Method for transmitting an optical signal through free space

A method for transmitting a signal for the transfer of information from a signal source ( 1 ) to a signal sink ( 7 ) spatially remote therefrom wherein, at least over a part of the path between the signal source and the signal sink, the signal is transmitted as an optical signal over at least one free optical link between an optical transmitter ( 3 ) and an optical receiver ( 5 ), is characterised in that prior to its transmission the signal to be transmitted is split into signal packets (SP), that each signal packet is assigned a signal sequence (OH) characteristic of the signal packet and is transmitted together with the relevant signal packet at a higher bit rate than the original signal, and that the characteristic signal sequences are used to detect, and optionally correct, errors in the transmitted signal and/or to synchronise the transmission path. In this way a reliable transmission of optical signals through free space can be ensured using very simple means.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates a signal transmission device for supporting the above described method variant according to the invention, which provides splitting of the signal to be transmitted into a plurality of identical signals with the same information content as the original signal, and the transmission thereof via their own respective free optical link. Here the signal to be transmitted is generated in a signal source 1 . At this point for example the signal in question can still be an electrical signal, but also already an optical signal. In a downstream signal splitter 2 , the signal to be transmitted is now multiplied into a plurality of identical signals, in the present case three signals, each of which are fed to an optical transmitter 3 , in particular a laser. From here the optical signals are each transmitted on their own respective free optical link, on which optical relays 4 such as amplifiers or deflectors can also be arranged, to a respective, associated optical receiver 5 . The received signals of the various optical receivers 5 are fed to a signal combiner 6 where they are combined to form one single signal and transmitted to a signal sink 7 which represents the destination of the overall signal transmission. The method according to the invention can also be implemented however in a considerably simpler signal transmission device with only one single free optical link. A crucial feature of the method according to the invention is the splitting of the signal to be transmitted, prior to its transmission, into different signal packets SP as schematically illustrated in the central part of FIG. 2 . Then each signal packet SP is assigned a signal sequence OH characteristic of the relevant signal packet SP and transmitted together with the relevant signal packet SP with a higher bit rate than the original signal, as indicated in the lower part of FIG. 2 . If the bit rate for the original signal amounted to X bit/s, the split signal is transmitted together with the characteristic signal sequences OH with a rate of (X&plus;N) bit/s. The characteristic signal sequences OH are then used to detect, and optionally correct, errors in the transmitted signal and/or to synchronise the transmission link.