Category Archives: WDM Optical Network

Installation Guide to CWDM MUX/DEMUX System

CWDM MUX/DEMUX System Overview

Coarse Wavelength Division Multiplexing (CWDM) is a wavelength multiplexing technology for access networks. It is designed to increase fiber optic network capacity without adding additional fibers. The wavelengths of CWDM channels range from 1270nm to 1610nm with 20nm spacing, which allows the use of cost-effective lasers. CWDM MUX/DEMUX system is a passive, optical solution to increase the flexibility and capacity of existing fiber lines in high-speed networks. By adding more channels into available fibers, the CWDM MUX/DEMUX system enables greater versatility for data communications in ring, point-to-point, and multipoint topologies for both enterprise and metro applications.

CWDM MUX/DEMUX System Components

All CWDM system components are passive and require no power supplies. They consist of the rack mount chassis, a set of CWDM MUX/DEMUX and CWDM OADM (Optical Add/Drop Multiplexing) modules with color-coded ports. The CWDM MUX/DEMUX takes 4 or 8 different wavelength channels and multiplexes them onto one common fiber cable for transmission to the network. Then it demultiplexes the channels it receives from the network and sends each channel to a different device. Multiple modules may be chained through the expansion port on the four-channel modules. Thus it increases flexibility and enables growth for evolving networks.

The CWDM OADM module can add or drop CWDM channels into an existing backbone ring. It provides the ability to drop one CWDM channel from the network fiber, while allowing all other channels to continue pass to other nodes. Similarly, the drop/insert module removes an individual channel from the network fiber, however, it also provides the ability to add that same channel back onto the network fiber. The drop/insert module supports two paths (east and west) for dropping and adding, so that network viability is maintained in a ring topology, even if a break occurs in the ring.

CWDM MUX/DEMUX System Installation Guide

Step1: Mount the system chassis on the rack. The CWDM rack-mount chassis can be mounted in a standard 19-inch cabinet or rack. Make sure that you install the rack-mount chassis in the same rack or an adjacent rack to your system so that you can connect all the cables between your CWDM MUX/DEMUX modules and the CWDM SFP transceivers.


Step2: Install the CWDM MUX/DEMUX modules. First loose the captive screws on the blank of module panel and remove the panel. Then align the module with the slot of the chassis shelf and gently push the module into the slot. Finally, ensure that you line up the captive screws on the module with the screw holes on the shelf and tighten them up.


Step3: Install CWDM SFP transceivers. Since each channel has a specific wavelength, transceivers must comply with the right wavelengths. Each wavelength must not appear more than once in the system. Device pairs must carry transceivers with the same wavelength.

Step4: Install the CWDM MUX/DEMUX to the switch. After inserting the CWDM SFP transceiver into the switch, single-mode patch cables are used to connect the transceiver to the CWDM MUX/DEMUX module.


Step5: Connect the CWDM MUX/DEMUX pairs. In a CWDM MUX/DEMUX system, multiplexer and demultiplexer must work in pairs. Two strands of single-mode patch cables are needed in the duplex MUX/DEMUX module and one strand for the simplex one. Simply insert single-mode cables from your system equipment to the appropriate port on the CWDM MUX/DEMUX or OADM module.


CWDM MUX/DEMUX system is an attractive solution for carriers who need to upgrade their networks to accommodate current or future traffic needs while minimizing the use of valuable fiber strands. With CWDM technology, you can accommodate Ethernet and SONET on a single fiber that enables converged circuit/packet networks at high demand access sites. Besides, CWDM MUX/DEMUX can work seamlessly with transceivers to optimize link length, signal integrity and network cost, thus becoming a single rack-mount solution for enhanced design, power and space efficiency.

Introduction to Optical Add-Drop Multiplexer (OADM)

There exist several different channel routing technologies in the field of optical communications. However, the evolution of single wavelength point-to-point transmission lines to wavelength division multiplexed optical networks has introduced a demand for wavelength selective optical add-drop multiplexers (OADM) to separate or route different wavelength channels. This article provides some fundamentals relevant to OADM.

What Is OADM?

Optical add-drop multiplexer (OADM) is a device used in wavelength-division multiplexing (WDM) systems. “Add” and “drop” is a capability device to add one or more new wavelength channels to an existing multi-wavelength WDM signal or to drop, which means to remove one or more channels, passing those signals to another network path. OADM can be used at different points along the optical link to insert, remove or route selected channels thus to increase the network flexibility. OADM is particularly important in metropolitan WDM light wave services where offices or sited can be connected by different add-drop channels.

A traditional OADM consists of three stages: an optical demultiplexer, an optical multiplexer, and between them a method of re-configuring the paths between the demultiplexer, the multiplexer and a set of ports for adding and dropping signals. The demultiplexer separates wavelengths in an input fiber onto ports. The reconfiguration can be achieved by a fiber patch panel or by optical switches which direct the wavelengths to the multiplexer or to drop ports. The multiplexer multiplexes the wavelength channels that are to continue on from demultiplexer ports with those from the add ports, onto a single output fiber.

The Functions of OADM

As we have mentioned above, the main function of an optical multiplexer is to couple two or more wavelengths into the same fiber. If place a demultiplexer and properly aligned it back to back with a multiplexer, there would exist two individual wavelength in the area between them. Then, this offers a chance for an enhanced function that individual wavelengths could be removed and inserted as well. The function would be called an optical wavelength drop and add demultiplexer/multiplexer—to make it briefly, optical add-drop multiplexer.

The model of an OADM is clearly shown in the picture below, where F1 signifies a filter selecting wavelength λ1 while passing through all other wavelength, and M1 signifies a multiplexer that multiplexes all wavelengths.


An even better view of OADM function is shown in the following picture. This function is often employed in WDM ring systems as well as in long-haul with drop-add features.


Types of OADM

There are two main types of OADM that can be used in WDM optical networks: fixed OADMs that are used to drop or add data signals on dedicated WDM channels, and re-configurable OADMs that have the ability to electronically alter the selected channel routing through the optical network.

The fixed optical add-drop multiplexer (FOADM) is a traditional wavelength arrangement scheme that can only input or output a single wavelength via the fixed port. FOADMs have pre-assigned channels at static nodes and allowed adding and dropping of individual or multiple wavelength channels from a DWDM.

The re-configurable optical add-drop multiplexer (ROADM), on the other hand, is a dynamic wavelength arrangement scheme, allows for dynamic wavelength arrangement scheme using a wavelength selective switch (WSS). The 8-dimensional cross-connect provided by the WSS enables quick service start-up, remote cross-connect and WDM mesh networking. The ROADM scheme can also achieve inputting/outputting a single wavelength or wavelength group via the fixed port. ROADM can add, block, pass or redirect modulated infrared (IR) and visible light beams of various wavelengths in a fiber optic network. Which featured by providing flexibility in rerouting optical streams, bypassing faulty connections, allowing minimal service disruption and the ability to adapt or upgrade the optical network to different WDM technologies.


To summarize, OADM plays a vital role in improving and optimizing the network performance and reliability. And it is fully compatible with both local area network (LAN) as well as long haul networks. Moreover, OADM also serves as an essential device to meet the requirement of the rapidly developed network.