基于质子交换和刻蚀工艺的体铌酸锂阵列波导光栅  

Arrayed Waveguide Grating Fabricated over Bulk Lithium-Niobate Substrate Based on Proton Exchange and Etching

作　　者：袁佳茜 刘嘉程 杜江兵[1] 何祖源 Yuan Jiaxi;Liu Jiacheng;Du Jiangbing;He Zuyuan(State Key Laboratory of Advanced Optical Communication Systems and Networks,Shanghai Jiao Tong University,Shanghai 200240,China)

机构地区：[1]上海交通大学区域光纤通信网与新型光通信系统国家重点实验室,上海200240

出　　处：《光学学报》2023年第13期20-26,共7页Acta Optica Sinica

基　　金：国家重点研发计划(2018YFB1801804);国家自然科学基金(61935011,62122047)。

摘　　要：提出一种将质子交换技术和刻蚀技术结合的体铌酸锂波导和器件加工方案,基于质子交换的铌酸锂晶体相变特性改变,降低了质子交换区直接刻蚀难度,结合质子交换的纵向折射率改变和刻蚀波导的横向结构改变,波导尺寸显著降低,采用粒子群算法优化波导尺寸,最小可达2.5μm。基于该工艺方案设计了中心波长为1550 nm、四通道且通道间隔为400 GHz的阵列波导光栅,该阵列波导光栅的传输损耗约为6 dB,相邻通道间串扰均低于22 dB,整体尺寸仅为850μm×620μm,在高密度铌酸锂光子集成互连等场景具有较大的应用潜力。Objective Lithium niobate(LN),as a key material in the photonic industry,exhibits a strong electro-optic(EO)effect,a large nonlinear optical coefficient,and chemical stability.Traditional LN waveguides are usually prepared through titanium(Ti)diffusion or proton exchange.Ti diffusion exchange causes an increase of 0.001-0.04 in the refractive index,which depends on Ti density,diffusion time,and temperature.Proton exchange can give rise to a change in the refractive index of up to 0.12.These waveguides have the disadvantage of low refractive index contrast between waveguide and cladding,which leads to weak optical constraints,a large mode area,and a millimeter-level bending radius.This is the major limitation of conventional bulk LN for broad applications with a large amount and a small size of LN chips.Therefore,it is necessary to develop a method with a low-cost wafer and high-index-contrast waveguide,which is also the main objective of this work.Methods This study mainly presents the theory and simulation.The LN material is chemically inert,and therefore,it can hardly be etched without any pre-treatment.In addition,mechanical processing of the LN material is also difficult to proceed due to its high hardness and wear resistance.It is worth noting that during the proton exchange reaction,ions diffuse into the LN substrate to exchange ions,which leads to the occurrence of phase transition and structural defects,and thus,the proton exchange region can be easily etched.Therefore,we present a process scheme combining proton exchange technology with etching technology.The LN substrate is submerged in the proton source at a high temperature for a long time to assure that the depth of the proton exchange should be equal to the required height of the waveguide at least.After the proton exchange,samples are etched by methods such as wet etching and plasma etching,and the waveguide is retained.The feasibility of the process is verified by simulations.Moreover,the proton exchange depth,etching width,and sidewall angle are

关 键 词：光栅 铌酸锂 质子交换 粗波分复用 阵列波导光栅 

分 类 号：TN256[电子电信—物理电子学]