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Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 22, Iss. 2 — Jan. 27, 2014
  • pp: 1426–1439
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Analytical modeling of cross-phase modulation in coherent fiber-optic system

Sina Naderi Shahi, Shiva Kumar, and Xiaojun Liang  »View Author Affiliations


Optics Express, Vol. 22, Issue 2, pp. 1426-1439 (2014)
http://dx.doi.org/10.1364/OE.22.001426


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Abstract

An analytical model to calculate the variance of cross-phase modulation (XPM) distortion in a wavelength-division multiplexed (WDM) fiber-optic system is developed. The method is based on the first order perturbation technique and it is applicable for both dispersion managed and dispersion uncompensated systems. For dispersion managed systems, it is shown that the variance of XPM distortion scales as Nx where N is the number of spans and x ∈ [1, 2] depending on the amount of inline-dispersion compensation. The analytical model is found to be in good agreement with simulations in most of the cases.

© 2014 Optical Society of America

1. Introduction

Since different wavelength-division multiplexed (WDM) channels have different group speeds in a dispersive fiber, symbols of a “fast” channel walk off the symbols of a “slow” channel. As the “fast” channel walks off, it induces phase distortion on the “slow” channel (due to cross-phase modulation (XPM)) and vice versa, and group velocity dispersion (GVD) converts the phase distortion into amplitude distortion [1

1. R. Hui, Y. Wang, K. Demarest, and C. Allen, “Frequency response of cross-phase modulation in multispan WDM optical fiber systems,” IEEE Photon. Technol. Lett. 10, 1271–1273 (1998). [CrossRef]

, 2

2. R. Hui, K. Demarest, and C. Allen, “Cross-phase modulation in multispan WDM optical fiber systems,” J. Lightw. Technol. 17, 1018–1026 (1999). [CrossRef]

]. XPM effect may be considered as a stochastic process if the symbol pattern in the other channels is unknown and it could lead to performance degradation [3

3. M. Eiselt, M. Shtaif, and L.D. Garrett, “Contribution of timing jitter and amplitude distortion to XPM system penalty in WDM systems,” IEEE Photon. Technol. Lett. 11, 748–750 (1999). [CrossRef]

].

Due to the impact of the XPM impairments on the performance of a WDM systems, they have drawn considerable attention [1

1. R. Hui, Y. Wang, K. Demarest, and C. Allen, “Frequency response of cross-phase modulation in multispan WDM optical fiber systems,” IEEE Photon. Technol. Lett. 10, 1271–1273 (1998). [CrossRef]

13

13. A. Mecozzi and Rene Essiambre, “Nonlinear Shannon limit in pseudolinear coherent systems,” J. Lightw. Technol. 30, 2011–2024 (2012). [CrossRef]

]. In [4

4. D. Marcuse, A.R. Chraplyvy, and R.W. Tkach, “Dependence of cross-phase modulation on channel number in fiber WDM systems,” J. Lightw. Technol. 12, 885–890 (1994). [CrossRef]

], XPM distortion and the effect of channel spacing on XPM are investigated based on numerical simulations. In [1

1. R. Hui, Y. Wang, K. Demarest, and C. Allen, “Frequency response of cross-phase modulation in multispan WDM optical fiber systems,” IEEE Photon. Technol. Lett. 10, 1271–1273 (1998). [CrossRef]

,2

2. R. Hui, K. Demarest, and C. Allen, “Cross-phase modulation in multispan WDM optical fiber systems,” J. Lightw. Technol. 17, 1018–1026 (1999). [CrossRef]

,5

5. A.T. Cartaxo, “Cross-phase modulation in intensity modulation-direct detection WDM systems with multiple optical amplifiers and dispersion compensators,” J. Lightw. Technol. 17, 178–190 (1999). [CrossRef]

], XPM distortion in multi-span intensity-modulation direct-detection (IM-DD) is investigated in frequency domain both experimentally and theoretically. The effects of bit rate and dispersion compensation on the system performance are also studied. In [6

6. Z. Jiang and C. Fan, “A comprehensive study on XPM-and SRS-induced noise in cascaded IM-DD optical fiber transmission systems,” J. Lightw. Technol. 21, 953–960 (2003). [CrossRef]

], XPM and stimulated Raman scattering (SRS) distortions for a IM-DD system are studied analytically and numerically. Effect of dispersion compensation on these distortions are also investigated. In [7

7. S. Kumar and D. Yang., “Second-order theory for self-phase modulation and cross-phase modulation in optical fibers,” J. Lightw. Technol. 23, 2073–2080 (2005). [CrossRef]

], the signal distortion due to self-phase modulation (SPM) and XPM is studied using the first and/or second order perturbation theory.

