SPICE and reservoir models for semiconductor optical amplifiers for high speed optical signal processing

Semiconductor Optical Amplifiers (SOA) are key components in the present day all optical networks. They are used as wavelength converters, optical logic gates, bit comparators and many other all-optical digital signal processing applications. To design the systems, fast and efficient models need be developed considering the basic physics of the SOA. In the present paper, we describe two models that are useful in explaining the high frequency and transient behaviour of SOAs. In the first one, developed by us, the rate equations for photons and carriers in a TW-SOA are suitably tailored so that physical quantities can be replaced by circuit elements like resistors and capacitors and current sources. The equivalent circuit can then be analysed by SPICE simulation. Parasitic elements can easily be included in the model. Satisfactory agreement with available experimental data and results with rigorous transfer matrix method has been obtained. The second model, the reservoir model, developed by, Mathlouthi et al based on wideband steady state Connelly model, is useful for predicting the transient and high frequency behavior of SOA-based gates. In our work the reservoir model has been applied to explain the cross gain modulation and gain transient effects for single and WDM signals. It works quite fast to describe the behaviour of long cascades of SOAs. The simulated results agree closely with the experimental results for 1 Gb/s bit stream applied to single and cascaded SOAs and also in WDM systems.