DWDM - The Innovation Technology
Today I am going to talk about the technology named as DWDM, DWDM stands for Dense Wavelength Division Multiplexing. So the question now is why and where we are using the DWDM technology and Who are using these technology.
DWDM is a technology used to used to increase bandwidth over existing fiber optics backbone and is generally used by the service provider across the globe. The need to have the higher bandwidth in the backbone because the count of the users and the customers increases day by day and service provider required higher bandwidth in the core or backbone networks.
The Technology behind the DWDM is used the multiple signals together at different wavelength on the same fiber. DWDM became market in the year of 1995 whilst CWDM (Coarse WDM) emerged after 2000, stimulated by using the telecom crisis.
CWDM brings less complicated technological standards as compared to DWDM, reducing down costs, but suits just the lower transmission ability markets, together with the metro and corporation networks. extra recently, new paradigmatic revolutions have made their manner into the optical communique market: ROADM (Reconfigurable Optical upload-Drop Multiplexing) and Coherent Optical systems. whilst those optical technology are the suitable solutions to fulfil the growing demand for bandwidth additionally they offer radical cost reduction in data transmission market.
CWDM brings less complicated technological standards as compared to DWDM, reducing down costs, but suits just the lower transmission ability markets, together with the metro and corporation networks. extra recently, new paradigmatic revolutions have made their manner into the optical communique market: ROADM (Reconfigurable Optical upload-Drop Multiplexing) and Coherent Optical systems. whilst those optical technology are the suitable solutions to fulfil the growing demand for bandwidth additionally they offer radical cost reduction in data transmission market.
Below is the example diagram showing the various channel signals transmitted to other end via MUX and the fiber used between two MUX's is a DWDM technology.
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| Fig 1.1- DWDM |
Current issues in WDM optical networking:
- Networks centered in voice services versus networks centered in data services
- IP and ATM over WDM
- The optical internet and MPLS
- DWDM and CWDM in Metropolitan Area Networks (MAN's)
- The LAN invades the WAN and WAN invades the LAN
- L-band EDFA optical amplifier (1570-1620nm)
- Ultra-wide band EDFA optical amplifier (1530-1620nm)
- Raman optical amplifiers
- DWDM in dispersion shifted (DS) fibers
- Dispersion compensation in DWDM systems using fiber Bragg gratings (FBG)
- Optical TDM - OTDM
- Link PMD
- PMD compensation
- Forward Error Correction - FEC
- DWDM in CATV networks
- FSO (Free Space Optical) communication systems - the optical wireless success
Optical communications is one of the most dynamic sectors in today's communications arena, due to optical's massive bandwidth capacity. The evolution of the net, one of the most important bandwidth-annoying applications, requires switch capacities as a way to very quickly exhaust non-optical procedures to communications.
An optical carrier supports modulation frequencies as much as 193 THz, much beyond the bounds of current non-optical technologies. A communications channel, or channel, regularly used all through this presentation, is related to a modulated optical carrier. Optical wavelengths, now and again called optical frequencies, are carried in the main thru optical fibers which could be given concurrently a mono mode propagation of many wavelengths, with minimum interaction between adjoining signals.
An optical carrier supports modulation frequencies as much as 193 THz, much beyond the bounds of current non-optical technologies. A communications channel, or channel, regularly used all through this presentation, is related to a modulated optical carrier. Optical wavelengths, now and again called optical frequencies, are carried in the main thru optical fibers which could be given concurrently a mono mode propagation of many wavelengths, with minimum interaction between adjoining signals.
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| Fig 1.2- DWDM Ring Network with the SDH connectivity |
The era of mixing or multiplexing many wavelengths into the identical mono modal optical fiber at the transmitter aspect and extracting the important wavelengths at the receiver aspect is known as wavelength department and multiplexing or WDM.
WDM is stated both as coarse WDM (CWDM), wherein wavelength separation is inside the order of 10 nm to twenty nm, or dense WDM (DWDM), where wavelength separation is less than 0.eight nm. a main undertaking is to acquire a smaller wavelength or channel separation together with better modulation prices of the optical carrier so one can increase transmission capability. the overall variety of channels available concurrently on the same optical fiber and the most bit-rate or modulation frequency carried via every channel determines the shipping ability of the optical fiber, which depends on to be had technology.
