Single Fiber CWDM MUX and DEMUX Tutorial

Posted on January 3, 2017
July 5, 2020

In CWDM networks, bidirectional CWDM MUX DEMUX (also called dual fiber CWDM MUX DEMUX) uses the same wavelengths for transmitting and receiving. It is often 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. However, in some cases, there is only one fiber available for network capacity expansion. Then, single fiber CWDM MUX and DEMUX is being used, which is very different from the dual-fiber one.

single fiber CWDM MUX and DEMUX

Understand Single Fiber CWDM MUX and DEMUX

The single fiber CWDM MUX DEMUX has a simplex line port (shown in the above picture), which is the biggest difference from the bidirectional CWDM MUX DEMUX on the appearance. There are also some single fiber CWDM MUX and 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.

single-fiber cwdm mux demux

The reason why single fiber CWDM MUX and DEMUX can achieve dual way transmission is because it uses the CWDM wavelengths in a different way compared with the bidirectional CWDM MUX DEMUX. In bidirectional 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-fiber CWDM MUX DEMUX, or use two wavelengths (one for TX and the other for RX) over simplex fiber with single fiber CWDM MUX DEMUX.

8 channel 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 and 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 and DEMUX achieving dual-way transmission.

How to Select Fiber Optic Transceiver for Single Fiber CWDM MUX and DEMUX

Some might get confused about how to select the CWDM 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 transceiver should be used. On site B, a 1290nm CWDM transceiver should be used. The fiber optic transceivers used for single fiber CWDM MUX and DEMUX are different on the two sites.

Single Fiber CWDM MUX DEMUX Case Study

Here offers a case of how to use single fiber CWDM MUX and 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 CWDM MUX DEMUX to show the details. These two single fiber CWDM MUX DEMUX can be used together. The following shows their channel port details.

FMU Single Fiber CWDM MUX DEMUX 4 channel-cwdm-mux-demux-1 4-channel-cwdm-mux-demux-2
TX (Transmit) 1470nm 1510nm 1550nm 1590nm 1490nm 1530nm 1570nm 1610nm
RX (Receive) 1490nm 1530nm 1570nm 1610nm 1470nm 1510nm 1550nm 1590nm

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 and 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.

4-channel single fiber CWDM

FS.COM Single Fiber CWDM MUX DEMUX Solution

The above mentioned products for CWDM network are all available in FS.COM. Various CWDM MUX DEMUX and CWDM 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 for more details if you are interested.