JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 20, NO. 12, DECEMBER 2002 2239

Tunable Chromatic Dispersion Compensationin 40-Gb/s Systems Using Nonlinearly Chirped

Fiber Bragg GratingsZ. Pan, Y. W. Song, C. Yu, Y. Wang, Q. Yu, J. Popelek, H. Li, Y. Li, and

Alan Eli Willner, Senior Member, IEEE, Fellow, OSA

AbstractChromatic dispersion management and tunable com-pensation are essential features of 40-Gb/s wavelength-division-multiplexed (WDM) systems. In this paper, we demonstrate bothsingle and multi channel 40-Gb/s tunable dispersion compensationusing nonlinearly chirped FBGs (NC-FBGs). For single channelcompensation, we show that the NC-FBG can be tuned over a mod-erate range ( 400 ps/nm) with tolerable third-order dispersion( 200 ps/nm2) within the channels data bandwidth (intrachannelthird-order dispersion). For multichannel systems, we demonstrate4 40-Gb/s tunable dispersion compensation using sampledNC-FBGs in two configurations. First, we show that a single, sam-pled NC-FBG with fairly low intrachannel third-order dispersioninduces negligible penalty on all four channels. This solution has alimited dispersion tuning range because of the deleterious intra-channel third-order dispersion. We show a moderate tuning rangefrom 300 ps/nm to 700 ps/nm. Second, we demonstrate thattwo inverse, concatenated, sampled NC-FBGs can cancel the highdeleterious intrachannel third-order dispersion, thus extendingthe dispersion tuning range. This solution provides both positiveand negative dispersion values by stretching the two NC-FBGsseparately. A tuning range of 300 ps/nm to+300 ps/nm with zerointrachannel third-order dispersion is shown.

Index TermsChromatic dispersion, fiber Bragg gratings(FBG), fiber-optic components, optical fiber communication.

I. INTRODUCTION

THE ACCURACY required for dispersion compensa-tion techniques increases dramatically as the data rateincreases. While the amount of residual dispersion that is con-sidered tolerable (induces 1 dB penalty) at 10 Gb/s is large [onthe order of 1000 ps/nm (nonreturn-to zero (NRZ) format)], in40-Gb/s systems this margin shrinks to only 60 ps/nm for theNRZ format [1]. A compensator must match the fiber dispersionto within a few percent of the required dispersion value. How-ever, any changes in environmental effects and/or in the signalpower levels may cause significant variations in the dispersionand system performance. For example, temperature changescan lead to variations in dispersion that may be significant

Manuscript received June 7, 2002; revised August 27, 2002.Z. Pan, Y. W. Song, C. Yu, Y. Wang, and A. E. Willner are with the Depart-

ment of Electrical EngineeringSystems, University of Southern California,Los Angeles, CA 90089-2565 USA (e-mail: zpan@usc.edu).

Q. Yu was with the Department of Electrical EngineeringSystems, Univer-sity of Southern California, Los Angeles, CA 90089-2565 USA. He is now withScientera Networks, San Jose, CA 95129 USA.

J. Popelek, H. Li, and Y. Li are with the Phaethon Communications, Fremont,CA 94538 USA.

Digital Object Identifier 10.1109/JLT.2002.806773

enough to impact the system. For a temperature change ofC, a distance of km, and a dispersion slope

of ps/nm /km [using single-mode fiber (SMF)],the thermally induced variation in dispersion is ps/nm[or the dispersion of 2 km of SMF, or 7.5 km of nonzero-dis-persion shifted fiber (NZDSF)] [2]. This amount is relativelyinsignificant in 10-Gb/s systems, but becomes significant in40-Gb/s systems. Moreover, several other vexing issues mayalso necessitate tunable dispersion compensation: i) inventorymanagement, ii) reconfigurable networking for which the pathchanges, iii) repairs and maintenance of the fiber plant, andiv) variable dispersion introduced by in-line components suchas optical filters [1].

It is evident that accurate compensation at 40 Gb/s wouldbenefit from tunable compensation modules. Tunable dispersioncompensation for 40-Gb/s signals has been previously reported.In one demonstration, a single fiber Bragg grating (FBG) wasthermally tuned to achieve a change of 900 ps/nm in induceddispersion [3]. In a second report, two nonlinearly chirped FBGs(NC-FBGs) were used in tandem to provide wide tunability andmitigation of any third-order dispersion effects on the signal dueto a dispersion-value curvature over the bandwidth of the signalitself [4]. However, there are no reports of using an FBG fortunable multichannel 40-Gb/s dispersion compensation.

