Firstly, 40 channels of 1310nm wavelength on the optical terminal were converted to 40 DWDM wavelengths through OTU.

Then 40 DWDM wavelengths were used to realize dual-fiber transmission by DWDM wavelength division multiplexer and combiner.

Due to the long distance transmission, the optical signal loss is large. After the combiner, the EDFA-BA/PA optical amplifier is used to enhance the transmission power of the signal in advance.

After amplification, the optical signal is combined into the transmission two-core fiber for transmission.

Due to the transmission distance of 120km, the transmission distance of DWDM transceiver used is only 80km. Due to the influence of fiber dispersion, it is necessary to use DCM module more than 40km for dispersion compensation.

When the optical signal is transmitted to the back end, the optical signal is amplified again by using the wave decoder and EDFA-PA optical amplifier.

DWDM wave division multiplexer and wave decoder are used to decompose the double fiber transmission composite optical signal.

OEO is used to convert the wavelength of DWDM into the wavelength signal received by the optical terminal.

In this scheme, a fiber attenuator is needed to adjust the optical power of the optical module at the receiving end to avoid excessive optical power damage to the optical module.