Bidirectional communication on a single optical fiber

The thing I can`t get an answer for myself is " How do you actually use a single optical fiber for bidirectional transmision?"

We have implemented optical networks in our company, but we have always used a separate fiber for the Tx and Rx directions. So how does bidirectional transmission on a single fiber work? For example most of the ports on Cisco and Juniper equipment are bidirectional.

As far as my theoretical knowledge goes, optical transmission is a light source going on and off, representing "0"s and "1"s. So how is it possible to have a signal in the opposite direction? I guess they alternate in some way, but I couldn`t find an appropriate explanation.

Thank you in advance

In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths (colours) of laser light to carry different signals. This allows for a multiplication in capacity, in addition to enabling bidirectional communications over one strand of fiber.If you do more research on this you will understand how it works .

Thank you for you answer Azilla.

Actually, I am quite familiar with WDM and DWDM multiplexing and know it is used to multiplex several wavelenghts on a fiber, but still they are going in the same direction. I believe it alternates light direction in addition to WDM in every direction, but I really couldn`t find any article or anything more specific on this matter.

I would greatly appreciate if you could point me to a source, or a link with such info.

The other thing I`m wondering is... I was told that bidirectional transmission should be supported by the SFP itself. Do you have any idea how their naming convention differs, and how can I know it is a bidirectional SFP, before actually deploying it.

Thank you in advance again !!!

Thanks Astram. Yeah that is a great question about bidirectional over fiber. I thought you were just asking how it is done technology wise. You sound very educated on fiber technology so if you do find the answer please let me know, I would love to know for myself the answer to your questions. I love Wdm and Dwdm I think the technology is wonderful I hope to work with this technology someday so I can see it hands on. GOod luck and take care buddy.

Hello astram and welcome to fw.cx

Actually, I am quite familiar with WDM and DWDM multiplexing and know it is used to multiplex several wavelenghts on a fiber, but still they are going in the same direction. I believe it alternates light direction in addition to WDM in every direction, but I really couldn`t find any article or anything more specific on this matter.

Experts, please correct me if I'm wrong.

The way I understand it is wither 2 lights travel in same or opposite directions, they wont interfere unless they have the same or very close wavelengths, which is not the case in WDM. It seams that difficulties in bidirectional transmission is related to transceivers and amplifiers manufacturing, rather than the theoretical possibility.

The concept seams new to the literature. This book might give a clue: "Fundamentals Of Bidirectional Transmission Over A Single Optical Fibre"

Solo pretty much nailed it on the head.

With a single fiber using CWDM you would shoot 1470nm for transmit and 1490nm for receive. Inline filters (mux/demux) can be used to break out the wavelengths before the transceiver equipment but this isn't the norm anywhere I have seen.