OADM (Optical Add-Drop Multiplexer)

Introduction

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 (OADMs) to seprarte/route different wavelength channels. OADM is a device used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of a singlemode fiber (SMF). This is a type of optical node, which is generally used for the construction of optical telecommunications networks.

add

Add refers to the capability of the device to add one or more new wavelength channels to an existing multi-wavelength WDM signal while “
drop

drop refers to drop or remove one or more channels, passing those signals to another network path.

An OADM may be considered to be a specific type of optical cross-connect. The main implementation technologies of OADM are WDM (Wavelength Division Multiplexing), O-CDMA (Optical Code Division Multiple Access) and OTDM (Optical Time Division Multiplexing). OADM is the key component of AON(All-Optical Network).

Structure and Working Principle of OADM

OADM working process as follows:

WDM signals from line contains N wavelength channel, enter the OADM “Main Input” side, depending on your business needs;
from N wavelength channel, selectively from the road-side (Drop) required by the output wavelength channel, accordingly from the road-end (Add) enter the desired wavelength channel.
Regardless of other local wavelength channel directly through the OADM, and routing wavelength channels multiplexed together, from the output terminals of the circuit of OADM (Main Output) output.

The following picture shows the basic operation of an OADM.

basic-operation-of-oadm

Types of OADM

Fixed Optical Add-Drop Multiplexers (FOADM)

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.

Reconfigurable Optical Add-Drop Multiplexers (ROADM)

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.

OTN