Mode Manipulation On Silicon-Based Waveguide System And Applications

Silicon-based optical interconnect plays an important role in era of big data and supercomputing in the future,mainly to solve the bandwidth,cost,power consumption and other issues of short-range optical communication.These are attributed to the high integration of silicon waveguide,CMOS compatibility,hybrid integration with other materials platform and other advantages.Wavelength division multiplexing is the most widely used to improve the communication capacity of optical interconnect.However,on-chip mode division multiplexing or polarization division multiplexing are not yet mature for industrial application,so it is necessary to further explore and improve the performance of silicon optical devices,especially in mode division multiplexing,polarization control and optical directional transmission control.In this thesis,the mode manipulation on silicon-based waveguide system was studied,including the control on the propagation constant ratios between different modes of symmetric coupled waveguide system,the control on the dispersion of the even symmetric mode and odd symmetric mode via sub-wavelength grating(SWG)structure,the control of evanescent wave in different polarization states of waveguide via SWG effectively anisotropic structure and the control of the imaginary part of the effective refractive index of the coupled waveguide mode by adding a patch slab waveguide.They are also applied to the key technologies of signal multiplexing and routing control in silicon-based optical interconnect,such as mode division multiplexing,multi-mode beam splitting,multi-mode switching,polarization beam splitting and time asymmetric transmission of mode field.Specifically,the concept of simultaneously controling and routing multiple mode signals based on densely packed waveguide array(DPWA)bus was proposed in this thesis.Multimode 3dB coupler and multimode optical swtich were designed and demonstrated experimentally,which are the first optical integrated device to control multiple modes simultaneously in the world.It is of great significance in simplifying network system,sharing switch resources and reducing power consumption and size We have also enriched and developed the concept of mode division multiplexing by introducing a densely packed uniform waveguide array(DPUWA)as a bus waveguide for the first time.In addition to being able to transmit multi-mode signals as a bus,the DPUWA can handle multimode signals more flexibly,for example,for multimode crossing or bending.By using SWG,the dispersion relationship between even symmetric and odd symmetric mode of the coupled waveguides can be modulated to improve the working wavelength bandwidth of the multimode 3dB coupler and the multimode optical switch greatly.By using the SWG equivalent anisotropy material,the decay coefficients of evanescent waves with different polarization of the coupled-waveguide are controlled.A high performance polarization beam splitter via cascaded SWG-based direction coupler is designed,which is the world record.Finally,by introducing a patch structure,the imaginary part of the effective refractive index of the coupled waveguide mode was modulated.We use the mode evolution method to explain the time asymmetric transmission and break through the traditional design of the asymmetric structure encircling around the exceptional point(EP).The key factor to realize the time asymmetric transmission of light field was discussed.The time asymmetric transmission of light in a symmetric structure is designed.The explanation for the phase anti-adiabatic jump and the design of the symmetric structure to realize time asymmetric evolution are general,which can be applied to other non-Hermitian coupled systems.And the gain can be introduced for the directional transmission control of light.