An optical communications system is provided compraising first and second signalling devices in which a duplex communication link between the signalling devices is establised. The first siganalling device includes a recto-reflector and the second signalling device includes at least one light source for directing light towards the recto-reflector. A full duplex communication link is described which uses small signal modulation techniques to differentiate the uplink modulation data transmitted from the second signalling device to the first signalling device from the downlink modulation data transmitted from the first signalling device to the second signalling device. The strength of the reflected signalis monitored and used as part of a control loop to control the power level of the transmitted light.
