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MIT International Journal of Electronics and Communication Engineering, Vol. 4, No. 2, August 2014, pp. 98–101 98

Erbium Doped Fiber Amplifier (EDFA) with Switches Technology for Optical Fiber

CommunicationShikha Gautam

Department of E&C EngineeringAjay Kumar Garg Engineering

College, Ghaziabad, U.P., INDIA

R.L. SharmaDepartment of E&C EngineeringAjay Kumar Garg Engineering

College, Ghaziabad, U.P., INDIA

Pankaj BhardwajAssistant Professor

Department of E&C EngineeringMIT,Moradabad,U.P.,INDIA

1. INTRODUCTIONInopticalcommunicationnetwork,signalstravelthroughfibersforverylargedistances.Opticalfiberamplifiersprovideinlineamplificationofopticalsignalsbyeffectingstimulatedemissionof photons by rare earth element ions implanted in the core of theopticalfiber.Erbiumisthepreferredrareearthelementforthispurpose.EDFAsareusedtoprovideamplificationinlongdistanceopticalcommunicationwithfiberlosslessthan0.2dB/kmbyprovidingamplificationinthelongwavelengthwindownear 1550 nm.EDFAs have been widely applied in optical networks as they have many unique properties which are suited for optical com-munications, such as: • Theyoperateinthetelecommunication wavelengthband

of 1530-1610 nmwith high gain, high output power(P > 100 mW) and low noise.

• High-power semiconductor laser diodes arepracticalsources to provide the light to pump EDFAs.

• TheEDFAisfiber compatible andcanbespliced intotransmission fiber withless thanonedBofinsertionloss.

• ThegainofEDFAsisunaffectedbysignalpolarization.Because saturation occurs in EDFAs on such a slow time scale (~10 msec), EDFAs are relatively immune to cross talk among wavelength multiplexed channels or pulse distortion in high-bit-rate systems.

This paper presents the introduction about the (EDFA) erbium doped fiber amplifier. Important amplifier parameters such as amplifier bandwidth, noise figure and EDFA gain spectrum. EDF amplifier is conventional silica doped with erbium type of material. EDF amplifier provides high power, high gain and low noise figure. EDFA implemented in the range of c band. The gain and the noise figure of EDFA changed by the use of different doping concentration and bandwidth. The EDFA amplifier is key component of the Wavelength division multiplexing (WDM) technology. In this paper presents the latest technology of EDF amplifier with switches, By Switches using to improve the gain and length of the fiber.Keywords: Erbium doped fiber amplifier (EDFA), Wavelength division multiplexing (WDM), and Optical fiber length, VOA (variable optical attenuator), SWs (optical switches).

ABSTRACT

2. PRINCIPLE OF EDF AMPLIFIEREDFA technology is the based on Erbium Doped Fiber (EDF), whichisaconventionalSilicafiberdopedwithErbiumtypeofmaterial [1]. When the Erbium is illuminated with energy that isintheformoflight,atasuitablewavelength(either980nmor 1480 nm) it is excited to a long life time intermediate state (Figure 1), which it decays back to the ground state (ground level)byemittinglightwithinthe1525-1565nmbandThus,ifa pump wavelength and a signal wavelength are simultaneously propagatingthroughanEDFamplifier,energytransferwillviathe Erbium from the pump wavelength to the signal wavelength, resultinginthesignalamplification

Fig. 1: Level diagram of Erbium ion and corresponding spontaneous lifetime

ISSN 2230- 7672 © MIT Publications


region).Oneisstrongpeakaround1530nm,anotherisaround1552nm.Itwasshownthatgainaround1552nmwasflattenedbyco-dopingAl(Er+3)toEDFfromtheearlyresearcheraaround1990.Thereafter,highAl concentrationdopingwas found toimprovegainflatnessaround1540nm–1560nm.AbsorptioncoefficientandgaincoefficientofEDFfordifferentAlconcen-tration are shown in Fig.3.1 and Fig. 3.TypeA,fiberisGe/Alco-dopedEDF,andTypeB,fiberisonlyhigh Al co-doped EDF. Emission of Type B does not indicate depression in 1540 nm as compared with Type A. This leads to flattenedgainspectraaround1540nm–1560nmregion.

