Wavelength converters are devices that convert data from one incoming wavelength to another wavelength. They enable optical channels to be relocated and are achieved using nonlinear optical effects. Wavelength converters are useful in WDM networks for three reasons: 1) data may enter the network at an unsuitable wavelength, 2) converters may improve wavelength utilization on network links, and 3) converters may be needed when networks managed by different entities do not coordinate wavelength allocation. Common types of wavelength converters include optoelectronic, optical gating using cross-gain modulation, and four-wave mixing approaches.