| In this era of big data traffic,transmission capacity and rate are particularly important,and Electro-Optic(EO)modulator,as one of the important components of optical communication system,determines the transmission capacity and rate to a certain extent.In recent years,EO modulator has made great achievements in optical fiber communication window,and people begin to pay attention to the mid-wave infrared(2-5 μm).The red shift of wavelength further expands the communication capacity,so it is very important to improve the performance of the EO modulator of mid-wave infrared.The mid-infrared(MIR)band of lithium niobate(LiNbO3,LN)material can reach 5.5 μm,and the transmission loss is low,and the EO effect of the material creates a new way for devices integration and low loss.Therefore,EO modulator based on EO effect has attracted more and more research.In this thesis,the modulation performance of Lithium Niobate on Insulator(LNOI)electro-optic intensity modulator is studied in 3 μm wavelength with LN as waveguide by simulation design,and the solutions are as follows:(1)The spatial expansion range of mid-infrared light wave is large,the field distribution is not concentrated,and the interaction with matter is generally weak,which is not conducive to improving the modulation efficiency of the device;(2)High-speed modulated electrode model matched with LN optical waveguide.In the multi-field cooperative study,the speed matching of transmitted light and modulated electrical signals in lithium niobate thin film optical waveguide;(3)Electro-optical optimization theory of overlap of light wave and electrode electric field,improving modulation efficiency and other problems.Therefore,our design scheme is as follows:(1)The optical waveguide model of LN Mach-Zehnder interferometer(MZI)and Multi-Mode Interference(MMI)structure is established,and the MODE Solution of Finite Diference Time Domain(FDTD)and Rsoft software are used to study the relationship between the structural parameters of waveguide and the MODE field distribution and transmission spectrum characteristics;(2)Study the structural parameter optimization of Coplanar Waveguide(CPW)traveling wave electrode using HFSS(High Frequency Simulator Structure);the interaction mechanism of electric field and transmitted light and intensity modulation voltage of electrode structure were studied based on COMSOL Multiphysics;(3)The overlapping electro-optical optimization model of the field distribution of the transmitted light and the electric field distribution of the pushpull traveling-wave electrode structure is studied,and a solution is proposed to solve the velocity mismatch between the radio frequency(RF)signal and the optical signal in the LN thin film optical waveguide in the case of multi-field coupling,so that the device can adapt to the requirements of high-frequency modulation rate.So far,we have proved that the mid-infrared electro-optic modulator based on lithium niobate can complete electric modulation related to field distribution at low half-wave voltage(8 V),with extinction ratio greater than 40 dB and electro-optic bandwidth up to 120 GHz.The results provide valuable references for potential applications such as space optical communication,molecular recognition sensing and detection.The innovations of the paper are as follows:In this thesis,an LNOI electro-optic modulator working at 3 μm mid-infrared wavelength is designed,which combines the MMI coupler with the cosine Y branch waveguide.The influence of the coating structure on the device performance is further studied.Finally,the high-speed modulation of the device is realized. |