Recently, the modeling of nonlinear distortion in coherent fiber-optic WDM systems has drawn significant interest [8

8. J. Tang, “The channel capacity of a multispan DWDM system employing dispersive nonlinear optical fibers and an ideal coherent optical receiver,” J. Lightw. Technol. 20, 1095–1101 (2002). [CrossRef]

13

13. A. Mecozzi and Rene Essiambre, “Nonlinear Shannon limit in pseudolinear coherent systems,” J. Lightw. Technol. 30, 2011–2024 (2012). [CrossRef]

]. In [8

8. J. Tang, “The channel capacity of a multispan DWDM system employing dispersive nonlinear optical fibers and an ideal coherent optical receiver,” J. Lightw. Technol. 20, 1095–1101 (2002). [CrossRef]

], the first order Volterra series is used to estimate the channel capacity of a dispersive nonlinear optical fiber. In [9

9. Z. Tao, W. Yan, L. Liu, L. Li, S. Oda, T. Hoshida, and J. C. Rasmussen, “Simple Fiber Model for Determination of XPM Effects,” J. Lightw. Technol. 29, 974–986 (2011). [CrossRef]

], an analytical model for XPM phase noise and polarization scattering is obtained based on Volterra analysis, and the variance and autocorrelation of the XPM phase noise and polarization scattering are calculated. In [10

10. M. Nazarathy, J. Khurgin, R. Weidenfeld, Y. Meiman, P. Cho, R. Noe, I. Shpantzer, and V. Karagodsky, “Phased-array cancellation of nonlinear FWM in coherent OFDM dispersive multi-span links,” Opt. Express 16, 15777–15810 (2008). [CrossRef] [PubMed]

], propagation impairment due to nonlinear interaction in coherent orthogonal frequency-division multiplexing (OFDM) systems is studied. In [11

11. A. Carena, V. Curri, G. Bosco, P. Poggiolini, and F. Forghieri, “Modeling of the impact of nonlinear propagation effects in uncompensated optical coherent transmission links,” J. Lightw. Technol. 30, 1524–1539 (2012). [CrossRef]

, 12

12. P. Poggiolini, A. Carena, V. Curri, G. Bosco, and F. Forghieri, “Analytical modeling of non-linear propagation in uncompensated optical transmission links,” IEEE Photon. Technol. Lett. 23, 742–744 (2011). [CrossRef]

], an analytical expression for the power spectral density (PSD) of the nonlinear interference in a dispersion uncompensated WDM system is developed by assuming that the nonlinear distortion can be modeled as Gaussian noise. To evaluate the PSD, it is necessary to carry out a triple numerical integration. In [13

13. A. Mecozzi and Rene Essiambre, “Nonlinear Shannon limit in pseudolinear coherent systems,” J. Lightw. Technol. 30, 2011–2024 (2012). [CrossRef]

], channel capacity of a nonlinear fiber-optic system is estimated using a first order perturbation theory.

This paper is organized as follows. In section 2, we present a first order perturbation theory for XPM effects in fibers. Analytical expressions are obtained for the first order corrections. In section 3, analytical expression for the variance of XPM impairment is obtained. In section 4, the theoretical model is validated by numerical simulations. Also, effect of launch power, fiber dispersion, system reach, and channel spacing on the XPM variance is examined. Finally, in section 5, the contributions of this paper are summarized.

2. SPM and XPM analytical model

The pulse propagation in optical fiber is described by the nonlinear Schrodinger equation (NLS),
jqzβ2(z)22qT2+γ0|q|2q=jα(z)2q,
(1)
where q is the electric field envelope, β2(z) is the dispersion profile, γ0 is nonlinear coefficient and α(z) is the fiber loss/gain profile. Using the transformation,
q(z,T)=exp[w(z)/2]u(z,T),
(2)
where w(z)=0zα(s)ds, Eq. (1) can be rewritten in the lossless form as
juzβ2(z)22uT2+γ(z)|u|2u=0,
(3)
where γ(z) = γ0 exp[−w(z)]. We consider the interaction between two channels of a WDM system. We spilt the field u into two parts,
u=u1+u2,
(4)
where uj is the field of channel j, j = 1, 2. Substituting Eq. (4) into Eq. (3) and ignoring the four wave mixing terms, we obtain
jukzβ2(z)22ukT2=γ(z)[|uk|2+2|ul|2]uk,k=1,2andl=3k
(5)
Without loss of generality, we consider the interaction between a pulse of channel 1 in symbol slot 0 and a pulse train of channel 2 consisting of random symbol pattern. We assume that the leading order solution of Eq. (5) is linear and treat the nonlinear terms appearing on the right hand side as perturbation. Assuming Gaussian pulse and quadrature amplitude modulation (QAM), we have
u1(0,T)=Pa0p(0,T),
(6)
u2(0,T)=Pnanp(0,TnTs)exp(jΩt),
(7)
p(0,T)=exp(T2/2T02)
(8)
where n shows the symbol location in time domain, Ts is the symbol interval, P is the power, Ω is the channel separation in radians, p(0, T) is Gaussian pulse shape at z = 0, T0 is the half-width at 1/e- intensity point [14

