Jørgensen, Bo Foged

Nissov, Morten

Pedersen, Rune Johan Skullerud

M. Nissov

R.J.S. Pedersen

B.F. Jorgensen

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Transmission performance through cascaded 1-nm arrayed waveguide multiplexers at 10 Gb/s

The transmission properties of cascaded arrayed waveguide multiplexers are examined in a recirculating loop experiment. We show that a cascade of 40 multiplexers each with 3-dB bandwidth of ∼1 nm can be passed penalty-free at 10 Gb/s. Furthermore, we show that the allowable fluctuation of the center frequency for a 10 Gb/s signal is reduced to 24 GHz at bit-error rate (BER)=10-9 for a concatenation of 40 multiplexers

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Downloaded from orbit.dtu.dk on: Dec 17, 2017Transmission performance through cascaded 1-nm arrayed waveguide multiplexers at10 Gbit/sNissov, Morten; Pedersen, Rune Johan Skullerud; Jørgensen, Bo FogedPublished in:I E E E Photonics Technology LettersLink to article, DOI:10.1109/68.593392Publication date:1997Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Nissov, M., Pedersen, R. J. S., & Jørgensen, B. F. (1997). Transmission performance through cascaded 1-nmarrayed waveguide multiplexers at 10 Gbit/s. I E E E Photonics Technology Letters, 9(7), 1038-1040. DOI:10.1109/68.5933921038 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 9, NO. 7, JULY 1997Transmission Performance Through Cascaded 1-nmArrayed Waveguide Multiplexers at 10 Gb/sMorten Nissov, Student Member, IEEE, Rune J. S. Pedersen, and Bo Foged JørgensenAbstract— The transmission properties of cascaded arrayedwaveguide multiplexers are examined in a recirculating loopexperiment. We show that a cascade of 40 multiplexers each witha 3-dB bandwidth of1 nm can be passed penalty-free at 10 Gb/s.Furthermore, we show that the allowable fluctuation of the centerfrequency for a 10 Gb/s signal is reduced to 24 GHz at bit-errorrate (BER) = 10 9 for a concatenation of 40 multiplexersIndex Terms— Laser stability, optical fiber communication,optical planar waveguide components, optical propagation,wavelength-division multiplexing.I. INTRODUCTIONCASCADED optical add–drop multiplexers (OADM) andoptical cross-connects (OXC) are key components inoptical wavelength division multiplex networks. OADM’s withfiltering of the passing signals and OXC’s can be constructedby use of wavelength division multiplexers (WDM). Cas-cadability of multiplexers is therefore vital for the networkperformance.The actual transfer function of multiplexers is important[1], since the available end-to-end bandwidth between con-nected nodes in optical networks with cascades of OXC’s andOADM’s is given by the product of the transfer functions. Acascade of 16 multiplexers in a ring network with a resulting3-dB bandwidth of 50 GHz was investigated at 10 Gb/s withemphasis on the impact of modulator chirp [2]. In [3], acascade of up to 15 narrow-band arrayed waveguide (AWG)multiplexers [4] each with a 3-dB bandwidth of 38 GHz wasinvestigated in a recirculating loop experiment at 10 Gb/s. Apenalty of 2–3 dB was measured after 10 multiplexers.In this letter, the cascadability of AWG multiplexers eachwith a 3-dB bandwidth of 1 nm and sharp roll-off charac-teristics is analyzed experimentally in a recirculating loop at10 Gb/s. We show that up to 40 multiplexers can be passedpenalty-free. Furthermore, the allowable fluctuation of thecenter frequency (ACF) is examined when up to 60 of thesemultiplexers are cascaded. The ACF is defined as the range ofcarrier frequencies for which the 10 Gb/s signal can achievea bit-error rate (BER) 10 for a fixed level of receivedManuscript received December 18, 1996; revised April 2, 1997. The workwas supported by CEC within the ACTS METON project and by the DanishTechnical Research Council.The authors are with the Department of Electromagnetic Systems, Centerfor Broadband Telecommunications, Technical University of Denmark, DK-2800 Lyngby, Denmark.Publisher Item Identifier S 1041-1135(97)05027-1.Fig. 1. Schematic diagram of recirculating loop setup for measuring cascad-ing properties of AWG-multiplexers.Fig. 2. Measured power transfer function for the two AWG-multiplexers(AT&T x1450D).optical power. We show that the ACF is 24 GHz when40 multiplexers are cascaded and that the ACF is reducedto almost zero for a cascade of 60 multiplexers.II. EXPERIMENTA recirculating loop experiment at 10 Gb/s is used toinvestigate the cascadability of arrayed waveguide (AWG)multiplexers. Fig. 1 shows the experimental setup.A 1.556- m distributed feedback (DFB) laser is used assignal source and the output light is modulated at 10 Gb/s byan external modulator using a pseudorandom binary sequencewith a word length of 2 1. The loop consists of 50 kmof dispersion shifted fiber (DSF) followed by two AWG-multiplexers. The transfer functions are shown in Fig. 2. The1041–1135/97$10.00  1997 IEEEAuthorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on April 13,2010 at 10:35:16 UTC from IEEE Xplore.  