Data Format Conversion From Non-return-to-zero To Return-to-zero Based On Lithium Niobate Waveguides

All-optical modulation format conversion between non-return-to-zero (NRZ) and return-to-zero (RZ) may become an important interface technology for future optical networks that will include both wavelength-division-multiplexing and optical time-division-multiplexing technologies. In this thesis, two schemes of NRZ-to-RZ conversion are proposed. In one scheme, modulation format conversion and wavelength conversion are achieved simultaneously, using the cascaded second harmonic generation and different frequency generation (SHG+DFG) in a periodically polled lithium niobate (PPLN) waveguide; in the another one only the modulation format conversion is achieved using the PPLN waveguide incorporated in a Mach-Zehnder interferometer (MZI) structure. We simulated the characteristic of SHG+DFG process in the PPLN waveguide and several experiments have also been carried out. The main achievement and inclusions are listed as follows:(1) Based on reported literatures, the research signification of all-optical format conversion is discussed. Configurations for format conversion are introduced.(2) The nonlinear instantaneous coupling-wave equations of SHG+DFG from the Maxwell and the Physical equations are deduced. Then, the key technology in the PPLN——quasi-phase-matched (QPM), is discussed.(3) Firstly, 80Gb/s NRZ-to-RZ conversion process is numerically simulated based on the coupled wave equations. Secondly, the dependence of the extinction ratio on the waveguide length, optical powers, and time-delay is analyzed and optimized. Thirdly, the conversion bandwidth is also discussed. It is found that the signal wavelength can be tuned in a wide wavelength range of approximately 90 nm. Finally, the performance of 40Gb/s,160Gb/s,and 320Gb/s format conversion is simulated and compared with the 80Gb/s conversion. The eye diagram of converted RZ signal is good.(4) All-optical format conversion for 10Gb/s and 20Gb/s signals are demonstrated experimentally, experimental results are discussed and analyzed.