Zheng Ze, Elkabbash Mohamed, Zhang Jihua, Guo Chunlei
Opt Lett. 2020 Jul 15;45(14):3937-3940. doi: 10.1364/OL.397601.
Geometric diodes represent a relatively new class of diodes used in rectennas that rely on the asymmetry of a conducting thin film. Here, we numerically investigate a plasmonic analogue of geometric diodes to realize nanoscale optical asymmetric transmission. The device operates based on spatial symmetry breaking that relies on a unique property of surface plasmon polaritons (SPPs), namely, adiabatic nanofocusing. We show that the structure can realize on-chip asymmetric electromagnetic transmission with a total dimension of ∼2µ×6µ. We demonstrate a signal contrast of 0.7 and an asymmetric optical transmission ratio of 4.77 dB. We investigate the origin of the asymmetric transmission and show that it is due mainly to asymmetric out-coupling of SPPs to far-field photons. We highlight the role of evanescent field coupling of SPPs in undermining the asymmetric transmission efficiency and show that by adjusting the plasmonic waveguide dimensions, a signal contrast of 0.94 and an asymmetric optical transmission ratio of 5.18 dB can be obtained. Our work presents a new paradigm for on-chip nanoscale asymmetric optical transmission utilizing the unique properties of SPPs.
几何二极管是用于整流天线的一类相对较新的二极管，它依赖于导电薄膜的不对称性。在此，我们通过数值方法研究几何二极管的等离子体模拟物，以实现纳米级光学不对称传输。该器件基于空间对称性破缺运行，这种对称性破缺依赖于表面等离激元极化激元（SPP）的一种独特属性，即绝热纳米聚焦。我们表明，该结构能够在芯片上实现总尺寸约为2µ×6µ的不对称电磁传输。我们展示了0.7的信号对比度和4.77 dB的不对称光学传输比。我们研究了不对称传输的起源，并表明这主要是由于SPP与远场光子的不对称外耦合所致。我们强调了SPP的倏逝场耦合在削弱不对称传输效率方面的作用，并表明通过调整等离子体波导尺寸，可以获得0.94的信号对比度和5.18 dB的不对称光学传输比。我们的工作为利用SPP的独特属性实现芯片上纳米级不对称光学传输提出了一种新范式。
