sending signals from both ends of an optical fibre at the same time

[rookie1010]

Hello

I was wondering if it is possible to send signals down both ends of an optical fibre at the same time.

i was trying to figure out how to dimension the Iu interface of UMTS, and wanted to know if i could transmit dl and ul traffic down a single optical fibre at the same time.

 

[Matthias99]

In theory... maybe. Photons don't cross-interfere, so you can put lasers going both ways in a single fiber and it should work OK. I'm not sure if you might also have problems with signal reflections coming back towards you; you might have to use different frequencies going each way to avoid that problem.

In practice... it's a hell of a lot easier to use two wires, which is what all fiber-based systems that I am aware of do. This way you don't have to try to splice an optical transmitter and receiver onto the same wire.

 

[rookie1010]

thanks for the reply

i was looking at this dimensioning and they were taking the higher of the 2 optical interfaces required(uplink and down,link) which led me to beleive perhaps they were "multiplexing(?)" the two streams on the same optical fibre.

do you think it is an industry practice. perhaps i should look at the block diagram of an rnc

the rnc uses a STM1/OC-3 interface, can signal be pumped both ways when using stm1/oc-3 interface

 

[Matthias99]

Originally posted by: rookie1010
thanks for the reply

i was looking at this dimensioning and they were taking the higher of the 2 optical interfaces required(uplink and down,link) which led me to beleive perhaps they were "multiplexing(?)" the two streams on the same optical fibre.

do you think it is an industry practice. perhaps i should look at the block diagram of an rnc

the rnc uses a STM1/OC-3 interface, can signal be pumped both ways when using stm1/oc-3 interface

Multiplexing is widely used (with multi-mode fiber) -- this sends signals on different frequencies in the same fiber, but in the same direction!

Like I said, sending signals both ways down a single fiber should be possible, but I do not believe it is commonly done. I've never dealt personally with any equipment that works like that (but I'm also not in telecommunications).

 

[rookie1010]

ah makes sense

thanks

 

[f95toli]

The answer is yes you can. In fact you can even send electrical signals "both ways" if the frequency is high enough (microwaves).
However, as Mattias99 points out the problem is that you need a transmisster/reciever at the ends of the cable and some way to separate the signals which is tricky at optical frequencies (with microwaves it is easy, you just use a circulator or a directional coupler).

 

[jmcoreymv]

There are a number of different optical directional couplers available to separate the signals.