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Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 4 — Feb. 25, 2013
  • pp: 4567–4577
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Improving performance of optical phase conjugation by splitting the nonlinear element

Monir Morshed, Arthur J. Lowery, and Liang B. Du  »View Author Affiliations


Optics Express, Vol. 21, Issue 4, pp. 4567-4577 (2013)
http://dx.doi.org/10.1364/OE.21.004567


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Abstract

We show that optical phase conjugation (OPC) based on third order nonlinear effects for mid-span spectral inversion (MSSI) can be improved by splitting the nonlinear element into two parts and adding an optical filter between them. This band-stop filter suppresses the cross-phase-modulation products that are generated around the pump, which, if not removed, will be shifted to fall around the output OPC signal band. Numerical simulations show that this method reduces the fundamental limitations introduced by OPC by 3 dB, which results in improvement of the maximum signal quality, Qmax, by 1 dB in a 10 × 80-km 4-QAM 224-Gb/s CO-OFDM system with MSSI.

© 2013 OSA

1. Introduction

In coherent optical systems, linear impairments such as chromatic dispersion (CD) and polarization mode dispersion (PMD) can be electronically compensated [1

1. A. J. Lowery and J. Armstrong, “Orthogonal-frequency-division multiplexing for dispersion compensation of long-haul optical systems,” Opt. Express 14(6), 2079–2084 (2006). [CrossRef] [PubMed]

4

4. L. B. Du and A. J. Lowery, “Practical XPM compensation method for coherent optical OFDM systems,” IEEE Photon. Technol. Lett. 22, 320–322 (2009).

]. Therefore, fiber nonlinearity is the major limiting factor of transmission distance and bandwidth in long haul high bandwidth optical communication systems [5

5. A. D. Ellis, J. Zhao, and D. Cotter, “Approaching the non-linear Shannon limit,” J. Lightwave Technol. 28(4), 423–433 (2010). [CrossRef]

, 6

6. P. P. Mitra and J. B. Stark, “Nonlinear limits to the information capacity of optical fibre communications,” Nature 411(6841), 1027–1030 (2001). [CrossRef] [PubMed]

]. Mid-span spectral inversion (MSSI) using optical phase conjugation (OPC) [7

7. S. Watanabe, “Cancellation of four-wave mixing in a single-mode fiber by midway optical phase conjugation,” Opt. Lett. 19(17), 1308–1310 (1994). [CrossRef] [PubMed]

] near the middle of the link, can mitigate fiber nonlinearity for on-off keyed systems [8

8. S. L. Jansen, D. van den Borne, P. M. Krummrich, S. Spalter, G. D. Khoe, and H. de Waardt, “Long-haul DWDM transmission systems employing optical phase conjugation,” IEEE J. Sel. Top. Quantum Electron. 12(4), 505–520 (2006). [CrossRef]

] and polarization multiplexed QPSK systems [9

9. S. L. Jansen, S. Spalter, G. D. Khoe, H. Waardt, H. E. Escobar, L. Marshall, and M. Sher, “16×40 gb/s over 800 km of SSMF using mid-link spectral inversion,” IEEE Photon. Technol. Lett. 16(7), 1763–1765 (2004). [CrossRef]

11

11. P. Martelli, P. Boffi, M. Ferrario, L. Marazzi, P. Parolari, R. Siano, V. Pusino, P. Minzioni, I. Cristiani, C. Langrock, M. M. Fejer, M. Martinelli, and V. Degiorgio, “All-Optical Wavelength Conversion of a 100-Gb/s Polarization-Multiplexed Signal,” Opt. Express 17(20), 17758–17763 (2009). [CrossRef] [PubMed]

]. MSSI has also been proposed for optical OFDM systems [12

12. X. Liu, Y. Qiao, and Y. Ji, “Reduction of the fiber nonlinearity impairment using optical phase conjugation in 40Gb/s CO-OFDM systems,” Opt. Commun. 283(13), 2749–2753 (2010). [CrossRef]

]. Compared with electronic fiber nonlinearity compensation techniques [13

13. E. Ip and J. M. Kahn, “Compensation of dispersion and nonlinear impairments using digital backpropagation,” J. Lightwave Technol. 26(20), 3416–3425 (2008). [CrossRef]

], MSSI can compensate many WDM channels simultaneously [8

8. S. L. Jansen, D. van den Borne, P. M. Krummrich, S. Spalter, G. D. Khoe, and H. de Waardt, “Long-haul DWDM transmission systems employing optical phase conjugation,” IEEE J. Sel. Top. Quantum Electron. 12(4), 505–520 (2006). [CrossRef]

].