Another technique demonstrated at 10 Gb/s employedstretching of a NC-FBG to successfully compensate for mul-tiple-channel dispersion [5]. When a nonlinearly chirped gratingis uniformly stretched by a single mechanical element, the timedelay curve is shifted toward longer wavelengths and the slopeof the ps-versus-nm curve (i.e., the dispersion compensation)at a specific channel wavelength changes continuously [6]. Ithas been shown that NC-FBGs offer great advantages as tunabledispersioncompensators.However, this single-grating techniquehas only been previously shown to compensate for 10-Gb/ssignals.

In this paper, we demonstrate both single channel and multichannel 40-Gb/s dispersion compensation using NC-FBGs. Forsingle channel compensation, we show that the NC-FBG canbe tuned over a moderate range ( 400 ps/nm) with tolerablethird-order dispersion ( 200 ps/nm ) within the channelsdata bandwidth (intrachannel third-order dispersion). Thepower penalty is 1 dB for tunable compensation of 120 kmLEAF fiber and an extra dispersion variation of 60 ps/nm. Formultichannel systems, we demonstrate 4 40-Gb/s tunabledispersion compensation using sampled NC-FBGs in two

0733-8724/02$17.00 2002 IEEE

2240 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 20, NO. 12, DECEMBER 2002

configurations. First, we show that a single sampled NC-FBGwith fairly low intrachannel third-order dispersion inducesa negligible penalty on all four channels. This solution hasa limited dispersion tuning range because of the deleteriousintrachannel third-order dispersion. We show a moderatetuning range from 300 ps/nm to 700 ps/nm. Second, wedemonstrate that two inverse, concatenated, sampled NC-FBGscan cancel the deleterious intrachannel third-order dispersion,thus extending the dispersion tuning range. With this solution,both positive and negative dispersion values may be obtainedby stretching the two NC-FBGs separately. The dispersiontuning range is from 300 ps/nm to 300 ps/nm with zerointrachannel third-order dispersion. In both the single FBG andcascaded FBG configurations, 3 dB penalty is achieved for a4 40-Gb/s wavelength-division-multiplexed (WDM) system,even though the eye is completely closed prior to compensation.

II. TUNABLE SINGLE-CHANNEL 40-Gb/s DISPERSIONCOMPENSATION

A. Nonlinearly Chirped Fiber Bragg GratingsIn order to realize dynamic dispersion compensation, the

amount of dispersion of the compensating grating should changeas the grating is stretched. Fig. 1(a) shows a typical group delaycurve vs. wavelength for a linearly chirped FBG. The slope ofthe curve corresponds to the dispersion at each wavelength.For a linearly chirped grating, the relative time delay decreaseslinearly as the wavelength increases, so the grating-induceddispersion is constant over the grating bandwidth. When thelinearly chirped grating is stretched, the time delay curve shiftsto longer wavelengths, but the slope remains unchanged. At anygiven wavelength, the slope of the time delay curve is constant,meaning that the grating-induced dispersion will not changewhether the grating is stretched or not.

Fig. 1(b) shows the time delay curve of a nonlinearly chirpedFBG. The time delay decreases nonlinearly versus the wave-length. Hence, the grating-induced dispersion (the slope of thetime delay curve) is different for different wavelengths withinthe grating bandwidth. As the grating is stretched, the accu-mulated delay curve shifts to longer wavelengths while main-taining its shape. At each wavelength, the slope of the timedelay curve (i.e., dispersion) increases from a shallow one toa much steeper one. Therefore, the amount of dispersion in-creases as the grating is stretched to longer wavelengths [6].However, within the signals bandwidth, the dispersion is notconstant, as shown in Fig. 1(c). This intrachannel third-orderdispersion of a NC-FBG can be appreciably large, especiallywhen the NC-FBG has a relatively large tuning range.

