Integrated-Optic Circuits for Recognition of Photonic Routing Labels

An optical fiber provides enormous capacity of more than tens terabits per second for transmission in photonic networks, whereas packet processing in network nodes will become a bottleneck for large-capacity networking. For realization of large-capacity and high-speed photonic networks, fast optical processing without conversion to electric signal is preferable (Seo et al., 1996; Blumenthal et al., 2000). Photonic routing has been attracting much interest to overcome the bottleneck of routing function in high-speed networks. In particular, photonic label routing network is expected to provide fast routing of packets at high-bit rate with simple processing. So far, various methods for optical label encoding and decoding have been studied (Kitayama et al., 2000; Goto & Miyazaki, 2005). As one of the nature of light, phase of coherent light has been effectively used in various optical systems, where the interference behavior between multiple signals can be easily used. Using this feature, label recognition techniques have been investigated for photonic routers based upon optical code correlation. However, most of the proposed systems cannot recognize all the binary codes because only the codes that provide enough discrimination between auto-correlation and cross-correlation can be recognized. In addition, in most systems, each optical integrated circuit recognizes only one label (Wada et al., 1999; Takiguchi et al., 2002). Therefore, it is necessary to prepare multiple correlators at each node in order to recognize all the routing labels. On the contrary, for processing of multiple labels, Moriwaki et al. (Moriwaki et al., 2005) and Cincotti (Cincotti, 2004) proposed label recognition systems where self-routing architecture was employed for phase-shift-keying (PSK) labels. On the other hand, Glesk et al. reported a demonstration of optical multiple label recognition for on-off keying (OOK) codes at 250Gbit/s using a selfrouting scheme (Glesk et al., 1997). The self-routing of label data stream for label recognition is one of promising methods in label decoding system. Hiura & Goto proposed a label recognition system for OOK labels (Hiura et al, 2005; Hiura et al, 2007a). Although the proposed system can recognize all the binary-code labels, the system requires many optical switches controlled by optical signals. A similar system was also reported by Kurumida et al. (Kurumida et al., 2006). On the other hand, Hiura et al. also proposed an all-optical passive label recognition system for all the binary codes in binary PSK (BPSK) format (Hiura et al., 2006; Hiura et al., 2007b). The label recognition system consists of a tree-structure connection of passive waveguide components named as