Circuit-Level Study On The Dynamic Behaviors Of Multiplexed Signals In Amplification Process

With the development of new communication services, the contents of information including voice, image and data increase quickly which bring a higher requirement for network's transmission capacity and distance. The technology of wavelength division multiplexing (WDM) system or subcarrier multiplexing (SCM) system combined with erbium-doped fiber amplifier (EDFA) is an effective method to realize high capacity, long haul, high speed communications, and can take fully advantage of the optical fiber's bandwidth. Therefore, studying on the dynamic behaviors of multiplexed signals in the amplification process has significant theoretical and practical meaning.In this paper, according to the basic physical equations of multiplexed signals in the amplification process, different from the traditional calculation methods, the electronic elements are adopted to describe the amplified behaviors of optical signals based on stimulated emission and the macro-model of transmission line is introduced to describe the time delay from the erbium-doped fiber. The equivalent circuit models of WDM signals and SCM signals including the chirping effect are established for the first time. Circuit-level simulation method is applied to investigate the amplified characteristics of multiplexed signals.Based on the equivalent circuit model, the dynamic simulations are implemented by performing the dc analysis, transient analysis and ac analysis through PSPICE. Typical characteristics are analyzed, including transient modulation, multi-channel output power spectrum and cross modulations of an eight-channel WDM. The intermodulation distortion and output power spectrum in an amplitude modulation SCM are demonstrated. The simulation results indicate that adjusting pump power properly can control transient effect, and increasing modulation frequency can weaken cross modulation, and decreasing frequency chirp of LD or enhancing the input power of signals can improve intermodulation distortion. These results will be useful for designing and optimizing the practical system and show that the method of circuit-level simulation based on circuit model is one of the effective methods in optoelectronic system simulations.