Abstract: In the transmitting node of an optical transmission system using wavelength multiplexing and including several channels the information content of each channel is transmitted onto its own wavelength (&lgr;1, &lgr;2, &lgr;3, &lgr;4) by modulating the laser transmitter producing the wavelength in question. The obtained optical signals are combined onto the same optical fibre. In the receiving node the sum signal is separated into different wavelengths by using a wavelength-selective optical separation component, whereby a predetermined wavelength and thus a channel is obtained from each output port of the separation component. In accordance with the invention, instead of using optical or electrical cross-connectors for re-routing a certain signal content to another destination, that transmission wavelength on which the signal content is transmitted is in fact changed at the signal transmission end.

Abstract: Individual wavelengths (&lgr;1, &lgr;2, &lgr;3, . . . &lgr;N) of a multicomponent light wave travelling in an optical fibre are monitored in such a way that e.g. a coupler is used to separate aside from the power of the light wave a small part, which is conducted into a narrowband tuneable optical filter. The filter tuning signal is used for controlling the filter in such a way that the wavelength window formed by its pass band will scan the entire wavelength range to be examined. The narrow-band optical signal obtained from the filter is conducted to a light detector, which converts the optical signal into an electric signal. As the window of the tuneable filter scans through the wavelength band, such an electric signal is obtained as a wavelength function which is proportional to the power of the optical signal and the peak points of which are located at the wavelength of each channel.

Abstract: In the transmitting node of an optical transmission system using wavelength multiplexing and including several channels the information content of each channel is transmitted onto its own wavelength (&lgr;1, &lgr;2, &lgr;3, &lgr;4) by modulating the laser transmitter producing the wavelength in question. The obtained optical signals are combined onto the same optical fiber. In the receiving node the sum signal is separated into different wavelengths by using a wavelength-selective optical separation component, whereby a predetermined wavelength and thus a channel is obtained from each output port of the separation component. In accordance with the invention, instead of using optical or electrical cross-connectors for re-routing a certain signal content to another destination, that transmission wavelength on which the signal content is transmitted is in fact changed at the signal transmission end.

Abstract: The invention is based on the idea that wavelength of a laser transmitter in a WDM system can be changed in a controlled fashion by inducing an accurately pre-defined change in the cooler control current TEC. This, in turn, effects a controlled change in the heating or cooling operation of the cooler. As a result, a predetermined change takes place in the wavelength of the light generated by the laser. The temperature control circuit ensures that the laser temperature and, thus, wavelength, are maintained exactly at the new value. For each desired wavelength, a parameter set consisting of a pre-set laser temperature value, a laser power value and laser modulation bias values has been saved in storage in advance. When the laser wavelength is to be changed, the parameter values corresponding to the wavelength are retrieved from the storage and fed to the laser. Retrieval and feeding can be pre-programmed or carried out manually.