Recently, we have experimentally demonstrated an improvement of 4.8 dB in the nonlinear threshold for a 10 × 80-km 604.7-Gb/s 16-QAM CO-OFDM super channel using MSSI [14

14. L. B. Du, M. M. Morshed, and A. J. Lowery, “Fiber nonlinearity compensation for OFDM super-channels using optical phase conjugation,” Opt. Express 20(18), 19921–19927 (2012). [CrossRef] [PubMed]

]. However, the performance at the optimal operating power for maximal signal quality only improved by 0.2 dB compared with a system without MSSI. This was because the OPC module itself introduces a performance penalty. We have presented a detailed theoretical analysis [15

15. M. Morshed, L. B. Du, and A. J. Lowery, “Performance Limitation of Coherent Optical OFDM Systems with non-ideal Optical Phase Conjugation,” in IEEE Photonics Conference TuU4, pp. 394-395, 23-27 Sept. 2012.

, 16

16. M. Morshed, L. B. Du, and A. J. Lowery, “Mid-Span Spectral Inversion for Coherent Optical OFDM Systems: Fundamental Limits to Performance,” J. Lightwave Technol. 31(1), 58–66 (2013). [CrossRef]

] showing that two two-stage nonlinear processes and amplified spontaneous emission (ASE) are the cause of this performance penalty.

In this paper, we present a method of reducing the intrinsic performance penalty seen in optical phase conjugators that use third order nonlinearity. We demonstrate the method by simulating the back-to-back performance penalty of a CO-OFDM system. Our method splits the nonlinear element into two parts; then inserts a band-stop filter (BSF) centered on the pump between them, to remove the XPM products and the pump. The pump is then reinserted into the second part. This novel method reduces the performance penalty due to a two-stage nonlinear process. Numerical simulations using the split-step Fourier method (SSFM) show that our two-part OPC module has a 3-dB better back-to-back maximum Q performance compared with a conventional OPC module. Simulation results also show that this better back-to-back performance results in an improvement of the maximum signal quality, Qmax, by 1 dB in a 10 × 80-km 4-QAM 224-Gb/s CO-OFDM system.

2. MSSI with a mid-way filter

2.1 Conventional OPC

Inset (i) in Fig. 1(b) shows the spectrum at the output of the χ(3) nonlinear element, which is a Highly Non-Linear Fiber (HNLF) in this paper. Inset (ii) shows the spectrum at the output of the MSSI module. Two types of nonlinear products, XPM-OPC (dark green) and FWM-OPC (dark blue) [15

15. M. Morshed, L. B. Du, and A. J. Lowery, “Performance Limitation of Coherent Optical OFDM Systems with non-ideal Optical Phase Conjugation,” in IEEE Photonics Conference TuU4, pp. 394-395, 23-27 Sept. 2012.

, 16

16. M. Morshed, L. B. Du, and A. J. Lowery, “Mid-Span Spectral Inversion for Coherent Optical OFDM Systems: Fundamental Limits to Performance,” J. Lightwave Technol. 31(1), 58–66 (2013). [CrossRef]

], fall within the band of the wanted OPC signal, so cannot be filtered out by the BPF. Thus, these two nonlinear products, along with ASE from the erbium doped fiber amplifiers (EDFA), cause a fundamental back-to-back performance penalty in conventional MSSI. As the insets show, XPM-OPC dominates over FWM-OPC [16

16. M. Morshed, L. B. Du, and A. J. Lowery, “Mid-Span Spectral Inversion for Coherent Optical OFDM Systems: Fundamental Limits to Performance,” J. Lightwave Technol. 31(1), 58–66 (2013). [CrossRef]

].

At IPC 2012, we presented a theoretical analysis of the back-to-back performance limitation of CO-OFDM systems using an OPC modeled with all nonlinear mixing terms [15

15. M. Morshed, L. B. Du, and A. J. Lowery, “Performance Limitation of Coherent Optical OFDM Systems with non-ideal Optical Phase Conjugation,” in IEEE Photonics Conference TuU4, pp. 394-395, 23-27 Sept. 2012.

]. An in-depth analysis shows that nonlinear products generated by two-stage mixing processes impose a fundamental performance limit [16

16. M. Morshed, L. B. Du, and A. J. Lowery, “Mid-Span Spectral Inversion for Coherent Optical OFDM Systems: Fundamental Limits to Performance,” J. Lightwave Technol. 31(1), 58–66 (2013). [CrossRef]

]. In the first stage, XPM products (light green) are generated by mixing between signal × pump × (signal)* tones and FWM products (light blue) are generated due to signal × signal × (signal)* mixing. In the second stage, XPM-OPC (dark green) products are generated by mixing between XPM products × pump × (signal)* and the FWM-OPC (dark blue) products are generated by pump × pump × (FWM tones)* mixing. Here, (x)* denotes the conjugate of the term x. In a conventional OPC, the first stage of these processes generates nonlinear products whose fields grow linearly along the whole length of the HNLF: because the second stage products require the first stage products as an input, they grow quadratically over the length for the HNLF. Thus the output end of the HNLF is responsible for the generation of most of the power in the unwanted products.

