Dagens, B.

Fjelde, Tina

Janz, C.

Kloch, Allan

Renaud, M.

Wolfson, David

D. Wolfson

A. Kloch

T. Fjelde

C. Janz

B. Dagens

M. Renaud

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40-Gb/s all-optical wavelength conversion, regeneration, and demultiplexing in an SOA-based all-active Mach-Zehnder interferometer

All-optical 2R and 3R regeneration techniques are investigated at 40 Gb/s, It is shown that an all-active SOA-based Mach-Zehnder device, employed as a,wavelength converter, is capable of improving the OSNR by more than 20 dB at this bit rate, thereby resulting in penalty reduction. Furthermore, simultaneous all-optical wavelength conversion and demultiplexing from 40 to 10 Gb/s is demonstrated showing that the scheme, which also has a 3R regeneration capability, is feasible in a combined OTDM/WDM network

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Downloaded from orbit.dtu.dk on: Dec 17, 201740-Gb/s all-optical wavelength conversion, regeneration, and demultiplexing in anSOA-based all-active Mach-Zehnder interferometerWolfson, David; Kloch, Allan; Fjelde, Tina; Janz, C.; Dagens, B.; Renaud, M.Published in:I E E E Photonics Technology LettersLink to article, DOI:10.1109/68.826931Publication date:2000Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Wolfson, D., Kloch, A., Fjelde, T., Janz, C., Dagens, B., & Renaud, M. (2000). 40-Gb/s all-optical wavelengthconversion, regeneration, and demultiplexing in an SOA-based all-active Mach-Zehnder interferometer. I E E EPhotonics Technology Letters, 12(3), 332-334. DOI: 10.1109/68.826931332 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 12, NO. 3, MARCH 200040-Gb/s All-Optical Wavelength Conversion,Regeneration, and Demultiplexing in an SOA-BasedAll-Active Mach–Zehnder InterferometerD. Wolfson, A. Kloch, T. Fjelde, C. Janz, B. Dagens, and M. RenaudAbstract—All-optical 2R and 3R regeneration techniques areinvestigated at 40 Gb/s. It is shown that an all-active SOA-basedMach–Zehnder device, employed as a wavelength converter, is ca-pable of improving the OSNR by more than 20 dB at this bit rate,thereby resulting in penalty reduction. Furthermore, simultaneousall-optical wavelength conversion and demultiplexing from 40 to10 Gb/s is demonstrated showing that the scheme, which also has a3R regeneration capability, is feasible in a combined OTDM/WDMnetwork.Index Terms—Amplifier noise, converters, optical amplifiers,optical communication, semiconductor devices.I. INTRODUCTIONOVER THE LAST decade, the telecommunication in-dustry has experienced an enormous increase in needfor transmission bandwidth. In order to fulfill these capacityrequirements, all-optical point-to-point wavelength-divi-sion-multiplexed (WDM) systems have already been installedworld-wide. Still, as IP traffic increases at an annual rate inexcess of 200%, the next step in optical network evolution willbe actual all-optical networking, where routing and switchingare performed in the optical domain. However, a very importanttopic of concern for optical networks is accumulation of,e.g., noise and jitter, which severely limits the network nodecascadability. Therefore, key technologies for future large-scaleoptical networks will be all-optical 2R and 3R regeneration.Several techniques for all-optical regeneration have beeninvestigated and some of the most promising results have beenachieved with interferometric wavelength converters [1]. More-over, as the channel bit rate in the optical network increasesto 40 Gb/s or more, a combination of both OTDM and WDMwill offer a flexible network, where switching and add/dropfunctionalities can be accomplished in both the wavelength andtime domains. In this scenario a very important need, will be foroptical building blocks performing wavelength conversion anddemultiplexing, operations which the interferometric devicesalso are able to perform [2].Manuscript received September 14, 1999; revised November 12, 1999. Partof this work has been carried out within the framework of the European researchproject ACTS REPEAT.D. Wolfson, A. Kloch, and T. Fjelde are with the Research Center COM,Technical University of Denmark, DK-2800 Lyngby, Denmark (e-mail:dw@com.dtu.dk).C. Janz, B. Dagens, and M. Renaud are with the OPTO+, Groupement d’In-térêt, Economique, Route de Nozay, 91460 Marcoussis, France, Alcatel Corpo-rate Research Center (e-mail: Christopher.Janz@ms.alcatel.fr).Publisher Item Identifier S 1041-1135(00)01984-4.Fig. 1. Experimental setup for all-optical 2R regeneration at 40 Gb/s using anall-active MZI.Here, we experimentally demonstrate all-optical 2R regener-ation at 40-Gb/s in an SOA-based all-active Mach–Zehnder in-terferometer as well as the suitability for 40 Gb/s 3R regenera-tion. Furthermore, it is demonstrated that the Mach–Zehnder in-terferometer (MZI) offers simultaneous wavelength conversionand demultiplexing from 40 to 10 Gb/s suitable for a combinedOTDM/WDM network.II. ALL-OPTICAL 2R REGENERATIONFig. 