Unlocking Success with OADM: A Comprehensive Guide to DWDM Network

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Date: 2025-09-05 16:04:17

OADM (Optical Add-Drop Multiplexer) plays a vital role in DWDM networks. It enables the selective dropping and inserting of optical signals into a transparent DWDM network. It offers high bandwidth, reliability and scalability, and low cost. This article provides a comprehensive guide to OADM.

What is OADM?
OADM is a passive optical device used in WDM networks for adding and dropping one/multiple 100 GHz DWDM channels in the C-band into one or two fibers while letting the rest of the wavelengths bypass to the needed destination. DWDM OADM modules are available in single-sided (East or West) and dual-sided (East and West) configurations, and plug-in, 1U rack mount, and ABS modules for various installation methods.

Typical Structure of OADM
A typical OADM consists of an optical multiplexer, an optical demultiplexer, a reconfiguration method between the optical demultiplexer and the optical multiplexer, and a set of ports for adding and dropping signals. A multiplexer couples two or more wavelengths into the same fiber. The reconfiguration is achieved by a fiber patch panel or optical switches that direct the wavelengths to the optical multiplexers or drop ports. A demultiplexer separates multiple wavelengths in an optical fiber and directs them to multiple optical fibers.

Configuration of OADM
OADM configuration uses a dielectric thin-film filter (TFF) and fiber Bragg grating (FBG). 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 is transmitted, and others are reflected. An arbitrary signal wavelength can be inserted/added into wavelength-multiplexed signals via a narrow BPF, whereby the desired signal wavelength transmitted is combined with the reflected signal wavelengths.

For OADM configuration 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.

How Does OADM Work?
OADM can add one or more wavelength channels to an existing multi-wavelength WDM signal or drop/remove one or multiple channels and pass those signals to a different network path. The OADM selectively drops a wavelength from numerous wavelengths in fiber and separates the signals from the particular channel. Thus, it adds the same wavelength in the same direction of data flow but with different data content.

What are the Types of OADM?
1) FOADM (Fixed Optical Add-Drop Multiplexer)
FOADM is used to improve the delivery of express traffic through networks without requiring expensive OEO (Optical-Electrical-Optical) regeneration. It uses 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.
2) ROADM (Reconfigurable Optical Add-Drop Multiplexer)
ROADM can add the ability to remotely switch traffic from the WDM system at the wavelength layer. 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 the inputting or outputting of a single wavelength or wavelength group via the fixed port. Unlike FOADM, ROADM allows users online reconfiguration without affecting traffic.

Application
OADM is used in metro/access/long-haul networks, OTN (Optical Transport Network), DWDM networks, OXC (Optical Cross Connection ), telecommunication networks, FTTx networks, etc.

Conclusion
OADM can add or drop signals with arbitrary wavelengths over multiplexed optical signals by assigning a wavelength to each destination. It provides low cost, high flexibility, easy upgrade, and amplification. In addition, it is suitable for short metro and long-haul networks.
Sun Telecom specializes in providing one-stop total fiber optic solutions for all fiber optic application industries worldwide. Contact us if you have any needs.

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