Research On Integrated Optoelectronic Devices Based On Graded Refractive Index Waveguide

Recent years,the traffic data brought by the Internet communication has increased rapidly.Therefore,the requirements for the quality of information transmission and bandwidth have been improved.Fortunately,due to the large communication capacity and low transmission loss,optical communication system becomes the primary information transfer method.Silicon-based optoelectronic is considered as a promising on-chip solution for future high-speed optical communication,data center interconnection and sensing technology.The research on integrated optical waveguide devices with graded refractive index distributions is a novel research field,the special refraction index distribution can be used to design small size and high performance devices.Further,the application of the new method provides an novel way for the design of high integrated devices..This thesis theoretically analyzes the propagation of light in graded-index optical waveguide based on the ray analysis of geometric optics.It’s revealed that the focusing constant is the critical parameter affecting the self-focusing period.The numerical simulation software is used to verify the relationship between the focusing period and the graded refractive index difference as well as the core layer size of the waveguide.Based on the theory of multi-mode interference,the differences and relations between the self-focusing and the self-imaging effect are analyzed detailedly.further,the relationship between the self-focusirg period and waveguide structure parameters are discussed.The focusing period and spot quality with different index distributions are analyzed thoroughly.We first demonstrate that the quality of the focusing spot is related not only to the field distribution of the graded refractive index fundamental mode,but also to the energy ratio of each mode.And that provides a novel theoretical support for the device design with graded refractive index waveguide.Combined with theoretical analysis and fabrication technology,we proposed a new type of spot-size converter based on the self-focusing effect of graded refractive index waveguide,the index distribution of the waveguide in this novel converter is with the form of square-law.The transmission efficiency of the novel converter,which the input waveguide width is 12μm and the output waveguide width is 0.5μm,is 97.8%,And a linear tapered transition waveguide is optimized for the reduction of mode field mismatch between the focused spot and the single-mode waveguide.The total length of the device is only 19.3μm,which is 6 times shorter than the previously reported spot-size converter,while the bandwidth is same.With the novel converter,the integration density of silicon photonic chip can be improved further.The new methodology of utilizing graded index can be applied to other devices and systems as well.In this thesis,the focus is on the self-focusing effect of graded refractive index waveguide,and a new spot-size converter is designed with that novel waveguide.This provides a new idea for the design of integrated optoelectronic devices with small volume and high performance,and thus could promote the development of large-scale optoelectronic integration.