Fig. 3:Absorptioncoefficientcomparisonsbetween different Al concentration

Fig. 4:Gain(Emission)coefficientcomparisonbetween different Al concentrations

5. DESIGN AND ANALYSIS In its most basic form the EDFA consists of a length of EDF (typically 10-30 m), a pump laser, and a component (often referredtoasaWDM)forcombiningthesignalandpumpwavelength so that they can propagate simultaneously through the EDF. In principle EDFA’s can be designed such that pump energy propagates in the same direction as the signal (forward pumping), the opposite direction to the signal (backward pump-

3. BASIC CONFIGURATION ThebasicconfigurationforincorporatingtheEDFAinanopticalfiberlinkisshowninFigure2.ThesignalandpumparecombinedthroughaWDMcouplerandlaunchedintoanerbium–dopedfiber[2].Itscoreistheerbium-dopedopticalfibersystem,whichis typicallyasingle-modefiber.In thispaper, theactivefiberis “pumped” with light from two laser diodes for bidirectional pumping, although unidirectional pumping in the forward or backward direction (co-directional and counter-directional pump-ing) is also very commonly used. The pump light, which most oftenhasawavelengtharound980nmandsometimesaround1450 nm, excites the erbium ions into the state, from where they canamplifylightinthe1.5-μmwavelengthregionviastimulatedemission back to the ground-state manifold.

Fig. 2:EDFAconfigurationswithPump

Theisolatorattheinputpreventslightoriginatingfromamplifiedspontaneous emission from disturbing any previous stages, whereas that at the output suppresses lasing, if output light is reflectedbacktotheamplifier.Withoutisolators,fiberamplifierscanbesensitivetoback-reflections.Apart from optical isolators in input, various other com-ponents can be contained in a commercial fiber amplifier For example, there can be fiber couplers and photo detec-tors for monitoring optical power level, pump laser diode with control electronics and gain-flattening filters. For particularly compact packages, various passive optical components can be combined into a photonic integrated circuit there are planar light wave circuit is used. Very high signal gains, as used, e.g., for the amplification of ultra short pulses to high energies, are usually realized with amplifier chains, consisting of several amplifier stageswithadditionalopticalelements(e.g.isolators,filters,or modulators) in between.The performance of an EDFA is characterized by a set of equations called rate equations and propagation equations. In this study, an EDFA simulation program has been written in MATLABtocharacterizeGain,NoiseFigureandASEpowervariations of a forward pumped EDFA operating in C band as functionsofEr3+fiber length,injectedpumppower,signalinput power.

4. EDFA GAIN ChARACTERSTICTheexpansionoftheamplificationbandofEDFamplifierwasachieved through modifying co- dopant composition of the EDF [3].TwogainpeakofEDFexistsin1.55µmregion(C-band



ing), or both direction together. The pump energy may either by 980nmpumpenergy1480nmpumpenergy,oracombinationofboth.Practically,themostcommonEDFAconfigurationistheforwardpumpingconfigurationusing980nmpumpenergy,asshown in Figure 4.

Fig. 5: Single stage EDFA diagram

Optical and electronic componentsused in a basic single stageEDFA.Thesignal enters theamplifier through theinputport,andthen passes through a tap which is used to divert a small percent-age of the signal power to an input detector. The signal then passes through an isolator, before being combined with pump energy emittedbythe980nmpumplaserdiode.Thecombinedsignalandpumpenergypropagate alongtheEDF,wheresignalamplificationoccurs, and then the amplified signal exits the EDF and passesthrough isolator. The purpose of the two isolators, which allow light to pass only in a single direction, is to ensure that lasing cannot take place within the EDF. Furthermore, the output isolator also acts as afilter for980nmlightpropagating intheforward direction, thusstoppingthe980nmlightfromexitingtheamplifieroutputport.

