Dispersion-managed Transmission Research Articles

PMD tolerant transmission using multiple optical phase conjugators in the discretely amplified systems

Abstract In this paper, the impact of polarization mode dispersion (PMD) on system performance in coherent optical transmission assisted by optical phase conjugation (OPC) technique is numerically investigated for a 9-channel PM-4QAM system at 128Gbit/s. The OPC-aided transmission, amplified with lumped erbium doped fiber amplifier (EDFA), is a variation of the conventional dispersion-managed link, which is also called dispersion-inverted link. We demonstrate that introducing more OPCs along the link can partly suppress the PMD-induced impairments and thus improve the system performance significantly. Results of 960-km dispersion-managed transmission show that PMD effect will cause a performance penalty of 1.8 dB when using mid-link OPC (i.e., only 1-OPC), while this penalty will decrease to about 0.4 dB when employing 6-OPCs along the link. Comparing with conventional digital back-propagation (DBP) technique, a performance improvement of about 3.1 dB is observed with multi-OPCs when fiber PMD is equal to 0.1ps/ k m $\sqrt{km}$ .

Intrachannel Four-Wave Mixing Compensation in Dispersion-Managed Transmission Links with Mid-Span Optical Phase Conjugation

Intrachannel Four-Wave Mixing Compensation in Dispersion-Managed Transmission Links with Mid-Span Optical Phase Conjugation

Improved compensation of intrachannel four-wave mixing in dispersion-managed transmission links with mid-span optical phase conjugation

Recently, a novel approach to satisfy the nonlinearity compensation criteria by mid-span optical-phase-conjugation (OPC) was proposed and excellent transmission performance was achieved, there the OPC propagation symmetry was obtained through optimized dispersion management with inverse-dispersion fiber (IDF). In this work, the author numerically investigates the possibilities of using dispersion-compensating fiber (DCF) instead of IDF for construction of the link. Nonlinearity compensation effectiveness of the two links are compared with respected to the intrachannel four-wave mixing (IFWM) induced intensity fluctuation of the ‘1’ bits and the generation of the ghost pulse. It is found that, by launching different powers (or energy of a limited bits) into the spans before and after the OPC, nonlinearity mismatch between the spans of the DCF-managed link can be counterbalanced with significantly improved transmission performance. For a given input energy, there exists an optimum ratio of the energies into the spans before and after the OPC, at which optimum nonlinearity compensation can be achieved, and the compensation effectiveness is very close to that of the IDF-managed link. Further studies show that the optimum energy ratio increases with the input energy but is independent of the span number of the link.

Fiber Nonlinearity Compensation: DBP Versus Link-Optimized OPC in Coherent Transmission

In this letter, we numerically compare the system performance of nonlinearity-compensated transmission based on digital back-propagation (DBP) and optical phase conjugation (OPC) technique in coherent transmission with lumped erbium doped fiber amplifiers (EDFAs). The tested transmission for DBP is a conventional dispersion-managed link, while it is an optimized design, the so-called dispersion inversion link for OPC-based system. Both of them have the same amount and type of fibers, and thus the same transmission reach. The numerical results show that DBP-aided systems have better performance for a shorter transmission reach while OPC technique presents its performance advantage when the transmission reach is increased. For a given transmission distance, the performance of OPC systems can further be improved by introducing additional OPCs. Results of 3840-km (<inline-formula> <tex-math notation="LaTeX">$48\times 80$ </tex-math></inline-formula>km) dispersion-managed transmission show that only mid-link OPC is enough to get similar performance with full-field DBP. By employing 6-OPCs in the links, the SNR of OPC-based system outperforms DBP by up to 1.9dB, while this SNR advantage will increase to 3dB after 5760-km (<inline-formula> <tex-math notation="LaTeX">$72\times 80$ </tex-math></inline-formula>km) transmission.

Improved Compensation of Intrachannel Four-Wave Mixing in Dispersion-Managed Transmission Links with Mid-Span Optical Phase Conjugation

Improved Compensation of Intrachannel Four-Wave Mixing in Dispersion-Managed Transmission Links with Mid-Span Optical Phase Conjugation

Fiber nonlinearity compensation using optical phase conjugation in dispersion-managed coherent transmission systems

Abstract In the discretely amplified transmission systems with erbium-doped fiber amplifiers, the system performance of nonlinearity-compensated optical transmission based on pre-dispersed spectral inversion (PSI) is investigated numerically. We find that PSI offers more significant performance improvement in dispersion-managed (DM) links than that in non-dispersion-managed (noDM) links. On the other hand, the DM link is more sensitive to the span offset from the center of the transmission link than noDM link. The performance difference between DM and noDM links is 1 dB if the span offset equals four spans in 20 × 90 km nonlinear transmission. Furthermore, we show that for the dispersion-managed transmission, in order to obtain the best system performance, the amount of pre-dispersion of the PSI, should be optimized over different dispersion maps.

