A wavelength tuneable laser at a local device is tuned using an optical feedback signal provided from a remote device

A wavelength tunable laser 118A in a slave transceiver module 104A (e.g. an optical network unit (ONU)) transmits an optical signal of a first wavelength to a master transceiver module 102 (e.g. an optical line terminal (OLT)). The master transceiver receives 110A the signal and generates therefrom an optical feedback signal 108A which it transmits to the slave transceiver. The feedback signal has a second wavelength different from the first wavelength. The slave module receives 120A the feedback signal and uses this to control the wavelength of the wavelength tuneable laser 118A. The master module may also provide a retransmission request in the feedback signal. This remote monitoring procedure obviates the provision of monitoring equipment in slave devices.