All-optical Parallel Format Conversion And Regeneration For Multi-channel New Modulation Formats Signals

Optical transmission networks are developing towards the aim of ultra high speed, large capacity, long distance transmission to accommodate the human’s increasing demand for information. Novel modulation formats with high spectrum efficiency and strong resistance of dispersion and nonlinearities have been used in the networks to increase the speed of single channel signal and the transmission distance. Different division multiplexing technologies have been used in the networks to enlarge the capacity of the communication system by increasing the amount of the channels. On the other hand, format conversion and regeneration are necessary at the node of the networks to make sure that each optical network transmits optimal format with longer distance. Thus, the research on the all-optical parallel format conversion and regeneration for different division multiplexed new modulation formats is very meaningful at the node of the optical networks.Sponsored by the National Basic Research Program of China (973) and the National Natural Science Foundation project, the crosstalk induced by the nonlinear effect in the semiconductor optical amplifier (SOA) during the all-optical parallel signal processing for the wavelength division multiplexed (WDM) or polarization division multiplexed (PDM) signals is fully investigated by theoretical simulation. The method of reducing the crosstalk is analyzed and explained. Thanks to the cross phase modulation (XPM) and gain saturation effect in the SOA and the method of reducing the crosstalk, the all-optical parallel format conversion and amplitude regeneration with tiny crosstalk for the WDM or PDM signals is realized. Overview of the full text, main research results are summarized as follows:(1) The basic theory of the polarized light and different representation methods of the state of the polarization are summarized. The multiplexing and de-multiplexing processes for the PDM signal are introduced. On this basis, the crosstalk during polarization division de-multiplexing is analyzed, which helps to explain the crosstalk problem during the parallel signal processing. The generation and demodulation of the differential phase shift keying (DPSK) and the differential quadrature phase shift keying (DQPSK) is analyzed. The nonlinear effects in the SOA is analyzed.(2) The crosstalk during format conversion from WDM non-return to zero (NRZ) to return to zero (RZ) is theoretically simulated. The method of reducing the crosstalk during the format conversion is explained. The parallel format conversion with tiny crosstalk from multi-channel NRZ on-off keying (OOK)/QPSK to RZ-OOK/QPSK is experimentally demonstrated. The principle of format conversion from WDM RZ-QPSK to NRZ-QPSK is theoretically explained. The format conversion from different duty cycle RZ-QPSK to NRZ-QPSK is simulated. The parallel format conversion from multi-channel RZ-QPSK to NRZ-QPSK is experimentally demonstrated by use of a SOA and delay interferometer (DI).(3) The nonlinear polarization rotation effect in the SOA is analyzed by theoretically simulating the change of the polarized light’s longitude and latitude. The change of the PDM signal’s orthogonality in the SOAs with different polarization-dependent gain (PDG) is simulated and analyzed, from which the method of reducing the amount of change of the PDM signal’s orthogonality can be obtained. The method of reducing the crosstalk during the parallel format conversion for the PDM signals is proposed and experimentally demonstrated. The format conversion with tiny crosstalk from WDM-PDM-NRZ-QPSK to WDM-PDM-RZ-QPSK is realized by use of a single SOA and DI at the total speed of800Gb/s.(4) The amplitude regeneration for the PDM-RZ-BPSK signal is proposed and experimentally demonstrated with gain saturation effect in SOA. The crosstalk during the amplitude regeneration is reduced by optimizing the input signal’s polarization. The method of reducing the phase noise induced by the Self phase Modulation (SPM) in the SOA is investigated and discussed. The amplitude regeneration for the NRZ-BPSK is proposed and experimentally demonstrated with two cascaded SOA and DI.(5) The format conversion from NRZ-OOK to NRZ-BPSK is experimentally demonstrated with XPM effect in the SOA. The amplitude fluctuation induced by the cross-gain modulation (XGM) is well reduced by use of a polarizer, resulting in the obtained NRZ-BPSK without amplitude fluctuation. The wavelength conversion with high extinction ratio can be realized together with the format conversion process.