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  • International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.346-351 “Measurements Of Optical Parameters On 40 Channel 10G Huawei DWDM System”AbstractThis project “Measurements Of Optical Generating the signal—The source, a solid-stateParameters On 40 Channel 10G Huawei DWDM laser, must provide stable light within a specific,System” is intended to get the real time narrow bandwidth that carries the digital data,perfomance characteristics of the DWDM system modulated as an analog signal. Combining thewhich has been operated by the Bharath Sanchar signals—Modern DWDM systems employNigam Limited (from Telephone Bhavan, multiplexers to combine the signals. There is someHyderabad, India ) for telecommunications inherent loss associated with multiplexing andthroughout the India, at each component level demultiplexing. This loss is dependent upon theand to suggest respective measures for the better number of channels but can be mitigated withfunctioning of the overall system. optical amplifiers, which boost all the wavelengthsWith today’s seemingly limitless demand for at once without electrical conversion.transmission capacity, service providers often Transmitting the signals—The effects of crosstalkcope with extreme fiber usage and exhaust across and optical signal degradation or loss must besignificant portions of their networks. reckoned with in fiber optic transmission. These. The telecommunications industry has so far met effects can be minimized by controlling variablesthese needs by using dense wavelength division such as channel spacings, wavelength tolerance, andmultiplexing (DWDM) systems. In allowing both laser power levels. Over a transmission link, thenew and existing fiber optic links to carry several signal may need to be optically amplified.channels simultaneously, DWDM can optimize Separating the received signals—At the receivingthe use of current facilities whilst offering greater end, the multiplexed signals must be separated out.capacities for the future. At the beginning of the Although this task would appear to be simply the1980s, time domain multiplexing (TDM) made it opposite of combining the signals, it is actuallypossible to increase the bit-rate Wavelength more technically difficult.division multiplexing (WDM), the simultaneous Receiving the signals—The demultiplexed signal istransmission of multiple signals at different received by a photodetector.wavelengths over a single fiber proved to be amore reliable 2. Transmission ChallengesThe disadvantage of this WDM technique was Transmission of light in optical fiberthat the multiplexed signal had to be separated presents several challenges that must be dealt with.each time before being electrically regenerated. These fall into the following three broad categories:Demands for new data services, home office and 1. Attenuation—decay of signal strength, or loss ofinternet applications all contribute to the light power, as the signal propagates through thepressure being placed on service providers fber.worldwide. Although 10 Gbps seems to be a 2. Chromatic dispersion—spreading of light pulsessufficiently high bit-rate for most networks as they travel down the fiber.today, this level of capacity may not be enough in 3. Nonlinearities—cumulative effects from thethe long term. interaction of light with the material through whichThe respective suggestions for the better it travels, resulting in changes in the light wave andimprovement of the DWDM System has been interactions between light waves.accepted by the BSNL authoritie’s. Each of these effects has several causes, not all of which affect DWDM. The discussion in the 1. Introduction: following sections addresses those causes that are The nature of the paper is to explain the relevant to DWDM.drawbacks faced by the current technology ofTelecommunications faced by the BSNL, India. Light Sources and DetectorsThis is the first of its kind to work on the Real Time Light emitters and light detectors are activeDWDM System to find the demerits and to propose devices at opposite ends of an optical transmissionthe drawbacks of the system that we presently use. system. Light sources, or light emitters, areThe contribution of the paper is to propose the transmit-side devices that convert electrical signalsrespective suggestions in a cost effective way for the to light pulses. The process of this conversion, orbetter possible working of the Telecommunucations modulation, can be accomplished by externallyvia Optical fiber by using DWDM system.The modulating a continuous wave of light or by using asystem performs the following main functions: device that can generate modulated light directly. Light detectors perform the opposite function of 346 | P a g e