2.2 Two-part OPC with mid-way filter

Our novel idea is to suppress the first-stage products at one or more places along the fiber, so the input to the second-stage process is suppressed. This is possible because the first-stage products fall outside the band of the wanted OPC signal. Figure 2
Fig. 2 Block diagram of the two-part OPC module; (i): spectrum after the first part; (ii): spectrum after the BSF; (iii): spectrum after the second half of HNLF; (iv): spectrum at the output of the OPC module.
shows the block diagram implementing this idea. The HNLF fiber, length L, has been divided in half, to form two OPC sub-modules. The output of the first OPC sub-module is passed through a band-stop filter to remove the XPM products generated within it. Unfortunately, the pump is also removed. The frequency response of the BSF is shown by the red dashed curve in Inset (i) and its output in Inset (ii). The pump is reintroduced after the filter. This must be coherent with the original pump to ensure that the new conjugate products generated in this second half add in phase with those created in the first half. The combined signal then travels along the second half (HNLF2), a BPF and an output EDFA. Inset (iii) shows the spectrum at the output of HNLF2, which shows that both the XPM and XPM-OPC products have been suppressed by a considerable amount. Inset (iv) shows the spectrum at the output of the second OPC module. The XPM-OPC products are several times smaller than those produced by a single stage OPC module. Thus, it is expected that the system performance should improve significantly using this new two-part OPC module, since the dominant nonlinear limiting factor, XPM-OPC has been suppressed. Obviously, XPM-OPC generated entirely within the first half, cannot be suppressed, as it already falls upon the conjugated signal’s spectrum. The same argument holds for XPM generated in the second half and converted to XPM-OPC in the second half. This implies that multiple filters could be used for even better performance.

3. Back-to-back performance

To quantify the maximum benefit of splitting the nonlinear element into two parts, we first considered a back-to-back system without transmission fiber, as shown in Fig. 1(a). The numerical simulations were conducted using VPItransmissionMaker v8.7. Table 1

Table 1. Simulation Parameters

table-icon
View This Table
gives the simulation parameters.

The OFDM signal was generated using MATLAB, using a 1024-point inverse fast Fourier transform (IFFT); 920 subcarriers were modulated with 4-QAM and a 32-point cyclic prefix (CP) was inserted before each OFDM symbol. The total bit rate was 224-Gb/s, resulting in a net data rate of 200-Gb/s after 12% overhead for FEC and training. At the receiver, a coherent OFDM receiver feeds a digital processor that removes the CP, performs a Fourier transform to separate the subcarriers, equalizes the phases of the subcarriers and then demodulates the subcarriers to recover the data in each subcarrier.

3.1 Improvement in back-to-back performance

Figure 3
Fig. 3 Back-to-back performance comparison between the conventional OPC module and the two-part OPC module with mid-way filtering.
shows the back-to-back Q versus input signal power into the HNLF. The blue curve with circles () shows the performance of the system with conventional MSSI and the red curve with squares () shows the performance with the proposed two-part OPC module. The orange line () shows the back-to-back performance without OPC (35 dB), which is limited due to DSP limitations. Splitting the OPC module into two parts with a mid-way filter improves the Q by 3 dB at the optimum signal power. The performance in the nonlinear threshold increases by 6 dB. Unfortunately, there still remains a 7-dB performance penalty because the XPM-OPC products generated within each part via XPM cannot be separated from the desired OPC signal. Also FWM-OPC products and amplified spontaneous emission (ASE) of the input and output EDFAs add to this penalty and cannot be removed by filtering. Further suppression of XPM-OPC products could be achieved using more than one filter, with the associated increase in complexity.

3.2 Dependence on pump power and HNLF length

In a practical OPC module, the product of the nonlinear coefficient of the HNLF and its length, γL, and the pump power are important parameters. Therefore, we have investigated the dependence of the performance improvement on pump power and HNLF length. The nonlinear coefficient, γ, has been kept at 11.5 W−1.km−1. The length of the HNLF, L, is 500 m (Fig. 4(a)
Fig. 4 Pump power and HNLF length dependence of performance improvement. All results are back-to-back.
), 1000 m (Fig. 4(b)) or 1500 m (Fig. 4(c)). The optimum signal input power is always used for each point. The results show that for higher pump powers and longer HNLF, the improvement due to suppression of the XPM products decreases. With a higher pump power and/or longer HNLF, the maximum signal quality becomes higher, which makes Qmax of the conventional MSSI modules approach the DSP limit of 35 dB. Thus the improvement using a two-part module is limited in these circumstances. However, as Fig. 4 shows, using a two-part module is more beneficial for higher conversion losses, i.e., for lower γL products and/or for lower pump powers. This may be helpful when designing OPC modules implemented with photonic integrated circuits (PICs) [17

17. B. J. Eggleton, T. D. Vo, R. Pant, J. Schroeder, M. D. Pelusi, D. Yong Choi, S. J. Madden, and B. Luther-Davies, “Photonic chip based ultrafast optical processing based on high nonlinearity dispersion engineered chalcogenide waveguides,” Laser Photon. Rev. 6(1), 97–114 (2012). [CrossRef]

