The present invention is an optical fiber system and method for carrying both CATV and Ethernet signals. The digital signals are translated into higher band by a direct up/down conversion so that analog signals and digital signals are treated as different frequency bands of electrical signals. Then, all the signals are mixed/divided by a power combiner/divider. And then, by using optoelectronic devices, the signals are processed with optoelectronic conversion. The converted optical signals are transmitted in a fiber or a related optical channel having low channel loss yet high capacity. To sum up, the present invention can transmit digital signals together with analog signals in a single wavelength to save the cost of an optical signal system and to provide a convenience on rearranging the system.