Lamar E. West

On determining the optimum modulation index for reverse path lasers in hybrid fiber/coax networks

Previous work in modeling laser clipping phenomena in hybrid/fiber coax uses a signal model consisting of equal amplitude subcarriers. This model is inappropriate for the case of the reverse path where there may be only a small number of subcarriers, or a small number of subcarriers may take on an amplitude that is significantly greater than the other subcarriers. A model is presented that produces a probability density function (pdf) for laser drive current that accurately reflects the various mixtures of subcarriers typically present in the reverse path. This pdf is used to determine the relationship between laser rms modulation index, /spl mu/, and clipping distortion power. A method is shown to combine this relationship with laser RIN, shot noise and receiver noise current performance in order to determine the value of /spl mu/ that produces optimum overall link performance.

The effect of preamplifier compression on measured noise power ratios

Noise power ratio (NPR) measurements are becoming widely used to characterize components (particularly optical components) for use in hybrid fiber/coax networks. Choice of this measurement technique is based on the assumption that the composite signal resulting from actual subcarrier loading will exhibit statistical characteristics that tend toward Gaussian. However, care must be taken to ensure that any test signals used in making NPR measurements are also Gaussian in nature. This paper examines the errors that may be produced in an NPR measurement if preamplifier compression results in a test signal that is non-Gaussian. Analytical as well as empirical results are presented.