, 18

18. M. D. Pelusi, F. Luan, D. Y. Choi, S. J. Madden, D. A. P. Bulla, B. Luther-Davies, and B. J. Eggleton, “Optical phase conjugation by an As2S3 glass planar waveguide for dispersion-free transmission of WDM-DPSK signals over fiber,” Opt. Express 18(25), 26686–26694 (2010). [CrossRef] [PubMed]

], where the γL product term is about 20 times smaller (9900 W−1km−1 × 6 cm) [18

18. M. D. Pelusi, F. Luan, D. Y. Choi, S. J. Madden, D. A. P. Bulla, B. Luther-Davies, and B. J. Eggleton, “Optical phase conjugation by an As2S3 glass planar waveguide for dispersion-free transmission of WDM-DPSK signals over fiber,” Opt. Express 18(25), 26686–26694 (2010). [CrossRef] [PubMed]

] than the value we have employed to represent a typical MSSI using HNLF (11.5 W−1 km−1 × 1000 m) when Stimulated Brillouin Scattering (SBS) limits pump power.

3.3 Bandwidth dependence

Figure 5
Fig. 5 Bandwidth dependence of performance improvement. All results are back-to-back.
shows the dependence of back-to-back performance improvement on the signal bandwidth. The blue curve with circles () shows the maximum signal quality, Qmax with conventional OPC module. The red curve with squares () shows Qmax with two-part OPC. It is interesting to note that in the region below 100 GHz, higher signal bandwidths give larger performance improvements with mid-way filtering. This is because, at bandwidths ≤ 100 GHz, the back-to-back performance using conventional OPC is already very high, that is, there is no significant performance penalty. Therefore, the improvement in this region with mid-way filtering is not significant. At higher bandwidths, the improvement saturates at 3 dB, shown by green curve with triangles (). These results show that our two-part OPC is more suitable for high bandwidth devices such as PICs [17

17. B. J. Eggleton, T. D. Vo, R. Pant, J. Schroeder, M. D. Pelusi, D. Yong Choi, S. J. Madden, and B. Luther-Davies, “Photonic chip based ultrafast optical processing based on high nonlinearity dispersion engineered chalcogenide waveguides,” Laser Photon. Rev. 6(1), 97–114 (2012). [CrossRef]

, 18

18. M. D. Pelusi, F. Luan, D. Y. Choi, S. J. Madden, D. A. P. Bulla, B. Luther-Davies, and B. J. Eggleton, “Optical phase conjugation by an As2S3 glass planar waveguide for dispersion-free transmission of WDM-DPSK signals over fiber,” Opt. Express 18(25), 26686–26694 (2010). [CrossRef] [PubMed]

].

The effect of chromatic dispersion is shown in the dashed lines in Fig. 5. The CD value for this simulation is 0.01 ps/nm/km, which is typical for an OFS HNLF. For signal bandwidths narrower than 400 GHz, CD has almost no effect in the conjugated signal quality. However, for signal bandwidths wider than 400 GHz, the effect of CD degrades the signal quality for a conventional OPC, and reduces the improvement achieved by the two-part OPC. This is because conversion efficiency for the conjugated signal decreases for broad band OPC due to phase mismatch effect of CD.

4. Performance improvement in a transmission system

4.1 Improvement in signal quality with transmission system

4.2 Transmission distance dependence

4.3 Signal bandwidth dependence in transmission system

Figure 8
Fig. 8 Signal bandwidth dependence of performance improvement in transmission system.
shows the signal bandwidth dependence of the performance improvement for the 10 × 80-km transmission system.

Again, the blue curve with circles () shows the maximum signal quality, Qmax, from the system with a conventional OPC module and the red curve with squares () is for the system with a two-part OPC. The green curve with triangles () shows the improvement in Qmax. The improvement increases with increasing bandwidth and reaches to about 2.0 dB with a signal bandwidth of 866 GHz. In contrast to the back-to-back case (Section 3.3), where the improvement saturated at 3 dB, the improvement in a transmission system increases gradually with signal bandwidth. In a transmission system using OFDM super channel which covers several hundred GHz of signal bandwidth, this method of OPC could become attractive for fiber nonlinearity compensation. Systems with wider bandwidths could be converted in parts, perhaps using an integrated device to save space.

4.4 Effect of pump phase difference

An open question is how the new OPC module will perform in a real implementation, where there could be some phase difference between the pumps used in the first and second parts of the module, thus, we simulated the performance penalty due to phase mismatches. The phase of the second pump was swept from 0 to 360 degrees relative to the first pump. The simulation results are plotted in Fig. 9
Fig. 9 Effect of phase difference between the pumps injected into the first and second part of the HNLF on performance improvement.
. For an absolute phase difference less than 20°, as shown in the shaded region in Fig. 9, the penalty is less than 0.05 dB. However, the penalty increases sharply for larger phase differences. Therefore, our new method of OPC can be implemented practically in a real system, provided that the pump phases can be controlled adequately, perhaps by integrating the system upon a photonic chip [17

