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Compensating for intercarrier nonlinear distortion allows launching higher power into the transmission fiber and it leads to an increase in the transmission distance. Numerical calculations show that the launch power is increased by 10 dB and the maximum transmission distance is more than tripled, when the optical repeater spacing of 80 km, dispersion-shifted fiber, and signal format of 10 Gb/s nonreturn-to-zero are assumed. It is experimentally demonstrated that waveform distortion due to the four-wave mixing (FWM) among different carriers in wavelength-division multiplexing (WDM) becomes deterministic by phase-locking optical carriers and that FWM distortion can be compensated at 5 Gb/s with three-channel condition by employing DSP at the transmitter or receiver.

A scheme that compensates the waveform distortion induced by nonlinear interchannel crosstalk such as four-wave mixing (FWM) and cross-phase modulation as well as self-phase modulation in phase-locked wavelength-division-multiplexing transmission systems is proposed. Reduction of FWM-induced waveform distortion by controlling the phase relationship between neighbouring channels and its cancellation by precompensation is successfully demonstrated

We present simultaneous measurement of femtosecond time-resolved nonlinear phase and amplitude changes around the excitonic resonance of the AlGaAs∕GaAs quantum well using polarization-division Sagnac interferometer. The nonlinear complex refractive index of the semiconductor material for all-optical devices is successfully determined from directly measured nonlinear phase and amplitude changes.

This paper introduces a technique that compensates for nonlinear inter-channel crosstalk in wavelength division multiplexing (WDM) transmission. Electronic pre- and post-compensation of four-wave mixing are experimentally shown in carrier phase-locked WDM.

A novel interferometer, a Sagnac interferometer (SI), is presented for the measurement of the difference phase and amplitude spectra induced by photoexcitation with a femtosecond time resolution. The SI has a remarkable advantage of high stability owing to the common-path configuration. In order to separate the phase and amplitude changes, the optical path difference is scanned between the probe and reference pulses making the best use of polarization. This improved polarization-division Sagnac interferometer (PSI) provides a nearly sinusoidal fringe. To demonstrate PSI we examined the nonlinear phase and amplitude changes in CS 2 and a GaAs/AlGaAs quantum well (QW) structure. The sepctral feature of the nonlinear dispersion relation in QW can be explained by the blue-shift of the excitonic resonance. The time dependence of these changes is observed to be determined by the exciton lifetime. These experimental results are consistently explained from neutralization of the built-in potential inside the QW sample.

The increase in WDM transmission distance at zero-dispersion wavelength made possible by pre-compensation to offset nonlinear interchannel crosstalk is studied. A simulation shows that pre-compensation allows higher fibre launched power and increases the transmission distance by 3.3 times for a 50 GHz-spaced 8-channel WDM system. Pre-compensation is shown to be limited by the undeterministic nonlinear distortion induced by the accumulated amplifier spontaneous emission noise from repeater amplifiers. Also, optical power tolerance of the pre-distorted waveform generated at the transmitter is studied.