Optical fibers are just the bodily support sporting indicators through an optical community. The network also carries a few other optical and digital elements, inclusive of lasers to generate the vendors, modulators, optical multiplexers to mix wavelengths, optical de-multiplexers to extract wavelengths, optical filters, optical switches, optical amplifiers, optical receivers, and electronic controllers.
WDM is stated both as coarse WDM (CWDM), wherein wavelength separation is inside the order of 10 nm to twenty nm, or dense WDM (DWDM), where wavelength separation is less than 0.eight nm. a main undertaking is to acquire a smaller wavelength or channel separation together with better modulation prices of the optical carrier so one can increase transmission capability. the overall variety of channels available concurrently on the same optical fiber and the most bit-rate or modulation frequency carried via every channel determines the shipping ability of the optical fiber, which depends on to be had technology.
Optical fibers are just the bodily support sporting indicators through an optical community. The network also carries a few other optical and digital elements, inclusive of lasers to generate the vendors, modulators, optical multiplexers to mix wavelengths, optical de-multiplexers to extract wavelengths, optical filters, optical switches, optical amplifiers, optical receivers, and electronic controllers.
Four-Wave Mixing (FWM) appears at the interaction of one or more wavelengths, producing new wavelengths with different intensities. The total intensity of all incident and resulting wavelengths is conserved during this parametric interaction. Four-wave mixing is the optical analog of non-linear mixing of electrical signals using the non-linear characteristic of a forward-biased diode. In the optical case, the mixing is produced by the non-linearity dependence of the refractive index on the intensity of the wave. The wavelengths resulting from four-wave mixing may interfere with the modulated carriers and can degrade signals.
Self-Phase Modulation (SPM) introduces a spectral broadening of a light pulse due to the time-dependence of the refractive index during the optical pulse, which produces a temporally varying phase of the optical pulse. For a constant frequency f of the generated light pulse, the wavelength λ(P) depends on the current pulse power P(t) and the wavelength λ(P(t)) is time-dependent:
λ(P(t))=c/[f·(n0+n2(χ)·P(t)/A)] (2)
where:
c is the speed of light in a vacuum,
n0 is the linear component of the refractive index,
n2(χ) is the non-linear index coefficient,
χ(3) is the third-order susceptibility tensor,
A is the effective area of the mode propagating in the optical fiber,
f is the frequency of the optical pulse, and
P(t) is the total optical power in the optical fiber
Cross-Phase Modulation (XPM) appears when two or more waves propagate inside the fiber and interact due to the non-linearity of the refractive index produced by the total power inside the fiber. This interaction comprises many phenomena, such as FWM, harmonic generation, SPM, Raman scattering, and Brillouin scattering.
Stimulated Raman Scattering (SRS) appears for extremely severe pump waves above the Raman threshold RT, that is within the range of 1W. SRS generates the Stokes radiation with wavelength λs that propagates dominantly within the ahead route with respect to the pump and incorporates most of the electricity of the pump wave. The electricity distinction among the pump and SRS waves propagates into the fiber as an acoustic wave. SRS can have a beneficial effect through turning the optical fibers into Raman amplifiers.
SRS can have additionally a dangerous impact with the aid of moving energy from decrease channels to higher channels, contributing to the crosstalk between channels. you could minimize the crosstalk by using cautiously choosing the pump wavelength λp to healthy the Raman-advantage spectrum of the fiber in the wavelength range of the channels to be amplified. another damaging impact of the usage of high pump strength to supply Raman amplification is to deliver the fiber middle into optical non-linear operation, developing situations that result in elastic interactions which includes four-wave blending, self-section modulation, and cross-phase modulation.
SRS can have additionally a dangerous impact with the aid of moving energy from decrease channels to higher channels, contributing to the crosstalk between channels. you could minimize the crosstalk by using cautiously choosing the pump wavelength λp to healthy the Raman-advantage spectrum of the fiber in the wavelength range of the channels to be amplified. another damaging impact of the usage of high pump strength to supply Raman amplification is to deliver the fiber middle into optical non-linear operation, developing situations that result in elastic interactions which includes four-wave blending, self-section modulation, and cross-phase modulation.