17. B. J. Eggleton, T. D. Vo, R. Pant, J. Schroeder, M. D. Pelusi, D. Yong Choi, S. J. Madden, and B. Luther-Davies, “Photonic chip based ultrafast optical processing based on high nonlinearity dispersion engineered chalcogenide waveguides,” Laser Photon. Rev. 6(1), 97–114 (2012). [CrossRef]

, 18

18. M. D. Pelusi, F. Luan, D. Y. Choi, S. J. Madden, D. A. P. Bulla, B. Luther-Davies, and B. J. Eggleton, “Optical phase conjugation by an As2S3 glass planar waveguide for dispersion-free transmission of WDM-DPSK signals over fiber,” Opt. Express 18(25), 26686–26694 (2010). [CrossRef] [PubMed]

], or adding an active phase control. The phases could be controlled by monitoring the OPC signal strength and adjusting the phase to maximize this, perhaps using a dither signal on the phase adjustment signal to enable the control system to resolve the direction it needs to adjust in to reach the peak of performance.

5. Discussion

An alternative method of implementing optical phase conjugation, by using second-order optical nonlinear process with periodically poled LiNbO3 (PPLN) waveguide has been reported for RZ-DPSK and RZ-DQPSK systems [20

20. A. Chowdhury, G. Raybon, R. J. Essiambre, J. H. Sinsky, A. Adamiecki, J. Leuthold, C. R. Doerr, and S. Chandrasekhar, “Compensation of intrachannel nonlinearities in 40-Gb/s pseudolinear systems using optical-phase conjugation,” J. Lightwave Technol. 23(1), 172–177 (2005). [CrossRef]

23

23. S. L. Jansen, D. van den Borne, P. M. Krummrich, S. Spälter, H. Suche, W. Sohler, G. D. Khoe, H. de Waardt, I. Morita, and H. Tanaka, “Applications of optical phase conjugation in robust optical transmission systems,” in Proc. SPIE 6783 Optical Transmission, Switching, and Subsystems V, 67830P (November 19, 2007).

]. Two cascaded second-order nonlinear processes take place inside a PPLN waveguide to generate the conjugated signal: (i) second harmonic generation (SHG) of the pump from a frequency ωp to 2ωp; (ii) difference frequency generation (DFG) of the SHG by mixing with the input signal ωs, giving conjugated signal at 2ωpωs.

One advantage of using PPLN is that no third-order nonlinear impairments such as self-phase modulation (SPM) and cross-phase modulation (XPM) occur in the phase conjugation process [23

23. S. L. Jansen, D. van den Borne, P. M. Krummrich, S. Spälter, H. Suche, W. Sohler, G. D. Khoe, H. de Waardt, I. Morita, and H. Tanaka, “Applications of optical phase conjugation in robust optical transmission systems,” in Proc. SPIE 6783 Optical Transmission, Switching, and Subsystems V, 67830P (November 19, 2007).

]. Using PPLN for OPC gave a 1.5-dB improvement in signal quality for a 3200-km 40-Gb/s RZ-DPSK system [20

20. A. Chowdhury, G. Raybon, R. J. Essiambre, J. H. Sinsky, A. Adamiecki, J. Leuthold, C. R. Doerr, and S. Chandrasekhar, “Compensation of intrachannel nonlinearities in 40-Gb/s pseudolinear systems using optical-phase conjugation,” J. Lightwave Technol. 23(1), 172–177 (2005). [CrossRef]

]. Similarly, Jansen et al. gained an improvement of 0.5 dB for a 5000 km system [22

22. S. L. Jansen, D. van den Borne, B. Spinnler, S. Calabrò, H. Suche, P. M. Krummrich, W. Sohler, G. D. Khoe, and H. de Waardt, “Optical phase conjugation for ultra long-haul Phase-Shift-Keyed transmission,” J. Lightwave Technol. 24(1), 54–64 (2006). [CrossRef]

].

A possible disadvantage of using PPLN is that it requires a relatively high pump powers to increase the efficiency of SHG, typically 20-27 dBm [20

20. A. Chowdhury, G. Raybon, R. J. Essiambre, J. H. Sinsky, A. Adamiecki, J. Leuthold, C. R. Doerr, and S. Chandrasekhar, “Compensation of intrachannel nonlinearities in 40-Gb/s pseudolinear systems using optical-phase conjugation,” J. Lightwave Technol. 23(1), 172–177 (2005). [CrossRef]

23

23. S. L. Jansen, D. van den Borne, P. M. Krummrich, S. Spälter, H. Suche, W. Sohler, G. D. Khoe, H. de Waardt, I. Morita, and H. Tanaka, “Applications of optical phase conjugation in robust optical transmission systems,” in Proc. SPIE 6783 Optical Transmission, Switching, and Subsystems V, 67830P (November 19, 2007).

