基于表面等离激元的偏振不灵敏型电光调制器的理论研究

Theoretical investigation of surface plasmonic polariton-based electro-optical modulator with low polarization dependence

由于受到表面等离激元(SPP)固有偏振性的影响,基于表面等离激元的波导型调制器只支持横磁模式(TM)传播。本文提出了一种在垂直方向和水平方向上均构建混合(hybrid)波导结构的表面等离激元电光调制器,以实现调制器的低偏振灵敏性。在组合的混合波导中,垂直和水平偏振方向上的表面等离激元被限制在相应的混合波导中。通过调控介质和ITO界面处形成载流子积累层中载流子浓度可实现光吸收调制。在经优化的结构中两个偏振态的消光比差为0.005d B/μm。通过3D-FDTD模拟调制器的光场调控,清楚地显示了传统硅波导与偏振不灵敏调制器间的耦合传输特性。两种偏振态下,偏振不灵敏调制器与硅波导之间的耦合效率均达到了74%以上。此项研究将为表面等离激元电光调制器在偏振不灵敏光集成回路中的应用提供解决方案,为其与具有偏振随机态光纤回路的集成奠定了基础。

Plasmonic modulators essentially support only transverse magnetic mode.A plasmonic modulator consisting of hybrid plasmonic waveguides in both vertical and horizontal directions is proposed to reduce the polarization-dependence.In a combined waveguide,surface plasmon polariton(SPP)modes polarized in the vertical and horizontal directions exist in the correspondingly oriented hybrid plasmonic waveguide.The light modulation is investigated by tuning the carrier density of the accumulated layer where occurs at the dielectric-ITO interfaces.In an optimized structure,aΔIER(a difference between the extinction ratios of two polarization modes)under 0.01 dB/μm is demonstrated at ITO“ENZ”-state by simulation.The energy flux clearly shows the polarization-selective coupling between the polarized guided modes in the feeding silicon waveguide and those in the combined waveguide.Coupling efficiency above 74%is obtained for both polarizations.The proposed plasmonic combined modulator has a potential application in guiding and processing of light from a fiber with a random polarization state.