Research Of Silicon-Based Integrated Nonreciprocal Devices

Because the integrated all-optical communication system has the advantages of more stable and cheaper,the research of developing integrated all-optical communication system has always been the focus and hotspot in the field of optics. Nonreciprocal devices are crucial components in integrated all-optical communication systems, whereas it is still facing lots of challenges because it is difficult to break the Lorentz reciprocal theory in the field of integrated optical devices. The approaches to break the Lorentz reciprocal theory can be divided into two categories: the magnetic and nonmagnetic approach. The magnetic approach has a good isolation performance, however, it is not compatible with the Complementary Metal-Oxide-Semiconductor(CMOS) process. The nonmagnetic approach does not need to integrate the magnetic-optical materials, whereas the isolation performance of the schemes still need to improved. The main job of this thesis is to find nonmagnetic approaches to nonreciprocal optical devices which has high isolation performance.Silicon photonics is an important platform due to the fact that it has the ability to integrate both photonic and electronic devices, compatible with CMOS process, as well as low fabrication costs. Research of nonreciprocal devices based on silicon photonics has great significance to the all-optical communication system. The achievements and contributions of the thesis are summarized as the followings:Firstly, a sectional modulated ring is designed to break Lorentz reciprocity based on space-time modulation. The result calculated in time coupled mode theory(TCMT) and finite-different time-domain(FDTD) shows that it achieves unidirectional photonic transition. Besides, the way of build an integrated optical isolator based on the proposed scheme is also discussed, which can be used in all-optical communication system.Secondly, a scheme with route-asymmetrical optical transmission is put forward in the thesis, route-asymmetrical optical transmission means that forward and backward propagation of an optical device have different transmittance provided they are not present simultaneously. Based on the optical gradient force between two single-mode waveguides hang in the air, the scheme shows route-asymmetrical optical transmission, which is demonstrated by the calculation in FDTD. The forward transmittance of the device is about-6 dB while the backward transmittance is suppressed below-20.5 dB in C + L bands. The proposed device has the advantage of being passive, wideband, and compatible with CMOS process. Based on the scheme proposed here, two examples of the applications of the route-asymmetrical device are listed, which are an all-optical switch and an all-optical AND gate.