This paper assesses the regenerative properties of nonlinear semiconductor optical amplifier (SOA)-based optical regenerators cascaded in high-speed transmission networks. It is shown that the fundamental condition that must be ensured to maintain optimum and constant regenerative properties along a chain of concatenated nonlinear optical regenerators is that the extinction ratio at the input of each regenerator is kept constant. This condition determines an important requirement on the regenerator; signal reshaping and noise suppression must take place while performing the necessary extinction ratio enhancement to maintain cascadability. Starting from the SOA nonlinear transfer function, we derive the relationship between the extinction ratio enhancement and the noise suppression for different SOA-based gate configurations and assess their cascadability properties. This analysis is supported by experimental results of transmission with cascaded optical regeneration in a reconfigurable transmission network over transoceanic distances on standard fiber.
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