TSTCNN). Fig. 1 shows the BER of the frst user against the near-far-ratio (NFR = EJE,, i = 2,3,4,5) with the signal-to-noiseratio (SNR) of user 1 being futed at 8dB. It can be seen from Fig. 1 that the TSTCNN detector outperforms the HNN detector over the NFR range. When the NFR is low, the TCNN detector has poor performance. As the NFR increases, the performance of both the TCNN detector and the TSTCNN detector approach that of the optimum detector closely. In Fig. 2, the average BERs of these detectors are plotted against SNR with all users having the same power. From this Figure, it can be seen that the performance of the TSTCNN detector tracks that of the optimum detector, while the performances of the HNN and TCNN detectors are obviously interference limited with the increase in SNR. Conclusion: A time-varying scaling-parameter transiently chaotic neural network has been developed for multiuser detection in DS/ CDMA systems. Compared with the HNN detector and TCNN detector, it has much better performance. The performance of the TSTCNN detector can closely approximate that of the optimum detector.

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Sung-Chan Cho et al. 109 We propose a novel very short (< 300 µm) vertical directional coupler switch with high extinction ratios larger than 30 dB. The device consists of a switching operation induced section (SOIS), an extinction ratio adjusted section (ERAS), and an extinction ratio enhanced section (ERES). These are achieved by changing the refractive index of one core. The switching operation is induced by changing the refractive index of one core in the SOIS. The improvement of extinction ratios larger than 30 dB for both the cross and bar states is made by controlling the asymmetry of the refractive indices of both cores in the ERES. Through the ERAS, different extinction ratios between the cross and bar states at the end of the SOIS are changed to the same value. For this reason, the optimum asymmetry of the refractive indices of the cores for the maximum extinction ratios and the lengths of ERES are the same for cross and bar states. Design guidelines for high extinction ratios with large tolerances are presented.

In future all-optical networks, it is likely that both WDM and OTDM will be incorporated, and there will be a need for all-optical data format conversion/reconversion between WDM and OTDM [1]. Nonretum-to-zero (NRZ) and retum-to-zero (RZ) formats are mostly used among a variety of data formats. NRZ format has the merit of lower bandwidth requirement and higher timing jitter tolerance than RZ format, while RZ format Is preferred in ultra-fest OTDM networks to make use of bit-interleaving technique. Some previous works have demonstrated NRZ-to- (inverted)-RZ converters using nonlinear optical loop mirror (NOLM) and cross-gain compression of semiconductor optical amplifier (SOA) [1]. NRZ-to-inverted-RZ converter based on cross-gain compression of SOA has the merit of simplicity in construction, though its extinction ratio (ER) is poor. To improve ER, we have serially added a modified terahertz optical asymmetric demultiplexer (TOAD) [2] to the converter. In this paper we propose and demonstrate ER enhanced NRZ-to-inverted-RZ converter.