Patent ID: 7957647

Claim:
A passive optical network system including an optical line termination device, an optical splitter, and a plurality of optical network units which are connected to the optical line termination device through optical fibers and the optical splitter, wherein the optical line termination device and the optical network units communicate in wavelength division multiplexing and in time division multiplexing of individual wavelengths; wherein: the passive optical network system has a first wavelength at which signals for performing predetermined ranging process between the optical line termination device and the optical network units are transmitted and received, and a plurality of second wavelengths at which the optical line termination device and the optical network units communicate; the optical line termination device performs the ranging process with respect to the optical network units by using the first wavelength, so as to give the individual optical network units instructions of an equalization delay for causing the respective optical network units to delay and transmit signals, in order that the optical line termination device itself and the plurality of optical network units may seem to be equally distant, and the optical line termination device communicates with the optical network units by using the second wavelengths; and each of the optical network units comprises: an equalization delay storage unit in which the equalization delay given by the optical line termination device is stored; a receiver which receives the signal at the set receiver wavelength; a transmitter which transmits the signal at the set transmission wavelength by being delayed on the basis of the equalization delay stored in said equalization delay storage unit; and a wavelength control unit which sets the transmission wavelength of said transmitter and the receiver wavelength of said receiver at the first wavelength, so as to transmit and receive the signals for the ranging process, and which sets the transmission wavelength of said transmitter and the receiver wavelength of said receiver at an assigned one of the second wavelengths after the ranging process, so as to communicate with the optical line termination device.