In CWDM networks, dual-fiber CWDM MUX/DEMUX, which uses the same wavelengths for transmitting and receiving, is usually used in dual way transmission applications. The working principle is easy to understand. A duplex fiber cable links two dual-fiber CWDM MUX/DEMUXs supporting the same wavelengths installed on each end of the fiber optic network. The wavelengths of the two fibers are the same, but they are running on the different directions for duplex transmission. The following picture shows how dual-fiber CWDM MUX/DEMUX is used for duplex transmission. However, in some cases, there is only one fiber available for network capacity expansion. Then, single-fiber CWDM MUX/DEMUX is being used, which is very much different from the dual-fiber one.
The single-fiber CWDM MUX/DEMUX has a simplex line port (shown in the above picture), which is the biggest difference from the dual-fiber CWDM MUX/DEMUX on the appearance. There are also some single-fiber CWDM MUX/DEMUX are made with a duplex port. But only one port of this duplex port is in use, the other is usually marked with N/A. For instance, our FMU single-fiber CWDM MUX/DEMUX also uses this design.
The reason why single-fiber CWDM MUX/DEMUX can achieve dual way transmission is because it uses the CWDM wavelengths in a different way compared with the dual-fiber CWDM MUX/DEMUX. In dual-fiber CWDM network, each wavelength runs on two opposite directions. However, in single-fiber CWDM network, each wavelength just runs on one direction. In other works, if you want to build a dual way transmission link between two sites, you can use one wavelength over duplex fiber with dual-way CWDM MUX/DEMUX, or use two wavelengths (one for TX and the other for RX) over simplex fiber with single-fiber CWDM MUX/DEMUX.
The above picture shows how CWDM wavelengths are used in a single-fiber CWDM network. In this network, 16 wavelengths are used to support 8 pairs of dual-way transmission. On site A, there deployed an 8-channel single-fiber CWDM MUX/DEMUX using 8 wavelengths for transmitting and the other 8 wavelengths for received. On the opposite site B, also a single-fiber CWDM MUX/DEMUX is deployed. However, the wavelengths for TX and RX are reversed. For instance, a pair of dual-way signal uses 1270nm for TX and 1290nm for RX on site A, while use 1290nm for TX and 1270nm for RX on site B. This is how the single-fiber CWDM MUX/DEMUX achieving dual-way transmission.
Some might get confused about how to select the transceivers for single-fiber CWDM network as there are two different wavelengths on a duplex channel port. The selection for single-fiber CWDM MUX/DEMUX is mainly based on the wavelength for TX. Still take the above mentioned example, on site A 1270nm is used for TX, thus, a 1270nm CWDM fiber optic transceiver should be used. On site B, a 1290nm CWDM fiber optic transceiver should be used. The fiber optic transceivers used for single-fiber CWDM network are different on the two sites.
Here offers a case of how to use single-fiber CWDM MUX/DEMUX to build CWDM network which supports four pairs of dual-way signals. To build such a single-fiber CWDM network, eight different wavelengths should be used. Here we use two of our FMU 4-channel single-fiber CWDM MUX/DEMUXs to show the details. These two single-fiber CWDM MUX/DEMUX can be used together. The following shows their channel port details.
The following picture shows how to build a 10G single-fiber CWDM network. As clearly showed, all the wavelengths just go in one direction. CWDM SFP+ transceivers working on 1470nm, 1510nm, 1550nm and 1590nm are linked with the CWDM MUX/DEMUX on one side of the network. The other CWDM MUX/DEMUX deployed on the other end of the network is connected with CWDM SFP+ transceiver working on wavelengths of 1490nm, 1530nm, 1570nm, 1610nm. Thus, eight wavelengths are used for 4 pair dual-way transmission in this single-fiber CWDM network.
The above mentioned products for CWDM network are all available in FS.COM. various CWDM MUX/DEMUXs and CWDM fiber optic transceivers including CWDM SFP/SFP+/XFP are available and can be customized. Please note the special ports like expansion port and monitor can also be added and they are all simplex. Kindly contact firstname.lastname@example.org for more details if you are interested.