1 shows the experimental setup, where the device usedfor the experiments is an all-active MZI [3]. The 40-Gb/s RZdata signal at 1554 nm (PRBS ) is generated by pas-sive multiplexing of externally modulated 10 GHz compressedpulses from a gain-switched DFB laser (FWHM ∼6 ps aftercompression). The signal is then injected into a subblock, wherethe optical signal-to-noise ratio (OSNR) can be controlled. Thesubblock consists of a variable attenuator followed by an EDFAand an optical filter. Thus, by controlling the input power to theEDFA, the OSNR into the MZI is controlled. After the subblockthe signal is split in two and injected into the signal input armsof the all-active MZI, i.e., SOA1 and SOA3, in order to exploit1041–1135/00$10.00 © 2000 IEEEAuthorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on November 30, 2009 at 08:45 from IEEE Xplore.  Restrictions apply. WOLFSON et al.: 40-Gb/s ALL-OPTICAL WAVELENGTH CONVERSION, REGENERATION, AND DEMULTIPLEXING 333a differential control scheme for high-speed operation [4]. Thesignal is converted to a continuous-wave (CW) signal at 1547nm and regeneration is accomplished. At the output of the con-verter a filter rejects the original data signal before the regener-ated signal is demultiplexed to 10 Gb/s in an EA-modulator anddetected for BER measurements.The excellent performance of the regenerator is illustratedin Fig. 2 showing the BER as a function of the receivedpower for the back-to-back signal and the regenerated signal.Note that the EDFA input power is high, i.e., the OSNRinto the regenerator is also high. The inset shows the eyediagram at the output of the regenerator. As seen, the eye di-agram is both clear and open with an extinction ratio of ∼10dB. Furthermore, the all-optical 2R regenerator introduces apenalty of only 0.6 dB at 40 Gb/s (a preamplified receiverwas used). With regard to the regenerative capabilities, Fig. 3shows the OSNR (@0.1 nm) at both the input and outputof the 2R regenerator as a function of the input power tothe in-line EDFA. As illustrated in Fig. 3, the all-opticalregenerator is capable of preserving a very high OSNR re-gardless of the OSNR at the input, since the spectrum afterthe device is determined by the spectrum of the CW sourceand the low ASE level from the regenerator. In this case theOSNR is kept above 37 dB even for an OSNR at the inputas low as ∼13 dB thus resulting in an improvement of ∼24dB. Clearly, the ability to ensure a high OSNR of regener-ated signals even at high bit rates is very important whenconsidering cascadability of the all-optical 2R regenerator.Furthermore, maintaining a high OSNR makes it possibleto keep repeater spacing high, thus resulting in cost-effec-tive transmission links. The noise suppression capabilities ofthe regenerator are also illustrated in Fig. 4, showing theexcess penalty as a function of the input power to the in-lineEDFA. As seen, a noise suppression capability is obtainedfor EDFA input powers below 20 dBm. As an example, atan excess power penalty of 2 dB (since a preamplifier wasused) a ∼2 dB lower input power to the EDFA is allowed.III. ALL-OPTICAL 3R REGENERATIONThe all-active MZI shown in Fig. 1 can also be used withinan all-optical architecture for 3R regeneration. The onlynecessary change in the set-up in Fig. 1 is that instead ofusing a CW-source, a 40-GHz clock signal extracted fromthe data signal is used. Here, in simulation of such a clock, again-switched DFB laser at 1547 nm is modulated at 10 GHzand the resulting 10-GHz optical clock signal is then passivelymultiplexed to 40 GHz and injected into the MZI at the input ofSOA2. With this scheme jitter on the data signal is transferredto minor amplitude modulation [5]. The good performance ofthe 3R regenerator is illustrated in Fig. 5 giving the BER as afunction of the received power for the back-to-back signal andthe regenerated signal. The inset shows the eye diagram at theoutput of the regenerator. The resulting penalty is as low as∼0.5 dB at 40 Gb/s and we note that the RZ signal format ispreserved at the output of the 3R regenerator emphasizing thefeasibility of this scheme at high bit rates.Fig. 2. BER as a function of the received power for the back-to-back signal at1554 nm and the 2R regenerated signal at 1547 nm. The inset shows the 40-Gb/seye diagram at the output of the regenerator. The EDFA input power is 0 dBm.Fig. 3. OSNR in 0.1 nm at the input and output of the all-optical 2Rregenerator as a function of the input power to the in-line EDFA.Fig. 4. Excess penalty with and without 2R regeneration at 40 Gb/s as afunction of the input power to the in-line EDFA.IV. ALL-OPTICAL OTDM/WDM SWITCHING DEVICEAn all-optical OTDM/WDM switching device offering si-multaneous wavelength conversion and demultiplexing capa-bility is easy to realize with the all-optical MZI [2]. Referring toAuthorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on November 30, 2009 at 08:45 from IEEE Xplore.  