Restrictions apply. NISSOV et al.: TRANSMISSION PERFORMANCE THROUGH CASCADED WAVEGUIDE MULTIPLEXERS 1039Fig. 3. Measured BER versus received power after transmission through: 4,20, 40, and 60 AWG-multiplexers.(a)(b)(c)Fig. 4. Eye diagrams after transmission through (a) 20, (b) 40, and (c) 60multiplexers. 20 ps/div.Fig. 5. Allowable fluctuation of center frequency after transmission through2, 20, 40, and 60 AWG multiplexers.insertion loss of the two multiplexers are 6.2 and 7.4 dB,respectively, and each has a 3-dB bandwidth of 0.95 nm.The power into the transmission fiber is 1.5 dBm. The twoerbium-doped fiber amplifiers (EDFA) compensate losses ofthe transmission fiber and the multiplexers.The signal is recirculated in the loop until the desired num-ber of multiplexers have been passed and the BER is measuredusing an optically preamplified receiver with an optical 3-dBbandwidth of 40 GHz and a back-to-back sensitivity of 37dBm at BER 10 .The ACF is measured by replacing the transmitting DFBlaser with a tunable external cavity laser and increasing the3-dB optical bandwidth of the receiver to 2.3 nm whichreduces the back-to-back sensitivity to 35 dBm at BER10 .III. RESULTSBER curves measured for a cascade of 4, 20, 40, and60 multiplexers are shown in Fig. 3. No significant penaltyis seen for cascades of up to 40 multiplexers whereas acascade of 60 multiplexers results in a penalty of 4 dB.Eye diagrams for 20, 40, and 60 multiplexers are shown inFig. 4. For 20 multiplexers (corresponding to 10 loop round-trips) the eye is symmetrical with no pulse distortion and theoperation is penalty free. For 40 multiplexers pulse distortionwith a flattening of the bottom of the eye can be seen,but the operation is still penalty free. After 60 multiplexersthe pulse distortion is more severe and results in a 4 dBpenalty.To further investigate the cascade properties of these mul-tiplexers the BER versus wavelength is measured for 2, 20,40, and 60 multiplexers for a constant receiver input powerof 30 dBm. These measurements are shown in Fig. 5. Fora cascade of two multiplexers the ACF is 190 GHz. Afteronly 20 multiplexers the ACF has decreased to 80 GHz andfor a cascade of 40 multiplexers the ACF is 24 GHz. ForAuthorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on April 13,2010 at 10:35:16 UTC from IEEE Xplore.  Restrictions apply. 1040 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 9, NO. 7, JULY 1997(a)(b)(c)Fig. 6. Eye diagram at (a) 1555.77 nm, (b) 1555.88 nm, and (c) 1556.16 nmafter 40 AWG multiplexers. 20 ps/div.a cascade of 60 multiplexers the ACF is reduced to almostzero.Eye diagrams after passing 40 multiplexers are shown inFig. 6 for a signal wavelength of 1555.77, 1555.88, and1556.16 nm, respectively. These eye diagrams clearly illustratethe pulse distortions caused by the cascaded multiplexers [5]for the signal being detuned from the optimum wavelength of1555.86 nm.IV. CONCLUSIONIt is shown experimentally that at least 40 arrayed wave-guide multiplexers with a 3-dB bandwidth of 1 nm can becascaded penalty-free at 10 Gb/s provided that the wavelengthof the signal laser is well aligned in the passband of themultiplexers. The requirement for alignment is quantified bymeasuring the allowable fluctuation of the center frequencyafter transmission through these 40 arrayed waveguide multi-plexers and it is found to be 24 GHz.ACKNOWLEDGMENTLycom A/S is acknowledged for supplying transmissionfiber and erbium-doped fiber.REFERENCES[1] M. J. O’Mahony, “Physical limitations in optical cross-connectnetworks,” presented at the 21st Eur. Conf. Optical CommunicationECOC’95, Brussels, Belgium, Sept. 17–21, 1995, paper Tu.B.T.3[2] F. Shehadeh, T. Suzaki, J.-C. Chiao, K. P. Ho, S. K. Liaw, and R. S.Vodhanel, “Impact of external modulator chirp for 10-Gb/s transmissionin an eight-wavelength eight-node WDM ring network,” presented atOptical Fiber Communication OFC’97, Dallas, TX, Feb. 16–21, 1997,paper TuE4.[3] C. Caspar, H.-M. Foisel, R. Freund, U. Kru¨ger, and B. Strebel, “Ca-cadability of arrayed-waveguide grating (de)multiplexers in transparentoptical networks,” presented at Optical Fiber Communication OFC’97,Dallas, TX, Feb. 16–21, 1997, paper TuE2.[4] C. Dragone, “An NN optical multiplexer using a planar arrangementof two star couplers,” IEEE Photon. Technol. Lett., vol. 3, no. 9, pp.812–815, Sept. 1991.[5] N. N. Khrais, F. Shehadeh, J.-C. Chiao, R. S. Vodhanel, and R. E.Wagner, “Multiplexer eye-closure penalties for 10 Gb/s signals in WDMnetworks,” presented at Optical Fiber Communication OFC’96, SanJose, CA, Feb. 25–Mar. 1, 1996, paper PD33.Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on April 13,2010 at 10:35:16 UTC from IEEE Xplore.  Restrictions apply. 

Transmission performance through cascaded 1-nm arrayed waveguide multiplexers at 10 Gbit/s

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Transmission performance through cascaded 1-nm arrayed waveguide multiplexers at 10 Gbit/s

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