Patent ID: 7539416

Claim:
An optical network terminal in a wavelength division multiplexing based optical network comprising: a modulation timing control signal generator receiving a downstream optical signal sent 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; a modulator receiving the upstream data and directly modulating the upstream data by amplifying the downstream optical signal and using the amplified downstream optical signal to produce the upstream optical signal and then output it to the central office; a monitor photo diode receiving a part of output optical signals of the modulator and then converting them into electrical signals; and a wavelength control circuit receiving the electrical signals, altering operating temperature of the modulator based on the magnitudes of the electrical signals, and shifting the center wavelengths of operation modes to perform a wavelength tracking for matching a center wavelength of the downstream optical signal harmonized with one of the center wavelengths of the operation modes when the electrical signal reaches a maximum value.