Optischer Sender

摘要

A laser (2) of an optical transmitter (1) for information transmission, particularly for the transmission of analog broadband signals for CATV, can be amplitude-modulated with a useful signal (N) in two different ways. In direct modulation, an unwanted additional frequency modulation occurs. In indirect modulation by means of an optical intensity modulator (3), Brillouin backscatter occurs in an optical fibre of the transmission link following the optical transmitter (1) even at transmitting powers of about 10 mW. Both types of modulation lead to distortion of the transmitted signal. To circumvent the disadvantages of the two types of modulation in a technically simple manner, the carrier emitted by a laser (2) is indirectly modulated with a useful signal (N) and the laser (2) is additionally weakly directly modulated with a dispersal signal (V). The weak direct modulation leads to a continuous slight change in the wavelength of the optical signal so that the Brillouin backscatter is reduced but, at the same time, dispersion distortion is avoided.