An optical communications system (300, 400, 500) comprising a first transmit unit (301, 401, 402) and a first receive unit (302, 401, 402). The first transmit unit comprises an electro-optical modulator (311) for modulating one or more radio channels bearing electrical signals with a total bandwidth B by a laser signal (310) with a laser frequency fL1, and the first transmit unit also comprises a transmit filter for outgoing signals from the electro-optical modulator. The first receive unit comprises an electro-optical demodulator (313) for demodulating the one or more electrical signals received from the first transmit unit by means of a Local Oscillator, LO (312), which produces an optical signal at a second frequency fL2, and B ranges from the lower of fL1 and fL2 to the higher of fL1 and fL2.