The single wavelength BiDi transmission technology offers a unique solution to meet these apparently conflicting goals at the same time, particularly in access networks such as FTTx and in wireless backhaul networks between a base station and antenna tower or aRRH, compared with the two-wavelength BiDi transmission and the duplex transmission which are currently in use. This article presents pros and cons between competing technologies, operating principles of the single wavelength transmission technology and its applications, and Fiberstore’s BiDi transmission products. For example, in a P2P upstream signal from the subscriber to the CO. The optical transceivers at two ends of a transmission link can be identical if one wavelength is used for both directions. However, the CAPEX and OPEX are much higher due to the cost for two fibers and their installation compared with other BiDi technologies described below which use a single fiber. This technology can be used in the wavelength division multiplexing(WDM) communication as well as in the P2P communication.
These wavelengths are separated widely from each other. For example, in a P2P access network, the downstream signal from the CO to a subscriber is at 1550 nm and the upstream signal from a subscriber to the CO is at 1310 nm. The fact that a different signal wavelength must be used in each opposite direction of transmission imposes on the network operators two disadvantages. For example, in a P2P access network , the wavelength can be at 1550nm (or 1310 nm) for both downstream and upstream signals. This reduces CAPEX and OPEX for the network operators since they need to deploy only one kind of optical transceivers at 1550 nm (or 1310 nm). This also guarantees a foolproof installation of transceivers without any confusion since all the transceivers are identical and there is one fiber. In a WDM BiDi system, this is only a viable approach for providing each channel a fully bi-directionally dedicated (or symmetric) bandwidth. This technology may face between upstream and downstream signals a crosstalk and an interferometric beat noise, both coming from reflections at the interface between a transceiver and a channel link fiber with PC (or UPC) type connectors , which may impose a limit on the maximum allowable channel loss, or in other words, the maximum transmission distance. These reflections, however, can be mitigated by using APC type connectors.
Here is a table that summarizes pros and cons of various BiDi transmission technologies. The single wavelength BiDi clearly shows its own unique advantages over two other competing technologies, two-wavelength BiDi and Duplex.
The single wavelength BiDi transmission technology allows over a single fiber a simultaneous communication in both directions at the almost same wavelength. Here is a figure that shows a simple of such transmission system:The signal wavelengths from two transceivers, downstream signal from Tx 1 and upstream signal from Tx 2, are very close to each other, which explains why this approach is named as “a single wavelength BiDi transmission”.
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