**DWDM:

**

• DWDM stands for Dense Wavelength Division Multiplexing.
• It is a technology that allows multiple information streams to be transmitted simultaneously over a single fiber.
• Each signal is carried at the same time on its own separate light wavelength.
• Dense wavelength division multiplexing (DWDM) is a fiber-optic transmission technique that employs light wavelengths to transmit data parallel-by-bit or serial
  -by-character.
• It provides a cost effective method to increase the capacity of the existing networks without the need to add additional fiber.
• This application explains capabilities of the OptiSystem software to explore different design structures.

• to optimize the performance of these networks for access and long-haul application.

• Applications:

  • Long-haul optical networks either in point-to-point or ring topology.
  • Expanding the capacity of an existing optical network.
  • Capacity leasing for network wholesalers.
  • DWDM allows providers to offer services such as e-mail, video, and
    multimedia carried as Internet protocol (IP) data over asynchronous transfer mode (ATM) and voice carried over SONET/SDH.
• Benefits:
  • New Bit Error Rate Test set enables the simulation of millions of bits for direct error counting.
  • Multi-parameter scanning enables system designers to study trade-offs with respect to parameters of interest and to choose an optimal design for deployments.
  • Enables users to analyze different algorithms for the electronic equalization.
  • Interfaces with popular design tools.
  • Significantly reduces product development costs and boosts productivity through a comprehensive design environment to help plan, test, and simulate optical links in the transmission layer of modern optical networks.
  • DWDM also gives service providers the flexibility to expand capacity in any portion of their networks an advantage no other technology can offer.

Dense Wavelength Division Multiplexing (DWDM) components:

DWDM contains five main components:

DWDM Terminal Multiplexer

• DWDM Terminal Multiplexer device contains a one wavelength converting transponder for each wavelength carried.
• It receives an input optical signal, converts it to an electrical signal and then retransmits it as an optical signal, that is, a process abbreviated as O/E/O) using a 1550 nm laser beam.
• The MUX (multiplexer) takes a number of 1550 nm optical signals and places them on a single optical fiber. This terminal multiplexer may also contain an EDFA (Erbium Doped Fiber Amplifier) to amplify the optical signal.

Intermediate Line Repeater:

• These are amplifiers placed every 80 to 100 kilometers to compensate for loss of optical power; amplification is done by an EDFA, usually consisting of several amplifier stages.

Intermediate Optical Terminal:

• This is a remote site amplifier placed where the signal may have traveled up to 140 kilometers; diagnostics and telemetry signals are extracted or inserted.

DWDM Terminal Demultiplexer:

• This device breaks the multi-wave signal back into individual signals; these may be sent to O/E/O output transponders before being relayed to their intended destinations, i.e. client-layer systems.

Optical Supervisory Channel (OSC):

• This channel carries information about the multi-wave optical signal and may provide data about conditions at the site of the intermediate line repeater.
• DWDM is sometimes called wave division multiplexing (WDM) and WDM is growing denser as the technology evolves.

Advantages of Optical networking:

• Optical Fiber Cables can run massive distances like 40 KM or much more (Single Mode Fiber Cables) without having to repeat the signal anywhere in-between.
• Normally, the Optical Fiber Cables do not have speed limits or bandwidth limitations. They can support any speed/ bandwidth depending only on the type of optics (active components) used at either end. But the distance over which they can support such speeds varies for each fiber material.
• Its normally enough to replace the optics (active components) at either end in order to upgrade the fiber communication to support higher bandwidths. There is no need to change all the underlying cabling.
• Optical Fiber Cables support duplex communications (simultaneous upstream and downstream), but they use two cores for doing so. One core is used for Transmission (Tx) and the other core is used for Reception (Rx).
• Optical Fiber Cables are flexible and can be laid both within the buildings (Indoor Fiber Cables) and outside the buildings (Shielded Fiber Cables). In most of the cases, they are buried under the ground (with a depth of minimum 3 feet) using a Trench and protective materials.
• Optical Fiber Cables are not affected by Electromagnetic Interference as they carry light, and hence can be used even for the most demanding industrial applications.
• They can also be used in lightning prone areas as they do not carry the electrical signals as such to affect switch ports, etc during a lightning.
• The danger of ignition during a fire is much less with optical fiber cables.
• There are optical taps that can be inserted in-between long running optical cables. There are two types of taps: Passive optical taps that do not require electrical power and are used for simple monitoring of OFC networks and Active optical taps that require electrical power and are used for manipulation or boosting of signals sent to the monitoring port.
• The low cost 850 nm Laser optimized 50/125 micro meter Multi-Mode Fiber (OM3 type) gives 10 GE performance for up to 300 meters. The optics associated with it are also moderately priced. So, these fibers can be used in the enterprise LAN segment for short distances, where the single mode optics might turn out more expensive.
• Even if many fibers run along side each other, the chances of cross talk (and hence signal loss) is very less, unlike Copper UTP Cables. Wire tapping with Optical Fiber Cables is more difficult.
• Trouble shooting an Optical Fiber Network is possible with equipments like the OTDR Tester (Optical Time Domain Reflectometer). Using this, one could measure the optical power loss and locate the faults caused due to fiber breaks, connectors or splicing.