OPTIMAL-DESIGN OF SUBCARRIER MULTIPLEXED LIGHTWAVE SYSTEMS EMPLOYING LINEARIZED EXTERNAL MODULATORS

A method is developed for calculating carrier-to-intermodulation product ratios for conventional modulators and for linearized modulators in which the third-order products are cancelled, and fifth-order products are dominant. Simple expressions are derived for the rms optical modulation index which optimizes system performance. The improvement in receiver sensitivity which can be achieved with linearized modulators is determined. For AM-VSB system operating with carrier-to-noise ratios of 50 dB, linearized modulators are predicted to yield an improvement in receiver sensitivity of 8 dB. It is shown that for other SCM system operating with CNR's of 25 dB or less, no performance improvement can be expected.