Optical signal transmission system and method of allocating center frequencies of if carriers for an fdm optical fiber link

An optical signal transmission system for allocating a center frequency of an IF carrier in a frequency multiplexing optical transmission link and a method thereof are disclosed. The optical signal transmission method comprises the steps of: determining a center frequency interval between modulated signals by using a bandwidth of a plurality of modulated signals or a center frequency of a modulated signal having the lowest center frequency among the plurality of modulated signals; reassigning the center frequencies of the modulated signals according to the center frequency interval between the modulated signals; and converting the modulated signals having the center frequency reassigned in an electric signal to an optical signal, and transmitting the modulated signals. The optical signal transmission system can prevent signal distortion without a distributed optical fiber or a complex signal treatment.