Optical/electrical/optical WC first converts optical signals into electrical signals, then periodically regenerates them to generate regenerated electrical signals and clock signals, and then re-modulates the laser with standard wavelength with the electrical signals, thus realizing wavelength conversion. Due to the mature photoelectric conversion technology, signal regeneration ability, large input dynamic range, no need for filter, insensitive to input polarization and many other advantages, it is the only very mature wavelength converter at present. However, it is opaque to the signal format and modulation rate, and the system upgrade and application range are limited. The main principle of coherent wavelength converter is the application of FWM principle. According to the different devices used, it can be divided into: based on FWM effect in passive waveguide; FWM effect in semiconductor laser: FWM effect in semiconductor optical amplifier. The wavelength converter based on optically controlled logic gates mainly adopts XGM effect and XPM effect. The devices used are similar to coherent wavelength converters and can also be divided into passive waveguide type, semiconductor laser type and semiconductor amplifier type.
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