Data Rate is 500 kbits/sec. As for the BER, i believe 10^-9 should be acceptable

[goddfather40]

The data rate is fairly slow, so you don't have to worry about reaching attenuation and dispersion limits at your 5 km max distance. I would use a FET front end on your receiver (the cheaper the better probably), since the really cheap BJT front ends are inferior at lower data rates such as yours. In fact your run of the mill Silicon MOSFET will do fine. Your detector can be a regular silicon photodiode as well. On the transmitter side, again, due to the relatively low data rate, use a LED source with a low threshold current so that you can directly drive the diode from the output of a TTL chip. I apologize if you were looking for specific part numbers and stuff, because a lot of my experience is only from school. Let me know if this helps or if you needed a bigger system view having to do with the topology and stuff.