DWDM
is an innovation that enables multiple optical carriers to travel in
parallel in a fiber. DWDM devices combine the output from several
optical transmitters for transmission across a single fiber. At the
receiving end, another DWDM device separates the combined optical
signals and passes each channel to an optical receiver. Only one optical
fiber is used between DWDM devices (per transmission direction). How
DWDM system works, and what components are needed in DWDM system? Keep
reading this article and you will find the answer.
Components Used in DWDM System
Typically,
the components used in a DWDM system include optical transmitters and
receivers, DWDM mux/demux, OADM (optical add/drop multiplexers), optical
amplifiers and transponders (wavelength converters). Following part
will introduce these devices respectively.
Optical Transmitters and Receivers
Transmitters
are described as DWDM components because they provide the source
signals which are then multiplexed. The characteristics of optical
transmitters used in DWDM systems is highly important to system design.
Multiple optical transmitters are used as the light sources in a DWDM
system which requires very precise wavelengths of light to operate
without interchannel distortion or crosstalk. Several individual lasers
are typically used to create the individual channels of a DWDM system.
Each laser operates at a slightly different wavelength.
DWDM Mux/DeMux
The
DWDM Mux (multiplexer) combines multiple wavelengths created by
multiple transmitters and operating on different fibers. The output
signal of an multiplexer is referred to as a composite signal. At the
receiving end, the DeMux (demultiplexer) separates all of the individual
wavelengths of the composite signal out to individual fibers. The
individual fibers pass the demultiplexed wavelengths to as many optical
receivers. Generally, Mux and DeMux components are contained in a single
enclosure. Optical Mux/DeMux devices can be passive. Component signals
are multiplexed and demultiplexed optically, not electronically,
therefore no external power source is required.
The
picture above shows the bidirectional DWDM operation. N light pulses of
N different wavelengths carried by N different fibers are combined by a
DWDM Mux. The N signals are multiplexed onto a pair of optical fibers. A
DWDM demultiplexer receives the composite signal and separates each of
the N component signals and passes each to a fiber. The transmit and
receive signal arrows represent client-side equipment. This requires the
use of a pair of optical fibers—one for transmit and the other for
receive.
OADM
OADM
is often a device found in WDM systems for multiplexing and routing
different channels of fiber into or out of a single-mode fiber (SMF). It
is created to optically add/drop one or multiple CWDM/DWDM channels
into a few fibers, providing the power to add or drop a single
wavelength or multi-wavelengths from a fully multiplexed optical signal.
This permits intermediate locations between remote sites gain access to
the regular, point-to-point fiber segment linking them. Wavelengths not
dropped pass-through the OADM and carry on towards the remote site.
Additional selected wavelengths may be added or dropped by successive
OADMs if required.
The
picture above demonstrates the operation of a one-channel OADM. This
OADM is designed to only add or drop optical signals with a particular
wavelength. From left to right, an incoming composite signal is broken
into two components, drop and pass-through. The OADM drops only the red
optical signal stream. The dropped signal stream is passed to the
receiver of a client device. The remaining optical signals that pass
through the OADM are multiplexed with a new add signal stream. The OADM
adds a new red optical signal stream, which operates at the same
wavelength as the dropped signal. The new optical signal stream is
combined with the pass-through signals to form a new composite signal.
Optical Amplifiers
Optical
amplifiers boost the amplitude or add gain to optical signals passing
on a fiber by directly stimulating the photons of the signal with extra
energy. They are “in-fiber” devices. Optical amplifiers amplify optical
signals across a broad range of wavelengths, which is very important for
DWDM system application.
Transponders (Wavelengths Converters)
Transponders
convert optical signals from one incoming wavelength to another
outgoing wavelength suitable for DWDM applications. Transponders are
optical-electrical-optical (O-E-O) wavelength converters. A transponder
performs an O-E-O operation to convert wavelengths of light. Within the
DWDM system, a transponder converts the client optical signal back to an
electrical signal (O-E) and then performs either 2R (reamplify,
reshape) or 3R (reamplify, reshape and retime) functions.
The
picture above shows bi-directional transponder operation. A transponder
is located between a client device and a DWDM system. From left to
right, the transponder receives an optical bit stream operating at one
particular wavelength (1310 nm). The transponder converts the operating
wavelength of the incoming bit stream to an ITU-compliant wavelength. It
transmits its output into a DWDM system. On the receive side (right to
left), the process is reversed. The transponder receives an
ITU-compliant bit stream and converts the signals back to the wavelength
used by the client device.
Summary
This
article provides some basic information about the components used in a
DWDM system. All of the components compose the integrated DWDM system.
And they are indispensable. Hope the information in this article is
helpful when building your DWDM system.
Originally published: www.fiberopticshare.com/introduction-components-used-dwdm-system.html
