基于铌酸锂薄膜的低损耗切趾光栅耦合器  

Low-Loss Apodized Grating Couplers Based on Lithium Niobate on Insulator

作　　者：刘亚康 佘玄[1] 刘红硕 黄飞[1] 陈侃[1] 毕然[1] 王磊[1] 舒晓武[1] Liu Yakang;She Xuan;Liu Hongshuo;Huang Fei;Chen Kan;Bi Ran;Wang Lei;Shu Xiaowu(College of Optical Science and Engineering,Zhejiang University,Hangzhou 310027,Zhejiang,China)

机构地区：[1]浙江大学光电科学与工程学院,浙江杭州310027

出　　处：《光学学报》2023年第19期204-211,共8页Acta Optica Sinica

基　　金：浙江省自然科学基金(Q18F050002)。

摘　　要：基于铌酸锂薄膜提出了一种新型的低损耗切趾光栅设计方案,在线性改变填充因子的同时根据布拉格条件对每个光栅周期进行调控。此方案不仅提高了向上衍射效率,还增加了向上衍射模斑和单模光纤模斑的重叠积分,极大地提高了耦合效率。1550 nm处对于TE模式耦合效率达到81.3%(0.90 dB),是目前已报道的基于无反射层铌酸锂薄膜的光栅耦合器设计方案中耦合效率最高的。考虑到实际工艺下波导存在刻蚀倾角,基于合理推广的布拉格条件同样对光栅周期进行调控,优化了带刻蚀倾角的切趾耦合光栅,耦合效率高达60.0%(2.22 dB)。Objective Lithium niobate on insulator(LNOI)is an interesting material for high-density photonic integrated circuits because of the high refractive-index contrast between lithium niobate(LN)and silicon dioxide,which also retains the excellent optical properties of LN.Based on LNOI,many photonic devices with outstanding performances have been demonstrated such as tunable frequency combs and high-frequency electro-optical modulators driven by low voltage.To link to off-chip systems,low-loss coupling between an LNOI waveguide and a conventional single-mode fiber(SMF)is necessary.At present,two mainstream methods are edge coupling and grating coupling.However,the edge couplers with low alignment tolerance can only be located on the edge of the chip and require intensive post-fabrication processing,such as cleaving and facet polishing.In contrast,grating couplers with relaxed fiber-positioning tolerances can be located at any point on the chip to facilitate wafer-level testing anywhere on the chip.Reports of grating couplers fabricated on LNOI so far either have low coupling efficiency or require additional layers to realize high coupling efficiency.Therefore,it is important to identify ways to improve the performance of LNOI without additional layers.Methods We propose a novel strategy that allows designing low-loss apodized gratings on LNOI,where the filling factor is linearly varied while periods are tuned according to Bragg condition.Our apodized grating coupler consists of ten apodized diffraction units with filling factors and pitches both varying along the x-axis,followed by several uniform diffraction units with fixed filling factors and periods[Fig.2(c)].The apodized grooves are designed to reduce the modal mismatch and the reflection from the interface between the waveguide and grating coupler and improve upward transmission.The uniform grooves are employed to guarantee that almost all the lights are scattered upwards rather than transmitted through,and the filling factors and periods are the same as the ten

关 键 词：铌酸锂薄膜 低损耗 切趾光栅 布拉格条件 刻蚀倾角 

分 类 号：TN622[电子电信—电路与系统] TN256