ired power, the pulses are reshaped at the original form and the jitter is eliminated. This operation is carried out by simply receiving the signal and retransmitting it; thus, the regenerator is bit rate and modulation format specific. Even though 3R optical regenerators have been investigated for application in the trans- parent optical network [12], an optical transparent regenerator is generally imagined to accept a vast variety of optical signals, characterized by a different bit rate and modulation format, but it is not required to eliminate jitter (this is called a 2R regenerator) [13]. As we have seen, a WC is a device that changes the central wavelength of a signal ideally without altering it in other ways. Regenerators and WCs are both strongly nonlinear devices; thus, it is natural to try to exploit the nonlinear behavior of some known device. Several proposals have been put forward regarding the implementation of such devices, based on fibers nonlinearities [14,15], on nonlinear loop mirrors [16], and other nonlin- ear elements. Among these proposals, those based on SOAs have the advantage of being based on a component that can be produced in large volumes with a scalable technology exhibiting a strong nonlinearity with a characteristic time on the order of the bit time of a 0 Gbit/s signal. We will briefly review the architecture and potential performances of SOA-based com- ponents that well represent the state of the art in this field. 10.3.1.1 Nonlinear Behavior of Semiconductor Amplifiers SOAs, as described in Chapter 4, are essentially Fabry-Perot semiconductor lasers whose facets are antireflection coated. Amplification by stimulated emission happens in the intrinsic zone of an inversely polarized PIN junction. Since optical transitions happen between large bands where the electrons or holes energy levels are almost continuous, the gain bandwidth is quite large, and for applications in the third window, the local gain can be assumed in a first approximation independent from the frequency. Beside