Telecom | WDM and DWDM

WDM and DWDM

Wavelength Division Multiplexing

WDM is a technique used in telecommunication technology.  It multiplexes multiple optical carrier signals onto a single optical signal by using different wavelengths or different colours of laser light. It basically used at optical systems.

There are systems such as optical transport, multiplexer and transmitter used with WDM to join and multiply different signals. Most DWM systems use single mode fibre optical cables.

Similarly, the WDM can be further divided in to three different forms such as normal or DWM, dense or DWDM and coarse or CWDM. Between the two key technologies, the implementation depends on requirement of users and networks. Both the solution were available as active and passive systems of a network. CWDM supports up to 18 wavelength channels that to be transmitted in the fibre in a same time frame whereas, DWDM supports up to 80 wavelengths. Between CWDM and DWDM, DWDM connection can be used for longer distance transmission. Presently at the time of writing this blog, DWDM even supports up to 96 wavelength over one pair of fibre with channel spacing 0.8 nm or 0.4 nm. By using optical amplifier, it can be used up to 1000 KM of distance. Its mostly used for back bone networks for long transmission. To minimize the network risks and address to the network monitoring, here five DWDM solutions, such as OLP, OPD, OPM, ring network protection and complete protection are used.

How a DWDM system works? 

• The transponder accepts input as single-mode or multimode laser pulse signal. The input can come from multiple physical media and multiple protocols and traffic types.
• The wavelength of the transponder input signal is mapped in to a DWDM wavelength.
• DWDM wavelengths from the transponder are multiplexed with signals from the direct interface to form a composite optical signal which is launched into the fiber.
• A post-amplifier or booster amplifier, boosts the strength of the optical signal as it leaves the multiplexer.
• A pre-amplifier increases the signal strength before it enters the demultiplexer.
• The incoming signal is demultiplexed into separate DWDM wavelengths.
• The individual DWDM signals are either designed to the required output type through the transponder or they are passed directly to the site equipment.

OTN

Optical Transport Network (OTN) is an industry standard protocol and is bundle of Optical Network Elements connected by optical fiber links and provides services such as transmission, multiplexing, switching of optical channels carrying signals. OTN works with synchronous optical networking (SONET) and synchronous digital hierarchy (SDH), which uses a system of laser pulses or light emitting diodes for transmission.

OTN uses Wavelength Division Multiplexing (WDM). As per ITU-T recommendations the interfaces used by OTN is G.709. The OTN system in telecommunication system is a unique system that can integrate virtually with many applications such as voice, data, LAN, video, SCADA, etc. into one high speed network, using a fibre optic backbone.

ROADM 

A ROADM (reconfigurable optical add drop multiplexer) is a multiplexing device which can be used to work (add, drop or block) on multiple wavelengths at any node makes it simple for the SONET or SDH network. As we know, Bandwidth and wavelengths must be pre-allocated. There are two major ROADM technologies used such as wavelength blocking (WB) and planar light-wave circuit (PLC). It allows remote configuration and reconfiguration. ROADM networks allow adding new services without redesign or change to network.

It helps in improving network utilization, power balancing, end to end wavelength provisioning and flexibility.

-DR