What Is OADM (Optical Add Drop Multiplexer)?

Updated on Dec 21, 2023 by

Amidst the escalating demand for bandwidth within fiber infrastructure, Optical Add-Drop Multiplexers (OADMs) emerge as pivotal components in modern optical networks. These passive devices facilitate the selective manipulation of wavelength channels, enabling efficient wavelength management without necessitating additional power supply. This article elucidates the fundamental principles, configurations, and applications of OADMs, highlighting their indispensable role in achieving flexible, cost-effective, and scalable optical network architectures.

Introduction to OADM


The OADM full form is Optical Add-Drop Multiplexer. OADMs are crucial components in wavelength-division multiplexing (WDM) systems, responsible for routing different light channels into or out of a single-mode fiber (SMF). As bandwidth demand continues to rise, OADMs have become essential in metro and access networks for efficient wavelength management.

OADMs utilize low-loss, low-cost passive components, ensuring a reliable and scalable network. The use of OADM in DWDM (Dense Wavelength Division Multiplexing) and Ultra-Wide Wavelength Division Multiplexing (UW-WDM) networks facilitates the selective insertion and removal of optical signals. By coupling multiple wavelengths into the same fiber and properly aligning a demultiplexer with a multiplexer, OADMs efficiently manage individual wavelengths, optimizing network performance and capacity.

Components of An OADM

An OADM generally consists of three parts: an optical multiplexer and demultiplexer, a method of reconfiguring the paths between the optical demultiplexer and the optical multiplexer, as well as a set of ports for adding and dropping signals. The multiplexer is used to couple two or more wavelengths into the same fiber. Then the reconfiguration can be achieved by a fiber patch panel or by optical switches that direct the wavelengths to the optical multiplexer or to drop ports. The demultiplexer separates the multiple wavelengths into a fiber and directs them to many fibers.

Figure 1:Inside an OADM

Figure 1: Components of a Traditional OADM

Configurations and Functions of the OADM

Configurations of OADM

There are two basic configurations of an OADM: using dielectric thin-film filter (TFF) and fiber bragg grating (FBG).

Thin-Film Filter (TFF): For OADM configuration with TFF, an arbitrary signal wavelength is branched/dropped from wavelength-multiplexed signals via a narrow band-pass filter (BPF), whereby only the desired signal wavelength being transmitted while others reflected. Meanwhile, an arbitrary signal wavelength can be inserted/added into wavelength-multiplexed signals via a narrow BPF, whereby the desired signal wavelength being transmitted is combined with the reflected signal wavelengths.

Figure 4:Configutation of OADM with TFF

Figure 2: Configutation of OADM with TFF

Fiber Bragg Grating (FBG): While configuring an OADM with FBG, the wavelength-multiplexed signals enter an FBG through a circulator, where only one arbitrary signal wavelength is reflected while others are transmitted. The reflected signal wavelength is branched/dropped into a port other than that where the wavelength-multiplexed signals enter. In the case of wavelength multiplexing an arbitrary signal wavelength, the signal wavelength incident on the circulator is reflected by the FBG, and is inserted/added into the wavelength-multiplexed signals that are transmitted via the circulator.

Figure 5:Configuration of OADM with FBG

Figure 3: Configuration of OADM with FBG

Main Functions of OADM

As the name indicates, an OADM can add one or more new wavelength channels to an existing multi-wavelength WDM signal, or drop/remove one or more channels, passing those signals to another network path. The OADM selectively drops a wavelength from a multiplicity of wavelengths in a fiber, and thus separates the signals from the particular channel. It then adds the same wavelength in the same direction of data flow, but with different data content.

Figure 2:the function of OADM

Figure 4: The Function of OADM

Different Types of OADM

OADMs are classified as FOADM (Fixed Optical Add-Drop Multiplexer) and ROADM (Reconfigurable Optical Add-Drop Multiplexer). In fixed-wavelength OADM, the wavelength has been selected and remains the same until human intervention changes it. In reconfigurable wavelength OADM, the wavelengths between the optical demultiplexer/multiplexer may be dynamically directed from the outputs of the demultiplexer to any of the inputs of the multiplexer.

