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Fiber-based all-optical signal regeneration techniques are reviewed. In the first half of the paper, amplitude regeneration schemes for ON-OFF keying signals using self-phase modulation and four-wave mixing in fibers are classified and their features are described. In the second half of the paper, focus is placed on regeneration schemes of phase-encoded signals. In particular, we discuss the performance of the regenerators in which phase information is converted to/from amplitude information and noise suppression is done on the amplitude. Usefulness of phase-preserving amplitude-only regeneration in reducing nonlinear phase noise is also discussed. Some experimental results are shown. Finally, issues in applying all-optical regeneration to real transmission systems are mentioned.