It is unclear if the intrachannel of NC-FBGs is a se-rious problem at 40-Gb/s. In this paper, we show that the third-order dispersion of the FBG induces a negligible penalty whilemaintaining a moderate dispersion tuning range. In this section,we demonstrate that, when the dispersion is varied by up to60 ps/nm, the power penalty is 1 dB after compensation, eventhough an error-free signal could not be obtained prior to com-pensation [7]. We emphasize that, although our tuning range issmaller than previously reported results [3], we can expand thetuning range up to 400 ps/nm within the negligible third-orderdispersion regime ( 200 ps/nm ) for a NC-FBG with a 2 nm

(a)

(b)

(c)Fig. 1. Tunable dispersion compensation using chirped FBGs. (a) Linearlychirped FBG, (b) nonlinearly chirped FBG, and (c) nonzero intrachannelthird-order dispersion.

bandwidth. Furthermore, our technique is simpler to implementand provides a range of dispersion values that enables robustsystem operation under the majority of conditions.B. 40-Gb/s Experimental Setup

Fig. 2 shows the experimental setup of our 40-Gb/s trans-mission system using an NC-FBG as the tunable dispersioncompensator. Fig. 2(a) is the 40-Gb/s transmitter. A 10-Gb/sreturn-to-zero (RZ) signal generated by two external modula-tors at 1553.5 nm is compressed down to 10 ps using a phasemodulator followed by fiber-induced dispersion of 80 ps/nm.A two-stage optical multiplexer is used to generate a 40-Gb/sdata stream. Note that a polarization interleaver is used in thesecond stage to reduce coherent crosstalk. At the receiver,shown in Fig. 2(b), 10% of the incident light is tapped off andfed to the clock recovery unit. An injection-locked electroopticoscillator is used to recover the 10 GHz clock from the 40-Gb/sdata stream [8]. The bit error rate measurement is performedat 10-Gb/s after demultiplexing the 40-Gb/s data with an elec-troabsorption modulator electrically driven by the recovered10 GHz clock. Fig. 2(c) shows the entire transmission setup.

PAN et al.: TUNABLE CHROMATIC DISPERSION COMPENSATION IN 40-Gb/s SYSTEMS USING NC-FBGs 2241

(a)

(b)

(c)Fig. 2. 40-Gb/s experimental setup for evaluation of the tunable dispersion compensator. (a) Transmitter (Tx), (b) receiver (Rx), EA: Electroabsorption modulator,and (c) the entire transmission setup with tunable dispersion compensation.

After 120 km LEAF fiber with an extra 1 to 5 km of SMFto vary the accumulated dispersion, a mechanically stretchedNC-FBG is used for tunable dispersion compensation. TheFBG has a tunable dispersion range of 250 ps/nm, intra-channel third-order dispersion of 150 ps/nm over the entirebandwidth, and peak-to-peak ripple of 20 ps.

C. Simulation and Experimental ResultsIn 40-Gb/s optical transmission systems, the NC-FBGs

used for dispersion compensation must be carefully designed.They must have both a wide tuning range and negligiblethird-order-dispersion. Fig. 3 shows the simulated effects ofdispersion and intrachannel third-order dispersion at 40-Gb/s.PTDS simulation tool is used to calculate the penalty of a40-Gb/s, chirp-free NRZ/RZ signal, which is launched into afiber link with both nonzero second-order chromatic dispersion(ps/nm) and intraband third-order dispersion ps/nm . Therise-fall time of the transmitter is 0.25 bit period, and theelectrical bandwidth of the receiver is 30-GHz. The penaltyinduced by a given second-order chromatic dispersion or intra-band third-order dispersion is calculated from the simulated biterror rate (BER) as a function of the received optical power;we assume that amplified spontaneous emission (ASE) is thedominant noise source and the intraband third-order dispersionequals to zero when considering the second-order chromaticdispersion, and vice versa. In order to have a negligibleslope-induced penalty for both NRZ and RZ formats, the intra-channel third-order dispersion should be 200 ps/nm . In themeantime, the dispersion tuning range should be 120 ps/nm

(a)

(b)Fig. 3. (a) Simulated power penalty as a function of dispersion at 40-Gb/s.(b) Simulated power penalty of the 40-Gb/s signals as a function of intrachannelthird-order dispersion.