  • International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.346-351light emitters. They are receive-side opto-electronic signals.devices that convert light pulses into electricalTypical characteristics of light sourcePROPERTY LED LASER SINGLE LASERSpectral width (nm) 200–100 1–5 0–2Rise time (ns) 2–250 0.1–1 0.1–1Modulation B.W (MHz) < 300 < 2000 ~ 2000Coupling efficiency Very low Moderate ModerateCompatible fibre mode M.M. (Si and GI) M.M. GI & SM SingleTemperature sensitivity Low High HighCircuit Complexity Simple Complex ComplexLifetime (hours) 105 104–105 104–105Costs Low High HighestPath length Moderate Long Very longData rate Moderate High Very highMultichannel DWDM transmission system them as a multiplexed signal to an optical fiberA DWDM system can be described as a parallel set amplifier (OFA).of optical channels, each using a slightly different Depending on path length and type of fiber used,wavelength, but all sharing a single transmission one or more OFAs can be used to boost the opticalmedium or fiber. The functionality of a signal for long fiber spans. At termination on themultichannel DWDM transmission system when receiving end, the optical signals are preamplified,various 10 Gbps signals are fed to optical then separated using optical filters (demultiplexer)transmission modules the optical output signals are before being converted into electrical signals in theconverted to defined wavelengths in the 1550 nm receiver modules. For bidirectional transmission,window via wavelength transponders. An optical this procedure must be duplicated in the oppositeDWDM coupler (multiplexer) then ‗bunches‘ these direction to carry the signals in that particularoptical signals together on one fiber and forwards direction Comparision of Amplifiers: EDFA EWDA SOA UnitsOutput Power >15 >12 >13 dBmGain >24 >20 >25 dBNoise figure <6 <6 <8 dBMax G Deviate <0.75 <0.75 <0.1 dB/nmPDG <0.3 <0.5 <0.5 dB p-pPower Usage 1 1 1 WattsIn SONET/SDH systems, the limiting parameters a. core is not perfectly circular along itsare digital whereas in DWDM systems, with high overall lengthpower and high number of channels, it is usually b. core is not perfectly concentric with thethe analog impairments which limit the claddingtransmission. These impairments on singlemode c. fiber can be twisted, tapered, or bent atfibers can be divided into linear and nonlinear some points along the span.effects. At any given signal wavelength the PMD is a unstable phenomenon in contrast to the chromatic 3. Limiting Factors: dispersion which is relatively stable. What causes PMD? So, one of the two orthogonal polarisation modes Fiber optic cables are not perfect and can experience a increase in propagation velocity ifcontain fabrication defects where the: it sees a lower refractive index and the other way 347 | P a g e
  • International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.346-351round. Actually the index randomly varies along a temperature variations, external mechanicallong-haul fiber span. constrains etc.The PMD of a long fiber link is dependent onwavelength and fluctuates in time as a result ofThe maximum permissible PMD values for various bit values are shown in the following table:Gbps Max PMD (ps) PMD coefficient for 400km2.5 240 <2.010 10 <0.540 2.5 <0.125The PMD measurements must be performed: a. during the fiber fabrication process (plant) b. during the cable fabrication process (plant) c. after installation of the cable (field) d. at the planning to upgrade an existing network (field)The first level concerns the fiber manufacturerThe second level is also essential. Even if the different fibers used in a cable are low in PMD, the assemblingprocess may cause additional effects like stress which create higher PMDThe third level takes place once the cable is installed in the field.During installation the cable can be crushed, kinked or otherwise physically damaged.The last level of PMD testing occurs when telephone companies need to test existing cables, in order to upgradenetwork systems at a higher bit rate.Annexure:There are four types of chords:1. LOG chord means Lower Order Giga Bit Ethernet Chord2. TMX chord means Transponder Multiplexer Chord 348 | P a g e
