Communications device and method

A communications device, wherein the communications device comprises:

• a first acquiring unit, a first loopback unit, a first receiving unit, and a first control unit, wherein:
• the first acquiring unit is configured to acquire first specific wavelength light and second specific wavelength light from a first optical path;
• the first receiving unit is configured to convert the first specific wavelength light coming from the first acquiring unit into a first electrical signal;
• the first control unit is configured to send a first modulating signal to the first loopback unit according to the first electrical signal coming from the first receiving unit;
• and
• the first loopback unit is configured to modulate, according to the first modulating signal, the second specific wavelength light coming from the first acquiring unit, and loop the modulated second specific wavelength light back to a second optical path, wherein a transmission direction of an optical signal in the second optical path is opposite to a transmission direction of an optical signal in the first optical path.