Transmission method of optical network, optical network system and central device thereof

The passive optical network (PON) using fiber optics and optical coupler is installed in central device 10 with hub 16, multiple modems 17, mixer 18 and demultiplexer 19. Furthermore, allocate carrier wave with specified frequency to the multiple modems 17 and all subscribers 60. For downlink direction, hub 16 selects each modem 17 (e.g. each subscriber 60) and generates the modulated signal of the allocated carrier wave, which is further mixed by mixer 18 and then take it as FDM signal to be transmitted to subscriber 60 via first optical coupler 52. Each subscriber proceed signal demodulation with the allocated carrier frequency. For uplink direction, the first optical coupler 53 proceed frequency division multiplexing on the modulated signal coming from subscriber 60 and transmit it to central device 10. The demultiplexer 19 proceed demultiplexing to the allocated carrier wave at the central device and proceed demodulation via each modem 17 that the PON is implemented accordingly.