All-Optical Signal Processing with Semiconductor Optical Amplifiers and Tunable Filters

Abstract

All-optical signal processing has been and is receiving more and more attention all over the world because it can increase the capacity of the optical networks greatly in avoiding of the Optical-Electrical-Optical (O/E/O) conversion process, and it can also reduce the system power consumption to a great extend and then increase the system stability. All-optical signal processing can be widely used in optical signal regeneration and switching in nextgeneration optical networks (Yoo 1996; Danielsen et al. 1998; Saruwatari 2000), such as Optical Time Division Multiplexing (OTDM), Optical Orthogonal Frequency Division Multiplexing (OOFDM), Optical Code Division Multiplexing Accessing (OCDMA), Optical Packet Switching (OPS) and so on. There are many different elemental functions in alloptical signal processing: all-optical wavelength conversion, all-optical logic operation, alloptical 3R regeneration, all-optical format conversion, all-optical sampling, all-optical time demultiplexing, all-optical buffering, etc. It should be mentioned that all-optical wavelength conversion is one of the most important technologies, and it is the basis of other functions. In past two decades, many schemes have been proposed to demonstrate all-optical signal processing functions, and nonlinearities in passive and active waveguides, such as high nonlinear fiber (Olsson et al., 2001), periodic-poled LiNbO3 (Langrock et al., 2006), siliconbased waveguides (Hache & Bourgeois 2000), chalcogenide-based waveguides (Ta'eed et al., 2006) and semiconductor optical amplifiers (SOAs) (Liu et al., 2006; Stubkjaer 2000) , are elemental mechanisms for these schemes. SOA is one of powerful candidates for all-optical signal processing because of its various nonlinear effects, low power consumption, small footprint and possibility to be integrated, therefore, SOAs have been receiving the most widely attention and have been exploited to realize nearly all functions for all-optical signal processing. In SOAs, nonlinear effects such as cross-gain modulation (XGM), cross-phase modulation (XPM), four-wave mixing and transient cross-phase modulation can all be exploited to demonstrate all-optical signal processing functions (Durhuus et al., 1996; Stubkjaer 2000). Taking all-optical wavelength conversion as an example, XGM wavelength conversion has some advantages such as simple structure, large dynamic optical power range, high conversion efficiency and large operation wavelength range, but it also has some problems