14. G. P. Agrawal, Nonlinear Fiber Optics, 4 (Academic Press, 2007).

] and
an=xn+jyn2,
(9)
xn and yn are random variables that take values ±1, ±3,...,±(X − 1) and ±1, ±3,...,±(Y − 1) (X and Y are the number of amplitude levels of the in-phase and quadrature components, respectively.) with equal probability, respectively. Using the perturbation technique [7

7. S. Kumar and D. Yang., “Second-order theory for self-phase modulation and cross-phase modulation in optical fibers,” J. Lightw. Technol. 23, 2073–2080 (2005). [CrossRef]

, 15

15. S. Kumar, S. N. Shahi, and D. Yang., “Analytical modeling of a single channel nonlinear fiber optic system based on QPSK,” Opt. Express 20, 27740–27755 (2012). [CrossRef] [PubMed]

], the field envelope in channel k can be expanded as,
uk=uk0+γ0uk(1)+γ02uk(2)+,k=1,2
(10)
where γ0 is a small parameter and uk(m) denotes the mth order solution. Here uk(0) represents the 0th order solution which satisfies
juk(0)zβ222uk(0)T2=0.
(11)
Solving Eq. (11), the field uk(0) is given by [7

7. S. Kumar and D. Yang., “Second-order theory for self-phase modulation and cross-phase modulation in optical fibers,” J. Lightw. Technol. 23, 2073–2080 (2005). [CrossRef]

, 14

14. G. P. Agrawal, Nonlinear Fiber Optics, 4 (Academic Press, 2007).

]
u1(0)(z,T)=PT0T1a0exp[T22T12],
(12)
u2(0)(z,T)=PT0T1nanexp[(Tτn)22T12jΩt+jθ(z)],
(13)
where
T1=(T02jS(z))1/2,
(14)
τn=nTs+S(z)Ω,
(15)
θ(z)=S(z)Ω22,
(16)
and S(z) is the accumulated dispersion given by
S(z)=0zβ2(s)ds.
(17)
Our reference frame is fixed to channel 1. The pulse in channel 2 moves with an inverse group speed of β2Ω relative to channel 1.

Substituting Eq. (10) into Eq. (5) and collecting all the terms that are proportional to γ0, we obtain
juk(1)zβ2(z)22uk(1)T2=exp[w(z)][|uk(0)|2+2|ul(0)|2]uk(0).k=1,2andl=3k.
(18)
To solve Eq. (18), we first derive the following identity. Consider a differential equation,
jfzβ2(z)22fT2=F(z,T),
(19)
where the forcing function F(z, T) is of the form
F(z,T)=η(z)exp{k=13[TCk(z)]2Rk(z)},
(20)
The solution of Eq. (19) is given by (see the Appendix)
f(z,T)=j0zη(s)δ(z,s)R(s)exp[k=13Ck2Rk+C2R]exp[(D+jT)2δ(z,s)]ds,
(21)
where
R=R1+R2+R3,
(22)
C=C1R1+C2R2+C3R3,
(23)
D=jCR,
(24)
δ=1jRA(z,s)R,
(25)
A(z,s)=2[S(z)S(s)].
(26)
To find the first order correction for u1 due to XPM term, |u2(0)|2u1(0) in Eq. (18), we make use of the result given by Eq. (21). The forcing function F(z, T) in this case is
F(z,T)=2exp[w(z)]|u2(0)|2u1(0),=2P3/2a0η(z)mnaman*exp{k=13[TCk(z)]2Rk(z)},
(27)
where
η(z)=T03exp[w(z)]T1(z)|T1(z)|2,
(28)
C1(z)=τm(z),C2(z)=τn(z),C3(z)=0,
(29)
R1=R3=12T12,R2=12(T1*)2.
(30)
Using Eq. (21), the first order correction for u1 due to XPM is given by
u1(1),XPM(z,T)=j2P3/2a0mnaman*Xmn(z,T)
(31)
where
Xmn(z,T)=0zη(s)δ(z,s)R(s)exp[(D+jT)2δ(z,s)]ds,
(32)
η(s)=η(s)exp(k=13Ck2Rk+C2R),
(33)
The distortion due to the XPM is obtained by summation over all nonlinear distortions caused by nonlinear interaction between the pulses located in time intervals mTs and nTs.

