Optimization Design Of Silicon-organic Hybrid Integrated Electro-optic Modulator

The electro-optic modulator is the key unit of the microwave photonic link,which realizes the important function of transforming the microwave signal from the electric domain to the optical domain.High-performance electro-optic modulators should have large modulation bandwidth and high modulation efficiency to meet the need of microwave photonic link ultrawideband,large dynamic microwave optical transmission and microwave photonic signal processing applications.In this thesis,a silicon-organic hybrid integrated electro-optic modulator is investigated.The modulator takes advantage of the large-scale integration of silicon and the high electrooptic coefficient of organic polymers.The slot waveguide can be used to confine both optical field and electric field in the slot region filled with EO polymer,to achieve a large bandwidth and high efficiency modulation function.The main works are as follows:The silicon-organic hybrid slot waveguide structure is optimized.With the target of improving electro-optic modulation efficiency,the waveguide structure parameters such as slot width,silicon waveguide width and silicon slab layer height are optimized,and most of the optical power is concentrated at the slot;In order to improve the binding ability of RF electric field,the carrier concentration in the silicon slab layer is optimized.Without introducing excessive optical loss,the electric field of the RF signal is conducted to the slot region,so that the optical field and the electric field are overlapped perfectly.Then,the performance parameters of the modulator are analyzed,and the product of half-wave voltage and length is 0.91 V·mm and the modulation bandwidth limited by the RC time constant is up to 100 GHz.The mode coupler that connects the Slot waveguide to the straight waveguide is optimized.Two coupler structures are studied,which are tapered waveguide Strip-to-Slot mode coupling structure and MMI type Strip-to-Slot mode coupling structure.The Slot waveguide transition structure with and without a slab layer is also optimized to improve the coupling efficiency of different waveguide structure connections.The theoretical derivation and optimization of the modulation electrode are achieved.The microstrip line electrode and the coplanar line electrode structure are compared.The theoretical equations of the characteristic impedance and microwave transmission loss of the two electrodes are obtained.The theoretical estimation of the lumped electrode modulator's inability to modulate the high frequency signal is carried out.The reason that the phase velocity mismatch between the light and microwave reduces the modulation bandwidth of the modulator is analyzed.The structural parameters of the traveling wave electrode are optimized.The modulation bandwidth of the electrode structure under the constraint of microwave transmission loss and microwave light wave phase velocity mismatch is over 100 GHz.A preliminary experimental study on the silicon-organic hybrid integrated electro-optic modulator is carried out.The Slot waveguides with different slot widths in the range of 100nm~200nm are prepared by electron beam etching.The electro-optical polymer filling experiment is investigated,and the scanning electron microscope test is conducted.The results show that the organic polymer is fully filled into the slot.