2242 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 20, NO. 12, DECEMBER 2002

(a)

(b)Fig. 4. The FBG used as the tunable dispersion compensator. (a) Reflectionspectrum and (b) time delay curve.

to assure the penalty is 1 dB. There is a tradeoff between thetuning range and the of the NC-FBG. For a 2-nm band-width FBG, the tuning range can go up to 400 ps/nm withinthe negligible third-order-dispersion regime. It is believed that

400 ps/nm tuning range will enable robust system operationunder the majority of conditions.

Fig. 4 shows the reflected power spectrum [see Fig. 4(a)]and time delay curve [Fig. 4(b)] of the FBG. By stretching thegrating, the dispersion varies nonlinearly and smoothly from

250 to 500 ps/nm over the 2-nm bandwidth. The intra-channel third-order dispersion is 150 ps/nm over the wholetuning range. Therefore, the penalty induced by intrachannelthird-order dispersion is negligible and we observe no penaltycaused by this slope value in our experiment. By increasingthe bandwidth of the grating, the dispersion tuning range of theNC-FBG can be increased while the intrachannel third-order dis-persion remains less than 200 ps/nm . Note that the peak-to-peakgroup delay ripple and polarization mode dispersion (PMD)of this single channel NC-FBG is about 20 ps and 10 ps,respectively. And the loss profile of the NC-FBG is not uniformwithin the passband. Using apodization technique can reducedthe ripple and improve the profile uniformity dramatically.

Fig. 5 shows the tunable dispersion compensation resultsfor transmission over 120 km LEAF plus 1 to 5 km of SMFfiber. After demultiplexing the 40-Gb/s signal to four 10-Gb/s

(a)

(b)

Fig. 5. Tunable dispersion compensation for different dispersion variations.(a) Compensation result for D = 35 ps/nm and (b) compensation result forD = 60 ps/nm.

channels, the worst 10-Gb/s channel is measured. Comparedto the back-to-back sensitivity of 32.8 dBm for this channel,compensation of the total fiber link (120 km LEAF 5 kmSMF) has 1 dB power penalty. Reducing the link dispersionby 35 ps/nm (by removing 2 km SMF) without tuningthe FBG causes 1.8 dB penalty. Optimally stretching thegrating reduces the penalty to 1 dB [see Fig. 5(a)]. If thelink dispersion is changed by 60 ps/nm (by removing 4 kmSMF) without tuning the grating, the system cannot be errorfree. However, stretching the grating again corrects the systemback to 1 dB penalty [see Fig. 5(b)]. Note that the nonidealcharacteristics of the NC-FBG, such as nonuniform lossprofile, group-delay ripple and PMD, may distort the signal(asymmetric eyediagram) thus cause nonzero residual penalty.

PAN et al.: TUNABLE CHROMATIC DISPERSION COMPENSATION IN 40-Gb/s SYSTEMS USING NC-FBGs 2243

(a)

(b)Fig. 6. (a) Setup for multi- dispersion compensation using a single NC-FBG.(b) Tunability of multi- dispersion compensation achieved by mechanicallystretching a single FBG with negligible intrachannel third-order dispersion.

III. TUNABLE DISPERSION COMPENSATION FOR 4 40-GB/SUSING A SINGLE SAMPLED NC-FBG

To achieve multiple channel operation, one solution is tosample (or modulate) the phase profile of the single channelgrating design. As known from Fourier analysis, sampling afunction in real space (here, along the length of the grating)leads to repeated spectra in Fourier space (here, in the wave-length domain) [9]. One report that was demonstrated at10-Gb/s employed stretching of a sampled NC-FBG thatenables simultaneous multiple channel dispersion compensa-tion [5]. In this section, we demonstrate 4 40-Gb/s tunabledispersion compensation using a single sampled NC-FBG. Weshow that a sampled NC-FBG with fairly low intrachannelthird-order dispersion induces a negligible penalty on all fourchannels. This solution provides a moderate tuning range from

300 ps/nm to 700 ps/nm. Less than 3 dB penalty is achievedfor all four channels whereas the system is completely downwithout compensation.

A. Experimental Setup of Tunable 4 40-Gb/s DispersionCompensation

The experimental setup for tunable dispersion compensationusing a single, sampled NC-FBG is shown in Fig. 6(a). We usedthe same transmitter and receiver setup as for single channelexperiment, shown in Fig. 1(a) and (b). Fig. 6(b) shows lowintrachannel third-order dispersion across all WDM channelsand how tunability for multichannel dispersion compensationmay be achieved by mechanically stretching the NC-FBG.

