Experimental Study Of Electro-optic Modulation Based On Lithium Niobate With Microstructured Electrodes

In this thesis,we investigate the electro-optic modulation based on lithium niobate(LN)with micro-structure electrodes.In the first place,the developments and applications of electro-optic(EO)modulation devices are introduced.Next,we investigate the optical power modulation mechanism with the structure of the annealed proton-exchanged(APE)lithium niobate waveguide with micro serrated electrodes.However,due to the large mode size of the APE waveguide,it oftentimes needs driving voltage larger than 10 V in order to have high-depth modulation.In order to lower down the driving voltage and lower the energy consumption,we design an electro-optic device based on lithium niobate with micro-structured electrodes in order to have confinement in both the optical field(via SPR effect)and the electric field.This thesis investigates an electrooptic device based on the combination of EO effect of LN and the optical field localization effect via SPR.The device is based on Kretschmann configuration for SPR excitation and microstructure electrodes.This proposed structure provides certain new ideas for investigating novel electro-optic devices.Numerical calculation and verification of the electric field confinement ability of the microstructure electrodes are first carried out.The calculations are based on Finite Element Method implemented by commercial software Comsol Multiphysics where the field distribution of both the LN waveguide with serrated electrodes and LN with micro-structured electrodes are investigated.From the simulated field distribution,we verify the electric field localization ability of our designed serrated electrodes and micro-structured electrodes on LN.The simulation results also serve as guidance for the modulation experiment and help to understand the mechanism of the EO modulation experiment.In the experimental study,we first performed modulation with APE lithium niobate waveguide with serrated electrodes micro-structure.The driving voltages ranging from-25 V to 25 V with a step of 5 V is applied to the structure.The experimental results show that the transmitted power of light for the waveguide will increase with the increased voltages with a largest power variation of about 6.5 dB.The modulation process repeated for the voltage ranging from 25 V back to-25 V,the same power variation of 6.5 dB is achieved which shows the experiment has good repeatability.Secondly,through combing the electro-optic effect of lithium niobate with the field localized effect of SPR,we investigate the electro-optic modulation of lithium niobate with thin film electrodes microstructure by using the prism coupling Kretschmann configuration.At the first place,a super-continuum laser is employed as incident light and different voltages(0 V-1.2 V)are applied to the lithium niobate with thin film micro-structured electrodes.The experimental results show that the intensity of 482 nm will increase almost linearly with the increased voltages.Under the driving voltage of 1.2 V,the intensity has increased about 90% with respect to that of 0 V driving voltage.Whereas,around 656 nm,under the driving voltage of 1.2 V,the intensity has decreased about 18% with respect to that of 0V driving voltage.In addition,the 640 nm laser is also used as incident light for investigating the electro-optic modulation characteristics of the lithium niobate with thin film micro-structured electrodes.Lastly,we investigate the electro-optic modulation characteristics by comparing the spectra with respect to different modulated voltages to the spectrum with 0 V modulated voltage.