Fixed Optical Add Drop Multiplexers

FOADMs were originally developed to improve the delivery of "express" traffic through networks, without requiring expensive OEO regeneration. FOADMs use fixed filters that add/drop a selected wavelength "band" and pass the rest of the wavelengths through the node. Static wavelength-filtering technology eliminates the cost and attenuation to demultiplex all DWDM signals in a signal path. The solution is called FOADM because the wavelengths added and dropped are fixed at the time of add/drop filter installation on the optical path through a node. No additional filters can be added without interrupting express wavelengths traveling through the node.

Reconfigurable Optical Add Drop Multiplexers

ROADMs were developed to provide 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. It uses a Wavelength Selective Switch (WSS). The WSS has an 8-dimensional cross-connect and provides quick service start-up, remote cross-connect and WDM mesh networking. The ROADM scheme also allows inputting or outputting a single wavelength or wavelength group via the fixed port. In ROADM systems, we don’t need to convert the optical signals to electrical signals and route those signals by using conventional electronic switches then convert back again to optical signals just like FOADM does. ROADM can configure as required without affecting traffic.

WDM Basics: Understanding Wavelength Division Multiplexing Technology

Figure 5: The Principle of ROADM

Application of OADM

In conventional long-haul transmission systems, the focus has been on capacity and transmission distance. However, in metro/access networks, low cost and system flexibility are essential. Optical Add-Drop Multiplexers (OADM) meet both demands, supporting standard network topologies such as point-to-point and ring. OADM enables the selective insertion, removal, or routing of specific channels along the optical link, enhancing network flexibility. This is particularly important in metropolitan Wavelength Division Multiplexing (WDM) lightwave services, where different add-drop channels can connect offices or sites in an interoffice ring.

The primary application of OADM is in Metropolitan Area Networks (MAN), offering high flexibility, easy upgrades, and signal amplification. As an ideal multi-service transport platform, OADM supports wavelength multiplexing signals at different locations. In WDM systems, OADM allows specific wavelengths on a fiber to be demultiplexed (dropped) and remultiplexed (added) while allowing other wavelengths to pass. Additionally, OADM is used in Optical Cross Connects (OXC). Proposed equipment allows different networks to connect dynamic, on-demand wavelength resources and a wider range of network interconnection. OADM and OXC only need to download the information in the nodes to send the person that handles the equipment, including ATM switchboard, SDH switchboard, IP router etc., which greatly improve the efficiency of the node to process information.

Figure 6:Application of OADM

Figure 6: Application of OADM

FS OADM Products

The fusion of FS's optical communication products with DWDM/CWDM OADM technology offers a versatile, efficient, and reliable solution specifically designed for Metropolitan Area Networks (MAN) and other network environments. FS provides a wide range of OADM products, which boasts adaptable installation options like Plug-in, 1U Rack Mount, and ABS Modules, ensuring seamless deployment. Key features such as the Monitor Port for troubleshooting and the 1310nm Port for capacity enhancement enhance its capabilities. Through passive transparent any rate, any service multiplexing, it seamlessly adheres to ITU Grid standards, ensuring compatibility across various optical networking products. Additionally, its ability to operate effectively under industrial temperature conditions enhances its adaptability, making it an ideal choice for network optimization and cost-effectiveness.

Additionally, we specialize in customizable OADM solutions, offering a rich array of parameters for customization, including Transmission Direction, Housing, Channels, Grid Channel, Connector, and Special Service options. This extensive customization capability ensures that our OADM solutions can be precisely configured to suit the unique needs of any network environment. Furthermore, we also provide advanced ROADM products to meet your specific requirements.


To reduce costs in large-capacity transmission, signal processing needs to shift towards optical form, bypassing the conventional optical-to-electrical conversion. OADMs are pivotal for this optical signal processing. The use of OADM in optical communication enables flexible addition or removal of signals with different wavelengths over multiplexed optical signals, simplifying component configuration and reducing total network costs. Despite their small size, OADMs will continue to play a crucial role in developing compact, integrated, and cost-effective devices.

You might be interested in

See profile for Sheldon.
Decoding OLT, ONU, ONT, and ODN in PON Network
Mar 14, 2023
See profile for Irving.
What's the Difference? Hub vs Switch vs Router
Dec 17, 2021
See profile for Sheldon.
What Is SFP Port of Gigabit Switch?
Jan 6, 2023
See profile for Migelle.
PoE vs PoE+ vs PoE++ Switch: How to Choose?
May 30, 2024
See profile for Moris.
How Much Do You Know About Power Cord Types?
Sep 29, 2021