The first order correction for u1 due to SPM term, |u1(0)|2u1(0), can be easily obtained from Eq. (31) by setting the angular frequency Ω to 0, τm and τn to 0 and by replacing the XPM factor 2 with SPM factor 1, i.e.,
u1(1),SPM(z,T)=jP3/2a0|a0|20zη(s)δ(z,s)R(s)exp(T2δ(z,s))ds,
(34)
Total first order solution for u1 is obtained by adding the SPM and XPM contributions,
u1(1)=u1(1),SPM+u1(1),XPM.
(35)

3. Variance calculation

Now, total mean of absolute square can be obtained by adding Eqs. (47) and (49)
E{|δu1|2}=4γ02P3|a0|2(K12mmmmXmmXmm*+K2m|Xmm|2+K12mmmm|Xmm|2).
(52)
Finally, variance can be obtained by substituting Eqs. (42) and (52) in (36)
Var{δu1}=4γ02P3|a0|2(K2m|Xmm|2+K12mmmm|Xmm|2K12m|Xmm|2),=γ02P3|a0|2((K2K1)2m|Xmm|2+K12mmmm|Xmm|2).
(53)
In the case of QPSK, K1 = K2 = 1. So, for QPSK, Eq. (53) reduces to
Var{δu1}=γ02P3mmmm|Xmm|2.
(54)

4. Results and discussion

To validate the analytical model, we carried out numerical simulations of the dispersion uncompensated fiber-optic system shown in Fig. 1. Two WDM channels with QPSK modulation and Gaussian pulse shape are assumed. The wavelength division multiplexer (Mux) combines the two channels and the output of the multiplexer is launched to a multi-span fiber-optic system. The fiber loss is exactly compensated with an ideal noiseless amplifier. Amplified spontaneous emission (ASE) noise, laser phase noise, polarization effects, and the coherent receiver imperfections are ignored since the primary focus is to validate our analytical model for XPM impairments. After multi-span transmission, the channels are demultiplexed using an ideal bandpass filter whose bandwidth equals the channel spacing and passed to the optical receiver. The following parameters are used throughout the paper unless otherwise specified: amplifier spacing L = 80 km, channel spacing = 50 GHz, symbol rate = 10 Gbaud, pulse width TFWHM (full width at half maximum) = 50 ps, QPSK modulation, nonlinear coefficient and loss of transmission fiber are 1.1 W−1km−1 and 0.2 dB/km, respectively. A random bit sequence of 100 pulses is used for the pump channel (channel 2) and a single pulse is launched to channel 1. Number of Monte-Carlo simulation is 2000.

Fig. 1 Multispan WDM fiber-optic system.

To compute the distortion due to SPM, we turned off channel 2 in both analytical model and numerical simulations. The SPM distortion is obtained by subtracting the output field of channel 1 (when channel 2 is turned off) from its linear output obtained by assuming γ0 = 0. The XPM distortion is obtained by subtracting the SPM distortion from the output field of channel 1 when channel 2 is present.

To find the mean and variance numerically, Monte-Carlo simulation is carried out. Figure 2(a) shows the numerical and analytical first moments of SPM and XPM distortions. Figure 2(b) shows the numerical and analytical second moments of SPM and XPM. Finally, Fig. 3 shows the numerical and analytical XPM variances. The the following parameters are used for Figs. 2 and 3: peak power Ppeak = 0 dBm, fiber dispersion β2 = −10 ps2/km, and number of spans N = 10. As can be seen in the Figs. 2 and 3, the discrepancy between the analytical and numerical is more at the center of the pulse (higher power) than at the edges of the pulse (lower power). It is due to the fact that the first order perturbation technique is less accurate at higher powers. The maximum discrepancy between the analytical model and numerical simulations for the variance is less than 10%.

