Disclosed is a loop-back optical network terminal using a Febry-Perot laser diode as an active type optical modulator in a wavelength division multiplexing based optical network. In addition, a wavelength division multiplexing based optical network having the same is disclosed. The optical network terminal comprises a modulation timing control signal generator receiving a downstream optical signal transmitted from a central office and generating a timing control signal designating a start timing and an end timing for modulating an upstream optical signal to be transmitted from a user to the central office; an upstream data control circuit generating upstream data according to the timing control signal and controlling modulation of the upstream optical signal according to the timing control signal in response to generation of the upstream data; and a modulator receiving the upstream data and directly modulating the upstream data with loop-backing the downstream optical signal to produce the upstream optical signal and then output it to the central office.