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DWDM Operating Modes

DWDM Operating Modes : We all know that the dramatic growth of voice services and the emergence of various new services, particularly the accelerated transformation of IP technology, network capacity will inevitably face a significant challenge. This article will cover the DWDM Operating Modes and it will be explained how DWDM works with the help of optical fiber.

We all know that DWDM technology uses the better utilization of available fiber, space and power saving at intermediate station,low attenuation characteristics of single mode optical fibers, it adopts multiple wavelengths as carriers and allows them to be simultaneously transmitted across the fiber. Apart from all such information, in this article, we will discuss about the operating mode of DWDM which is now being told below.
DWDM Operating Modes

Two-fiber Bi-directional Transmission

Two-fiber bi-directional transmission DWDM system

As per above given image a single optical fiber implements only one directional transmission of optical signals. Hence the same wavelengths can be reused in two directions.

Such DWDM systems can effectively exploit the huge bandwidth resources of optical fibers and extend the transmission capacity of a single optical fiber over several or tens of times. In long haul networks, capacity can be expanded by gradually adding wavelengths, which is very flexible, according to the demands of practical traffic. This is under the condition that the actual fiber dispersion is not known, it is also an approach to use multiple 2.5Gbit / s systems to implement ultra-large capacity transmission, which would avoid adopting ultrahigh speed optical systems.

Single fiber Bi-directional Transmission

As shown in the image below, a single fiber transfers optical signals from two directions simultaneously, and signals in two different directions must be assigned at different wavelengths.
DWDM system which adopts single fiber bi-directional transmission
In the system of Single-fiber bi-directional transmission permit single fibers to carry full duplex channels and, typically, delivers one half of the fiber components of a unidirectional transmission. In single fiber bi-directional transmission since optical signals transmitted in the two directions and they do not interact and create FWM (Four-Wave Mixing) products, its total FWM products are much less than two-fiber unidirectional transmission. 

Here I would like to mention that disadvantage of this system is that a special measure is needed to deal with light reflections (including discrete reflections resulting from Rayleigh backward reflection of optical connectors and fibers) to avoid multi-path interference. If you would like to extended optical signals transmission to longer distances, components such as bi-directional optical fiber amplifiers and optical communicators have to be adopted, but their noise factor is slightly worse.

Add and Drop of Optical Signals

Optical add and drop transmission

Look at above image, using the optical add / drop multiplexer (OADM), optical signals of wavelength can be added and dropped at intermediate stations, namely the add / drop of optical paths can be applied. This type of method can be used to implement in the ring type networking of DWDM systems. Currently, OADMs can only be built as fixed wavelength add / drop devices and thus the flexibility of this operating mode is limited.

Application Modes of DWDM

Generally there are two application modes of DWDM System-
1. Open DWDM
2. Integrate DWDM

In Open DWDM system or we can say that the feature of open DWDM system is that it has no special requirements for multiplex terminal optical interfaces as long as optical interface standards meet to the defined in ITU-T G.957.

The DWDM system adopts wavelength conversion technology to convert optical signals of multiplex terminals to specific wavelengths. Optical signals from different terminal devices are converted to different wavelengths, meeting the ITU-T recommendation, then multiplexed.

Integrate the DWDM system without adopting the wavelength conversion technique, which requires that the optical signals of the multiplex terminal meet the wavelength DWDM system specifications. Different multiplex terminals deliver different wavelengths, meeting the recommendation of ITU-T. Thus, when connected to multiplexes, these wavelengths occupy different channels and multiplexing is implemented.

In the DWDM system the different types of application modes can be adopted according to the demands of engineering. In last I can say that in practical applications, open DWDM and integrate DWDM can be mixed.

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