A. R. Chraplyvy

Four-photon mixing and high-speed WDM systems

The trend toward higher bit rates in lightwave communications has increased interest in dispersion-shifted fiber to minimize dispersion penalties. At the same time optical amplifiers have increased interest in wavelength multiplexing. These two methods of increasing system capacity, if used together, can result in severe degradation due to fiber nonlinearity. This paper discusses the impact of the principal nonlinearity, four-photon mixing, and describes strategies that allow simultaneous use of high bit rates and WDM. >

Reduction of four-wave mixing crosstalk in WDM systems using unequally spaced channels

Crosstalk due to four-wave mixing (FWM) is the dominant nonlinear effect in long-haul multichannel optical communication systems employing dispersion-shifted fiber. A technique to design the channel frequency allocation in order to minimize the crosstalk due to FWM is presented. It is shown that suitable unequal channel separations can be found for which no four-wave mixing product term is superimposed on any of the transmitted channels. This is obtained at the expense of some expansion of the system bandwidth. Simulations are presented to show the effectiveness of this technique in a 10-channel, 10-Gb/s per channel, system.<<ETX>>

WDM systems with unequally spaced channels

Crosstalk due to four-wave mixing (FWM) is the dominant nonlinear effect in long-haul multichannel optical communication systems employing dispersion-shifted fiber. A method is discussed to find non-uniform channel separations for which no four-wave mixing product is superimposed on any of the transmitted channels, therefore suppressing FWM crosstalk. The residual crosstalk, due to channel power depletion only, is analytically evaluated for intensity-modulated repeaterless wavelength-division-multiplexed (WDM) systems and compared to experimental results. The theory includes the effect of the channel depletion on the amplitude of each phase-matched FWM wave. The probability of error is evaluated including the statistics of the pattern dependent channel depletion. The BER curve computed for an 8-channel WDM system is found to be in good agreement with experimental results. In the experiment, repeaterless transmission of eight 10 Gb/s WDM channels over 137 km (11 Tb/s-km) of dispersion-shifted fiber was demonstrated and error-free operation was achieved over a wide range of input powers using unequally spaced channels. The same system with equally spaced channels could not achieve a probability of error lower than 10/sup -6/. The use of unequal channel spacing allowed fiber input power to be increased by as much as 7 dB, which could be translated into a fivefold increase of the bit rate per channel (and therefore of the system capacity), or to an increase in the system length of about 30 km. >

Equalization in amplified WDM lightwave transmission systems

The authors introduce simple techniques to solve gain equalization problems in amplified wavelength-multiplexed lightwave transmission systems. By adjusting the channel powers at the terminals in a prescribed way, either the output powers or the output signal-to-noise ratios of all the channels can be equalized. All adjustments can be made using information provided by system telemetry. No new equipment, upgrades, or adjustments are required at intermediate amplifier sites.<<ETX>>

Fast-link control protection of surviving channels in multiwavelength optical networks

Link control, a new technique for protecting surviving channels on a per-link basis from fast power transients resulting from network reconfigurations or line failures, is demonstrated in a 560-km eight-amplifier wavelength division multiplexed link carrying seven 2.5-Gb/s channels plus the link control channel.

All-optical regeneration in one- and two-pump parametric amplifiers using highly nonlinear optical fiber

We describe the operation of a two-pump parametric optical regenerator. It is shown that higher order parametric coupling provides optical regeneration with a high extinction ratio. Excessive spectral broadening is studied in a two-pump architecture and compared with that of the one-pump parametric regenerator. We show that the spectral widths of the higher order terms can be controlled in amplifiers by using counterphased optical pumps.

1-Tb/s transmission experiment

A 1-Tb/s aggregate capacity (50 channels each at 20 Gb/s) was transmitted through 55 km of nonzero-dispersion fiber. Fifty channels were generated by polarization multiplexing 25 wavelengths.

8*10 Gb/s transmission through 280 km of dispersion-managed fiber

Eight WDM channels each operating at 10 Gb/s were transmitted through 280 km of dispersion-shifted fiber concatenated with small amounts of conventional fiber. No degradations from optical nonlinearities were observed.<<ETX>>

Simple multichannel optical equalizer mitigating intersymbol interference for 40-Gb/s nonreturn-to-zero signals

We present a simple, silica waveguide optical equalizer that significantly mitigates intersymbol interference (ISI) impairments for many wavelength-division multiplexed (WDM) channels simultaneously. We study the mitigation of ISI arising from band-limited transmitters, narrow-band optical filtering, chromatic dispersion, and polarization-mode dispersion (PMD). We demonstrate significant improvements, both single- and multichannel, at 40 Gb/s with a single, potentially set-and-forget device.

High-Capacity Optical Transmission Systems

The 25 years since the founding of the Journal of Lightwave Technology have seen more than three orders of magnitude increase in the capacity of optical transmission systems. This dramatic increase was brought about by the deployment of WDM and advances in high-speed transmission technologies.