Fig. 2 (a) Absolute of mean XPM distortion, and (b) Mean of absolute square of XPM distortion. Following parameters were assumed: Ppeak = 0 dBm, β2 = −10 ps2/km, and no. of spans = 10.
Fig. 3 Variance of XPM impairment. Parameters are the same as that of Fig. 2.

As can be seen in Fig. 3, the variance of XPM distortion varies as a function of the temporal position within the symbol interval. So we define the mean variance as
σXPM2=Var{δu1}¯=1Ts0TsVar{δu1}dt.
(55)
The variance is calculated by assuming that probe receiver is placed at the end of each span and dispersion is fully compensated before the variance calculation.

Figure 4(a) shows the mean XPM variance versus peak power. When the launch peak power is 0 dBm, the discrepancy between the analytical model and numerical simulation is less than 10%, whereas it increases to 20% when the launch peak power is 8 dBm which is due to the inaccuracy of first order perturbation technique. To get a better accuracy, higher order perturbation technique can be used [7

7. S. Kumar and D. Yang., “Second-order theory for self-phase modulation and cross-phase modulation in optical fibers,” J. Lightw. Technol. 23, 2073–2080 (2005). [CrossRef]

].

Fig. 4 The mean XPM variance versus (a) peak power, and (b) fiber dispersion. The other parameters are same as that of Fig. 2.

Figure 4(b) shows the dependence of mean XPM variance on the fiber dispersion. From Eq. (54), we find that the variance is caused by the pulse overlapping. So, when the dispersion is low, pulses do not overlap significantly and hence, the variance is quite small. However, the variance grows quickly and beyond 10 ps2/km, it decays slowly. When the dispersion is very large, the XPM effect is reduced since pulses walk-off quickly. The maximum discrepancy between the model and the simulation is less than 10% in this example.

Fig. 5 The mean XPM variance versus (a) no. of spans, and (b) channel spacing. The other parameters are same as that of Fig. 2.

Figure 5(b) shows the XPM variance versus channel spacing. As can be seen, XPM variance decreases significantly as channel spacing increases. This is because as the channel spacing increases, the “fast” channel walks off quickly the “slow” channel and hence, the nonlinear interaction time is reduced.

Fig. 6 The mean XPM variance versus peak power for (a) 2-channel WDM, and (b) 5-channel WDM system. 28 Gbaud WDM system and the standard single-mode fiber (SSMF) with the following parameters is used: β2 = −22 ps2/km, γ = 1.1 W−1km−1 and loss α = 0.2 dB/km The other parameters are same as that of Fig. 2.

4.1. Dispersion-managed system

In this section, accuracy of the model is verified for the dispersion-managed system. Figure 7 shows a typical fiber-optic system with pre-, inline-, and post-compensation. Parameters of the transmission fiber (TF) are as follows: fiber loss αTF = 0.2 dB/km, fiber nonlinearity γTF = 1.1 W−1km−1, fiber dispersion β2,TF = −10 ps2/km, and fiber length LTF = 80 km. Dispersion compensating fiber (DCF) is used for inline compensation. The parameters of DCF are as follows: fiber loss αDCF = 0.5 dB/km, fiber nonlinearity γDCF = 4.4 W−1km−1, fiber dispersion β2,DCF = 150 ps2/km. The virtual DCFs are used in digital domain for pre- and post- compensation. The parameters of the virtual DCF are the same as the real DCF except that its nonlinear coefficient is set to zero. Pre- and post-compensation fibers’ lengths are calculated based on the pre-compensation ratio defined as,
Pre-compensationratio=LpreLpre+Lpost×100,
(56)
where Lpre and Lpost are pre- and post-compensation fiber lengths, respectively. The pre-, inline-, and post-compensation fiber lengths are chosen so that the total accumulated dispersion at the receiver is zero.

Fig. 7 A typical fiber-optic transmission system with inline-compensation. TF:transmission fiber, DCF:dispersion compensating fiber.

Figure 8 shows the XPM variance versus the pre-compensation ratio after after 10 spans of transmission. The variance of XPM distortion is nearly independent of the pre-compensation ratio. In contrast, the variance of intrachannel impairments shows a strong dependance on the pre-compensation ratio [16

16. D. Yang and S. Kumar, “Analysis of intrachannel impairments for coherent systems based on phase-shift keying,” J. Lightw. Technol. 27, 2916–2923 (2009).

]. From Fig. 8, we find that the maximum discrepancy between the model and simulations is 6%.

