WDM (wavelength division multiplexing, WDM) technology is to transmit multiple wavelength optical carrier signals at the same time, and each optical carrier operates in FDM or TDM mode, and each carrier has multiple analog or digital signals. The basic principle is to combine (multiplex) the optical carrier signals of different wavelengths on the transmission side, and couple them to the same optical fiber for transmission on the line. When arriving at the receiving end, the optical carrier signals of different wavelengths will be separated (demultiplexed), so that the number of optical fibers laid in the main transmission link will be doubled. Therefore, this technology is called optical wavelength division multiplexing, which is called optical wavelength division multiplexing Reuse technology.