Three-dimensional Silicon Photonic Devices For Mode-devision Multiplexing

With the rapid development of communication technology,the demand for large volume transmission is in high demanded.Due to the intrinsic barrier of capacitance and inductance effect,the Moore's law is unable to work anymore.Optical communications have merits of wide band,low loss,and etc.Individual functional element can be integrated on one substrate,which could offer compact,multifunctional working.However,with the increment of complexity,two-dimensional planar integration is hard to provide further capacity enlargement.Three-dimensional integration could further increase the transmission capacity and signal processing with feature of compactness.In this work,key devices in mode division multiplexing(MDM)technology,the 3D mode coupler/intercrossing,mode MUX/De MUX,and optical switch have been investigated systematically,including(1)The research background of integrated photonics has been introduced.The basic principles of mode coupling theory and waveguide design have been discussed.(2)To overcome the difficulty of interlayer mode coupling and optical interconnection,3D optical coupler and optical crossing have been designed based on the mode coupling theory.The length of 3D optical coupler is 7.3?m,while the coupling efficiency reaches to 99.7%,which could offer the single mode coupling between the upper and lower waveguide.Besides,the functional and ellipse type waveguide crossing have been proposed,too.The lengths of two devices are both less than 20?m.Especially,the functional type 3D waveguide crossing shows a low crosstalk around-59.7 d B at 1550 nm,while ellipse type waveguide crossing exhibits a favorable crosstalk about-57.8 dB.(3)The 3D mode MUX has been proposed and optimized.Through the refractive index matching,the TE₁₁ mode in the lower silicon waveguide can be converted to TE₁₁ TE₁₂?TE₂₁?TE₃₁ and TE₂₂ model in the upper silicon bus waveguide.The converting efficiencies are all over 57%,which proves the feasibility of 3D silicon waveguide mode MUX/De MUX.(4)As a key device in MDM system,optical switch element plays an important role in the determination of optical switch array.Here,a MMI-MZI 2×2 optical switch constructed on the carrier dispersion is designed and optimized.Push-pull modulation is adopted during working.The simulation results show that the crosstalk is smaller than-27 d B and the transmission loss is about 1 d B.With the adjustment of primary phase by PIP doping and thermo-optic tuning,the issue of unbalance between two branch arms of MZI is ameliorated.The Benes switch array constructed by proposed switch element shows the favorable crosstalk less than-25 d B and an transmission loss about 3 dB.