WDM transmission and dispersion compensation at 40 Gbit/s over 200 km standard fibre is demonstrated on a 100 GHz grid using four high power single-polarisation single-sided output DFB fibre laser based transmitters and a single 4 channel WDM chirped fibre Bragg grating dispersion compensator

Fu, A.

Geiger, H.

Ibsen, M.

Laming, R.I.

English

Southampton (e-Prints Soton)

1Optoelectronics Research Centre, University of Southampton, UKFig. 1: Schematic diagram of the experimental setup.Fibre DFB lasers in a 4x10 Gbit/s WDM link with a single sinc-sampled fibre grating dispersioncompensatorMorten Ibsen, Alexander Fu, Harald Geiger and Richard I. LamingAbstract: WDM transmission and dispersion compensation at 40 Gbit/s over 200 km standard fibre is demonstratedon a 100 GHz grid using four high power single-polarisation single-sided output DFB fibre laser basedtransmitters and a single 4 channel WDM chirped fibre Bragg grating dispersion compensator.IntroductionWDM transmission systems have received growingattention over the last few years because of their In this paper we combine the devices andobvious advantages when upgrading existing demonstrate for the first time a WDM systemsystems to operate at higher data-rates. Operatingcomprising 4 high power DFB fibre lasersat bit-rates of 10 Gbit/s and above requires op rating with single sided and single polarisationcompensation of the chromatic dispersion sufferedoutputs. The lasers are demonstrated to be reliablein the existing fibres. Dispersion compensation signal sources in a 4x10 Gbit/s, 100 GHz channelwith single channel chirped fibre gratings has beenspecing WDM transmission experiment over 200demonstrated on numerous occasions [1,2]. km of standard fibre with robust dispersionTransmitting multiple WDM-channels the relativecompensation performed by a single 4 channel 100channel spacings are of great importance. The GHz spacing chirped sinc-sampled fibre Braggperiodic spectral response and identical multiple grating.chanel characteristics of the recently developedsinc-sampled grating [3] makes it a very attractiveWDM device.DFB fibre lasers exhibit ideal source polarisation asymmetric DFB-fibre lasers of lengthcharacteristics being an inherently fibre compatible5 cm separated in frequency by 100 GHz. Thedevice. The operating wavelengths [4] can readilylasers have 8/4 phaseshifts offcentred by 4 mm.be manufactured with high accuracy to achieve Each is pumped at 980 nm with 60 mW powerconstant frequency separation using current gratingfrom a pump diode, resulting in single sided outputwriting techniques [5]. They can also be designedpowers of 7.1 dBm, 7.7 dBm, 7.0 dBm, and 7.7to lase in a single polarisation whilst single-sided dBm, and operating wavelengths of 1547.6 nm,lasing output by offsetting the phase-shift from thecentre position [6] increases the potential further.Exp rimentThe experimental setup (Fig. 1) consists of 4 single1548.4 nm, 1549.2 nm and 1550.0 nmrespectively. The signal to noise ratiobetween the 4 DFB signal channels isin excess of 50 dB (0.08 nmresolution) and the linewidth of thedevices has been measured to be ~10kHz. The polarisation states of the lasers areindividually aligned using polarisationcontrollers to allow modulation in asingle modulator. The excess power ofthe lasers allows their output to becombined in an all-fibre multiplexerconsisting of three 1550 nm 3 dBsplitters, before each channel ismodulated using a lithium niobate(LiNbO) modulator. Fig. 2a shows the3output spectra of the 4 DFB fibre1547 1548 1549 155005001000150020002500Wavelength [nm]1547 1548 1549 1550-24-16-808Channel 4Channel 3Channel 2Channel 1c)b)1547 1548 1549 1550-60-50-40-30-20-100 a) DFB no. 4DFB no .3DFB no. 2DFB no. 12 Optoelectronics Research Centre, University of Southampton, UKFig. 3: Bit error rate performance ofsimultaneous 4x10Gbits WDM transmissionsystem.       (Insert) Dispersion compensatedeye of channel 4.lasers measured directly after the modulator. TheWDM channels are mplified and then transmittedover a 200 km standard telecommunication fibre B t error rate (BER) vs. received power for the 4(D=16 ps/nm/km @ 1.55µm) link. Ultimately thedispersion compensated channels and back-to backhigh power of the fibre DFBs will obviate the with DFB laser no.1 are shown in Fig. 3. Therequirements for amplification prior to figure shows a maximum power penalty of 1 dBtransmission. After transmission the channels are for error free operation. This variation could be duesimultaneuosly dispersion compensated with a 4chanel sinc-sampled fibre grating [3], which iswavelength matched to the transmitted channels(Fig. 2). The grating has a sampling period of 1mm and is 25.8 cm long. It is chirped over 0.8 nmand is apodised over 10 % of the total length ateither end to reduce