Research On Silicon Based Photonic Couplers And Multilayer Integrated Photonic Platforms

With the development of information technology and the increased amount of information,the traditional electrical chip has been losing their advantages in the field of information because of its inherent bottlenecks such as capacitors,inductors and resistors and can not meet the current needs.Then the optical chips come into being.As a carrier of information,photon has faster transfer rate and can realize high-speed communication.In the field of optical communication,photonic chips have made great achievements.The filter,as a key device in the photonic chips,has important research significance.At the same time,as the integrated density of photonic chips increases,planar photonic integrated circuit is also facing crosstalk,heat and other issues,so people have began to research and develop the three-dimensional integrated chips.Under these research backgrounds,we study a new type grating-assisted contra-directional coupler in this paper to overcome the shortcomings of the traditional filters.We also discuss the vertical coupling technology in the three-dimensional integrated chips and build the foundation for the development of the three-dimensional integrated chips.Our work contents can be summarized as follows:(1)The importance of silicon photonics and three-dimensional integration is analyzed.Compared to other filters,the advantages of the grating-assisted contra-directional coupler are introduced.And the coupling mode theory is discussed in detail,which provide the theoretical foundation for the later proposed different couplers.(2)Coupling mode theory is used to analyze the principle and transmission model of the contra-directional coupler.And the key factor that will influence the bandwidth of the contra-directional coupler are theoretically deduced.The transmission characteristics of the sub-wavelength grating(SWG)waveguide are also briefly introduced.(3)In order to solve the problem in the contra-directional coupler with narrowband and large size,a subwavelength grating waveguide with the transmittance more than99% is first designed.Based on this waveguide,a novel wideband and compact contra-directional coupler is proposed and the reason is also analyzed from the effective index,dispersion and coupling coefficient of this device.The simulation results show that the bandwidth reaches 29 nm,and the extinction ratio is 30 d B.The coupling length is only 50 ?m.(4)A vertical taper coupler is designed to realize the connection in three-dimensional integrated chips.By optimizing the parameters of the coupler,the coupling efficiency of 97% is achieved and the crosstalk is also less than-40 d B.In order to reduce the gap between the simulation results and the measurement results,the fabrication tolerance is also discussed.Then the fabrication process for three-dimensional integrated chips is introduced in detail and the key points which should be noticed are also figured out.Finally,a silicon—silicon nitride(Si Nx)vertical coupler is fabricated on this basis.The measurement of the coupling efficiency is more than 60% over a bandwidth of more than 50 nm,and the crosstalk is about-30 d B,which proved the feasibility of this programme.Meanwhile,two solutions to the problems occurred in the experiment are proposed,which can provide new thought for the future experiments.