V. Mikhailov

Electronic dispersion compensation by signal predistortion using digital Processing and a dual-drive Mach-Zehnder Modulator

We propose and investigate a novel electronic dispersion compensation technique, in which signal precompensation is achieved using a dual-drive Mach-Zehnder modulator, driven by adaptive nonlinear digital filters. The results demonstrate effective compensation of over 13600 ps/nm, equivalent to 800 km of standard single-mode fiber, at 10 Gb/s.

Reduction of intrachannel nonlinear distortion in 40-Gb/s-based WDM transmission over standard fiber

Intrachannel cross-phase modulation and four-wave mixing in high-bit-rate WDM transmission systems employing standard single-mode fiber are investigated. The effects of imperfect third-order dispersion compensation are included in the study and analytical expressions giving optimum values of dispersion precompensation minimizing the distortion due to the intrachannel nonlinear effects are derived.

Performance of single-mode fiber links using electronic feed-forward and decision feedback equalizers

The performance limits of optically amplified links using electronic feed-forward equalizers and decision feedback equalizers are experimentally and numerically investigated. A 10-Gb/s transmission over 140 km of standard single-mode fiber with 22.7-dB optical signal-to-noise ratio sensitivity at 10/sup -9/ bit-error rate is demonstrated, allowing single-span operation with 4-dB margin.

Prediction of transmission penalties due to cross-phase modulation in WDM systems using a simplified technique

Cross-phase modulation (XPM) is a dominant impairment in WDM networks employing high bit-rates and narrow channel spacing. The optimization of future networks requires rapid and accurate techniques to predict XPM-induced penalties. We demonstrate the accuracy of predicting penalties from the distortion of a CW probe channel and show that as a consequence, XPM penalties can be calculated by a simplified numerical technique.

Electronic dispersion compensation by signal predistortion using a dual-drive Mach-Zehnder modulator

We propose the technique of signal predistortion using a dual-drive Mach-Zehnder modulator and nonlinear digital filters, and demonstrate compensation of 13600 ps/nm, equivalent to 800 km of standard single mode fibre, at 10 Gbit/s.

Experimental investigation of SPM in long-haul direct-detection OFDM systems

We experimentally investigate the effect of self-phase modulation on direct-detection orthogonal frequency division multiplexed (OFDM) transmission at 11.1 Gb/s over 960km and 1600km uncompensated standard single-mode fiber links. We show that for long-haul systems, the penalties due to nonlinear distortion in OFDM systems are comparable to those in links employing electronic predistortion.

Cascadability Properties of Optical 3R Regenerators Based on SOAs

This paper assesses the regenerative properties of nonlinear semiconductor optical amplifier (SOA)-based optical regenerators cascaded in high-speed transmission networks. It is shown that the fundamental condition that must be ensured to maintain optimum and constant regenerative properties along a chain of concatenated nonlinear optical regenerators is that the extinction ratio at the input of each regenerator is kept constant. This condition determines an important requirement on the regenerator; signal reshaping and noise suppression must take place while performing the necessary extinction ratio enhancement to maintain cascadability. Starting from the SOA nonlinear transfer function, we derive the relationship between the extinction ratio enhancement and the noise suppression for different SOA-based gate configurations and assess their cascadability properties. This analysis is supported by experimental results of transmission with cascaded optical regeneration in a reconfigurable transmission network over transoceanic distances on standard fiber.

Investigation of the optimum alternate-phase RZ modulation format and its effectiveness in the suppression of intrachannel nonlinear distortion in 40-Gbit/s transmission over standard single-mode fiber

The results of a detailed study of the performance of 40-Gbit/s optical transmission over standard single-mode fiber with alternate-phase return-to-zero (AP-RZ) modulation formats are presented. While in the highly dispersed propagation regime, the use of RZ format signals with alternate phase between adjacent pulses can lead to a significant reduction in nonlinear interaction between pulses, allowing increased launch powers and, hence, increased transmission distances, this has not been systematically investigated. In this paper, we investigate the use of AP-RZ formats, both numerically and experimentally, to explain and quantify the effects of varying the peak-to-peak phase modulation, the amount of precompensation at the transmitter and the presence of multiplexer prefiltering for the case of wavelength-division multiplexing systems with high spectral efficiency. It is shown that, while the use of pulses with alternate /spl pi//2 rad phase shifts minimizes the build-up of shadow pulses in the zero bit slots due to intrachannel four-wave mixing, the best overall performance is obtained with /spl pi/ rad peak-to-peak phase modulation. We show experimentally, for the first time, that the optimum value of precompensation to minimize intrachannel nonlinear distortion is dependent on the signal format used.

Investigation of nonlinear distortion in 40-Gb/s transmission with higher order mode fiber dispersion compensators

The performance of 40-Gb/s transmission systems is limited by the nonlinearity of the transmission and dispersion compensating fibers, and hence, optimized dispersion map designs and signal formats are required to extend error-free transmission distances. In this paper, we describe systematic experiments and simulations of return-to-zero (RZ) and nonreturn-to-zero (NRZ) 40-Gb/s transmission over nonzero dispersion-shifted fiber using higher order mode fiber dispersion management devices. We compare the single channel transmission limits due to nonlinear distortion with dispersion compensators positioned at the start and end of each amplifier span (pre- and postcompensation) and show that the transmission distance of NRZ signals can be extended with the use of precompensation due to the reduced self-phase modulation in the transmission fiber. In contrast, the combination of precompensation and RZ format was found to give poor performance, and analysis shows that this is a result of intrachannel four-wave mixing. The best performance was obtained using an RZ signal format and postcompensated spans. The performance of wavelength-division multiplexing (WDM) signal transmission over the link was then investigated. The simultaneous transmission of multiple 40-Gb/s channels over long-distances was achieved, demonstrating broad-band compensation of the dispersion and dispersion-slope using higher order mode fiber. Results of experiments assessing cross-phase modulation between 40-Gb/s WDM channels spaced by 100 GHz are presented, and the penalties due to inter- and intrachannel nonlinear effects are compared.

Limitation to WDM transmission distance due to cross-phase modulation induced spectral broadening in dispersion compensated standard fiber systems

We describe large spectral broadening due to the interaction of cross-phase modulation/self-phase modulation and fiber dispersion, and explain its contribution to the penalties in standard fiber systems pre- and postcompensated by dispersion compensating fiber. To our knowledge, this is the first measurement of this effect in a dense WDM transmission system at 10 Gb/s with this dispersion management scheme and good agreement is reported with the numerical modeling results.