the ripples in the dispersioncharacteristics. Each dispersion-compensatingchannel of the grating exhibit a reflectivity of ~ 60% and dispersions of -3263 ps/nm, -3206 ps/nm,-3250 ps/nm and -3238 ps/nm respectively with amaximum in-band time delay ripple of ~50 ps (Fig.2b&c). A uniform fibre grating used in an add-drop configuration, selects the channel under testand drops it onto the receiver and error detector.All the fibre gratings used in this experiment aremanufactured using a continuous grating writingtechnique [3] which allows very complex gratingstructures to be formed.Fig. 2a) DFB lasing spectra after the modulator.2b) Reflection and c) time delay characteristic of the4 channel chirped sinc sampled fibre Bragg grating.Results and discussionto the fact that a different pick-out grating is usedfor each channel. In order to test the quality of thedispersion compensating grating, a wavelengthscan across the bandwidth of channel 2 was made,but not shown here due to limited space. In thiscase the received power was kept constant at -34.5dBm and the BER was recorded. A variation of 2 orders of magnitude in the errorrate around 10  was measured, corresponding to a-8less than ±0.75 dB power penalty (Fig. 3). Theeffect of cross talk between adjacent channels wasalso evaluated by comparing BER data for theWDM system with data obtained whentransmitting only one of the wavelength channels ata time. No degradation in the performance of thesystem was observed. In order to compare theperformance of the fibre DFB laser transmitterswith a traditionally used tunable laser sourc(TUNICS) a single channel BER measurementtuned onto channel 3 using this source wasperformed. Again no significant difference wasobserved (Fig. 3).3Optoelectronics Research Centre, University of Southampton, UKConclusionsWe have demonstrated the first 4 channel 40 source for WDM systems’, Electron.Gbit/s NRZ WDM transmission experiment overa 200 km standard fibre link employing high powerall-fibre DFB lasers as signal sources.Simultaneous dispersion compensation of the 4channels was performed using a sinc-sampledmultichannel fibre grating that exhibits identicaldispersion characteristics on a 100 GHz comb ofwavelength channels. We believe that thisexperiment demonstrates that the technology offibre DFB lasers has matured and that they are anattractive transmitter alternative to semiconductorDFB lasers and are ready to take part in therealisation of all-fibre WDM transmission systems.AcknowledgementsThe authors wish to thank Martin J. Cole andMichael K. Durkin for help in establishing thegrating writing setup, Erland Rønnekliev andGregory J. Cowle for discussions on DFB fibrelasers, together with Sze Y. Set and PeriklesPetropoulos for system oriented aspects. This workwas in part supported by Pirelli Cavi SpA, Milan.The Optoelectronics Research Centre is an EPSRC(UK) funded interdisciplinary research centre.References1. Ouellette, F., Krug, P.A., Stephens, T.,Dhosi, G. and Eggleton, B.J.: ‘WDM andbroadband disperion compensation usingchirped sampled fibre Bragg gratings’,Electron. Lett., 31, (11), pp. 899-901,1995.2. Dong, L., Cole, M.J., Ellis, A.D., Durkin,M., Ibsen, M., Gusmeroli, V. and Laming,R.I.: ‘40 Gbit/s 1.55 µm transmissionover 109 km of nondispersion shiftedfiber with long continuously chirped fibergratings’, OFC’97, paper PD6, Dallas,USA.3. Ibsen, M., Durkin, M.K., Cole, M.J. andLaming, R.I.: ‘Sinc-sampled fibre Bragggratings for identical multiple wavelengthoperation’, IEEE Photon. Technol. Lett.,10, (6), pp. 842-844, 1998.4. Hhbner, J., Varming, P. and Kristensen,M.: ‘Five wavelength DFB fibre laserLett., 33, (2), pp. 139-140, 1997.5. Cole, M.J., Loh, W.H., Laming, R.I.,Zervas, M.N. and Barcelos, S.: ‘Movingfiber/phase mask scanning technique forenhanced flexibility in producing fibergratings with a uniform phase mask’,Electron. Lett., 31, (12), pp. 1488-1489,1995.6. Lauridsen, V.C, Srndergaard, T.,Varming, P. and Povlsen, J.H.: ‘Design ofdistributed feedback fibre lasers’, ECOC‘97, 3, Session WeC1, pp. 39-42,Edinburgh, UK.

40 Gbit/s 1.55 µm transmission over 109 km of nondispersion shifted fiber with long continuously chirped fiber gratings’, OFC’97, paper PD6,

Five wavelength DFB fibre laser

Moving fiber/phase mask scanning technique for enhanced flexibility in producing fiber gratings with a uniform phase mask’,

Sinc-sampled fibre Bragg gratings for identical multiple wavelength operation’,

WDM and broadband dispersion compensation using chirped sampled fibre Bragg gratings’,

Fibre DFB lasers in a 4x10 Gbit/s WDM link with a single sinc-sampled fibre grating dispersion compensator

Fibre DFB lasers in a 4x10 Gbit/s WDM link with a single sinc-sampled fibre grating dispersion compensator

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