]. These high powers cause photorefractive damage, unless the PPLN is heated above 100°C [11

11. P. Martelli, P. Boffi, M. Ferrario, L. Marazzi, P. Parolari, R. Siano, V. Pusino, P. Minzioni, I. Cristiani, C. Langrock, M. M. Fejer, M. Martinelli, and V. Degiorgio, “All-Optical Wavelength Conversion of a 100-Gb/s Polarization-Multiplexed Signal,” Opt. Express 17(20), 17758–17763 (2009). [CrossRef] [PubMed]

]. In addition, the pump frequency is strictly determined by the period of the poling. OPC using third-order nonlinearity does not have these issues; therefore, with our improvements, it is a viable alternate to PPLN devices. A common analysis framework, including SBS, would need to be developed to quantify the relative performance of these methods.

6. Conclusion

We have proposed a new design of an OPC to improve the back-to-back performance of CO-OFDM systems using MSSI. The new design reduces the performance penalty introduced by a conventional OPC module by 3 dB. We have shown that this back-to-back performance improvement results in a 1-dB improvement in a 10 × 80-km 4-QAM 224-Gb/s CO-OFDM system. The improvement increases gradually with higher signal bandwidths, which is useful for ultrahigh bandwidth transmission. Finally, we have shown that our new system would have almost no degradation due to the phase difference between the injected pumps, provided that this is controlled to within +/− 20 degrees.

Acknowledgment

This research was conducted by the Australian Research Council Centre of Excellence for Ultrahigh bandwidth Devices for Optical Systems, CUDOS (Project number CE110001018). We should like to thank VPIphotonics.com for the use of VPItransmissionMaker.

References and links

1.

A. J. Lowery and J. Armstrong, “Orthogonal-frequency-division multiplexing for dispersion compensation of long-haul optical systems,” Opt. Express 14(6), 2079–2084 (2006). [CrossRef] [PubMed]

2.

W. Shieh, X. Yi, Y. Ma, and Y. Tang, “Theoretical and experimental study on PMD-supported transmission using polarization diversity in coherent optical OFDM systems,” Opt. Express 15(16), 9936–9947 (2007). [CrossRef] [PubMed]

3.

L. B. Du and A. J. Lowery, “Pilot-based cross-phase modulation compensation for coherent optical orthogonal frequency division multiplexing long-haul optical communications systems,” Opt. Lett. 36, 3 (2011).

4.

L. B. Du and A. J. Lowery, “Practical XPM compensation method for coherent optical OFDM systems,” IEEE Photon. Technol. Lett. 22, 320–322 (2009).

5.

A. D. Ellis, J. Zhao, and D. Cotter, “Approaching the non-linear Shannon limit,” J. Lightwave Technol. 28(4), 423–433 (2010). [CrossRef]

6.

P. P. Mitra and J. B. Stark, “Nonlinear limits to the information capacity of optical fibre communications,” Nature 411(6841), 1027–1030 (2001). [CrossRef] [PubMed]

7.

S. Watanabe, “Cancellation of four-wave mixing in a single-mode fiber by midway optical phase conjugation,” Opt. Lett. 19(17), 1308–1310 (1994). [CrossRef] [PubMed]

8.

S. L. Jansen, D. van den Borne, P. M. Krummrich, S. Spalter, G. D. Khoe, and H. de Waardt, “Long-haul DWDM transmission systems employing optical phase conjugation,” IEEE J. Sel. Top. Quantum Electron. 12(4), 505–520 (2006). [CrossRef]

9.

S. L. Jansen, S. Spalter, G. D. Khoe, H. Waardt, H. E. Escobar, L. Marshall, and M. Sher, “16×40 gb/s over 800 km of SSMF using mid-link spectral inversion,” IEEE Photon. Technol. Lett. 16(7), 1763–1765 (2004). [CrossRef]

10.

L. Marazzi, P. Parolari, P. Martelli, R. Siano, P. Boffi, M. Ferrario, A. Righetti, M. Martinelli, V. Pusino, P. Minzioni, I. Cristiani, V. Degiorgio, C. Langrock, and M. M. Fejer, “Real-Time 100-Gb/s POLMUX RZ-DQPSK Transmission over Uncompensated 500 km of SSMF by Optical Phase Conjugation,” in National Fiber Optic Engineers Conference, (Optical Society of America, 2009), paper JWA44.

11.

P. Martelli, P. Boffi, M. Ferrario, L. Marazzi, P. Parolari, R. Siano, V. Pusino, P. Minzioni, I. Cristiani, C. Langrock, M. M. Fejer, M. Martinelli, and V. Degiorgio, “All-Optical Wavelength Conversion of a 100-Gb/s Polarization-Multiplexed Signal,” Opt. Express 17(20), 17758–17763 (2009). [CrossRef] [PubMed]

12.

X. Liu, Y. Qiao, and Y. Ji, “Reduction of the fiber nonlinearity impairment using optical phase conjugation in 40Gb/s CO-OFDM systems,” Opt. Commun. 283(13), 2749–2753 (2010). [CrossRef]

13.

E. Ip and J. M. Kahn, “Compensation of dispersion and nonlinear impairments using digital backpropagation,” J. Lightwave Technol. 26(20), 3416–3425 (2008). [CrossRef]

14.

