一种电光可调的铌酸锂/钠基表面等离子体定向耦合器

Electro-optic tunable directional coupler based on a LiNbO_(3)/Na surface plasmonic waveguide

为了满足日益增加的集成光子器件设计的需求,本文研究了一种铌酸锂/钠表面等离子体波导(LiNbO3/Na surface plasmonic waveguide,LNSPW),并利用LNSPW构成电光可调的定向耦合器(directional coupling,DC).利用有限元方法(finite element method,FEM)对波导的模式特性和耦合器的耦合特性进行了分析.结果表明,随着波导尺寸的增大,传播长度可达约200μm,归一化有效模场面积小于0.4.通过调节耦合间距(W_(gap))、耦合长度(L_(C))和工作波长(λ)等参数,铌酸锂钠表面等离子体波导构建的定向耦合结构可实现3 dB耦合.当W_(gap)=100 nm和L_(C)=17μm时,DC在V_(0)=53 V时可实现3 dB耦合,且具有较好的方向性和隔离度.LNSPW的研究为实现可调的DC提供了一种可行的方案,在集成电光可调器件研究领域有潜在的应用前景.除此之外,LNSPW还可广泛应用于非线性光学、光信号处理及光全息存储等领域.

To meet the increasing demand of integrated photonic device design,a LiNbO_(3)/Na surface plasmonic waveguide(LNSPW)is demonstrated,and a directional coupler(DC)based on the LNSPW is also studied.The mode characteristics of the LNSPW and the coupling performances of the DC are simulated by the finite element method(FEM).There are four modes in the LNSPW when its width(w_(1))and the thickness(h_(1))are less than 600 nm and 400 nm,respectively.The number of the modes in the LNSPW increases with waveguide size increasing.To achieve the single-mode propagation,w_(1) and h_(1) are chosen to be 300 nm and 200 nm,respectively.The effective refractive index(n_(eff)),propagation length(L_(p)),and normalized effective mode area(A_(eff)/A_(0))are analyzed with different dimensional parameters of the LNSPW.The value of L_(p) is~200μm,and A_(eff)/A_(0) is less than 0.4.In order to demonstrate the electro-optic tunable performance,the normalized output power(P_(norm))values of the DC are calculated based on the LNSPWs with different values of coupling interval(W_(gap)),coupling length(L_(C)),and operating wavlength(λ).The P_(norm) values of the output ports(port 2 and port 3)vary with Wgap and L_(C).Owing to the electro-optic effect of LiNbO_(3)(L_(N)),P_(norm) of the DC can be adjusted by changing the applied electrostatic voltage(V_(0)).The influence of V_(0) on P_(norm) increases when Wgap is larger than 100 nm and L_(C) is greater than 12μm.The larger the value of L_(C) and Wgap,the stronger the effect of V_(0) on P_(norm) is,but P_(norm) values from two output ports decrease with Wgap and LC increasing.A 3 dB coupler can be achieved by changing V_(0) to 53 V when W_(gap)=~100 nm,L_(C)=~17μm,and λ=1.55μm,and has good directivity and isolation.The LNSPW provides a feasible scheme to realize the tunable DC,and has potential applications in integratable electro-optic tuanble devices,nonlinear optics,optical signal processing,and optical holographic storage.