The present disclosure relates to an optical line terminal, the disclosure includes: an optical transmitter for generating a low speed downstream optical signal; a wavelength-multiplexer for wavelength-multiplexing the downstream optical signal; a first optical power branching tap coupler for allowing wavelength-multiplexed downstream optical signal to branch off; a wavelength band separator/coupler for separating between the wavelength-multiplexed downstream optical signal and a wavelength-multiplexed upstream optical signal; a circulation type wavelength-demultiplexer for wavelength-demultiplexing a downstream optical signal branched off by the first optical power branching tap coupler and an upstream optical signal separated by the wavelength band separator/coupler; an optical receiver for outputting a downstream electrical signal by using the wavelength-demultiplexed optical signal; and a signal processing module for controlling an optical power and a wavelength of the optical transmitter according to a strength of the downstream electrical signal.