L. B. Du, M. M. Morshed, and A. J. Lowery, “Fiber nonlinearity compensation for OFDM super-channels using optical phase conjugation,” Opt. Express 20(18), 19921–19927 (2012). [CrossRef] [PubMed]

15.

M. Morshed, L. B. Du, and A. J. Lowery, “Performance Limitation of Coherent Optical OFDM Systems with non-ideal Optical Phase Conjugation,” in IEEE Photonics Conference TuU4, pp. 394-395, 23-27 Sept. 2012.

16.

M. Morshed, L. B. Du, and A. J. Lowery, “Mid-Span Spectral Inversion for Coherent Optical OFDM Systems: Fundamental Limits to Performance,” J. Lightwave Technol. 31(1), 58–66 (2013). [CrossRef]

17.

B. J. Eggleton, T. D. Vo, R. Pant, J. Schroeder, M. D. Pelusi, D. Yong Choi, S. J. Madden, and B. Luther-Davies, “Photonic chip based ultrafast optical processing based on high nonlinearity dispersion engineered chalcogenide waveguides,” Laser Photon. Rev. 6(1), 97–114 (2012). [CrossRef]

18.

M. D. Pelusi, F. Luan, D. Y. Choi, S. J. Madden, D. A. P. Bulla, B. Luther-Davies, and B. J. Eggleton, “Optical phase conjugation by an As2S3 glass planar waveguide for dispersion-free transmission of WDM-DPSK signals over fiber,” Opt. Express 18(25), 26686–26694 (2010). [CrossRef] [PubMed]

19.

P. Minzioni, F. Alberti, and A. Schiffini, “Techniques for nonlinearity cancellation into embedded links by optical phase conjugation,” J. Lightwave Technol. 23(8), 2364–2370 (2005). [CrossRef]

20.

A. Chowdhury, G. Raybon, R. J. Essiambre, J. H. Sinsky, A. Adamiecki, J. Leuthold, C. R. Doerr, and S. Chandrasekhar, “Compensation of intrachannel nonlinearities in 40-Gb/s pseudolinear systems using optical-phase conjugation,” J. Lightwave Technol. 23(1), 172–177 (2005). [CrossRef]

21.

S. L. Jansen, D. van den Borne, C. Climent, M. Serbay, C. J. Weiske, H. Suche, P. M. Krummrich, S. Spalter, S. Calabro, N. Hecker-Denschlag, P. Leisching, W. Rosenkranz, W. Sohler, G. D. Khoe, T. Koonen, and H. de Waardt, “10,200 km 22×2×10 Gbit/s RZ-DQPSK dense WDM transmission without inline dispersion compensation through optical phase conjugation,” Optical Fiber Communication Conference, 2005. Technical Digest. OFC/NFOEC, 6, PDP 28, 6-11 March 2005.

22.

S. L. Jansen, D. van den Borne, B. Spinnler, S. Calabrò, H. Suche, P. M. Krummrich, W. Sohler, G. D. Khoe, and H. de Waardt, “Optical phase conjugation for ultra long-haul Phase-Shift-Keyed transmission,” J. Lightwave Technol. 24(1), 54–64 (2006). [CrossRef]

23.

S. L. Jansen, D. van den Borne, P. M. Krummrich, S. Spälter, H. Suche, W. Sohler, G. D. Khoe, H. de Waardt, I. Morita, and H. Tanaka, “Applications of optical phase conjugation in robust optical transmission systems,” in Proc. SPIE 6783 Optical Transmission, Switching, and Subsystems V, 67830P (November 19, 2007).

OCIS Codes
(060.4080) Fiber optics and optical communications : Modulation
(060.4510) Fiber optics and optical communications : Optical communications
(070.4340) Fourier optics and signal processing : Nonlinear optical signal processing
(070.5040) Fourier optics and signal processing : Phase conjugation
(190.4380) Nonlinear optics : Nonlinear optics, four-wave mixing

ToC Category:
Nonlinear Optics

History
Original Manuscript: November 29, 2012
Revised Manuscript: January 31, 2013
Manuscript Accepted: January 31, 2013
Published: February 14, 2013

Citation
Monir Morshed, Arthur J. Lowery, and Liang B. Du, "Improving performance of optical phase conjugation by splitting the nonlinear element," Opt. Express 21, 4567-4577 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-4-4567


