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Optik 125 (2014) 905– 907

Contents lists available at ScienceDirect

Optik

jou rn al homepage: www.elsev ier .de / i j leo

60 Gbps S-band WDM transmission system over 1400 km usingTUT-652a and ITUT-655 fibers with low dispersion accumulation

ajandeep Singha,∗, Maninder Lal Singha, Jaswinder Singhb

Department of Electronics Technology, GNDU, Amritsar, IndiaDepartment of Electronics and communication, BCET, Gurdaspur, India

r t i c l e i n f o

rticle history:eceived 15 February 2012ccepted 26 June 2012

a b s t r a c t

Dispersion accumulation with the distance effects optical WDM system’s performance severely. For everymodulation format used there is a limit on maximum transmission distance due to dispersion accumu-lation. So dispersion compensation is required. But dispersion compensation can be avoided to a largeextent by alternatively using different fiber standards. In this paper it has been proposed that the dis-

eywords:-bandow dispersion accumulationER-factor

persion accumulation can be reduced to a large extent by alternatively transmitting in S-band and usingfiber standards ITUT-652a and ITUT-655. To validate the claim, performance of a 16 channel 10 GbpsWDM system with the proposed method has been analyzed in terms of BER and Q-factor. And it has beenobserved that with the proposed scheme without any dispersion compensation the system performs wellup to 1400 km.

ispersion compensation

. Introduction

Accumulated dispersion and some nonlinear effects are respon-ible for signal degradation. Dispersion accumulation limits theaximum reach of a WDM system, so dispersion accumulation

ps/nm) must be low. One alternative is to design a fiber withery low dispersion (ps/nm/km), but keeping very low disper-ion value is also not solution as it enhances some nonlinearffects like four wave mixing [1–3] and cross phase modula-ion (XPM) [4–7]. Nonlinear effects affect the system performanceeverely [3]. If dispersion (ps/nm/km) is kept low, nonlineari-ies increase while if dispersion is kept high signal distortionakes place due to high dispersion which leads to the needf dispersion compensation. In the proposed method of usingTUT-652a and ITUT-655 fibers alternatively, signal experiencesigh dispersion in ITUT-652a fiber and the dispersion intro-uced by this fiber is compensated by next fiber module which

s ITUT-655 which has negative dispersion value in S-band1460–1530 nm). Hence the signal experiences high dispersionn each fiber but low effective dispersion accumulation. This

ethod reduces the effective dispersion accumulation to a large

xtent so that the need of additional dispersion compensation iseduced.

∗ Corresponding author.E-mail addresses: rajandeep1987@gmail.com (R. Singh), mlsingh7@gmail.com

M.L. Singh), j singh73@rediffmail.com (J. Singh).

030-4026/$ – see front matter © 2013 Elsevier GmbH. All rights reserved.ttp://dx.doi.org/10.1016/j.ijleo.2012.06.108

© 2013 Elsevier GmbH. All rights reserved.

2. Proposed method of reducing accumulated dispersion

Fig. 1(a) shows the dispersion profile of fiber ITUT-652a,ITUT-655 alone and effective dispersion (ps/nm/km) in S-band(1460–1530 nm) when ITUT-652a and ITUT-655 fibers are alterna-tively used in 1:1 ratio of lengths. It is clear from the Fig. 1(a) thatthe fiber ITUT-652a has high positive dispersion throughout the S-band, dispersion is always more than 11 ps/nm/km. so if ITUT-652afiber alone is used for 1000 km, the accumulated dispersion will bemore than 11000 ps/nm.

The fiber ITUT-655 has negative dispersion in S-band. If thesetwo fibers are used alternately to cancel dispersion introducedby each other the net dispersion accumulation will be quite low.Fig. 1(a) also shows the net dispersion (ps/nm/km) if the ITUT652aand ITUT-655 fibers are used in 1:1 ratio of lengths. In S band1460–1490 nm wavelength region is very important because ofgood response of Thulium doped fiber for this region. Fig. 1(b)shows the dispersion profile in 1460–1490 nm region, when ITUT-655 and ITUT-652a fibers are used in 1:1 ratio of lengths. Fromthe figure it is evident that dispersion in this 30 nm region variesfrom −1 to 3 (ps/nm/km) which is quite low but still the signalexperiences high dispersion in ITUT-655 and ITUT-652a modulesdifferently. Fig. 2(a) shows the dispersion profile for 1460–1530 nmif the fiber lengths are used in 0.9:1.1 ratios. This shifts thezero effective dispersion value to little higher wavelength around

1475 nm, Fig. 2(b) shows the dispersion profile for 1460–1490 nmwhen fibers are used in 0.9:1.1 ratio now the zero effective disper-sion occurs at 1475 nm which bisects the region 1460–1490 nm.For this region dispersion varies from about −2.5 to +2.5 ps/nm/km

906 R. Singh et al. / Optik 125 (2014) 905– 907

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Fig. 3. Simulation setup for 16 × 10 Gbps WDM system with proposed method.

ig. 1. Dispersion profile for (a) ITUT-655 and ITUT-652a fibers are used in 1:1 ratiof lengths in entire S-band (b) ITUT-655 and ITUT-652a are used in 1:1 ratio ofengths in 1460–1490 nm.

nd zero dispersion is at 1475 nm. To validate the claim 16 channel0 Gbps WDM system is simulated.

