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Analysis for dispersion-induced composite frequency distortion of AM signal at 1.5 um

The frequency domain analysis for nonlinear distortion of 1.5 micrometers AM signal transmitted in single mode fiber is presented which drives, for the first time in our knowledge, approximate analytical solutions for composite-second order (CSO) and composite-triple beat (CTB) distortion. The results here can be applied conveniently to engineering, and are somewhat better than those given by Bergmann et al (1990), by Phillips et al (1991) or by Kuo (1993). All their expressions for CSO or CTB are dependent on a product of fiber dispersion coefficient times laser chirp rate, that causes a problematic inference fiber dispersion cannot cause nonlinear frequency distortion of pure AM signal (without laser chirping). Our expressions and curves for calculating CSO and CTB in practical CATV signal transmission at 1.5 micrometers are indicated, and also compared with the published theoretical and experimental results. Computation shows that pure AM signal suffers from fiber dispersion as well, the CSO and CTB of which are both proportional to second power of dispersion phase-shift angle, but proportional to first power and second power of AM index respectively. The curves of CSO and CTB versus transmission distance are also presented. It turns out that the results here include distortion effect of higher order.