Abstract: Frequency stabilizing in a, for instance star/branched-tree shaped, network can be well executed by locking the frequencies (f1) of the transmitters (T1) in the network center to a common reference frequency source (CFC) and, moreover, per duplex connection, locking (at a fixed frequency distance) the frequency (f2) of the subscriber's transmitter (T2) to the transmission signal (t1) as received from the network center's transmitter (T1). Per duplex connection only the subscriber's local oscillator (L2) has to be tuned so that the transmission signal from the network center is received optimally.

Abstract: The invention relates to a method for compensating, in a coherent optical communication system with heterodyne detection, at the receiving side phase noise of the transmitting and of the local laser. Characteristic of the present method is that the phase-noise compensation takes place in the LF domain. The two MF heterodyne signals (Imf and Pmf) are first demodulated into LF signals (in which there is still noise), which are subsequently subtracted from one another, due to which the respective noise components cancel out each other. Preferably a local laser signal which is, qua frequency, between the two other HF signals is chosen. This offers the advantage that the two MF heterodyne signals can be modulated by one and the same demodulator; because for the compensation of phase noise the demodulated MF signals (Iif respectively Pif) which are, qua phase noise, in opposite phase with regard to each other are then added to one another.