Coquelin, A.

Fjelde, Tina

Gaborit, F.

Guillemot, I.

Janz, C.

Kloch, Allan

Poingt, F.

Renaud, M.

Wolfson, David

We experimentally investigate a pass-through scheme for all-optical noise suppression in a SOA-based interferometric structure at 10 Gb/s. An input power dynamic range of ~8 dB as well as a noise suppression capability of ~4.5 dB has been demonstrated. Furthermore, the transmission properties have been investigated showing a small pre-amplified penalty of ~0.3 dB after transmission over 31 km of standard single mode fiber

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Downloaded from orbit.dtu.dk on: Dec 17, 2017Experimental investigation at 10 Gb/s of the noise suppression capabilities in a pass-through configuration in SOA-based interferometric structuresWolfson, David; Fjelde, Tina; Kloch, Allan; Janz, C.; Coquelin, A.; Guillemot, I.; Gaborit, F.; Poingt, F.;Renaud, M.Published in:I E E E Photonics Technology LettersLink to article, DOI:10.1109/68.853517Publication date:2000Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Wolfson, D., Fjelde, T., Kloch, A., Janz, C., Coquelin, A., Guillemot, I., ... Renaud, M. (2000). Experimentalinvestigation at 10 Gb/s of the noise suppression capabilities in a pass-through configuration in SOA-basedinterferometric structures. I E E E Photonics Technology Letters, 12(7), 837-839. DOI: 10.1109/68.853517IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 12, NO. 7, JULY 2000 837Experimental Investigation at 10 Gb/s of theNoise Suppression Capabilities in a Pass-ThroughConfiguration in SOA-Based InterferometricStructuresD. Wolfson, T. Fjelde, A. Kloch, C. Janz, A. Coquelin, I. Guillemot, F. Gaborit, F. Poingt, and M. RenaudAbstract—We experimentally investigate a pass-through schemefor all-optical noise suppression in an SOA-based interferometricstructure at 10 Gb/s. An input power dynamic range of 8 dB aswell as a noise suppression capability of 4.5 dB has been demon-strated. Furthermore, the transmission properties have been inves-tigated showing a small pre-amplified penalty of 0 3 dB aftertransmission over 31 km of standard single mode fiber.Index Terms—All-optical regeneration, amplifier noise, con-verters, high-speed optical techniques, semiconductor opticalamplifiers.I. INTRODUCTIONFUTURE high-speed optical networks will need all-opticalregeneration in order to suppress signal degradations in-duced by accumulation of noise, jitter and dispersion, whichotherwise would severely limit the network size. Several tech-niques for all-optical 2R and 3R regeneration have been inves-tigated, however the most promising results have been achievedwith SOA-based interferometric wavelength converters (IWC)[1], [2]. Still, in most of the schemes reported so far, the regen-eration has been performed with simultaneous wavelength con-version at the expense of an increased complexity, i.e., a CWlaser as well as an optical filter at the output of the converteris needed. In a novel approach [3], all-optical 2R regenerationcan be achieved in an SOA-based interferometric structure usingonly the data signal, thereby making the scheme very simple andcompetitive in parts of the optical network, where wavelengthconversion is not needed. Additionally, this regeneration schemehas been shown feasible at 40 Gb/s [4].Here, we experimentally investigate the noise suppression ca-pabilities as well as the transmission performance of an SOA-based interferometer used in the pass-through configuration at10 Gb/s. A high input power dynamic range, excellent noise sup-pression capabilities as well as good transmission properties il-lustrate the good performance of the pass-through scheme.Manuscript received November 9, 1999; revised March 27, 2000.This workwas supported in part by the European research program ACTS, REPEAT.D. Wolfson, T. Fjelde, and A. Kloch are with Research Center COM, Tech-nical University of Denmark, Lyngby, Denmark; (e-mail: dw@com.dtu.dk).C. Janz, A. Coquelin, I. Guillemot, F. Gaborit, F. Poingt, and M. Renaud arewith OPTO+, Groupement d’Intérêt Economique, Alcatel Corporate ResearchCenter, Marcoussis, France (e-mail: Christopher.Janz@ms.alcatel.fr).Publisher Item Identifier S 1041-1135(00)05826-2.Fig. 1. Principle of the pass-through regeneration scheme. (Left) schematicof an SOA-based interferometric structure biased at I and I on the lowerand upper interferometer arm, respectively. It is assumed that I is larger thanI . (Right) (a) and (b) shows the gain (G ;G ) and phase shift ( ;  ) inthe