WDM Optical MUX Technology Introduction

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 With the exponential growth in
communications, caused largely by the wide acceptance of the Internet, many
carriers have found their estimates of fiber needs have been highly
underestimated. Although most cables included many spare fibers when installed,
this growth has used many of them and new capacity is required. Make use of a
number of ways to improve this problem, eventually the WDM has shown more cost
effective in most cases.

 

WDM Definition:

 

Wave Division Multiplexing (WDM) enables
multiple data streams of varying wavelengths (“colors”) to become
combined right into a single fiber, significantly enhancing the overall
capacity from the fiber. WDM can be used in applications where considerable
amounts of traffic are needed over long distance in carrier networks. There’s
two types of WDM architectures: Course Wave Division Multiplexing (CWDM) and
Dense Wave Division Multiplexing (DWDM).

 

WDM System Development History:

 

A WDM system uses a multiplexer in the
transmitter to become listed on the signals together, and a demultiplexer at
the receiver to separate them apart. With the right type of fiber it is
possible to have a device that does both simultaneously, and can work as an
optical add-drop multiplexer. The optical filtering devices used have
conventionally been etalons (stable solid-state single-frequency Fairyrot
interferometers by means of thin-film-coated optical glass).

 

The idea was first published in 1980, and
by 1978 WDM systems appeared to be realized in the laboratory. The first WDM
systems combined 3 signals. Modern systems are designed for as much as 160
signals and can thus expand a fundamental 10 Gbit/s system over a single fiber
pair to in excess of 1.6 Tbit/s.

 

WDM systems are well-liked by
telecommunications companies because they allow them to expand the capacity of
the network without laying more fiber. By utilizing WDM and optical amplifiers,
they can accommodate several generations of technology rise in their optical
infrastructure without needing to overhaul the backbone network. Capacity of a
given link can be expanded by simply upgrades towards the multiplexers and
demultiplexers at each end.

 

This is often made by use of
optical-to-electrical-to-optical (O/E/O) translation in the very edge of the
transport network, thus permitting interoperation with existing equipment with
optical interfaces.

 

WDM System Technology:

 

Most WDM systems operate on single-mode
fiber optical cables, which have a core diameter of 9 µm. Certain forms of WDM
may also be used in multi-mode fiber cables (also referred to as premises
cables) which have core diameters of fifty or 62.5 µm.

 

Early WDM systems were expensive and
complicated to operate. However, recent standardization and better
understanding of the dynamics of WDM systems make WDM less expensive to deploy.

 

Optical receivers, as opposed to laser
sources, tend to be wideband devices. Therefore the demultiplexer must provide
the wavelength selectivity of the receiver in the WDM system.

 

WDM systems are split into different
wavelength patterns, conventional/coarse (CWDM) and dense (DWDM).
Conventional WDM systems provide up to 8 channels within the 3rd transmission
window (C-Band) of silica fibers around 1550 nm. Dense wavelength division multiplexing
(DWDM) uses the same transmission window but with denser channel spacing.
Channel plans vary, but a typical system would use 40 channels at 100 GHz
spacing or 80 channels with 50 GHz spacing. Some technologies are capable of
12.5 GHz spacing (sometimes called ultra-dense WDM). Such spacing’s are today
only achieved by free-space optics technology. New amplification options (Raman
amplification) enable the extension of the usable wavelengths towards the
L-band, pretty much doubling these numbers.

 

Coarse wavelength division multiplexing
(CWDM) in contrast to conventional WDM and DWDM uses increased channel spacing
to allow less sophisticated and thus cheaper transceiver designs. To supply 8
channels on one fiber CWDM uses the whole frequency band between second and
third transmission window (1310/1550 nm respectively) including both windows
(minimum dispersion window and minimum attenuation window) but the critical
area where OH scattering may occur, recommending using OH-free silica fibers in
case the wavelengths between second and third transmission window ought to be
used. Avoiding this region, the channels 47, 49, 51, 53, 55, 57, 59, 61 remain
and these are the most commonly used. Each WDM Optical MUX includes its optical
insertion loss and isolation measures of every branch. WDMs are available in
several fiber sizes and kinds (250µm fiber, loose tube, 900µm buffer, Ø 3mm cable,
simplex fiber optic cable or duplex fiber cable).

 

WDM, DWDM and CWDM are based on the same
idea of using multiple wavelengths of sunshine on one fiber, but differ within
the spacing of the wavelengths, quantity of channels, and also the capability
to amplify the multiplexed signals within the optical space. EDFA provide an
efficient wideband amplification for that C-band, Raman amplification adds a
mechanism for amplification in the L-band. For CWDM wideband optical
amplification is not available, limiting the optical spans to many tens of kilometers.

 

Regardless if you are WDM
Optical MUX expert or it is your first experience with optical
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