I. Introduction
All-optical logic gates have attracted considerable research interests because of their numerous potential applications in optical signal processing systems, such as addressing and data encoding, or optical label recognition for optical switching [1]. Such logic gates become more important to cope with the ever-increasing bandwidth requirements of information signal processing systems for the future high-speed data computation and ultra-high capacity optical communications [2] [3]. The present data and signal processing is limited to the low speed of electronic logic circuits due to the presence of optical-to-electrical and electrical-to-optical conversions. This trend urges the development of highly-efficient, all-optical logics which could operate at high speed, wideband and low loss to avoid inefficient, low-speed optical-electrical-optical processes.