The Study Of The Si-based Ring-resonator Optical Modulator And Switch

Optical modulators and optical switches play very important roles in the operation and construction of optical communication networks. The optical modulators and optical switches provided by the fabrication technology of the planar light circuits (PLC) offer many advantages: low cost, compact structure and high degree of integration. But they still have to be improved from these aspects: extinction ratio, power consumption and speed limit.The optical modulators and optical switches based on ring resonators are the new types of the optical devices of optical fiber communication systems. They have been developed in recent years, and expected to be applied in the large-scale photonic integrated circuits (PIC). The ring resonators do not require facets or gratings for feedback of light. Their planar nature is compatible with monolithic fabrication technologies. The compact structure configuration is good for raising the degree of integration. The resonant nature benefits the reduction of the phase change required for modulating or switching the light. Thus the ring resonators have great promise as the fundamental building blocks of PICs. The high refractive index difference from silicon-on-insulator (SOI) materials can be used to reduce the dimensions of the ring resonators. The fabrication technology of the SOI-based optical devices is compatible with the mature complementary metal oxide semiconductor (CMOS) foundry. Based on the free carrier dispersion effect in silicon, it was demonstrated that the speed of the SOI-based optical modulators could exceed tens of gigabits per second. The optical modulators and optical switches based on SOI materials exhibit great potential in the high-speed optical networks. This thesis focuses on the ring resonators, and develops the study of new technology of optical modulators and optical switches. This thesis makes innovative works mainly in the four aspects, as follows:1. The modulation sensitivities and the phase change required for a 10-dB extinction ratio have been investigated for the ring-resonator-based optical modulators and optical switches. The comparative analysis result shows that the asymmetry spectral responses or asymmetry modulation curves can be used to reduce the phase change for modulating or switching the light, and lower the power consumption.2. The potential of the dual-bus-coupled ring resonators in acting as a two-beam interferometer has been presented in this thesis. By tuning the phase difference between the two interference arms, the Fano-resonance line shapes can be generated in the transmitted spectral responses. This method offers a new way to obtain the Fano-line shapes in the output responses of the ring resonators. It can be utilized in the applications of optical modulators, optical switches and sensors.3. A kind of Mach-Zehnder optical switch with a cross-ring resonator as a two-beam interferometer has been proposed in this thesis. The structure configuration of the switch is very compact and simple. The switch can be provided by the fabrication technology of the planar light circuits, and is capable of obtaining high-extinction ratios and low crosstalk in both of the off and on state.4. In the experimental study, several types of the ring-resonator optical modulators have been successfully fabricated on SOI materials through the mature CMOS foundry. For the single-bus-coupled ring-resonator modulators, over 10-dB extinction ratios have been obtained, and the injected currents are less than 7mA. For the ring-enhanced Mach-Zehnder optical modulators, the injected current can be reduced less than 5mA. The improved Mach-Zehnder switch proposed in this thesis has been fabricated. A double-ring coupler is chosen to replace the cross-ring resonator, and acts as the two-beam interferometer. The asymmetry Fano-resonance line shapes have been observed in the output responses of the switch. By injecting the currents, the effects of the phase change in the interference arms and the ring waveguide on the asymmetry of the Fano-line shapes have been demonstrated.