WAVELENGTH-DIVISION MULTIPLEXING

(WDM)

COARSE WDM (CWDM)

DENSE WDM (DWDM)

Nortel's WDM System

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DEFINITION I

Fiber-optic communications is based on the principle that light in a glass medium

can carry more information over longer distances than electrical signals can carry

in a copper or coaxial medium or radio frequencies through a wireless medium.

The purity of today’s glass fiber, combined with improved system electronics,

enables fiber to transmit digitized light signals hundreds of kilometers without amplification.

With few transmission losses, low interference, and high bandwidth potential, optical fiber is an almost ideal transmission medium.

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WDM SYSTEMS

A WDM system uses a multiplexer at the transmitter to join the signals together, and a demultiplexer at the receiver to split them apart.

With the right type of fiber it is possible to have a device that does both simultaneously, and can function as an optical add-drop multiplexer.

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OPTICAL ADD-DROP MULTIPLEXER

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An optical add-drop multiplexer (OADM) is a device used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of a single mode fiber (SMF).

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WDM SYSTEMS (CONT)

The optical filtering devices used have traditionally been etalons, stable solid-state single-frequency Fabry-Perot interferometers in the form of thin-film-coated optical glass.

The first WDM systems only combined two signals. Modern systems can handle up to 160 signals and can thus expand a basic 10 Gbit/s fiber system to a theoretical total capacity of over 1.6 Tbit/s over a single fiber pair.

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COARSE WDM

meant two (or possibly more) signals multiplexed onto a single fiber, where one signal was in the 1550 nm band, and the other in the 1310 nm band.

The Ethernet LX-4 10 Gbit/s physical layer standard is an example of a CWDM system in which four wavelengths near 1310 nm, each carrying a 3.125 gigabit-per-second (Gbit/s) data stream, are used to carry 10 Gbit/s of aggregate data.

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DENSE WAVELENGTH DIVISION MULTIPLEXING (DWDM)

Short for Dense Wavelength Division Multiplexing, an optical technology

used to increase bandwidth over existing fiber optic backbones.

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DEFINITION II

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.

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DEFINITION II (CONT)

DWDM works by combining and transmitting multiple signals simultaneously at different wavelengths on the same fiber. In effect, one fiber is transformed into multiple virtual fibers. So, if you were to multiplex eight OC -48 signals into one fiber, you would increase the carrying capacity of that fiber from 2.5 Gb/s to 20 Gb/s.

Currently, because of DWDM, single fibers have been able to transmit data at speeds up to 400Gb/s.

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DEFINITION II (CONT)

In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths (colors) of laser light to carry different signals. This allows for a multiplication in capacity, in addition to enabling bidirectional communications over one strand of fiber. This is a form of frequency division multiplexing (FDM) but is commonly called wavelength division multiplexing.[1]

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DEFINITION II (CONT)

The term wavelength-division multiplexing is commonly applied to an optical carrier (which is typically described by its wavelength),

whereas frequency-division multiplexing typically applies to a radio carrier (which is more often described by frequency).

However, since wavelength and frequency are inversely proportional, and since radio and light are both forms of electromagnetic radiation, the two terms are equivalent in this context.

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PROTOCOL- AND BIT-RATE-INDEPENDENT

A key advantage to DWDM is that it's protocol- and bit-rate-independent.

DWDM-based networks can transmit data in IP, ATM, SONET /SDH, and Ethernet, and handle bit rates between 100 Mb/s and 2.5 Gb/s.

Therefore, DWDM-based networks can carry different types of traffic at different speeds over an optical channel.

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COMPONENTS OF A DWDM SYSTEM

A DWDM system can be described as a parallel set of optical channels, each using a slightly different wavelength, but all sharing a single transmission medium or fiber.

See figure on next slide showing a multichannel with various 10Gbps fed into an optical medium:

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COMPONENTS OF A MULTICHANNEL SYSTEM

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SIMPLE DESCRIPTION

10 Gbps input channels w/frequencies Up to 48 channels transmitted All multiplexed into a single fiber for

transmission Optical Fiber Amplifier (OFA) for boosting

the signals Up to 48 channels received Demultiplexed into respective

frequencies

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CONCLUSION

This concludes my presentation on DWDM (not really emerging)

Although this presentation deals with emerging technology

The fact that the US is not implementing this technology nationwide is interesting.

Eventually the US will catch up with the rest of the world based on it!

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