All-Optical Format Conversion Based On Fiber Nonlinearities

Return-to-zero (RZ) format, which occupies only a part of the whole bit period, is widly used in high speed backbone optical networks, for it's high tolerance of polarization mode dispersion (PMD) and resistance of nonlinearities. Compared with RZ format, non-return-to-zero (NRZ) format is wildly used in the low bit rate access optical networks, for it's high spectrum efficiency, simply modulation, and largely time jitter tolerance. Therefore, it is necessary for RZ and NRZ format conversion at the interface between the high-speed backbone networks and low-speed access networks.In this work, I investigate an all-optical format conversion scheme based on cross-phase modulation (XPM) in highly nonlinear fiber (HNLF) and offset filtering subsequently, and it is including:(1) A numerical model for format convertor utilizing the XPM effect in highly nonlinear fiber and offset filtering sunsequently is established based on nonlinear Schrodinger equation. Performances of converted NRZ signals from RZ data streams with different duty cycles are analyzed and compared. Results indicate that the duty cycle of RZ data does affect the converted NRZ signal, with a rational value between 30% and 50%. In addition, in order to evaluate the performance of the format convertor futher, super-Gaussian RZ to NRZ conversion is invesitated as well.(2) RZ to NRZ format conversion is experimentally demonstrated in 10-Gbit/s data rate with 33% duty cycle optical system. Signal spectrum before and after HNLF, typical eye diagrams and bit-error-rate (BER) are measured. Less than 1-dB power penalty is obtained at 10-9 BER after the format conversion.(3) We numerically investigate a scheme of all-optical on-off keying (OOK) to binary phase-shift keying (BPSK) and quaternary phase-shift keying (QPSK) format conversion based on cross-phase modulation in the highly nonlinear fiber in 40-Gbit/s OOK optical system. The effect of polarization between the input OOK signal and pump on the coverted PSK signal is discussd detailed.