Large-signal spurious-free dynamic range due to static and dynamic clipping in direct and external modulation systems

Abstract

Large-signal spurious-free dynamic range (SFDR) is useful in an optical system with a high intensity noise level, which can be due to optical reflections or optical beat interference, and with large modulating signals to achieve sufficient carrier-to-noise ratio (CNR). A closed-form analysis on large-signal SFDR due to static and dynamic clipping for direct and external modulation systems is presented in this paper. The analysis can be applied to laser diodes (LD's) and external modulators with arbitrary transfer functions. We have used the analysis to predict the theoretical upper-bound for large-signal SFDR due to static clipping in an ideal LD add external modulators with various linearization techniques. We have also used the analysis to predict the dynamic-clipping-induced nonlinear distortions (NLD's) id. a weakly clipped LD, and confirm that dynamic clipping is more important to consider than static clipping when weak LD clipping takes place. Large-signal SFDR's in practical LD's and external modulators were also compared. The validity of our analysis is confirmed through computer simulation and actual measurement of clipping-induced NLD's in a typical CATV-quality DFB LD.