The Research Of MZI Switch On Thin-film Lithium Niobate

Optical switch,as one of the most important components in optical communication and information processing systems,plays an important role in data centers,sensing,quantum computing and so on.To satisfy the ever-increasing demand in these fields,it is urgently needed to develop high-performance optical switches with compact footprint,high speed,and low power consumption.Compared with other integrated optics platforms,lithium niobate on insulator(LNOI)can not only retain the excellent electrooptic(EO)characteristics of lithium niobate crystal,but also enable high-index-contrast waveguide and,hence,is very suitable for making compact high-speed EO switches.To realize high-performance Mach-Zehnder interferometer(MZI)optical switch,it is necessary to have the 3 d B coupler with uniform light splitting and two identical phase shift arms.However,due to unavoidable fabrication errors in the fabrication process,it is difficult to ensure that the parameters of the fabricated device are exactly the same as the designed values.To address these issues,the study on design and fabrication of highperformance MZI EO switches on LNOI have been carried out in the thesis,the main contents of which are as follows:1.The research background and significance of optical switches are described,and the research progress of lithium niobate optical switch at home and abroad is reviewed.Meanwhile,the theoretical basis of MZI EO switches on LNOI is introduced,including the analysis method of rib waveguide,the main performance indexes of EO switches,the working principle of MZI EO switches,and the self-imaging effect of MMI coupler,etc.2.A broadband and low-random-phase-errors optical switch based on LNOI is proposed and demonstrated experimentally.The proposed optical switch employs typical MZI structure with 3 d B 2×2 MMI couplers,and the few-mode waveguides(FEWs)are used as the phase shifters to reduce the random phase errors.The proposed switch was analyzed systematically and deigned in detail,and then fabricated and characterized carefully.The experimental results show that the fabricated switch almost works on the initial operating state of low crosstalk,which confirms the achievement of low random phase errors.The fabricated switch has a switching voltage of ～7.3 V,with a rise time of～134.4 ns and a fall time of ～8.8 ns.Moreover,the switch achieves an extinction ratio larger than ～16 d B and a crosstalk less than ～-16 d B over a wavelength range from 1530 nm to 1605 nm,indicating a wide optical bandwidth.3.A MZI optical switch with adjustable MMI coupling ratio based on LNOI is proposed.By lengthening the length of the MMI coupler’s multimode waveguide at the input end of the optical switch,and placing tuning electrodes above it,the proposed switch can use the EO effect of lithium niobate to adjust the coupling ratio of the MMI.This method can improve the deterioration of the coupling ratio caused by fabrication errors.The experimental results of MMI with tuning electrodes show that the coupling ratio of MMI can be changed within a certain range after applying voltage to the electrode.And the initial operating state of the switch is improved to some extent by using the tuning electrode,and the large crosstalk caused by fabrication errors is reduced.Over a wide optical bandwidth from 1530 nm to 1605 nm,the switch can achieve an extinction ratio larger than 11 d B and a crosstalk less than-11 d B.In addition,the switching voltage is～5.6 V.The rise and fall times are ～85.3 ns and ～13.5 ns,respectively,which indicates the switch can realize high-speed switching operation.