Disclosed herein are a CDMA optical system and encoder and decoder included therein. Time domain encoding means creates a time domain code having a sequence according to inputted data bits or a complementary code which is complementary to the time domain code. An optical modulation means selectively outputs lights, in which the lights are incident upon the optical modulation means from the outside, to two output leads, respectively, according to chip bits of the time domain code or the complementary code. A wavelength domain encoding means encodes the light outputted from a first output lead of the optical modulation means to a wavelength domain sequence (two dimensional code), transmits the wavelength code to the base station, encodes the light outputted from a second output lead to a complementary sequence of the wavelength domain sequence, and transmits the complementary code of the two dimensional code to the base station.