lower and upper interferometer arm, respectively, whereas (c) shows theresulting phase difference a signal would experience in the interferometer.II. PRINCIPLE OF THE PASS-THROUGH SCHEMEIn Fig. 1 the principle of the regeneration scheme is illus-trated. As shown in the figure an SOA-based Michelson inter-ferometer (MI) is biased at and in the lower and upperinterferometer arm, respectively. In the pass-through configu-ration an input signal is injected into the interferometer, whereit splits equally in the upper and lower interferometer arm andafter traversing the interferometer arms, the signal is reflected atthe end facet after which it propagates in the opposite direction.Finally, the signal recombines at the input, either constructivelyor destructively depending on the phase difference between theinterferometer arms. This phase difference is achieved by asym-metric biasing of the interferometer arms. In the following, it isassumed that is larger than . Since a higher bias currentis applied to the upper interferometer arm, this will result in ahigher gain and a lower saturation input power compared to thelower interferometer arm [see Fig. 1(a)]. Consequently, as seenin Fig. 1(b), the phase shift in the upper interferometer arm willstart to increase at a lower input power than in the lower inter-ferometer arm resulting in a total phase difference close to that1041–1135/00$10.00 © 2000 IEEEAuthorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on February 8, 2010 at 09:20 from IEEE Xplore.  Restrictions apply. 838 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 12, NO. 7, JULY 2000Fig. 2. Measured signal output power as a function of the input power. Thesignal wavelength is 1550 nm.Fig. 3. Experimental setup for 2R regeneration using the pass-through schemeat 10 Gb/s. The dashed line indicates the back-to-back setup.of an decision gate [Fig. 1(c)]. Therefore, the same will apply tothe transfer function of the input power. This is showed in Fig. 2giving the measured output power from the MI as a function ofthe input power [3]. As can be seen, the transfer function forthis regeneration scheme is close to that of a decision gate. Wenote that this is in contrast to the sinusoidal transfer function ob-tained from a Michelson interferometer performing wavelengthconversion. It should also be mentioned, though, that since thereis a different gain in the interferometer arms, the destructive in-terference at low input powers will not be perfect, why the re-shaping capabilities will be better for a logical “1” than for alogical “0.” In Fig. 1, an MI is shown; however, it is emphasizedthat the principle is the same for a Mach–Zehnder interferom-eter (MZI).III. EXPERIMENTAL SETUPThe experimental setup is shown in Fig. 3. The data signal at10 Gb/s with a wavelength of 1550 nm (NRZformat) is first transmitted through an inline EDFA. Here, theattenuator before the EDFA controls the input power by whichthe signal-to-ASE ratio at the input of the MI can be controlled.The signal is then coupled into the MI, where it splits equallyin the interferometer arms. After traversing the interferometerarms, the signal is reflected at the end facet. Finally, the signalrecombines at the input, either constructively or destructivelydepending on the phase difference between the interferometerarms as explained above. The optical circulator separates theoutput signal from the input signal before final detection. It isemphasised that no filter is applied at the output of the MI, i.e.,no additional ASE filtering is performed compared to back-to-back.Fig. 4. Receiver penalty as a function of the signal input power to theMichelson interferometer at 10 Gb/s. The wavelength is 1550 nm, and the inputpower to the EDFA is 0 dBm.Fig. 5. Receiver penalty as a function of the EDFA input power with andwithout regeneration in a Michelson interferometer. The bit rate is 10 Gb/s, andthe wavelength is 1550 nm.IV. RESULTS AND DISCUSSIONAn important benefit coming from the fact that the transferfunction of the pass-through scheme is close to that of an deci-sion gate, is a large input power dynamic range (IPDR). This isdemonstrated in Fig. 4, showing the receiver penalty as a func-tion of the input power to the MI. We note, that penalty free op-eration is achieved over a range of 4.5 dB, whereas the IPDR isdB [@ 2 dB of preamplified penalty]. The noise suppressioncapabilities of the MI are demonstrated in Fig. 5 showing the re-ceiver penalty with and without regeneration as a function of