Restrictions apply. 334 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 12, NO. 3, MARCH 2000Fig. 5. BER as a function of the received power for the back-to-back signal at1554 nm and the “3R regenerated” signal at 1547 nm. The inset shows the eyediagram at 40 Gb/s at the output of the regenerator.Fig. 1, simultaneous wavelength conversion and demultiplexingcan be achieved by using an optical clock signal at 10 GHz de-rived from the data signal instead of the CW laser source. If theclock pulse width is sufficiently short (in these experiments thepulse widths were ∼6 ps), then by controlling the time delay ofthe 10-GHz clock signal, any of the four multiplexed 10-Gb/ssignals in the 40 Gb/s signal can be demultiplexed. To verifythis Fig. 6(a) shows the pulse trace of a 40-Gb/s signal at 1554nm, while Fig. 6(b) and (c) shows two different wavelength con-verted and demultiplexed pulse traces at 1547 nm. It must bementioned that the reason for the pulse overlap in Fig. 6(a) is dueto the limited bandwidth of the photodetector (30 GHz). Still,the pulse traces in Fig. 6(b) (“1110”) and 6(c) (“1011”) clearlydemonstrate that demultiplexing is achieved with a strong sup-pression of the other three OTDM channels. In order to assessthe performance of the technique Fig. 7 shows the BER as afunction of the received power for the back-to-back case (de-multiplexing performed with an EA modulator as in previousresults) and for demultiplexing performed with the MZI. Theinset shows an eye diagram at 10 Gb/s after demultiplexing inthe MZI. As seen in Fig. 7, the scheme introduces a preamplifiedpenalty of ∼3 dB for wavelength conversion and demultiplexingfrom 40 to 10 Gb/s. It should be emphasized that this scheme in-herently has a 3R regeneration capability since a retimed clocksignal is used for demultiplexing.V. CONCLUSIONIn this letter, all-optical regeneration techniques based onSOA-interferometers, and suitable for high-speed operation,have been investigated. In particular, all-optical 2R regenera-tion, and suitability for 3R regeneration, has been demonstratedat 40 Gb/s. It has been shown that the regenerator is capableof improving the OSNR by more than 20 dB thereby resultingin penalty reduction. Furthermore, simultaneous all-opticalwavelength conversion and demultiplexing from 40 to 10 Gb/shas been demonstrated showing that the scheme, which alsohas a 3R regeneration capability, is feasible in a combinedOTDM/WDM network. Finally, it is emphasized that all resultshave been achieved using the same all-active MZI.Fig. 6. (a) 40-Gb/s input pulse trace at 1554 nm and (b) and (c) two differentdemultiplexed 10-Gb/s signals at 1547 nm.Fig. 7. BER as a function of the received power for the back-to-back signal at1554 nm demultiplexed with an EA-modulator and the converted signal at 1547nm demultiplexed by the all-optical Mach–Zehnder interferometer. The insetshows an eye diagram at 10 Gb/s after demultiplexing performed with the MZI.REFERENCES[1] B. Lavigne, D. Chiaroni, P. Guerber, L. Hamon, and A. Jourdan, “Im-provement of regeneration capabilities in semiconductor optical ampli-fier-based 3R regenerator,” in Tech. Dig. OFC’99, San Diego, CA, 1999,paper TuJ3.[2] M. Duelk, St. Fischer, E. Gamper, W. Vogt, E. Gini, H. Melchior, W.Hunziker, M. Puleo, and R. Girardi, “Full 40 Gbit/s OTDM to WDMconversion: Simultaneous four channel 40 : 10 Gbit/s all-optical demulti-plexing and wavelength conversion to individual wavelengths,” in Tech.Dig. OFC’99, San Diego, CA, 1999, paper PD17.[3] C. Janz, B. Dagens, A. Bisson, F. Poingt, F. Pommereau, F. Gaborit, I.Guillemot, and M. Renaud, “Integrated all-active Mach–Zehnder wave-length converter with record signal sensitivity and large dynamic rangeat 10 Gbit/s,” in Tech. Dig. OFC’99, San Diego, CA, 1999, paper FB3.[4] B. Mikkelsen, K. S. Jepsen, M. Vaa, H. N. Poulsen, K. E. Stubkjaer, R.Hess, M. Duelk, W. Vogt, E. Gamper, E. Gini, P. A. Besse, H. Melchior,S. Bouchoule, and F. Devaux, “All-optical wavelength converter schemefor high-speed RZ signal formats,” Electron. Lett., vol. 33, no. 25, pp.2137–2139, 1997.[5] K. S. Jepsen, A. Buxens, A. T. Clausen, H. N. Poulsen, B. Mikkelsen,and K. E. Stubkjaer, “20 Gbit/s optical 3R regeneration using polariza-tion-independent monolithically integrated Michelson interferometer,”Electron. Lett., vol. 34, no. 5, pp. 472–474, 1998.Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on November 30, 2009 at 08:45 from IEEE Xplore.  Restrictions apply. 

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40-Gb/s all-optical wavelength conversion, regeneration, and demultiplexing in an SOA-based all-active Mach-Zehnder interferometer

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