Investigation On Dynamic Characteristic Of Semiconductor Optical Amplifier

Semiconductor optical amplifier (SOA) has been widely applied in all optical signal processing for next generation optical network, and the dynamic characteristic of carriers inside the device is a key factor that greatly affects the output performance. The ultra-fast dynamic characteristic of SOA and its improvement schemes were investigated theoretically and experimentally, under the support of National natural foundation and the Program for New Century Excellent Talents in University of Ministry of Education. The studies are carried out as the followings:1. A relatively rigorous SOA high-speed dynamic model is established, via the analysis of the advantages and disadvantages of reported SOA models. The model considers as many factors as possible, including nonuniform distribution of photon intensity and carrier density along active region, gain spectral dispersion, spontaneous emission spectrum and facet reflectivity, and is applicable under the condition that the pulse width of injecting signal is wider than 10 picoseconds. It provides a convenient and effective theoretical platform for SOA dynamic characteristic study.2. The ultrafast nonlinearities are analyzed thoroughly, including carrier heating, spectral hole burning and two-photon absorption effects, which appear seriously if subpicosecond pulses are input, and the generating requirements, phenomena and mathematical expressions of the nonlinearities are described further in detail.3. A novel method based on spectrum analysis is proposed out to study SOA ultrafast dynamic response. In the established ultrafast dynamic model, pulse spectrum is segmented for gain spectral dispersion consideration, the ultrafast nonlinearities are taken into count as well except for ASE noise and the walk-off effect between different wavelengths. This model is regarded as a basis for the succeeding work of SOA ultrafast dynamic performance research and achievements of ultrafast all optical signal processing employing SOAs.4. Researches are executed on the reported schemes of SOA dynamic characteristic improvement, which are also validated using the high-speed dynamic model. Moreover, a conclusion is drawn that photon density is one of the key factors that affect the device performance.5. A novel scheme that improves SOA dynamic performance via increasing properly the facet reflectivity of device is proposed, and is validated in theory by the high-speed dynamic model. Simulation results show evidently that this scheme is superior to other schemes in the efficiency of dynamic characteristic improvement, steady-state gain, output ratio and external condition requirements.6. Experiments are executed to validate the reported schemes and the proposed new scheme, employing SOA-XGM wavelength conversion configuration. The observed results and simulated results agree well, and both consistently prove that increasing the facet reflectivity properly can effective improve the device performance.