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Types of Multiplexing

Types of Multiplexing : This article will try to give complete information about the types of multiplexing and optical multiplexing technology. So to get complete information, you have to read the entire article. Multiplexing is a technique through which one or many signals are transmitted concurrently over a single data link. A multiplexed system consists of n number devices that share the capacitance of a link, so a link means multiple paths can have multiple channels.

Many devices pass their transmission streams to multiplexers which are all merged into a single stream. And a single stream on the receiver is directed to the demultiplexer which is then transmitted to the component transmission and sent to the integrated receiver.
Types of Multiplexing

Types of Multiplexing

Multiplexing is sending process of multiple signals or streams of information over a circuit at the same time in the form of a single, complex signal and then recovering the separate signals at the receiving end.

The basic type of multiplexing involves frequency division. (FDM), time division (TDM), and wavelength division (WDM), with TDM and WDM Optical circuits are being widely used by telephone and data service providers. By the way, multiplexing is usually divided into four parts.

1. Frequency Division Multiplexing (FDM)
2. Time division Multiplexing (TDM)
3. Wavelength Division Multiplexing (WDM)
4. Code Division Multiplexing (CDM)

Frequency Division Multiplexing (FDM)

FDM which is an analog technique which is implemented when the link ie the bandwidth of the path is more than the bandwidth of the merge transmit signal. Each sending device produces signals that are modulated at different carrier frequencies. To hold the modulated signal, the carrier frequencies are separated by sufficient bandwidth.

Time division Multiplexing (TDM)

Time-division multiplexing (TDM) is a method of combining several independent data streams into a single data stream by merging the signals according to a defined sequence. Each independent data stream is retrieved at the receiving end based on sequence and time.
Type of Multiplexing

Synchronous optical network (SONET), asynchronous transfer mode (ATM) and Internet protocol (IP) use TDM techniques. As per modern telecommunications networks, 
by the SONET network element TDM signals are converted from electrical to optical signals , for transport over optical fiber .

Wavelength Division Multiplexing (WDM)

WDM combines multiple optical TDM data streams over a single fiber through the use of multiple wavelengths of light. Each individual TDM data stream is sent to a separate laser that transmits a unique wavelength of light.

In the other word we can say that in time division multiplexing (TDM) each time slots are fixed sequentially for different signals. If there is an empty time slot that can be used for other signals, using STDM - (Statistical Time Division Multiplexing).

The basic advantage of wavelength division multiplexing (WDM) is to multiply the capacity of the fiber at a given bitrate; Ideally, WDM-devices show as separate fibers for port transmission equipment.While doing that a lot of regeneration can be removed from the network, and the system is higher bitrate irrational.

WDM Transmission over one pair of fiber

Main components of the WDM system

There are certain main components of the WDM system, which are given below-

•Transmitters with stabilized wavelength lasers
•WDM Multiplex (WDM-MUX), combines multiple laser sources into one fiber
•Optical amplifiers: Boosters to boost optical power after WDM-MUX (and compensate for WDM-MUX loss), optical pre amplifier to compensate for WDM-DEMUX losses and increase receiver sensitivity by ~ 10 dB. You have to remember that WDM-DEMUX acts as a narrow-band filter for the pre-amplifier.

Type of WDM System

Early WDM systems delivered two or four wavelengths that were widely spaced. The "follow-on" technologies of WDM and CWDM and DWDM are well developed. Beyond this initial range. 

Traditional, passive WDM systems are expanded with 2, 4, 8, 12 and 16 channels being the normal deployments. This technique usually has a distance limit under 100 km.

≻Bidirectional WDM (BWDM)
≻Coarse WDM systems (CWDM)
≻Dense WDM systems (DWDM)

Bidirectional WDM (BWDM): Such as 1.3 / 1.55 mm WDM. 1.3 mm is used for one signal, 1.55 mm for the other. It is possible Used to make a 2 channel link on a pair of fibers; Or a channel bi-directional link On a single fiber.

Coarse WDM systems (CWDM) : Large distances between wavelengths; Something ... almost. 10 wavelengths. Limited Increase in capacity but cheaper components can be used (e.g. unleaded laser). 

These days, coarse WDM (CWDM) typically uses 20-nm spacing (3000 GHz) of up to 18 channels. The CWDM provides a grid of wavelengths for target distances up to about 50 km on single mode fibers. The CDDM grid is composed of 18 wavelengths spanning 20 nm between 1270 nm to 1610 nm.

