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What is the need of DWDM? Explain its working principal?

Subject: Advanced Network Technologies

Topic: Optical Networking

Difficulty: Medium

1 Answer
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Telecommunications makes wide use of optical techniques in which the carrier wave belongs to the classical optical domain. The wave modulation allows transmission of analog or digital signals up to a few gigahertz (GHz) or gigabits per second (Gbps) on a carrier of very high frequency, typically 186 to 196 THz. In fact, the bitrate can be increased further, using several carrier waves that are propagating without significant interaction on a single fiber. It is obvious that each frequency corresponds to a different wavelength. Dense Wavelength Division Multiplexing (DWDM) is reserved for very close frequency spacing.

Dense wavelength division multiplexing (DWDM) is a technology that puts data from different sources together on an optical fiber, with each signal carried at the same time on its own separate light wavelength. Using DWDM, up to 80 (and theoretically more) separate wavelengths or channels of data can be multiplexed into a lightstream transmitted on a single optical fiber.

A key advantage to DWDM is that it’s protocol and bitrate independent. DWDM-based networks can transmit data in IP, ATM, SONET, SDH and Ethernet. Therefore, DWDM-based networks can carry different types of traffic at different speeds over an optical channel. Voice transmission, email, video and multimedia data are just some examples of services which can be simultaneously transmitted in DWDM systems. DWDM systems have channels at wavelengths spaced with 0.4 nm spacing.

WORKING PRINCIPAL

  1. The transponder accepts input in the form of a standard single-mode or multimode laser pulse. The input can come from different physical media and different protocols and traffic types.

  2. The wavelength of the transponder input signal is mapped to a DWDM wavelength.

  3. 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.

  4. A post-amplifier (booster amplifier) boosts the strength of the optical signal as it leaves the multiplexer.

  5. An OADM is used at a remote location to drop and add bitstreams of a specific wavelength.

  6. Additional optical amplifiers can be used along the fiber span (in-line amplifier) as needed.

  7. A pre-amplifier boosts the signal before it enters the d e muliplexer.

  8. The incoming signal is demultiplexed into individual DWDM wavelengths.

  9. The individual DWDM lambdas are either mapped to the required output type through the transponder or they are passed directly to client-side equipment.

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