Large signal analysis of fiber dispersion effect on photonic up-conversion in radio over fiber link using dual electrode Mach-Zehnder external modulator

摘要

A large signal theory is performed to analyze linear fibre dispersion effect on the intensity modulated dual-electrode Mach-Zehnder Modulators (DE-MZMs) when used for millimetre-wave harmonic up-conversion (MWHU) through photonic mixing in Radio over Fiber (RoF) systems. Closed form expressions are derived for the directly detected photocurrent spectrum in general case of MWHU and for general operating conditions of DE-MZM such as biasing, driving level, phase shifted and unbalanced drives. The analytical expressions derived here are much more useful than just numerical simulations or measurements. They provide fast and accurate analysis and better insight into harmonic up-conversion in terms of dispersive fading, amplitude and phase ripples. Harmonic up-conversion products are given in the case of any local oscillator (LO) order. Harmonic up-conversion is analysed in terms of dispersion induced power penalty (DIPP) and intensity modulation depth (IMD) of the up-converted signal. The special cases of double sideband (DSB) and single sideband (SSB) modulation of balanced drives of DE-MZM are studied in detail. The DIPP and IMD are expressed for different bias point configurations. Optimum LO modulation index that maximizes the IMD and reduces the DIPP is also calculated. The obtained new results are compared to previously published works.