微纳螺旋凹槽结构检测光子自旋角动量

Detection of Optical Spin Angular Momentum with Micro-nano Helical Groove Structure

建立螺旋凹槽结构模型,具有不同自旋角动量的光束入射到该结构后激发表面等离激元,螺旋凹槽结构的螺旋性与光子自旋角动量耦合,使得不同自旋偏振光激发的表面等离激元具有不同的强度分布.通过螺旋凹槽激发的表面等离激元的强度分布获得入射光的自旋角动量.利用有限元方法计算了左旋偏振光与右旋偏振光激发的表面等离激元在螺旋凹槽中心的光场强度比,最大消光比达到168,实现对光子的自旋角动量的检测.在数值仿真中,分析了不同入射光波长的消光比,入射光波长在600～740nm范围内消光比高于50,其中入射光波长为670nm时的检测效果最佳;此外,研究螺旋凹槽结构参量对消光比的影响,当凹槽宽度为200nm,凹槽深度为70nm,匝数为2时,消光比最大,螺旋凹槽结构检测光子自旋角动量的能力最强.该研究可为集成光学中光子自旋角动量的检测提供一种新途径.

A model of helical groove structure is proposed.The surface plasmons excited by the incident light with different spin angular momentum have different intensity distributions on the structure,attributed to the coupling of the helical groove structure and the optical spin angular momentum.So the spin angular momentum of incident light can be obtained by the intensity distribution of surface plasmons excited by the helical groove structure.The finite element method is used to calculate the extinction ratio of the surface plasmon excited by the left-handed polarized light and the right-handed polarized light at the center of the spiral groove.The maximum extinction ratio reaches168,which can distinguish the photons with different spin angular momentum.In the numerical simulation,the intensity extinction ratio for different incident wavelengths is analyzed.The extinction ratio of the incident light wavelength in the range of 600~740 nm is above 50,with a best extinction ratio in the wavelength of 670 nm.In addition,the effect of the helical groove structure parameters on the extinction ratio is illustrated.And the maximum extinction ratio is obtained with the groove width of 200 nm,the groove depth of 70 nm,and the turn number of 2,at this time,the spiral groove structure has the best ability to detect the optical spin angular momentum.This work could provide a new approach to detect the optical spin angular momentum in integrated optics.