Introduction to the Components Used in CWDM System

CWDM system is a passive optical solution for increasing the flexibility and capacity of existing fiber lines in high-speed networks. It increases fiber capacity by placing widely spaced, separate wavelengths (between 1310 nm and 1610 nm) from multiple ports onto a single-mode fiber pair on the network. The CWDM system components are passive and require no power supplies. This article will introduce the components used in CWDM system.

CWDM System Components

Generally, there are three basic components in a CWDM system, which are the multiplexer/demultiplexer (Mux/Demux), the drop/pass module and drop/insert module. CWDM applications are described in terms of an east-west connection. Different colors represent individual channels. Westbound traffic is represented by dashed lines, while eastbound traffic is shown with solid lines.



The Mux/Demux based on film filter is the most mature component used in CWDM system. It combines different channels onto a single outbound (TX) fiber. Simultaneously, the Mux/Demux receives the same channels from a single inbound (RX) fiber, separates them into individual wavelengths, and delivers each to the appropriate local interface. This process expand the capacity of the existing network fiber cable. The following is an example of four channel Mux/Demux.


The four-channel Mux/Demux can be configured to support additional channels through the expansion port. By cascading the modules in series, you can increase the total number of available network channels. The channels connecting to the expansion port must differ from those on the Mux/Demux to which they are being cascaded.

Drop/Pass Module

The drop/pass module removes one wavelength-specific channel from the east-bound fiber and allows the remaining channels to pass straight through to other nodes along the network. When the drop/pass module drops the channel from the network, it sends the data to a local interface. The local interface sends the same channel back to the drop/pass module for transmission in the westbound direction, thus completing the point-to-point connection between the local interface and another device located in the west. That other device may be a Mux/Demux, drop/pass, or drop/insert module.

drop and pass

Drop/Insert Module

The drop/insert module provides two local interface ports. One port removes a wavelength-specific channel from the network fiber in one direction, and the other port adds that same channel back onto the fiber in the opposite direction. Because the drop/insert module supports two separate pathways going in opposite directions, network viability in a ring topology is ensured even if there is a break in the network.

On the west side, the drop/insert module removes a wavelength-specific channel from the eastbound fiber and sends it to Local Interface A. To complete the westbound connection, the drop/insert module receives the same channel from Local Interface A and inserts it onto the westbound fiber. The same happens on the east side, except in the opposite direction. The drop/insert module removes the channel from the westbound fiber and sends it to Local Interface B. To complete the eastbound connection, the drop/insert module receives the same channel from Local Interface B and inserts it onto the east-bound fiber. The drop and insert completes the point-to-point connections between the two local interfaces and two other devices located in the east and west. The other device may be a Mux/Demux, drop/pass, or drop/insert module.

drop and insert


CWDM is a simple and affordable method to maximize existing fiber by decreasing the channel spacing between wavelengths. Since CWDM is a passive technology, it allows for any protocol to be transported over the link, as long as it is at a specific wavelength. Because the multiplexers simply refract light at any network speed, regardless of the protocol being deployed, CWDM can help to future proof the networking infrastructure. In all, CWDM is a low-cost and effortless technology to implement. FS.COM provides a whole series of WDM system components including CWDM and DWDM. If you need, you can visit for the details.

Related article: CWDM & DWDM Mux/Demux Overview

Related article: Traditional CWDM Mux/DeMux vs. FMU Series CWDM Mux/DeMux