Optical Bus

Hello, i've this problem and i will thank anyone with an idea: I need to make an optical bus, i 've an optical signal that have to be a trigger for 10 modules along 10Km or 30000 feet. Thus any receivers modules is isolated and can receive the optical signal (the trigger). The receiver is battery powered. My ideas are:

1) 10 optical led trasmitter and 10 optival reciver connect with multimode (it's hard long distance) 2) 1 laser and 10 beam splitter, 10 pin optical receiver with multimode or singlemode fiber

Any help will be good. Matteo

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I'd suggest using SM fibre, because (a) it's much cheaper, and (b) it has much lower loss. You can get SM couplers in any split ratio you like, but there are sort-of standards. If you use one SM fibre with 9 couplers, you can do the following:

Tap # % power left in fibre split ratio tap power, % of total

1 100 90:10 10 2 90 90:10 9 3 81 90:10 8.1 4 72 90:10 7.2 5 64 80:20 12.8 6 51 80:20 10.2 7 40 80:20 8 8 32 60:40 12.8 9 19 50:50 9.5 10 9 100:0 9

It won't be quite this good, because you have some excess loss on each tap, but you get the idea.


Phil Hobbs

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Phil Hobbs

To expand on Phil's plan... Regarding sources, what rate and encoding are you transmitting?

100Mbps NRZ? FP or DFB Laser Diodes coupled to SMF are reliable links. DFB source probably have an isolator even though distance is 10km to prevent stacked reflection from all those taps. Is space qualification required? Environmental condition (temp, hum. range) effects decision on type of LD package you want (commercial module, TO, TOSA, other or custom). PiN receivers in combination with DFB LD should work at these reachessplits and have same packaging mentioned above.
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