In the past, I have dealt with fiber optic network communication devices that utilize two fibers, RX and TX, each being dedicated to one direction. I was under the impression that two fibers are always required for bidirectional communication.
However, recently I have encountered several devices that utilize a single fiber while providing bidirectional communication. These devices are present in telephone and intercom systems. An example is this device which provides two zero-latency analog audio channels plus a 10/100 Ethernet port over a single fiber.
From this document, I understand that single fiber bidirectional mode uses different wavelengths for send and receive modes, and filters on each end of the circuit to pass only the desired wavelengths.
I am not sure if the aforementioned devices use this method, or if they use some form of half-duplex interleaving to send and receive in separate time windows. Since the spec says a maximum of 50Mbps Ethernet transmission is possible, I am assuming a half-duplex method is being used, but this is not clearly stated anywhere.
How does the bidirectional communication of these devices work? does it use either of the above methods, or something else?
Why would anyone want to use two fibers when one can accomplish the task?
Is there some sort of performance or other benefit to having two fibers? The aforementioned unit even provides a 10/100 Ethernet jack in addition to two zero-latency voice channels, so it appears bandwidth isn't an issue. I can understand if this method employs interleaving, the bandwidth would be drastically reduced, but if two different wavelengths are used, it should permit full-duplex transmission.
Thank you for any explanations of this, references etc.