Performance evaluation of optical analog SCM AM-VSB systems using a microwave subcarrier to up-shift CATV channels

In lightwave TV systems it often is desirable to increase the channel capacity and the covered distance. In some cases, extended distance may be obtained if the conventional CATV channel spectrum is up-shifted to a low microwave frequency range, with the use of a 1-2-GHz subcarrier, before modulating the laser. It is shown that the up-shift procedure may yield a composite second-order (CSO) elimination, at the expense of increasing the composite triple beat (CTB). The benefit of CSO elimination may overcome the CTB increase, allowing for an additional increase in channel capacity or covered distance. This last increase may compensate for the modest price paid for the additional up-shift equipment. All the performance evaluations are carried out using a rigorous numerical model and assuming the lightwave systems are using the AM-VSB format, as well as direct laser diode modulation.