KAZMIERSKI, C., OUGAZZADEN, zyxwvutsrqponm A., ROBEIN, D., MATHOORAZING, D., BLEZ, M., and MIRCEA, A.: ‘20GHz bandwidth 1 . 5 ~ wavelength VUG DFB laser using a zero net strain In,Ga,,As,P,,, well active structure grown at constant y’, zyxwvutsrqpo Electron. Lett., 1993, zyxwvutsr 29, pp. 1290- 1292 DERKSEN, R H., and WERNZ, H.: ‘Silicon bipolar laser driving IC for 5Gb/s and 45-mA modulation current and its application in a demonstrator system’, IEEE J. Solid-State Circuits, 1993, 28, (7), vv. 824-828 zyxwvutsrqpon _ _ 10 GNAUCK, AH., and BOWERS, J.E.: ‘16GbitIs direct modulation of an InGaAsP laser’, Electron. Lett., 1987, 23, pp. 801-803 40Gbit/s error free transmission over a 68km distributed erbium doped fibre amplifier A. Altuncu, L. Noel, W.A. Pender, A.S. Siddiqui, T. Widdowson, A.D. Ellis, M.A. Newhouse, A.J. Antos. G. Kar and P.W. Chu Indexing terms: Erbium-dopedfibre ampl$ers, Fibre amplijiers Optical communication The error ratio peroformance of soliton like transmission over a 68km distributed erbium fibre link is reported. The transmission link had a net gain of only 2dB, with remarkably low signal power excursions and a penalty of <ldB was observed at 40 Gbitk. Introduction: In long haul soliton transmission systems operating at bit rates higher than 10Gbit/s, one of the principal limitations is perturbations in soliton power which arises from distributed loss and discrete amplification [ 11. Usually for stable transmission, the amplifier spacing must be significantlyless than the soliton period which is proportional to the square of FWHM pulse width (+). This severe constraint on the amplifier spacing in high capacity systems (low z) can be effectively solved by eliminating the signal power perturbations using distributed erbium doped fibres as a transmission medium. Previously, the transmission of soliton pulses over distributed EDFAs (DEDFAs) has been demonstrated experimentally by several research groups [2 - 61 for pulse widths as short as 440fs [2], repetition rates up to 80GHz [6] and dis- tances up to 90km [5]. Error ratio measurements have also been carried out over a moderate length of fibre (35km) at 20Gbit/s [7]. In this Letter we report for the first time transmission of a 40Gbib‘ s data stream with 7.8ps pulse widths over a 68km DEDF with a peak to peak signal excursion of <2dB and a BER performance exhibiting negligible power penalty. . . . : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I : : . . . . ............................................................................................ . . . . . . . . . . . , . . . . . . . . . : I , I . . . ................... I ............................... ! ................. / . .... I . . $ bLi . . ....... i ........ ! ...... j;l ......... __ _- . . -- -__-_--- . . . . . . . . zyxwvutsrqponm g -\ . . . . . . . In- ......... i ................... :... ....................... : ...................................... ......... ! ................................ I ......... : ......... i ......... ; ....... .j ......... .............. I ......... : ......... i ......... 1 ....... .i ......... zyxwvutsr 0 I : : . ; . : . : I : ; . ! : , : ; I : ; ; ; N . . . . . . . . . . . . . . . . . - . , . . . . . . . . . . . . . . . ................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 16 32 48 64 80 distance, k m Pig. 1 Gain distribution along 68km DEDF observed on OTDR Experimental details: The 68km transmission link was comprised of five lengths of lightly Er-doped dispersion shifted fibre with nearly equal unpumped attenuation coefficients of -0.68dBlkm. The mean dispersion zero wavelength and the dispersion slope of the total link were 1532.6nm and 0.07ps/nmz/km, respectively. Consequently, the average dispersion of the fibre was 0.165psld zyxwvut km at the signal wavelength of 1535nm. The fibre was bi- ELECTRONICS LETTERS zyxwvutsr 1st February 1996 Vol. 32 directionally pumped with a total of l00mW of 14801x11 pump power. For an input signal power of --3dBm a net intrinsic fibre gain of 2dB was achieved, compensating for the loss of the two WDM couplers. The gain distribution along the 68km DEDFA for small mean signal powers was obtained by an OTDR equipped with a DFB laser of -1535nm (Fig. 1) confirming a negligible sig- nal power excursion allong the entire fibre length. A schematic dia- gram of the experimental configuration used is shown in Fig. 2. inter leaver lOGHz synthesiser pattern generator 68km DEDF receiver demultiplexer I DUmD 2 /535121 Fig. 2 Experimental setup used for 40Gbit/s transmission and BER measurements For simplicity, the amplifiers and the filters used in the experiment have not been shown in this figure. The pulses were generated by a mode locked external cavity semconductor laser (ECL) driven by a synthesiser with a repetition rate of l0GHz and compressed in a 200m dispersion compensating fibre to produce stable transform limited pulses with a 7.8ps FWHM pulse width and a time band- width product (TBP) of 0.4. The pulse train was modulated with a 10Gbit/s electrical NRZ 27 - 1 pseudo-random bit stream (limited by receiver electronics) to produce a 10Gbit/s RZ data pattern which was passively interleaved to 40Gbib‘s. The received data stream was demultiplexed using two electro-absorption modulators in series tlo obtain one of the four OTDM channels at IOGbib‘s rate [8]. To synchronise the demultiplexers and the receiver a 4OGHz electronic clock recovery circuit was used [9]. The performance of the received data stream was monitored by means of BER test equipment. Additionally autocorrelator traces, spectra and eye diagrams for the input and output signals were also obtained. Fig. 3 Autocorrelator r‘ruces before and after 68km transmission ut 40 Gbit/s a Before transmission b After transmission The FWHM pulse width and TBP of the received pulses at 40GbiUs were 7.2 and 0.38ps, respectively. A soliton mean power of --2dBm and a soliton period of -150km were calculated for a 40Gbit/s data stream using the measured fibre and pulse parame- ters. Therefore, although the pulses had only traversed -0.4 of a soliton period, some ‘degree of soliton shaping had occurred in No. zyxwvu 3 233