Research On All-optical Wavelength Conversion For Advanced Modulation Formats And All-optical Logic Gates

With the rapid development of optical fiber communication on signal bit rate and transmission capacity, various advanced optical modulation formats have been extensively investigated and gradually applied to enhance the transmission system performance. On the other hand, all-optical signal processing is another attractive and necessary technique in future high-speed optical network in order to overcome speed limitations faced by conventional electronics processing at network nodes. This dissertation undertakes a detailed study of all-optical wavelength conversion for different advanced modulation formats and all-optical logic gates. The main points are as follows:A scheme for all optical logic NOR and OR gates is proposed utilizing cross polarization modulation effect in a semiconductor optical amplifier (SOA) in this dissertation. The two logic functions are achieved in the same setup and the selection is simple. The polarization control is simplified for this scheme based on theoretical analysis. The NOR and OR gates are successfully experimentally demonstrated at 10 Gbit/s with two and three input signals. The experiment results show good dynamic extinction ratio of more than 11.0dB for logic outputs. Furthermore, an all-optical AND gate is proposed requiring only input signals without an additional continuous-wave beam, which saves optical sources and simplifies the configuration. The AND scheme is numerically simulated and experimentally demonstrated at a bit rate of 10Gb/s.Differential phase shift keying (DPSK) and differential quaternary phase shift keying (DQPSK) have attracted significant attention and are now considered as the most promising candidates for the next generation high-speed long-haul transmission systems. All-optical wavelength conversion for DPSK and DQPSK signal becomes a hot academic topic. In this dissertation, wavelength conversion of a 40Gb/s RZ-DPSK signal is demonstrated based on four-wave mixing effect in an SOA. Furthermore, the first experiments on RZ-DQPSK wavelength conversion in an SOA are demonstrated at a very high speed of 107Gb/s. Error-free conversion operation is obtained at 107Gb/s with a power penalty of less than 3dB. The influence of input optical power, SOA current and signal pulse width on the conversion performance is analyzed in detail.Besides phase information, optical polarization information is also utilized extensively in advanced modulation formats, however, up to now few study on all-optical wavelength conversion for polarization modulated signal has been carried out. In this dissertation, a simple and effective method of wavelength conversion for polarization modulated signal is proposed, which makes use of polarization property of four-wave mixing effect. Using this method, wavelength conversion experiment for polarization shift keying (PolSK) signal is demonstrated for the first time at 10Gb/s with 1.6dB power penalty. Based on this principle, another application is proposed for all-optical PolSK/DPSK orthogonal label encoding in all-optical label swapping.For the implementation of all-optical logic gates, reported schemes are mostly based on nonlinearities of SOAs or optical fiber. In this dissertation, a scheme based on injection-locking effect in a semiconductor laser is proposed for all-optical NOR logic gate. Theoretical analysis for this scheme is carried out by using a model to describe the dynamics of the injection-locked laser. According to detailed numerical simulation, the logic gate can be operated at 10Gb/s or higher. The influence of key parameters on the NOR performance is also analyzed via numerical simulation.