Devices for Terabit Optical Networks, an Overview and Trends

Today’s communication WDM or OTDM networks, packetor circuit-switched, are characterized by hybrid architectures. In these architectures, electronic nodes are connected by optical links and switching is usually performed electronically using optoelectronic devices. However, the relatively low transmission bandwidth of the electronics and the associated optoelectronic interfaces, present an obstacle to fully utilize the large bandwidth offered by optical fibers. This obstacle can be eliminated if signals remain in optical form during address recognition/demultiplexing, switching, and other signal processing such as clock recovery. The first step in completing all-optical path is to eliminate an opto-electronic conversion associated with packet address reading and use all-optical address recognition/demultiplexing instead. The second step to complete the all-optical transmission path is to replace gigahertz bandwidth (opto)electronic switches with terahertz bandwidth all-optical routing switches. All-optical switches also avoid the delays associated with optoelectronic conversion, and if needed, can preserve the phase information carried by the light. In contrast to electronic switches, large throughput can be achieved in all-optical switching architectures through very high transmission bandwidth rather than large dimensionality. The third step in completing the all-optical path is to replace the electronic signal processing associated with switching by all-optical signal processing. One very important issue is selfsynchronization of an optical node based on clock extraction. If this can be achieved all-optically it can avoid a data flow bottleneck at the input to the photonic switch and also can reduce the need for flow control.