**6. All optical converters**

The implementation of simple converters can be considered an enabling technology for taking the full advantage of the wavelength dimension in WDM networks. A straightforward implementation of a converter would be a detector followed by an electronic amplifier and a transmitter with the desired new output format/wavelength. However this principle suffers from both a high component count and a high power consumption making the approach impractical for use in large optical switches. Therefore, much attention has been devoted to the realization of all optical converters exploiting the properties of nonlinear devices relying on mechanisms such as cross gain modulation (XGM), cross phase modulation (XPM) and four-wave mixing (FWM) in nonlinear devices [55].
