DWDM (Dense Wavelength Division Multiplexing) is a fiber optic transmission technique that employs multiple light wavelengths to transmit data in parallel through a single fiber. It revolutionized transmission technology by increasing the capacity of embedded fiber and addressing the reduced availability of fibers. DWDM allows many discrete transport channels by combining and transmitting multiple signals simultaneously at different wavelengths on the same fiber. This effectively transforms one fiber into multiple virtual fibers and significantly increases bandwidth. Key components of a DWDM system include transmitters, optical multiplexers/demultiplexers, optical amplifiers, optical fiber, and receivers.

1. DWDM
Introduction:-
• One of the major issues in the networking industry today is tremendous demand for
more and more bandwidth.
• Before the introduction of optical networks, the reduced availability of fibres
became a big problem for the network providers.
• Dense wavelength-division multiplexing (DWDM) revolutionized transmission
technology by increasing the capacity signal of embedded fibre.
• The existing SONET/SDH network architecture is best suited for voice traffic rather
than today’s high-speed data traffic.
• To upgrade the system to handle this kind of traffic is very expensive and hence the
need for the development of an intelligent all-optical network.
• Dense wavelength division multiplexing (DWDM) is a fibre-optic transmission technique
that employs multiple light wavelengths to transmit data in parallel through a single fibre.
Development of DWDM Technology:-
• Early WDM began in the late 1980s using the two widely spaced wavelengths in the
1310 nm and 1550 nm (or 850 nm and 1310 nm) regions, sometimes called wideband
WDM.
• The early 1990s saw a second generation of WDM, sometimes called narrowband
WDM, in which two to eight channels were used.
• By the mid-1990s, dense WDM (DWDM) systems were emerging with 16 to 40
channels and spacing from 100 to 200 GHz.
• By the late 1990s DWDM systems had evolved to the point where they were capable of
64 to 160 parallel channels, densely packed at 50 or even 25 GHz intervals.
Varieties of WDM:-
1. WDM

2. – Traditional, passive WDM systems are widespread with 2, 4, 8, 12, and 16 channel
counts being the normal deployments.
2. CWDM
– Today, coarse WDM (CWDM) typically uses 20-nm spacing (3000 GHz) of up to 18
channels.
– The CWDM grid is made up of 18 wavelengths defined within the range 1270 nm to
1610 nm spaced by 20 nm.
3. DWDM
– Dense WDM common spacing may be 200, 100, 50, or 25 GHz with channel count
reaching up to 128 or more channels at distances of several thousand kilometres with
amplification and regeneration along such a route.
DWDM System Function:-
• Dense wavelength division multiplexing systems allow many discrete transports
channels by combining and transmitting multiple signals simultaneously at different
wavelengths on the same fibre.
• In effect, one fibre is transformed into multiple virtual fibres.
• So, if you were to multiplex 32 STM-16 signals into one fibre, you would increase the
carrying capacity of that fibre from 2.5 GB/s to 80 GB/s.
• A key advantage to DWDM is that it's protocol and bit rate-independent. DWDM-based
networks can transmit data in SDH, IP, ATM and Ethernet etc.
• Therefore, DWDM-based networks can carry different types of traffic at different
speeds over an optical channel. DWDM is a core technology in an optical transport
network.
• Dense WDM common spacing may be
– 200 GHz or 1.6 nm,
– 100 GHz or 0.8 nm,
– 50 GHz or 0.4 nm,
– 25 GHz with channel count reaching up to 128 or
More channels at distances of several thousand kilometres with amplification and
regeneration along such a route.
Overview of DWDM:-
• DWDM systems in enabling service providers to accommodate consumer demand for
ever-increasing amounts of bandwidth.

3. • DWDM allows the transmission of different formats like Internet protocol (IP),
asynchronous transfer mode (ATM), and synchronous digital hierarchy (SDH),
respectively, over the optical layer.
DWDM System Components:-
• Transmitter (transmit transponder)
• Optical Multiplexer/ de-multiplexer
• Optical Amplifier
• Optical fibre (media)
• Receiver (receive transponder)
• Transmitter (transmit transponder)
– Changes electrical bits to optical pulses.
– Uses a narrowband laser to generate the optical.
• Optical Multiplexer/ de-multiplexer.
– Combines/separates discrete wavelengths.
• Optical Amplifier
– Pre-amplifier, Post-amplifier and in line amplifiers.
(ILA)
– EDFA (Erbium Doped Fibre Amplifier) is the most popular amplifier.
• Optical Fibre (Media)
– Transmission media to carry optical pulses.
– Many different kinds of fibre are used.
• Receiver (receive transponder)
– Changes optical pulses back to electrical bits.
– Uses wideband laser to provide the optical pulse.
Benefits of DWDM:-
• Increases bandwidth (speed and distance).
• Does not require replacement or upgrade their existing legacy systems.
• Provides "next generation" technologies to meet growing data needs.
• Less costly in the long run because increased fibre capacity is automatically available;
don't have to upgrade all the time.
Conclusion:-
• DWDM promises to solve the "fibre exhaust" problem and is expected to be the central
technology in the all optical networks of the future.
• This technology responds to the growing need for efficient and capable data
transmission by working with different formats, such as SONET/SDH, while increasing
bandwidth.