Chi, Nan

Holm-Nielsen, Pablo Villanueva

Jeppesen, Palle

Peucheret, Christophe

Zhang, Jianfeng

Online Research Database In Technology

DC-balanced line encoding for optical labelling scheme using orthogonal modulation

It is shown both theoretically and experimentally that 8B/10B encoding is an efficient technique to mitigate the inherent modulation crosstalk in optical labeling scheme using orthogonal modulation

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Downloaded from orbit.dtu.dk on: Dec 17, 2017DC-balanced line encoding for optical labeling scheme using orthogonal modulationZhang, Jianfeng; Holm-Nielsen, Pablo Villanueva; Chi, Nan; Peucheret, Christophe; Jeppesen, PallePublished in:Optical Fiber Communication Conference, 2004. OFC 2004Link to article, DOI:10.1109/OFC.2004.1359610Publication date:2004Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Zhang, J., Holm-Nielsen, P. V., Chi, N., Peucheret, C., & Jeppesen, P. (2004). DC-balanced line encoding foroptical labeling scheme using orthogonal modulation. In Optical Fiber Communication Conference, 2004. OFC2004 IEEE. DOI: 10.1109/OFC.2004.1359610WF2 DC-balanced line encoding for optical labeling scheme using orthogonal modulation Jianfeng Zhang, Pahln V. Holm-Nielsen, Nan Chi, Christnphe Peucheret, Palle Jeppesen Research Cemer COM. Technicof Liniverrify of D r n m h  2Mo Kgs. Lyngby. Dennmrk Phone c45 452.76605 F a :  +45 45936581 Emrril:k@corn.dtu.dk Abstract: It is shown both theoretically and experimentally that 8Bl10B encoding is an efficient technique to mitigate the inherent modulation crosstalk in optical labeling scheme using orthogonal modulation. 02003 Optical Society of America OCIS Codes: (060.4250) Networks, (060.2360) Fiber optics l i t k  and subsystems 1. Introduction An orthogonal modulation method, differential-phase-shift-keying/intensity modulation (DPSIUIM) or frequency- shift-keying/intensity modulation (FSWIM), has been proposed and demonstrated as an efficient labeling scheme to implement optical label switching [1]-[2]. However, proper detection of the DPSK or FSK label usually requires the IM extinction ratio to be reduced [3], which results in a poor payload sensitivity and degraded transmission performance. It has been shown that a DC-balanced encoding of the payload, Manchester encoding, can effectively improve the modulation performance of the optical labeling scheme using orthogonal modulation [4]. However. Manchester code has a poor coding efficiency since it doubles the bandwidth requirements on the payload transmitter/receiver. 8BllOB is another kind of DC-balanced code, which specifies no more than 4 sequential identical hits and a running disparity less than +/-I across data words of IO bits [ 5 ] .  Compared with the 100% extra bandwidth for the Manchester code, it only requires an extra 25%. thus having higher bandwidth efficiency. 8BllOB encoding is widely employed in Gigabit Ethernet (1.25 Gbls), Fiber channel (1.06 Gb/s) and other high-speed networks. In addition, the generation of 10 Gh/s 8B/10B code has been demonstrated through the proper configuration of an electrical multiplexer [6] .  In this paper, we investigate the possibility of applying 8BllOB encoding to the orthogonal optical labeling scheme. The performance of a BBIIOB-encoded payload in optical labeling is theoretically analyzed and compared with Manchester- and NRZ-encoded payloads. It is shown that 8BllOB encoding can also effectively improve the label receiving performance if the label bit-rate is limited below certain values. In the experiment, 8BllOB encoding is applied to an optical FSK labeled signal transmission link consisting of a I O  Ghls IM payload and a 156 Mb/s FSK label. A good modulation performance is achieved. 2. Theoretical Analysis In an orthogonal modulation scheme, the power spectral density (PSD) of the optical intensity of the demodulated label is given by [7] where m and n represent the intensity modulation depth of the optical payload and demodulated optical label respectively while Lp(@ and P p ( @  represent the PSD of the label and the payload information respectively. As indicated by equation (I), the IM payload induces two crosstalk components that stem from spectral overlap with the label, hence degrading the label receiving performance. S(O) .x [ ~ ( w )  +n*L,(w) + m ’ ~ , ( w )  +mzn2Lp(o) 8 P,(o)] (1) A signal to noise ratio (SNR) is defined to evaluate the modulation crosstalk according to, ‘y, jL,(ru)da 0 0 1 mz “ “ I  Ic(n)2P,(w)+L,(w)OP,(w) do SNR = where y is the effective bandwidth of the label electrical receiver. Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on January 22, 2010 at 09:30 from IEEE Xplore.  