6. SWITChING TEChNOLOGY Concept of theSW-EDFA (Switching Erbium doped fiberamplifi er) withVOAs,AnSW-EDFA cons ists ofmultipleamplifier stages, SWs, andVOAs, usedfortheamplificationmedium. The different combinations with different discrete EDF lengths change the amplifier gain and byusing theswitchingthecoverageareaisincrease.TheVOAs(variableoptical attenuators) adjust the gain so that a continuous gain is obtained between the discrete gains. The SW-EDFA varies the total EDF length by using switching the signal route and EDF combination.TheflattenedgainoftheSW-EDFAtracesseveralgain lines, while that of a conventional EDFA traces only one gain linebecausetheconventiongainisthesinglestageconfigurationprocess.TheresultisthattheVOAattenuationrangeismuchsmaller for theSW-EDFA.ThesmallVOAattenuationrangemeansthatthedegradationoftheNoisefigureofthisamplifierislessthanthatofaconventionalvariablegainamplifier.The pump adding to powers required in the SW-EDFA may be smaller. A portion of the launched pump power is wasted in a conventional EDFA due to the high gain in and the large attenua-tionoftheVOA,whiletheSW-EDFAhaslessVOAattenuation,

which provides the potential to use the pump powers launched intoEDFsefficientlyinswitchingtechnology.

Fig. 6:CombinationofEDFswitcheswithVOAs

There are the combinationof the switchingandVOAwithEDFamplifiers.Conceptofswitchweusethe2×2,1×2,1×3switchescombinationareused.Fig5showstheconfigurationofSW-EDFA.EDF0×EDF1, EDF0×EDF2, EDF0×EDF3,EDF0×EDF1×EDF2,EDF0 ×EDF1×EDF2, EDF0×EDF1×EDF2×EDF3.These sixcombination weareusing toim-prove thelength oftheoptical fiber.

7. CONCLUSIONThe successful introduction of commercial WDM system and abrief introduction to the EDFA that is the most important compo-nentsinWDMcommunications, enabledbypractical EDFAs,hasit turn fuelled the developed of high – power, wide bandwidth, low noise,gainflattenedopticalamplifiers.Theimportant issuesrelatedtotheamplifier performance, namely theoptical noisefigure andbandwidth. In this paper show that gain is increase then the noise figureisdecreaseatdifferentwavelength.Thegainandnoisefigure(NF)forthemultichannel amplificationis investigated at different pump powers. Figure 7 show the gain variation of each channel for different pump powers at a constant inputpowerof-26dBm,whereasFigure8showtheNFvariationofeach channel for different pump powers at a constant input power of -26dBm. Thegain isdirectly proportional to thepump powerwhereas the NF is inversely proportional to the pump power.

Fig. 7:Variationofoutputpoweralongthefiberlengthfordifferentpump power at a constant input power.



Fig. 8:Gainvariationofchannelamplificationfordifferentpumppower.

Fig. 9:Noisefigurevariationperchannelfordifferentpumppower.

As the pump power increases, and the gain increases. But, the NF decreases as the pump power increases. The pump power of 50 mW has low gain and higher NF, which show that it does not offer good performance for the system. By comparing Figure 8 andFigure9,pumppowerof250mWischosenduetoitshighgain and low NF.

REFERENCES

1. YanSun,JianhuiZhau,“OpticalFiberAmplifiersforWDMopticalNetworks”, Bell Labs Technical Journal,March1999.

2. R.A.Olivares,J.R.Souza,“AnalysisofPowerTransientsinErbiumDopedFiberAmplifiers,withApplicationtoWavelengthRoutedOpticalNetworks”,Journal of Microwave and Optoelectronics, Vol. 2, 2002.

3. StephanicsNorakandRichardGieske,“SimulinkModelforEDFADynamicsApplied toGainModulation”,Journal of Lightwave Technology,Vol.20,No.6,June2002.

4. Masanu Fukushina, “RecentProgressofErbiumDoped FiberAmplifierandTheirComponents”,Invitepaper,2007.

5. Whziz Yon, “Introduction to EDFA Technology”, White Paper, June2009.

6. WenZhu,“ImplementaionofThreeFundamentalDevicesusingErbium- Doped Fibers an Advance Photonics Lab”, University of Toronto, Canada, 2010.

7. M.A.Othman,M.M. Ismail,“ErbiumDopedFiberAmplifier(EDF A) for C-band Optical Communication Systems”,International Journal of Engineering & Technology, Vol. 4, 2012.

8. Hirotaka Ono,“W ide-Range Variable Gain Fiber AmplifierWith Erbium Doped Fiber Switching”, Journal of Light Wave Technology, Vol. 31, No.12, June 15, 2013.


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