When designing the fiber optical network, we used to choose the duplex fiber cable as the first choice to finish the dual-way transmission, which transmits the dual-way signals via two separate simplex cables from the opposite sides. However, in some typical dual-way applications like working with BiDi fiber optic transceiver, the simplex fiber cable is required to transmit the dual-way signals respectively over only one fiber cable by using two different wavelengths that has a more complicated working principle than the duplex one. If we want to deploy a single fiber CWDM network, the basic principle is similar to simplex fiber cable but would be much more complicated, which will be explained detailedly in this post.
Single fiber CWDM network is a special kind of WDM network that can greatly increase the network capacity by combining and transmitting several pairs of signals with different wavelengths over a single fiber, with the aim of supporting several dual-way connections at the same time. To deploy the single fiber CWDM network, a pair of single fiber CWDM multi-channel Mux/Demux and several pairs of CWDM transceivers are needed. When the single fiber CWDM network works, the two single fiber Mux Demux require different wavelengths for each pair of dual-way transmission, which is very different from the dual fiber Mux Demux using the same wavelength for a pair of dual-way transmission. That’s to say, there are only four different wavelengths used for 4-channel dual fiber CWDM Mux Demux, but eight different wavelengths divided into four pairs for 4-channel single fiber CWDM Mux Demux.
Before talking about the single fiber CWDM network, let’s take a simple BiDi network as an example first. In the BiDi network, only one simplex fiber cable and a pair of BiDi fiber optic transceivers are required to finish the dual-way connection. In details, the two BiDi fiber optic transceivers should be almost the same but has reversed wavelengths for TX and RX. For instance, if one transceiver with 1490nm for TX and 1310nm for RX is installed in one end of the fiber link, the other one in the opposite end should use 1310nm for TX and 1490nm for RX, as shown in the following figure. Hence, the dual-way signals with two different wavelengths can be transmitted over only one fiber cable.
As for the single fiber CWDM network, its basic principle is similar to the BiDi network but would be much more complicated, which can be also learned from the following figure. In the figure, there are two 4-channel single fiber CWDM Mux Demux connected to each ends of the single fiber, and four pairs of CWDM SFP+ transceivers designed with eight different wavelengths, totally achieving the 4-channel single fiber CWDM network. It is easily to learn that these eight different wavelengths are divide into four pairs and each pair has the complete reversed TX and RX. For instance, the first pair of CWDM transceivers consist of a transceiver with 1490nm for TX and 1310nm for RX in the left side and a transceiver with 1490nm for TX and 1310nm for RX in the right side, thereby a pair of dual-way signals with two different wavelengths will be transmitted through the first channel. To better understand how does the single fiber CWDM network work, the following table lists the eight ports with four pairs of wavelengths for TX and RX that are all reversed to ensure the dual-way transmission.
The single fiber CWDM network can greatly increase the network capacity for transmitting larger dual-way data signals, which is able to combine several pairs of signals with different wavelengths into an integrated signal and carry it through a single fiber. To build a smooth single fiber CWDM network, you should firstly install the CWDM fiber optic transceivers into two switches and then connect them into the channel ports of the two single fiber CWDM Mux Demux, finally use a single-mode simplex fiber cable to link the two CWDM Mux Demux together. Besides, to ensure the performance of the single fiber CWDM network, there are some important factors like light loss, transmission distance, and optical signal dropping and adding should also be taken into consideration.
Fiber Optic Communication 