. Simulation setup

The Optiwave9.0 simulator has been used for the simulations.t the transmitter side 16 transmitters (1468–1480 nm) equallypaced with 0.8 nm channel spacing have been used. For all theransmitters duobinary modulation format is used and also laserower has been set to be 0 dB at all wavelengths.

A multiplexer with channel spacing 0.8 nm has been used toultiplex all the wavelength signals. A single loop consists of a

3 km ITUT-652a fiber followed by a 77 km of ITUT-655 fiber, afteroth the fibers optical amplifiers with 13.5 dB gain and 4 dB noisegure have been used. Effective area of both types of fibers has beenept constant at 65 �m2. Loop controller is set for 10 loops so theistance is varied from 140 km to 1400 km in steps of 140 km. Athe receiver side demultiplexer separates different wavelengths,t each demultiplexer output, a PIN photo detector has been usedith responsivity of 1 A/W and dark current of 10 nA, also a bandass Bessel filter has been used to remove the noise from the signalnd at the end an eye diagram analyzer has been used to measureER and Q-factor.

. Results

The performance of the 16 channel WDM system as shownn simulation setup (Fig. 3) is observed in terms of Q-factor andER after each loop. Fig. 4 shows the Q-factor variation w.r.t theistance for 1st channel, 8th channel and 16th channel. Fig. 4(a)

hows the Q-factor variation w.r.t. the transmission distance. It haseen observed that at the end of first loop i.e. 140 km fiber (63 km

TUT-652a and 77 km ITUT-655) Q-factor is 14.14 dB, 15.39 dBnd 16.13 dB for 1st, 8th and 16th channel respectively. There is

ig. 2. Dispersion profile for (a) ITUT-652a and ITUT-655 fibers in 0.9:1.1 ratio ofengths in entire S-band (b) ITUT-652a and ITUT-655 fibers in 0.9:1.1 ratio of lengthsn 1460–1490 nm.

Fig. 4. (a) Q-factor at channel 1, 8 and 16 for distance 140–1400 km. (b) BER atchannel 1, 8 and 16 for distance 140–1400 km.

very slight variation of Q-factor among different channels becausethe accumulated dispersion variation among all the channels isvery small. As the number of loops are increased the distanceincreases with 140 km per loop, the Q-factor decreases very sharply,this trend remains same throughout the simulation distance of140–1400 km. Q-factor for 1st. 8th and 16th channel remainsacceptable (>6 dB) upto a transmission distance of 1400 km. At1400 km, Q-factor at 1st channel is 6.85 dB, at 8th channel is10.68 dB and at 16th channel is 10.07 dB.

Fig. 4(b) shows the BER variation w.r.t distance for the simula-tion setup. BER variation behavior is similar to Q-factor variation,after first loop (140 km) the BER is very low of the order of 10e−46at all three channels. As transmission distance increases with everyloop the BER increases. BER remains acceptable (<10e−12) till1400 km. At 1400 km BER at 1st channel is 10e−12, at 8th channelis 10e−27 and at 16th channel is 10e−24.

5. Conclusion

This paper deals with the reduction of accumulation of chro-matic dispersion in S-band WDM system. The proposed scheme ofusing ITUT-655 and ITUT-652a fiber segments alternately reducesthe dispersion accumulation and hence increases maximum trans-mission distance without any special dispersion compensation.With the proposed method the system itself acts as the dis-persion compensator. The performance of 16 × 10 Gbps WDMsystem is evaluated in terms of Q-factor and BER and it has beenobserved that the system performance is significantly improvedupto transmission distance of 1400 km without any extra disper-sion compensation. It has been observed that at 1400 km, the valuesfor the Q-function obtained for the three channels under investiga-

tion (1st, 8th and 16th channel) are 6.85 dB, 10.68 dB and 10.07 dBrespectively. Similarly the BER values obtained for the three chan-nels (1st, 8th and 16th channel) are 10e−12, 10e−27 and 10e−24,respectively which are quite acceptable.

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