Progress in externally modulated AM CATV transmission systems

Recent advances in electronic linearization of AM CATV transmitters based on externally modulated diode pumped Nd:YAG lasers are presented. The theoretical principles and practical issues related to the methods of feedforward and predistortion linearization, the factors affecting system performance and the emerging devices, circuits, subsystems, and systems architectures are reviewed. In experiments based on a predistortion linearized system, transmission over two fibers of 30 km each, wherein each fiber carries 80 NTSC channels, is now routinely achieved with a CNR>50 dBc, a CTB<-65 dBc, and a CSO of typically -70 dBc. As the number of channels broadcast over each fiber is reduced from 80 to 60, CNR increases to 52 dBc. The fiber links served by the system under test each have 12-dB link budget, and include four connectors per fiber, with no degradation observed in one link when the connectors were opened on the other link.

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