Evaluation of the impact of higher-order energy enhancement characteristics of solitons in strongly dispersion-managed optical fibers

We study the propagation properties of nonlinear pulses with periodic evolution in a dispersion-managed transmission link by means of a variational approach. We fit the energy enhancement required for stable propagation of a single soliton in a prototypical commercial link to a polynomial approximation that describes the dependence of the energy on the map strength of the normalized unit cell. We present an improvement of a relatively old and essential result, namely, the dependence of the energy-enhancement factor of dispersion-management solitons with the square of the map strength of the fiber link. We find that adding additional corrections to the conventional quadratic formula up to the fourth order results in an improvement in the accuracy of the description of the numerical results obtained with the variational approximation. Even a small error in the energy is found to introduce large deviations in the pulse parameters during its evolution. The error in the evaluation of the interaction distance between two adjacent time division multiplexed pulses propagating in the same channel in a prototypical submarine link is of the same order as the error in the energy.

Higher-order interaction-induced effects between strong dispersion-managed solitons with dissimilar powers

We address one of the major penalties associated with the transmission of optical solitons in fiber-optic networks: the intrachannel interactions between pulses in a single channel strong dispersion-managed transmission link. We calculate the interaction length between sets of two and three pulses as a function of the ratio of dissimilar peak powers of interacting solitons by means of a variational approach to the generalized nonlinear Schrodinger equation describing the evolution of optical soliton pulses. We find a maximum of this colliding length for specific values of pulse energies. The effect of higher-order perturbation terms, such as third-order dispersion, Raman scattering, and self-steepening, shows an enhancement of the interaction distance in a broad range of dispersion difference values. We conclude that the transmission characteristics of soliton trains may be improved by means of using specific values of unequal energies and taking into account higher-order correction terms.

Large predispersion for reduction of intrachannel nonlinear impairments in strongly dispersion-managed transmissions

Predispersion for reduction of intrachannel nonlinear impairments in quasi-linear strongly dispersion-managed transmission system is analyzed in detail by numerical simulations. We show that for a moderate amount of predispersion, there is an optimal value at which reduction of the nonlinear impairments can be obtained, which is consistent with previous well-known predictions. However, we found improved transmission performance than that of the previous predictions can be obtained if predispersion is increased to some extent. For large predispersion, the nonlinear impairments reduce monotonically with increasing predispersion, and tend to become stable when predispersion is further increased. Thus, transmission performance can be efficiently improved by inserting a high-dispersive element, such as a chirped fiber bragg grating (CFBG), at the input end of the transmission link to broaden the signal pulses while, at the output end, using another CFBG with the opposite dispersion to recompress the signal.

Analytical expressions for the nonlinear interference in dispersion managed transmission coherent optical systems

Closed-form expressions of nonlinear interference of dense wavelength-division-multiplexed (WDM) systems with dispersion managed transmission (DMT) are derived. We carry out a simulative validation by addressing an ample and significant set of the Nyquist-WDM systems based on polarization multiplexed quadrature phase-shift keying (PM-QPSK) subcarriers at a baud rate of 32Gbaud per channel. Simulation results show the simple closed-form analytical expressions can provide an effective tool for the quick and accurate prediction of system performance in DMT coherent optical systems.

Generation of 1024-Tb/s Nyquist-WDM phase-conjugated twin vector waves by a polarization-insensitive optical parametric amplifier for fiber-nonlinearity-tolerant transmission

We experimentally demonstrate the generation of 1.024-Tb/s Nyquist-WDM phase-conjugated vector twin waves (PCTWs), consisting of eight 128-Gb/s polarization-division-multiplexed QPSK signals and their idlers, by a broadband polarization-insensitive fiber optic parametric amplifier. This novel all-optical signal processing approach to generate WDM-PCTWs enables a 2-fold reduction in the needed optical transmitters as compared to the conventional approach where each idler is generated by a dedicated transmitter. Digital coherent superposition of the twin waves at the receiver enables more than doubled reach in a dispersion-managed transmission link. We further study the impact of polarization-mode dispersion on the performance gain brought by the phase-conjugated twin waves, showing a gain of ~3.8 dB in signal quality factors.