  • International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.346-3513. LWF WAN means Line Wavelength Filter Wide Area Network4. LWF SDH means Line Wavelength Filter SDH40 lambda or channels= 40 slots LOG chords=8,16,24,32,40(5slots)TMX chords=3,4,5,6,11,12,13,14,19,20,21,22,27,28,29,30,35,36,37,38(20slots)LWF chords=1,2,7,9,10,15,17,18,23,25,26,31,33,34,39(15slots)In readings, if Power= -60 indicates that the line is not used or the respective optical fiber cable is faulted.Conclusion:In designing DWDM systems, limiting physical effects (particularly nonlinear) need to be taken into account.Impairment Cause Effect CompensationAttenuation Material Absorption Decrease of Peak Shorter spans, Power Purer fiber materialCD Wavelength a. Decrease of Use of Fibers Dependent Peak Power or Modules Group Velocity b. Pulse with CD values. Broadening. (DCF / DCM) c. Bit errorsPMD Fiber Imperfections a. Decrease of New Fiber with low due to statistically Peak Power PMD values, changing b. Distortion of Exact fiber refractive index Pulse shape Geometry, c. Bit errors Carefull fiber Laying (No Stress).FWM Interference a. Power Use of Fibers of Signals transfer to with CD, 349 | P a g e
  • International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.346-351 Original Irregular Channel signal to Spacing. New signal Frequencies b. Production of Sidebands (Harmonics) c. Channel Crosstalk d. Bit errorsSPM Intensity dependent a. Spectral Use of fibers Refractive Index. Broadening. with CD. (Kerr Effect) b. Initial Pulse Compression c. Accelerated Pulse Broadening.XPM Intensity dependent a. Spectral Use of fibers Refractive Index. Broadening. with CD. (Kerr Effect) b. Initial Pulse Compression c. Accelerated Pulse Broadening.SRS Inetraction of a. Decrease of Careful power level photons with Peak Power. Design. Optical photons. b. Decrease of OSNR. c. Cross talk in especially in Bidirectional DWDM Systems and Bit errorsSBS Interaction of a. Decrease of Spectral broadening Photons with Peak Power. of the light Accoustic photons. b. Decrease source. of OSNR. c. Signal Instability. d. Optical crosstalk In especially Bidirectional DWDM systems. e. Bit errors.Parameters effecting impairment (denoted by ―X‖):Parameter Noise CD PMD FWM SPM XPM SRS SBSChannel X XSpacingNo of Channels X X X X X XChannel X X X X X XPowerNo of spans X X X X X X XChannel bit-rate X X X X X XFiber effective X X X X Xarea 350 | P a g e
  • International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.346-351Empty spaces in the table donot necessarily meanthe impairment is not effected by the parameter.However there are parameters which are notrepresented in the table. For example MechanicalStress effects PMD while temperature has animpact on both PMD and CD. In 40 Gbpstransmissions the DCMs have to be adjustable tocorrect the CD value which itself varies withtemperature.References : [1] R. T. Chen and G. F. Lipscomb, Eds., .WDM and Photonic Switching De-vices for Network Applications,. Proceedings of SPIE, vol. 3949, 2000. [2] C. DeCusatis, E. Maass, D. P. Clement, R. C. Lasky, Eds., .Handbook of Fiber Optic data Communication,. Academic Press, San Diego: 1998. [3] K. Okamoto, .Fundamentals of Optical Waveguides,. Academic Press, New York: 2000. [4] Telcordia documents: GR-1209-CORE; FOTP-205. [5] J. Colachino, .Mux/DeMux Optical Specifications and Measurements,. Lightchip Inc. white paper, Lightreading, July 2001. [6] V. Tandon, M. Volanthen, M. van der Vliet and J. Boner, .Standardized Pa- rameters for AWGs would Ease System Design,. WDM Solutions, August 2001. [7] C. Dragonne, .An N × N optical multiplexer using a planar arrangement of two star couplers,. IEEE Photon. Technol. Lett., 3, 812-815, 1991. 351 | P a g e