B. Tunable 4 40-Gb/s Dispersion Compensation ResultsFig. 7 shows the reflected power spectrum [Fig. 7(a)] and

time delay curve [Fig. 7(b)] of the sampled NC-FBG. When thegrating is stretched, the dispersion varies nonlinearly from 800to 200 ps/nm over the entire 2.5 nm channel bandwidth for allfour channels. Considering the 40-Gb/s RZ data bandwidth, theactual usable bandwidth of the NC-FBG for multiple channelsis 1.5 nm, corresponding to a tuning range from 300 ps/nmto 700 ps/nm. Fig. 7(b) also illustrates that the dispersion isnot uniform within each channels bandwidth. The intrachannel

(a)

(b)Fig. 7. The sampled NC-FBG used for tunable dispersion compensation.(a) Reflection spectrum, and (b) time delay curve.

third-order dispersion is 200 ps/nm over the whole tuningrange, which is below the intrachannel third-order dispersionlimit. Therefore, the penalty induced by intrachannel third-orderdispersion is negligible.

System performance is measured in a 4 40-Gb/s WDMsystem. After the dispersion compensator, the 40-Gb/s signal isdemultiplexed to 10-Gb/s to take BER measurements for eachof the four channels at the receiver. Fig. 8 shows the tunablecompensation results at 320 and 640 ps/nm dispersionvalues using a single NC-FBG for compensation. Less than3 dB penalty is obtained for all channels, even though the eyeis completely closed without compensation. Note here that theresidual power penalty may be due to the group delay ripple andPMD of the NC-FBG. In our systems, the sampled NC-FBGhas 30 ps of group delay ripple and 10 ps of PMD. Sincethe group delay ripple is more severe in the sampled NC-FBGthan in the single channel NC-FBG, higher residual penaltyremains in the 4 40-Gb/s systems. Another important issue forsampled NC-FBG is the channel spacing. There is a trade-offbetween the tuning range and channel spacing in order tohave tolerant intrachannel third-order dispersion. For example,100 GHz channel spacing will limit the dispersion tuning rangeto 150 ps/nm. For the total channel number, it is possible tocompensate up to 16 channels simultaneously by using onesampled NC-FBG.

2244 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 20, NO. 12, DECEMBER 2002

Fig. 8. Tunable dispersion compensation results for all four channels at different dispersion values (320 ps/nm and 640 ps/nm).

IV. TUNABLE SLOPE-FREE DISPERSION COMPENSATION FOR4 40-Gb/s USING TWO INVERSE SAMPLED NC-FBGs

One report has shown that, for a single channel, the higherorder dispersion of an NC-FBG may be canceled by using twosuch gratings in cascade with inverse curvatures [4]. Moreover,two such gratings enable a compensator that can be tuned toboth negative and positive dispersion values. In this section, wedemonstrate that two inverse concatenated sampled NC-FBGscan cancel the deleterious higher order dispersion for tunable,multichannel, 40-Gb/s dispersion compensation. The disper-sion tuning range is from 300 ps/nm to 300 ps/nm with zerointrachannel third-order dispersion. Again, 3 dB penalty isachieved for a 4 40-Gb/s WDM system even though the eye iscompletely closed without compensation for both positive andnegative accumulated dispersion.

A. Concept and Experimental SetupFig. 9(a) shows the configuration of two cascaded NC-FBGs

for dispersion compensation. The signal is launched into afour-port circulator and is reflected off two identical FBGs inturn. The two FBGs are inversely cascaded so that the higherorder dispersion of the NC-FBGs is canceled. Fig. 9(b) isa conceptual diagram showing the tuning of two cascaded,sampled NC-FBGs for multichannel dispersion compensation.This configuration can compensate dispersion for many WDMchannels simultaneously and can provide both negative andpositive dispersion values via separately stretching or com-pressing the two NC-FBGs. Furthermore, the intrachannelthird-order dispersion induced by the first NC-FBG is canceledby the second NC-FBG for all WDM channels.