Fig. 8 The mean XPM variance versus pre-compensation percent. Following parameters were assumed: Ppeak = 0 dBm, length of inline DCF Linline = 4.8 km.

Next, we define inline-compensation ratio as
η=AccumulateddispersionofinlineDCFperspanAccumulateddispersionofTFperspan×100.
(57)
Figure 9 shows the mean XPM variance as a function of η when the pre-compensation ratio is 50%. When η = 100%, it corresponds to a resonant dispersion map in which the residual dispersion per span is zero. As can be seen, this is the worst case since the XPM distortion in each span is identical (up to the first order) and they add up coherently. When η = 0%, dispersion is compensated equally at the transmitter and receiver with no inline-compensation, which is the same as the dispersion uncompensated case except for the fact that pre- and post-compensating fibers have nonlinearity. From Fig. 9, we find that η = 70% is the optimum value which corresponds to a residual dispersion Dres of 185 ps/nm per span. The maximum discrepancy between the model and simulations in this example is 10%.

Fig. 9 The mean XPM variance versus inline-compensation ratio. Pre-compensation ratio = 50%, Ppeak = 0 dBm, and no. of spans = 10.

Figure 10 shows the XPM variance as a function of the number of spans N. When η = 100%, a curve fitting to the simulation data shows that variance scales as N1.95 while it scales as N1.75 when η = 90% and N1.54 when η = 80%. Typically, it varies as Nx where x ∈ [1

1. R. Hui, Y. Wang, K. Demarest, and C. Allen, “Frequency response of cross-phase modulation in multispan WDM optical fiber systems,” IEEE Photon. Technol. Lett. 10, 1271–1273 (1998). [CrossRef]

, 2

2. R. Hui, K. Demarest, and C. Allen, “Cross-phase modulation in multispan WDM optical fiber systems,” J. Lightw. Technol. 17, 1018–1026 (1999). [CrossRef]

]. It can be explained as follows. For a resonant map (η = 100%), XPM distortion in each span is identical and the coherent addition of XPM fields leads to N2 dependence. For a non-resonant map (η = 0%), the XPM distortion in different spans are nearly independent and hence, the variances due to each span can be added which leads to a linear scaling of XPM variance with N. For the other values of η, there is some correlation between the XPM distortions arising from different spans and hence, the variance scales as Nx where x ∈ (1, 2). It may be noted that variance builds up slowly for the cases of η = 80% and η = 90% as compared to the case of η = 100%. The maximum discrepancy between the model and simulations in this example is less than 10%.

Fig. 10 The mean XPM variance versus no. of spans for η = 100% (Dres = 0 ps/nm), 90% (Dres = 61 ps/nm), and 80% (Dres = 123 ps/nm). Pre-compensation ratio = 50%, and Ppeak = 0 dBm.

5. Conclusions

A time domain approach based on the first order perturbation theory to calculate the variance of XPM distortion in a WDM fiber-optic system is developed. The analysis is applicable to dispersion uncompensated as well as dispersion managed systems. Validity of this approach is examined by comparing it with Monte-Carlo simulations for a range of launch power, dispersion coefficient, number of spans and channel spacing. In the case of dispersion uncompensated system, it is found that the variance scales almost linearly with the number of spans whereas dispersion managed system, the variance scales as Nx where x ∈ [1

1. R. Hui, Y. Wang, K. Demarest, and C. Allen, “Frequency response of cross-phase modulation in multispan WDM optical fiber systems,” IEEE Photon. Technol. Lett. 10, 1271–1273 (1998). [CrossRef]

, 2

2. R. Hui, K. Demarest, and C. Allen, “Cross-phase modulation in multispan WDM optical fiber systems,” J. Lightw. Technol. 17, 1018–1026 (1999). [CrossRef]

] depending on the dispersion map. In a dispersion managed system, the XPM variance is independent of pre-compensation ratio, but it is sensitive to the inline-compensation ratio. The optimum inline-compensation ratio is 70% for the parameter space of this paper.

