Abstract: Disclosed herein is an optical access network system in which the transmission quality of an upstream signal is remarkably improved in an optical access network in which a Reflective Semiconductor Optical Amplifier (RSOA) is used as the light source for each subscriber. The most important characteristics of the present invention are that a Manchester modulation format is used as a modulation format for a downstream signal in an optical access network system in which an RSOA is used as the light source for each subscriber, so that the problem of deterioration of the transmission quality of a remodulated upstream signal, occurring when an RSOA is used as the light source for each subscriber, is solved, and thus the transmission performance of an upstream signal and the power budget performance of the entire system are improved.