B. Tunable 4 40-Gb/s Dispersion Compensation ResultsFig. 10(a) and (b) show the measured time delay curves

for the two NC-FBGs. When the gratings are stretched, thedispersion varies nonlinearly from 800 to 200 ps/nm or

800 to 200 ps/nm over the entire 2.5 nm channel bandwidthfor the first and second NC-FBGs, respectively. Fig. 10(a) and(b) also illustrate that the dispersion is not uniform within eachchannels bandwidth. When two cascaded NC-FBGs are usedas a tunable dispersion compensator, the usable bandwidth is

1 nm. Fig. 10(c) shows the measured resultant time delaywhen the two cascaded NC-FBGs are tuned to achieve either

(a)

(b)Fig. 9. Dispersion compensator using two cascaded sampled FBGs. (a) Con-figuration and (b) illustration of tunability and zero intrachannel third-orderdispersion.

of the two extreme dispersion values from 300 ps/nm to300 ps/nm, as well as when tuned to zero dispersion. It is

clear that the intrachannel third-order dispersion is canceledwithin the signals bandwidth after cascading two inverseNC-FBGs. Moreover, the overall tuning range is increased andranges from both positive to negative dispersion values.

Again, the system performance is measured in a 4 40-Gb/sOTDM-WDM system. Fig. 11 shows the tunable compen-sation results for both positive ( 300 ps/nm) and negative( 200 ps/nm) dispersion using two cascaded NC-FBGs. Ineach case, 3 dB penalty is obtained for all channels, while thesystem cannot be error free without compensation. Note herethat the residual power penalty may be due to the group delayripple and PMD of the NC-FBGs, an effect that can be moresignificant here than in a single grating compensator. The twosampled NC-FBGs we used have 30 ps of group delay rippleand 10 ps of PMD. It is clear that higher residual penaltyremains compared to the single grating solution. However,since the intrachannel third-order dispersion is canceled bycascading the two FBGs, there is no limitation on the tuningrange even for 100 GHz channel spacing. In order to cascaded

PAN et al.: TUNABLE CHROMATIC DISPERSION COMPENSATION IN 40-Gb/s SYSTEMS USING NC-FBGs 2245

(a)

(b)

(c)Fig. 10. Group velocity dispersion for (a) FBG1, (b) FBG2, and (c) twocascaded FBGs for three tuning cases (negative, zero, and positive dispersion).

Fig. 11. Tunable dispersion compensation results for all four channels atpositive (+300 ps/nm) and negative (200 ps/nm) accumulated dispersion.

more NC-FBGs, the group delay ripple and PMD have to bedecreased to 10 ps and 1 ps, respectively.

V. SUMMARYChromatic dispersion is a critical issue which can severely

influence system performance at 40 Gb/s. Tunability is con-sidered a key enabler for 40-Gb/s systems, and such a tunablecompensator should accommodate multiple WDM channels.We demonstrated tunable dispersion compensation for singleand multichannel 40-Gb/s systems using NC-FBGs in differentschemes. The advantages of our method include: 1) wide tuningrange for 40 Gb/s, 2) negligible intrachannel third-order disper-sion, and 3) both positive and negative dispersion values. Webelieve that this technique may offer one of the most cost-effec-tive dispersion compensation solutions for 40-Gb/s systems.

REFERENCES[1] A. E. Willner and B. Hoanca, Fixed and tunable management of fiber

chromatic dispersion, in Optical Fiber Telecommunications IV, I. P.Kaminow and T. Li, Eds. New York: Academic, Mar. 2002.

[2] T. Kato, Y. Koyano, and M. Nishimura, Temperature dependence ofchromatic dispersion in various types of optical fibers, in Proc. OpticalFiber Commun., OFC00, 2000, Paper TuG7, pp. 104106.

[3] T. N. Nielsen, B. J. Eggleton, J. A. Rogers, P. S. Westbrook, P. B. Hansen,and T. A. Strasser, Dynamic Post dispersion optimization at 40 Gb/susing a tunable fiber Bragg brating, IEEE Photon. Technol. Lett., vol.12, pp. 173175, Feb. 2000.

[4] J. A. J. Fells, S. E. Kanellopoulos, P. J. Bennett, V. Baker, H. F. M.Priddle, W. S. Lee, A. J. Collar, C. B. Rogers, D. P. Goodchild, R. Feced,B. J. Pugh, S. J. Clements, and A. Hadjifotiou, Twin fiber grating tun-able dispersion compensator, IEEE Photon. Technol. Lett., vol. 13, pp.984986, Sept. 2001.