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References

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  3. L. B. Du and A. J. Lowery, “Pilot-based cross-phase modulation compensation for coherent optical orthogonal frequency division multiplexing long-haul optical communications systems,” Opt. Lett.36, 3 (2011).
  4. L. B. Du and A. J. Lowery, “Practical XPM compensation method for coherent optical OFDM systems,” IEEE Photon. Technol. Lett.22, 320–322 (2009).
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  9. S. L. Jansen, S. Spalter, G. D. Khoe, H. Waardt, H. E. Escobar, L. Marshall, and M. Sher, “16×40 gb/s over 800 km of SSMF using mid-link spectral inversion,” IEEE Photon. Technol. Lett.16(7), 1763–1765 (2004). [CrossRef]
  10. L. Marazzi, P. Parolari, P. Martelli, R. Siano, P. Boffi, M. Ferrario, A. Righetti, M. Martinelli, V. Pusino, P. Minzioni, I. Cristiani, V. Degiorgio, C. Langrock, and M. M. Fejer, “Real-Time 100-Gb/s POLMUX RZ-DQPSK Transmission over Uncompensated 500 km of SSMF by Optical Phase Conjugation,” in National Fiber Optic Engineers Conference, (Optical Society of America, 2009), paper JWA44.
  11. P. Martelli, P. Boffi, M. Ferrario, L. Marazzi, P. Parolari, R. Siano, V. Pusino, P. Minzioni, I. Cristiani, C. Langrock, M. M. Fejer, M. Martinelli, and V. Degiorgio, “All-Optical Wavelength Conversion of a 100-Gb/s Polarization-Multiplexed Signal,” Opt. Express17(20), 17758–17763 (2009). [CrossRef] [PubMed]
  12. X. Liu, Y. Qiao, and Y. Ji, “Reduction of the fiber nonlinearity impairment using optical phase conjugation in 40Gb/s CO-OFDM systems,” Opt. Commun.283(13), 2749–2753 (2010). [CrossRef]
  13. E. Ip and J. M. Kahn, “Compensation of dispersion and nonlinear impairments using digital backpropagation,” J. Lightwave Technol.26(20), 3416–3425 (2008). [CrossRef]
  14. L. B. Du, M. M. Morshed, and A. J. Lowery, “Fiber nonlinearity compensation for OFDM super-channels using optical phase conjugation,” Opt. Express20(18), 19921–19927 (2012). [CrossRef] [PubMed]
  15. M. Morshed, L. B. Du, and A. J. Lowery, “Performance Limitation of Coherent Optical OFDM Systems with non-ideal Optical Phase Conjugation,” in IEEE Photonics Conference TuU4, pp. 394-395, 23-27 Sept. 2012.
  16. M. Morshed, L. B. Du, and A. J. Lowery, “Mid-Span Spectral Inversion for Coherent Optical OFDM Systems: Fundamental Limits to Performance,” J. Lightwave Technol.31(1), 58–66 (2013). [CrossRef]
  17. B. J. Eggleton, T. D. Vo, R. Pant, J. Schroeder, M. D. Pelusi, D. Yong Choi, S. J. Madden, and B. Luther-Davies, “Photonic chip based ultrafast optical processing based on high nonlinearity dispersion engineered chalcogenide waveguides,” Laser Photon. Rev.6(1), 97–114 (2012). [CrossRef]
  18. M. D. Pelusi, F. Luan, D. Y. Choi, S. J. Madden, D. A. P. Bulla, B. Luther-Davies, and B. J. Eggleton, “Optical phase conjugation by an As2S3 glass planar waveguide for dispersion-free transmission of WDM-DPSK signals over fiber,” Opt. Express18(25), 26686–26694 (2010). [CrossRef] [PubMed]
  19. P. Minzioni, F. Alberti, and A. Schiffini, “Techniques for nonlinearity cancellation into embedded links by optical phase conjugation,” J. Lightwave Technol.23(8), 2364–2370 (2005). [CrossRef]
  20. A. Chowdhury, G. Raybon, R. J. Essiambre, J. H. Sinsky, A. Adamiecki, J. Leuthold, C. R. Doerr, and S. Chandrasekhar, “Compensation of intrachannel nonlinearities in 40-Gb/s pseudolinear systems using optical-phase conjugation,” J. Lightwave Technol.23(1), 172–177 (2005). [CrossRef]
  21. S. L. Jansen, D. van den Borne, C. Climent, M. Serbay, C. J. Weiske, H. Suche, P. M. Krummrich, S. Spalter, S. Calabro, N. Hecker-Denschlag, P. Leisching, W. Rosenkranz, W. Sohler, G. D. Khoe, T. Koonen, and H. de Waardt, “10,200 km 22×2×10 Gbit/s RZ-DQPSK dense WDM transmission without inline dispersion compensation through optical phase conjugation,” Optical Fiber Communication Conference, 2005. Technical Digest. OFC/NFOEC, 6, PDP 28, 6-11 March 2005.
  22. S. L. Jansen, D. van den Borne, B. Spinnler, S. Calabrò, H. Suche, P. M. Krummrich, W. Sohler, G. D. Khoe, and H. de Waardt, “Optical phase conjugation for ultra long-haul Phase-Shift-Keyed transmission,” J. Lightwave Technol.24(1), 54–64 (2006). [CrossRef]
  23. S. L. Jansen, D. van den Borne, P. M. Krummrich, S. Spälter, H. Suche, W. Sohler, G. D. Khoe, H. de Waardt, I. Morita, and H. Tanaka, “Applications of optical phase conjugation in robust optical transmission systems,” in Proc. SPIE 6783 Optical Transmission, Switching, and Subsystems V, 67830P (November 19, 2007).

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