6. Appendix: Differential equation solution

Taking the Fourier transform of Eq. (19), we have
df˜(z,ω)dzjω2β2(z)2f˜(z,ω)=jF˜(z,ω),
(58)
where (z, ω) is the Fourier transform of f (z, T) and
F˜(z,ω)=η(z)exp(k=13Ck2Rk)exp[RT2+T(2C+iω)]dT=πηRexp[ω24RDω],
(59)
where
R=R1+R2+R3,C=C1R1+C2R2+C3R3,
(60)
D=iCR,
(61)
η(z)=η(z)exp(k=13Ck2Rk+C2R).
(62)
The solution of Eq. (58) with the initial condition (0, ω) = 0, is
f˜(z,ω)=j0zF˜(s,ω)exp[jω2A(z,s)/4]ds,
(63)
where
A(z,s)=2[S(z)S(s)].
(64)
Using Eq. (59) in Eq. (63) and inverse Fourier transforming, we obtain
f(z,T)=jπ2π0zη(s)R(s)exp[4ω2δω(D+jT)]dωds,
(65)
where
δ(z,s)=1R(s)jA(z,s).
(66)
After evaluating the inner integral in Eq. (65), we obtain
f(z,T)=j0zη(s)δ(z,s)R(s)exp[(D(s)+jT)2δ(z,s)]ds.
(67)
Using Eqs. (60)(62) and Eq. (67), and after some algebra, we arrive at Eq. (21).

References and links

1.

R. Hui, Y. Wang, K. Demarest, and C. Allen, “Frequency response of cross-phase modulation in multispan WDM optical fiber systems,” IEEE Photon. Technol. Lett. 10, 1271–1273 (1998). [CrossRef]

2.

R. Hui, K. Demarest, and C. Allen, “Cross-phase modulation in multispan WDM optical fiber systems,” J. Lightw. Technol. 17, 1018–1026 (1999). [CrossRef]

3.

M. Eiselt, M. Shtaif, and L.D. Garrett, “Contribution of timing jitter and amplitude distortion to XPM system penalty in WDM systems,” IEEE Photon. Technol. Lett. 11, 748–750 (1999). [CrossRef]

4.

D. Marcuse, A.R. Chraplyvy, and R.W. Tkach, “Dependence of cross-phase modulation on channel number in fiber WDM systems,” J. Lightw. Technol. 12, 885–890 (1994). [CrossRef]

5.

A.T. Cartaxo, “Cross-phase modulation in intensity modulation-direct detection WDM systems with multiple optical amplifiers and dispersion compensators,” J. Lightw. Technol. 17, 178–190 (1999). [CrossRef]

6.

Z. Jiang and C. Fan, “A comprehensive study on XPM-and SRS-induced noise in cascaded IM-DD optical fiber transmission systems,” J. Lightw. Technol. 21, 953–960 (2003). [CrossRef]

7.

S. Kumar and D. Yang., “Second-order theory for self-phase modulation and cross-phase modulation in optical fibers,” J. Lightw. Technol. 23, 2073–2080 (2005). [CrossRef]

8.

J. Tang, “The channel capacity of a multispan DWDM system employing dispersive nonlinear optical fibers and an ideal coherent optical receiver,” J. Lightw. Technol. 20, 1095–1101 (2002). [CrossRef]

9.

Z. Tao, W. Yan, L. Liu, L. Li, S. Oda, T. Hoshida, and J. C. Rasmussen, “Simple Fiber Model for Determination of XPM Effects,” J. Lightw. Technol. 29, 974–986 (2011). [CrossRef]

10.

M. Nazarathy, J. Khurgin, R. Weidenfeld, Y. Meiman, P. Cho, R. Noe, I. Shpantzer, and V. Karagodsky, “Phased-array cancellation of nonlinear FWM in coherent OFDM dispersive multi-span links,” Opt. Express 16, 15777–15810 (2008). [CrossRef] [PubMed]

11.

A. Carena, V. Curri, G. Bosco, P. Poggiolini, and F. Forghieri, “Modeling of the impact of nonlinear propagation effects in uncompensated optical coherent transmission links,” J. Lightw. Technol. 30, 1524–1539 (2012). [CrossRef]

12.

P. Poggiolini, A. Carena, V. Curri, G. Bosco, and F. Forghieri, “Analytical modeling of non-linear propagation in uncompensated optical transmission links,” IEEE Photon. Technol. Lett. 23, 742–744 (2011). [CrossRef]

13.

A. Mecozzi and Rene Essiambre, “Nonlinear Shannon limit in pseudolinear coherent systems,” J. Lightw. Technol. 30, 2011–2024 (2012). [CrossRef]

14.

G. P. Agrawal, Nonlinear Fiber Optics, 4 (Academic Press, 2007).

15.

S. Kumar, S. N. Shahi, and D. Yang., “Analytical modeling of a single channel nonlinear fiber optic system based on QPSK,” Opt. Express 20, 27740–27755 (2012). [CrossRef] [PubMed]

16.