[5] J.-X. Cai, K. Feng, A. Willner, V. Grubsky, D. Starodubov, and J. Fein-berg, Sampled nonlinearly-chirped FBG for tunable dispersion com-pensation of many WDM channels simultaneously, in Proc. OpticalFiber Commun., OFC99, 1999, Paper FA7.

[6] K.-M. Feng, J.-X. Cai, V. Grubsky, D. S. Starodubov, M. I. Hayee, S.Lee, X. Jiang, A. E. Willner, and J. Feinberg, Dynamic dispersion com-pensation in a 10-Gb/s optical system using novel voltage tuned nonlin-early-chirped fiber Bragg grating, IEEE Photon. Technol. Lett., vol. 11,pp. 373375, 1999.

[7] Z. Pan, Q. Yu, Y. W. Song, and A. E. Willner, 40-Gb/s RZ 120-kmtransmission using a nonlinearly-chirped fiber Bragg grating (NL-FBG)for tunable dispersion compensation, in Proc. Optical Fiber Commun.,OFC02, 2002, Paper ThGG50, pp. 682683.

[8] B. Mikkelsen, G. Raybon, R.-J. Essiambre, A. J. Stentz, T. N. Nielsen,D. W. Peckham, L. Hsu, L. Gruner-Nielsen, K. Dreyer, and J. E.Johnson, 320-Gb/s single-channel pseudolinear transmission over 200km of nonzero-dispersion fiber, IEEE Photon. Technol. Lett., vol. 12,pp. 373375, Oct. 2000.

[9] M. Ibsen, M. K. Durkin, M. J. Cole, and R. I. Laming, Sinc-sampledfiber Bragg gratings for identical multiple wavelength operation, IEEEPhoton. Technol. Lett., vol. 10, pp. 842845, 1998.

Z. Pan, photograph and biography not available at the time of publication.

Y. W. Song, photograph and biography not available at the time of publication.

C. Yu, photograph and biography not available at the time of publication.

Y. Wang, photograph and biography not available at the time of publication.

Q. Yu, photograph and biography not available at the time of publication.

J. Popelek, photograph and biography not available at the time of publication.

H. Li, photograph and biography not available at the time of publication.

Y. Li, photograph and biography not available at the time of publication.

2246 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 20, NO. 12, DECEMBER 2002

Alan Eli Willner (S87M88SM93) received the B.A. degree from YeshivaUniversity, New York, NY, and the Ph.D. degree in EE from Columbia Univer-sity, New York, NY.

He has worked at AT&T Bell Labs and Bellcore and is Professor of ElectricalEngineering at USC. He has more than 300 publications, including one book.His research is in optical fiber communication systems.

Dr. Willner is a Fellow of the Optical Society of America (OSA) andwas a Fellow of the Semiconductor Research Corporation. He has receivedthe NSF Presidential Faculty Fellows Award from the White House, theDavid and Lucile Packard Foundation Fellowship, the NSF National YoungInvestigator Award, the Fulbright Foundation Senior Scholar Award, theIEEE LEOS Distinguished Lecturer Award, the USC/Northrop OutstandingJunior Engineering Faculty Research Award, the USC/TRW Best EngineeringTeacher Award, and the Armstrong Foundation Memorial Prize. His activitieshave included Vice-President for Technical Affairs for IEEE LEOS, ElectedMember of the LEOS Board of Governors, Cochair of the OSA Science andEngineering Council, Photonics Division Chair of the OSA, General Chairof the IEEE LEOS Annual Meeting, Program Cochair of the OSA AnnualMeeting, Program Cochair of CLEO, Steering and Technical Committee ofOFC, and Program Committee Member of ECOC. He is Editor-in-Chiefof the JOURNAL OF LIGHTWAVE TECHNOLOGY; Editor-in-Chief of the IEEEJOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS; Guest Editorof the JOURNAL OF LIGHTWAVE TECHNOLOGY Special Issue on WavelengthDivision Multiplexing; and Guest Editor of the IEEE JOURNAL OF QUANTUMELECTRONICS.

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