Study On Fabrication Tolerance Of Broadband Silicon Photonic Directional Couplers

Silicon-based chip is the cornerstone of modern information technology.With the development of the information,people's requirements for compute performance are increasing,and the requirements for communication network transmission speed are also increasing.The traditional silicon-based electronic chip has reached the limit in these fields,showing more and more restrictions in anti-interference and loss.Optical communication technology has been the inevitable trend of data communication.Due to its low cost and compatibility with CMOS technology,silicon-based photonic devices show great potential.As an important part of silicon photonic devices,silicon-based directional couplers(DCS)are widely used in photonic integrated circuits(PIC),such as wavelength division multiplexing,optical switches,filters and so on.However,the splitting ratio of the traditional directional couplers are very sensitive to wavelength,which limits the bandwidth of the device and degrades the transmission in the WDM system.In order to reduce the wavelength sensitivity of the split ratio of directional couplers and achieve a large working bandwidth,we design and verify two kinds of broadband directional couplers with different structures by theoretical calculation and simulation.Through optimization,both two directional couplers achieve a working bandwidth over 100 nm.During the process of fabrication,the fabrication variation is inevitable for the devices on chips,even if the chips are fabricated in good CMOS foundries.The fabrication variation will lead to the performance disparity between device design features and experiment results,because the device may deviate from the original design dimension.In this paper,the fabrication variations are described in detail,and the possible effects of fabrication variation on the device performance are pointed out.For directional couplers(DC),we consider two scenarios,the synchronous variation and the differential variation in width of waveguide.In order to assess the fabrication tolerance of the two directional couplers,simulations are carried out.Assuming that the waveguide width variation is symmetric with respect to the waveguide center,and the positions of the centers of two waveguides remain the same during the variation,we consider the variations in the width of the waveguide and gap between two waveguides.Simulation results show that when the width of the waveguide varies synchronously,the curved waveguide directional couplers show better fabrication tolerance,but for the differential variation scenario,both DCs do not work in this scenario.Due to the large thermo optic coefficient of silicon material,many devices based on thermo optic effect,such as thermal phase shifter and thermo optic switch,have been explored.Meanwhile,the temperature variation will also lead to the performance disparity of traditional optical devices such as directional couplers is.In order to further analyze the influence of thermo optic effect on directional couplers,the temperature tolerance of two broadband directional couplers is evaluated in this paper.In the 3D-FDTD simulation,the working temperature changes from 0 ° C to 200 ° C,the results show that the two directional couplers show good temperature tolerance.In the end,based on the previous work about directional couplers,we simulated and calculated the thermo optic switch comprised by two broadband DCs.