A wavelength conversion scheme based on a quantum-dot semiconductor optical amplifier and a delay interferometer

Interferometric schemes based on the cross-phase modulation properties of nonlinear devices have been widely used to develop high performance signal processing subsystems, such as wavelength converters and regenerators. However, there is also another category of devices characterized by limited cross-phase modulation nonlinearity. In this category belong quantum dot semiconductor optical amplifiers, which have demonstrated unique ultra-fast nonlinear properties for high bit rate applications. Cross-gain modulation (XGM) is considered in this case as the prime nonlinear mechanism, but it traditionally suffers from severe extinction ratio limitations. In this paper we introduce an interferometric configuration for enhancing the XGM performance of these devices. The proposed concept is experimentally validated at 40 Gb/s using a QD-SOA as nonlinear medium. It is shown that the extinction ratio of the cross gain modulated signal can be greatly improved.