thein-line EDFA input power. Clearly, the input signal is regener-ated in the MI and very good noise suppression performance isachieved. As demonstrated, a 4.5-dB lower input power to theEDFA is allowed by applying the MI [@ 2 dB penalty].An important issue for practical use of all-optical regenera-tors is the transmission performance of regenerated signals. In-terferometric structures performing wavelength conversion havea 2R regeneration capability but in order to obtain a high con-version speed, out-of-phase operation is preferable, i.e., the con-verted signal is inverted compared to the input signal. However,the transmission distance of out-of-phase converted signals islimited due to the chirped output signal [5]. The pass-throughscheme has been proven to be feasible at high bit rates, i.e.,Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on February 8, 2010 at 09:20 from IEEE Xplore.  Restrictions apply. WOLFSON et al.: EXPERIMENTAL INVESTIGATION AT 10 Gb/s OF THE NOISE SUPPRESSION CAPABILITIES 839Fig. 6. BER as a function of the received power for back-to-back and aftera MZI in the pass-through scheme, both before and after 31-km standardsingle-mode fiber. The bit rate is 10 Gb/s and the wavelength is 1550 nm.40-Gb/s 2R regeneration has been reported [4]. Additionally, thetransmission properties are good due to in-phase operation (seeFig. 2). In order to verify the latter, Fig. 6 shows the BER as afunction of the received power for back-to-back and the regen-erated signal after transmission over 31 km of standard singlemode fiber (BER measurements before transmission are also in-cluded in the figure). We note that the input signal to the regen-erator in this case is taken directly from the transmitter. In thisexperiment a MZI was used, however, it is emphasised that thechirp characteristics of a MI and a MZI are similar when mod-ulated in the same fashion. Therefore, the results also apply forthe pass-through scheme when using a MI. As seen, traversingthe MZI and transmitting 31 km results in a preamplified penaltyof only 0.3 dB. We note that the reason for the improved sen-sitivities after transmission compared to the case without trans-mission is only due to the chirp added by the electro-opticalLiNbO modulator used in the transmitter, which results in apulse compression after transmission.V. CONCLUSIONA pass-through scheme for all-optical 2R regeneration in anSOA-based interferometric structure has been investigated ex-perimentally at 10 Gb/s. An input power dynamic range ofdB as well as a noise suppression capability of 4.5 dB has beendemonstrated in a Michelson interferometer. Furthermore, thetransmission properties have been investigated showing a smallpreamplified penalty of 0.3 dB after transmission over 31 kmof standard single-mode fiber. Therefore, taking the simplicityof the regeneration scheme as well as the good performance intoaccount, this approach is a feasible and competitive technique,where wavelength conversion is not needed.REFERENCES[1] B. Lavigne, D. Chiaroni, L. Hamon, C. Janz, and A. Jourdan, “Experi-mental analysis of SOA based 2R and 3R optical regeneration for futureWDM networks,” in Tech. Dig. OFC, , San Jose, CA, paper Th07, 1998.[2] 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, San Diego, CA, paperTuJ3, 1999.[3] D. Wolfson, P. B. Hansen, A. Kloch, and K. E. Stubkjaer, “All-optical2R regeneration based on interferometric structure incorporating semi-conductor optical amplifiers,” Electron. Lett., vol. 35, no. 1, pp. 59–60,1999.[4] D. Wolfson, P. Hansen, A. Kloch, T. Fjelde, C. Janz, A. Coquelin, I.Guillemot, F. Gaborit, F. Poingt, and M. Renaud, “All-optical 2R regen-eration at 40 Gbit/s in an SOA-based Mach-Zehnder interferometer,” inTech. Dig. OFC, San Diego, CA, paper PD36, 1999.[5] T. Durhuus, B. Mikkelsen, C. Joergensen, S. L. Danielsen, and K. E.Stubkjaer, “All-optical wavelength conversion by semiconductor opticalamplifiers,” J. Lightwave Technol., vol. 13, pp. 942–954, June 1996.Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on February 8, 2010 at 09:20 from IEEE Xplore.  Restrictions apply. 

Experimental investigation at 10 Gb/s of the noise suppression capabilities in a pass-through configuration in SOA-based interferometric structures

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Experimental investigation at 10 Gb/s of the noise suppression capabilities in a pass-through configuration in SOA-based interferometric structures

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