The invention relates to a system comprising an optoelectronic modulator device and demodulator device for establishing communication between optical communication systems by means of differential modulation with eight phase changes. Said system can increase the information transmission capacity by up to three times that of a system with two phase changes. The modulation formats transmittable by the system are called: NRZ-D8PSK, RZ-D8PSK, D8PSK. The invention also relates to the design of the modulator which is formed by a differential modulation precoder and optical signal phase modulators, in which the signals leaving the precoder control the phase modulators in order to perform differential modulation with eight phase changes in relation to the optical signal originating from a semiconductor laser. The invention further relates to the design of a demodulator positioned at the terminal end of the communication system, formed by three receiver branches each containing different electronic devices used for the electronic processing of the signals received.