A nonlinear optical fiber loop mirror (NOLM) adapted for all-optical 2R operation at ultrahigh bit-rates was experimentally and theoretically investigated. The proposed NOLM was created by adding inline/external fiber polarizers and also an inline optical phase-bias compensator (OPBC) to a standard NOLM. A theoretical investigation revealed that the operation of the standard NOLM became unstable due to residual polarization crosstalk of the polarization-maintaining optical components making up the NOLM, and that it could be dramatically improved with the inline/external polarizers. The NOLM with the polarizers ensured stable switching operation with high switching-dynamic-range (>30 dB) against the change of the wavelength of the input clock pulses, and the change of the environment temperature. We also experimentally verified that the OPBC played a dramatic role to ensure excellent dynamic switching performance of the NOLM, and to achieve signal-Q-recovery of the regenerated signals. All optical 2R experiments at 40 Gb/s and 160 Gb/s were performed with the modified NOLM. Signal regeneration with improved extinction ratio and signal Q value was successfully demonstrated. Q-recovery to the input of the control pulses degraded with ASE noise accumulation was also successfully achieved.

In this paper, the interpolation line search (ILS) algorithm to find the desirable step length in a numerical optimization method is investigated to determine the optimal saturation limits with non-smooth nonlinearities. The simple steepest descent algorithm is used to illustrate that the ILS algorithm can provide adequate reductions in an objective function at minimal cost with fast convergence. The power system stabilizer (PSS) with output limits is used as an example for a nonlinear controller to be tuned. The efficient computation to implement the ILS algorithm in the steepest descent method is available by using the hybrid system model with the differential-algebraic-impulsive-switched (DAIS) structure. The simulation results are given to show the performance improved by the ILS algorithm.

A new theoretical approach for the evaluation of the in-band nonlinear distortion effects on the performance of DS-CDMA systems is presented. Rather than widely used models of treating the effects of nonlinear distortion as additive Gaussian noise, the new approach is based on the asymptotic clipping and shot noise theories, which offer important insights into true nature of clipping process and can be further extended to many communications systems with high PAPR and peak-limited nonlinearities.

This study is a detailed numerical investigation on the relations between the performance of the RZ format single-channel transmission, and the chromatic dispersion of transmission fiber and pre-compensation ratio. We observed the transition from the SPM dominant low dispersion region to the intra-channel nonlinearities dominant high dispersion region, and found that the EOP is very sensitive to the pre-compensation ratio when the dispersion assumes a intermediate value. Furthermore, by analyzing the optical power-dependence of the EOP and other nonlinear impairments, we found that the amplitude fluctuation resulting from IFWM is dominant in determining the EOP in the transmission systems employing highly dispersed pulses.