Line codes for photonically amplified digital links

In noise-limited optical links with cascaded amplifiers, we show that coding gains can be obtained from sparse codes, but will be limited by dispersion. Dispersion limitations are determined by a complex combination of intersymbol interference and laser nonlinearities, so that determination of the worst-case patterns requires computation of laser dynamics. Rates for line codes that eliminate these patterns are shown to be strongly dependent on which patterns one wishes to eliminate. Under the best codes, performance of the system is limited by a combination of noise and dispersion, and performance evaluation will then demand new computational tools