Restrictions apply. WF2 By inserting P(@ for the power spectra of the NRZ (unencoded), Manchester and 8BllOB code. we can calculate the label SNR value in the above cases. In the calculations, the label is assumed to have a typical NRZ spectrum, and the optical label demodulator is assumed to operate in an ideal condition, thus n has a value of I .O. . ....... ... . . .... ..... . ....... . OY , oc , I I . , . , I 2 1  44 e4 84 IM 124 0 2 4 6 8 10 12 14 Ram of payload bitrafsllabel b#rate Eninctim Ratio 01 Pa$& (W) (a) (b) Fig. 1 S N R  performance of label in the presence of NRZ/Manchester/8B/IOB payloads As Fig. I(a) shows, a SNR improvement of the received label can he achieved if Manchester or 8BllOB encoding is applied. Such a SNR improvement will be greatly enhanced at lower label rates. In 8BllOB case, the label hit-rate should be lower than 1/20 of the payload hit-rate to achieve an acceptable SNR value of 15.6 dFl (corresponding to Q factor of 6.0). Then, by setting the ratio of payload hit-rate to label bit-rate to be 64, we calculate the relation between label S N R  and payload extinction ratio (ER). As Fig. I(b) shows, the label SNR is strongly degraded by a high-ER of the NRZ-payload. Thus the ER has to he kept below 7 dJ3 to ensure acceptable label detection. On the other hand, through 8BllOB encoding, the label S N R  is improved more than 15 dB, hence overcoming the limitations on ER. As Manchester encoding can suppress more low frequency contents, it has an even better performance than XBllOB, as indicated in both figures. However, considering the coding efficiency, 8B/IOB is a more suitable scheme when a stringent bandwidth efficiency requirement is imposed on the labeled signal transmission link. 3. Experimental Setup and Results PRBS 210-I. 156 Mb/s PRBS2~-1,or8B110B 10 Gbls Fig. 2 Experimental setup of an optical FSK labeled signal transmission link In order to verify the performance of 8BllOB encoding when it is applied to the optical labeling scheme using orthogonal modulation, we have experimentally set up an optical link shown in Fig. 2. Two pseudo-random-bit-sequence (PRBS) data pattern generators were used to generate the payload and label information. A directly modulated DFB laser integrated with an electro-absorption (EA) modulator performed the optical FSK modulation. The FSK tone spacing was set to be 20 GHz, and the label bit-rate was set to be 156 Mb/s. The payload information is then added through an intensity modulator operating at IO Gb/s. At the receiver node, the labeled signal was split using a 3 dEi coupler. The signal in one arm was directly detected and input into the payload receiver. In the other arm, a Fahry-Perot (FP) filter with 20 GHz full-width half-maximum (FWHM) bandwidth was used to achieve the FSK demodulation. The demodulated label was then received by an electrical receiver with 600 MHz bandwidth. The 8B/10B code is directly generated through encoding a PRBS 29-1 by programming the data pattern generator, corresponding to a periodical data pattern of 1280 bits. As shown in Fig. 3(a), the low frequency components of the payload specmm below 100 MHz are greatly suppressed through 8B/IOB encoding. Thus with Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on January 22, 2010 at 09:30 from IEEE Xplore.  Restrictions apply. WF2 -30 - -32 - - E % E -34- ._ > (n .- - .  .- f -36- .- t ’  E -38- d -40 - +-&wlad: PRBS2’-1 --.-paylaad: 8blW code 1. 2. 3. 4. 5. 6. 7. 4. Conclusions It is shown that 8BllOB encoding of the payload can effectively improve the optical labeling performance if the label bitkate is limited below certain values. In the experiment, 8BllOB encoding is applied to an optical FSK labeled IO Gbls signal transmission link. A good modulation performance is achieved. References T.Koonen. Sulur, LT. Momy. I. lennen and H.de. W d l ,  “Optical labeling of packets in IP-Over-WDM Network?. 5.5.2. ECOC‘OZ. 7M7 _””_ M. Hickey and L. Kazovsky, ‘me STARNET cohemnl WDM computer communication network: experimental vaoscciver employing a novel modulation format ”, 1. Lightwave Teehnol.. 6,876484 (1994) N. Chi, 1. Zhang, P. V. Holm-Nielsen. L Xu, 1. T. Monmy. C. Peucherel. K Yvind, L. 1. Chistiansen and P. lepperen, “Experimental demonsmtion of cascaded vaosmission and all-optical label swapping of orthogonal IMlFSK laNed signal”, Elecuonics Letters, 39.676- 678 (2003) 1. Zhang, N. Chi. P. V. Halm-Nielsen. C. Peucheret and P. lepperen. “10 Gbitls Manchester encoded FSK-labelled optical signal transmission lit&”, Uecuonicr Leuen. 39. 1193-1 194 (2033) A. X. Widmer and P. A. Franasek, “A DC-balanced, panitioned-blqck.8BIlOB wnsmissian code” , IBM J. Res. Develop., 27, W 5 1  (1983) T. K Wwdward. AL. Lentine. I. D. Fields. G. Giaretta. and R. Limacher. “Fint Demonstration of Native Elhemet O o t i d  Transam System Prototpi a1 10 Gb/s Flied on Multiplexing of &gabit Ethemet Signals”, IEEE Photon. Techno. Lenn.. 12, liC&ilO2 (io00) 1. sang, N. Chi. P. V. Holm-Nielsen. C. Peucheret and P. Ieppesen. “‘Performance of Manchester-coded payload in an optical FSK labeling scheme”. IEEE Photonics Technology Letters, 15,1174-1176 (2003) Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on January 22, 2010 at 09:30 from IEEE Xplore.  Restrictions apply. 

DC-balanced line encoding for optical labeling scheme using orthogonal modulation

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DC-balanced line encoding for optical labeling scheme using orthogonal modulation

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