Design, Fabrication Of Microring Resonators And Their Applications In All-Optical Signal Processing

With the widespreading of internet, the network datas are increasing continuously and the development of optical communication system is rapid. Instead of optical electrical optical switching in photonic nodes, all-optical signal processing technology can enhance the efficiency of signal processing. Some key functions are needed in all-optical network, including multiplexing and demultiplexing, optical delay line, wavelength conversion, logic gate and so on. For these reasons, much effort has been spent in the past to design optical signal processing subsystems that are optically controlled and can be realized with integration technologies. As one of the important integrated optoelectronic devices, microring resonators find wide applications in all-optical signal processing.In this thesis, the basic theory and parametric model of the microring resonator are firstly introduced along with the designing and fabrication technics. Then the applications in all-optical signal processing based on the linear and nonlinear properties of microring resonators are analysed, including simultaneous RZ-OOK to NRZ-OOK and RZ-DPSK to NRZ-DPSK modulation format conversion based on the periodic comb filtering property of a single silicon microring resonator, clock recovery from RZ signal in a silicon microring resonator and a3-order nonlinear series-coupled microring resonator and all-optical AND logic gate using four-wave mixing in a microring resonator. The major research achievements of this thesis are as follows:(1) We firstly derive the light propagation equations in the waveguide and introduce the two fundamental optical modes in microring resonator. After giving the concept and classification of microring resonators, their power and phase transmission characteristics under three different coupling conditions through parametric model are discussed. Using full vectorial mode-matching method and coupled mode theory, we introduce the designing and fabrication process of silicon microring resonator with an experiment example.(2) Simultaneous RZ-OOK to NRZ-OOK and RZ-DPSK to NRZ-DPSK modulation format conversion in a single silicon microring resonator with free spectral range equal to twice the signal bit rate is experimentally demonstrated. First, we introduce the principal of the scheme. Then we analyze the effect of the coupling coefficient of the microring resonator and the bandwidth of the following optical bandpass filter on the conversion results. After designing and fabricating the optimized microring resonator, we present simultaneous conversion for both OOK and DPSK formats at41.6Gb/s.(3) Research background for all-optical clock recovery is briefly introduced. First, we compare the amplitude ripples of the clock pulses extracted from one single and cascaded2-order microring resonators, respectively. Then the principal of high speed clock recovery from RZ signal in a silicon microring resonator and a3-order nonlinear series-coupled microring resonator is analyzed. Simulation results of clock recovery from40Gb/s RZ signal based on a theoretical model show that the clock pulses can be achieved with only1dB amplitude ripple and short rise-and fall-times.(4) Based on a nonlinear theoretical model taking two-photon absorption (TPA) and TPA induced free carrier absorption into account, wavelength conversion based on degenerate FWM in silicon waveguides and microring resonators has been experimentally and theoretically analyzed. The impacts of input pump power, waveguide length, propagation loss and microring resonator position are evaluated. Compared with a3.5mm waveguide,15dB enhancement of conversion efficiency with1mW signal power and5mW pump power is achieved experimentally in a microring resonator with radius of47μm.(5) An all-optical AND logic gate in a single silicon microring resonator is experimentally demonstrated at10Gb/s with50%RZ-OOK signals. By setting the wavelengths of two intensity-modulated input pumps on the resonances of the microring resonator with an FSR of1.73nm and a Q-factor of12000, field-enhanced four-wave mixing with a total input power of only8.5dBm takes place in the ring, resulting in the generation of an idler whose intensity follows the logic operation between the pumps. Clear and open eye diagrams with error-free operation are achieved.