Dense WDM systems (DWDM) : The dense WDM common spacing with channel count can be 200, 100, 50, or 25 GHz Reaching 128 or more channels at a distance of several thousand kilometers amplification and regeneration along such a route.

Very high capacitance with multiple wavelengths, typ. 32-40 in commercial systems in use In the traditional band, the same or more in the longer wavelength band. Hundreds Performed in the laboratory. Uses Erbium Doped Fiber Amplifiers (EDFA) typically operating at 1530..1565 nm Band (1570..1610 L-band also possible). This means that the wavelengths are close The resulting tight tolerance of the filtering components and laser wavelengths to each other Stability.

DWDM is an expensive technology but it is also true that still much cheaper than digging ground. DWDM technology is used in today's network for the  long haul transmission systems.
Comparison of BWDB,CWDM and DWDM 

Optical Multiplexing Technology

In the Optical multiplexing technologies DWDM and WDM systems have revolutionized the use of optical fiber networks. In other words we can call wavelength different colors of light, that combined into one optical signal and sent over a fiber-optic cable to a far-end optical multiplexing system.

Optical Multiplexing Filters

The diagram below shows that a filter is a physical device that connects each wavelength with other wavelengths. Multiplexing uses several techniques, including:

•Thin-film filters
•Bragg gratings
•Arrayed wave-guide gratings (AWGs)
•Interleavers, periodic filters, and frequency slicers)

WDM Filter

Thin-Film Filter

Thin film filter (TFF) is a device that is used to multiplex and demultiplex optical signals in some optical networks. TFFs are devices that use multiple ultra-thin layers. Coating dielectric material deposited on a glass or polymer substrate.

It substrate only photons of a specific wavelength can be made to pass through, while all others are reflected. By integrating several of these components, you can then demultiplex Multiple wavelengths. As per given image shows what happens with the four wavelengths.
Thin-Film Filter Concept
The first TFF section passes through wavelengths 1 and represents 2, 3 and 4 Then passes through 2 and denotes 3 and 4. This allows for demultiplexing or multiplexing Optical signal.

Fiber Bragg Gratings

A Bragg grating is made up of a small section of fiber that has been modified by exposure. For ultraviolet radiation to create periodic changes in the refractive index of the fiber. As given below the image, the result is that the light traveling through Bragg gritting is refracted and then slightly reflected back, usually at a particular wavelength.
Fiber Bragg Grating
The reflected wavelength, known as the Bragg resonance wavelength, depends on the amount of refractive index change applied to the Bragg grating fiber and it also depends on how far these changes are for refraction.

Arrayed Wave-guides

In the transmitted direction, the AWG merges individual wavelengths, also known as lambda (λ) from various lines etched into the AWG substrate (the base material it supports) Waveguides in an etched line) is called an output waveguide, allowing a multiplexer.

we are looking the below image in the opposite direction, the AWG can demultiplex the composite λs onto individual etched lines. Usually one is for AWG Transmit and the other is for AWG to receive. Demultiplexing direction or receive.
Arrayed Waveguide (Demultiplexer)

AWG can replace multiple Bragg grates, each Bragg grating supports only one Wavelength and 8-λ have the same physical location as AWG. Multiple brag Grating also costs more than a single AWG. For some applications, AWG provides a higher channel capacity at a lower cost per Channel with a small footprint. It provides for fewer components and results Component integration (eg, switching, variable optical attenuators).

Periodic Filters, Frequency Slicers, Interleavers

The image below shows that there are periodic filters, frequency slices, and interlever devices can share the same functions and are usually used together. Stage 1 is one of a kind Periodic filter, an AWG. Stage 2 is representative of a frequency slicer at its input, in This example, another AWG; And an interlever function at the output, provided by six Bragg gratings.

Six λ are received at the input of AWG, which is then broken. Bottom sign in odd λ and even λ. Strange λ and even λ go to their respective Phase 2 frequency slicers and then six are distributed by the interlever Discrete interference-free optical channels for end-customer use.
Combined Devices

By dividing a DWDM spectrum into several complementary sets of periodic spectra, combined devices can create a hierarchical suite of wavelengths for the more complex wavelength routing and switching.

Last Words

Friends, I have tried my best to give you complete information about multiplexing, yet if there is any shortage then you can give suggestions regarding multiplexing. How is multiplexing in telecom or in which network multiplexing is required, this article will make you understand easier. How did you like this article "Types of Multiplexing", tell me by commenting and also share it to your friends.

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