| 摘要 |
Automatic feedback control of the output power of a semiconductor laser employed in a transmitter of an optical transmission system, which also includes a receiver, involves use of both the transmitter and the receiver. The mean value of the power, as transmitted via a fibre (23), received by a photodiode (27) is compared with a predetermined value and the output of the laser (25) adjusted to achieve equalisation therewith. The necessary return link between the photodiode and the laser may comprise a second fibre, particularly the other fibre of a two-fibre duplex optical link, or may use the same fibre (23). The two fibres of such a link transmit respective data signals, output from respective semiconductor lasers, in opposite directions between the ends of the link. Each transmitted data signal is modulated at a low frequency whose value is indicative of the necessary change in the output of the semiconductor laser, at the other end of the link to the laser that is transmitting the respective data signal, which is required to equalise the received power with the predetermined level. <IMAGE> |