Multi-channel nonlinearity compensation of PDM-QPSK signals in dispersion-managed transmission using dispersion-folded digital backward propagation

We demonstrate nonlinearity compensation of 37.5-GHz-spaced 128-Gb/s PDM-QPSK signals using dispersion-folded digital-backward-propagation and a spectrally-sliced receiver that simultaneously receives three WDM signals, showing mitigation of intra-channel and inter-channel nonlinear effects in a 2560-km dispersion-managed TWRS-fiber link. Intra-channel and adjacent inter-channel nonlinear compensation gains when WDM channels are fully populated in the C-band are estimated based on the GN-model.

强色散管理准线性传输信道内非线性效应及其抑制研究

强色散管理准线性传输信道内非线性效应及其抑制研究

Statistical characterization of the nonlinear noise in 28 Tbit/s PDM-16QAM CO-OFDM system

We show for the first time through comprehensive simulations under both uncompensated transmission (UT) and dispersion managed transmission (DMT) systems that the statistical distribution of the nonlinear interference (NLI) within the polarization multiplexed 16-state quadrature amplitude modulation (PM-16QAM) Coherent Optical OFDM (CO-OFDM) system deviates from Gaussian distribution in the absence of amplified spontaneous emission (ASE) noise. We also observe that the dependences of the variance of the NLI noise on both the launch power and the transmission distance (logrithm) seem to be in a simple linear way.

Compensation of Intrachannel Cross-phase Modulation (IXPM) Induced Phase perturbation in Dispersion Managed Transmission over Uncompensated Single Fiber Line

Compensation of Intrachannel Cross-phase Modulation (IXPM) Induced Phase perturbation in Dispersion Managed Transmission over Uncompensated Single Fiber Line

In-Line Polarization-Insensitive Parametric Tunable Dispersion Compensator for WDM Signals

We develop frequency-preserving parametric tunable dispersion compensator (P-TDC) with polarization diversity for simultaneous dispersion compensation of wavelength division multiplexing channels. The in-line polarization-insensitive P-TDC is composed of cascaded parametric tunable frequency converters based on degenerate four-wave mixing process in polarization-maintaining highly nonlinear fibers with a low dispersion slope. Dispersion-managed error-free transmission of four channels of 43 Gb/s nonreturn-to-zero ON-OFF keying signal is successfully demonstrated over 126 km dispersion-shifted fiber with the in-line polarization-insensitive P-TDC.

System performance influenced by channel plan for coherent PDM-QPSK/OOK hybrid transmission systems

The impact of channel occupancies on polarization division multiplexed quadrature phase-shift keying (PDM-QPSK)/on-off keying (OOK) hybrid systems is investigated numerically over a dispersion-managed transmission link. In addition to keep large residual dispersion per span, we find that suitable channel occupancy also help to improve the nonlinear tolerance of such hybrid systems significantly. About 2.4-dBm more nonlinear threshold (NLT) and 75% increase of transmission reach can be obtained under suitable channel plan for 112-Gb/s PDM-QPSK/OOK hybrid systems.

Field Demonstration of Parametric Tunable Dispersion Compensator Employing Polarization Diversity Scheme

We report long-term polarization-insensitive operation of a parametric tunable dispersion compensator (P-TDC) in 43-Gb/s NRZ-OOK transmission over 105-km field-installed fiber. The P-TDC employs polarization diversity loop using polarization-maintaining highly nonlinear fiber with a low dispersion slope. Stable dispersion-managed transmission for more than 8 hours is achieved under the polarization-fluctuating conditions in the field-installed fiber.

Average Optical Phase Shift as an Indicator of the Dispersion Management Optimization in PSK-Modulated Transmission Systems

In the context of single-channel quadrature phase-shift keying dispersion-managed transmission systems, we numerically investigate the signal impairments due to the deterministic interaction between chromatic dispersion and nonlinearities. We first observe that received signal constellations exhibit an average optical phase shift exceeding the nonlinear cumulative phase. We then show that this exceeding phase shift yields useful indications for the optimization of dispersion-managed system design.

Mitigation of fiber nonlinear impairments in polarization division multiplexed OFDM transmission

Fiber nonlinear effects are found to cause severe signal degradation in long-haul coherent optical OFDM (CO-OFDM) transmission, particularly in dispersion-managed transmission. We present promising techniques to mitigate the fiber nonlinear impairments in both single-channel and wavelength division multiplexed (WDM) transmission. For single-channel transmission, we discuss a joint self-phase modulation (SPM) compensation scheme that is applicable to polarization division multiplexed (PDM) CO-OFDM signals. Experimental demonstration of this joint SPM compensation scheme is also presented. For WDM transmission, we describe an OFDM frame design and a dispersion management scheme that reduce the cross-phase-modulation (XPM) penalty among the WDM channels. The impact of XPM from WDM channels with different signal formats and data rates is briefly discussed. é 2010 Alcatel-Lucent.