D. Yang and S. Kumar, “Analysis of intrachannel impairments for coherent systems based on phase-shift keying,” J. Lightw. Technol. 27, 2916–2923 (2009).

OCIS Codes
(060.1660) Fiber optics and optical communications : Coherent communications
(060.2310) Fiber optics and optical communications : Fiber optics
(060.4370) Fiber optics and optical communications : Nonlinear optics, fibers

ToC Category:
Optical Communications

History
Original Manuscript: August 19, 2013
Revised Manuscript: October 16, 2013
Manuscript Accepted: November 6, 2013
Published: January 15, 2014

Citation
Sina Naderi Shahi, Shiva Kumar, and Xiaojun Liang, "Analytical modeling of cross-phase modulation in coherent fiber-optic system," Opt. Express 22, 1426-1439 (2014)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-2-1426


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References

  1. R. Hui, Y. Wang, K. Demarest, C. Allen, “Frequency response of cross-phase modulation in multispan WDM optical fiber systems,” IEEE Photon. Technol. Lett. 10, 1271–1273 (1998). [CrossRef]
  2. R. Hui, K. Demarest, C. Allen, “Cross-phase modulation in multispan WDM optical fiber systems,” J. Lightw. Technol. 17, 1018–1026 (1999). [CrossRef]
  3. M. Eiselt, M. Shtaif, L.D. Garrett, “Contribution of timing jitter and amplitude distortion to XPM system penalty in WDM systems,” IEEE Photon. Technol. Lett. 11, 748–750 (1999). [CrossRef]
  4. D. Marcuse, A.R. Chraplyvy, R.W. Tkach, “Dependence of cross-phase modulation on channel number in fiber WDM systems,” J. Lightw. Technol. 12, 885–890 (1994). [CrossRef]
  5. A.T. Cartaxo, “Cross-phase modulation in intensity modulation-direct detection WDM systems with multiple optical amplifiers and dispersion compensators,” J. Lightw. Technol. 17, 178–190 (1999). [CrossRef]
  6. Z. Jiang, C. Fan, “A comprehensive study on XPM-and SRS-induced noise in cascaded IM-DD optical fiber transmission systems,” J. Lightw. Technol. 21, 953–960 (2003). [CrossRef]
  7. S. Kumar, D. Yang., “Second-order theory for self-phase modulation and cross-phase modulation in optical fibers,” J. Lightw. Technol. 23, 2073–2080 (2005). [CrossRef]
  8. J. Tang, “The channel capacity of a multispan DWDM system employing dispersive nonlinear optical fibers and an ideal coherent optical receiver,” J. Lightw. Technol. 20, 1095–1101 (2002). [CrossRef]
  9. Z. Tao, W. Yan, L. Liu, L. Li, S. Oda, T. Hoshida, J. C. Rasmussen, “Simple Fiber Model for Determination of XPM Effects,” J. Lightw. Technol. 29, 974–986 (2011). [CrossRef]
  10. M. Nazarathy, J. Khurgin, R. Weidenfeld, Y. Meiman, P. Cho, R. Noe, I. Shpantzer, V. Karagodsky, “Phased-array cancellation of nonlinear FWM in coherent OFDM dispersive multi-span links,” Opt. Express 16, 15777–15810 (2008). [CrossRef] [PubMed]
  11. A. Carena, V. Curri, G. Bosco, P. Poggiolini, F. Forghieri, “Modeling of the impact of nonlinear propagation effects in uncompensated optical coherent transmission links,” J. Lightw. Technol. 30, 1524–1539 (2012). [CrossRef]
  12. P. Poggiolini, A. Carena, V. Curri, G. Bosco, F. Forghieri, “Analytical modeling of non-linear propagation in uncompensated optical transmission links,” IEEE Photon. Technol. Lett. 23, 742–744 (2011). [CrossRef]
  13. A. Mecozzi, Rene Essiambre, “Nonlinear Shannon limit in pseudolinear coherent systems,” J. Lightw. Technol. 30, 2011–2024 (2012). [CrossRef]
  14. G. P. Agrawal, Nonlinear Fiber Optics, 4 (Academic Press, 2007).
  15. S. Kumar, S. N. Shahi, D. Yang., “Analytical modeling of a single channel nonlinear fiber optic system based on QPSK,” Opt. Express 20, 27740–27755 (2012). [CrossRef] [PubMed]
  16. D. Yang, S. Kumar, “Analysis of intrachannel impairments for coherent systems based on phase-shift keying,” J. Lightw. Technol. 27, 2916–2923 (2009).

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