电信级纳米单向光传输：非对称Tamm等离子体激元-极化子

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"该文提出了一种用于电信级单向光传输的纳米级集成光学设备，基于金属-电介质-金属(MDM)波导。该波导的核心设计为不对称，包括一维光子晶体(PhC)、银(Ag)薄膜和介电层。通过在PhC两侧非对称地激发和传输Tamm等离子体激元-极化子(TPP)，实现了单向传播。TPP只在PhC与Ag薄膜界面处激发，而不在PhC的另一侧激发。正向传输时，TPP能穿透银膜并耦合到表面等离振子-极化子(SPP)，借助法布里-珀罗(FP)共振在电介质层中继续传播。相反，反向传输时，TPP无法穿越PhC的光子带隙，从而被困，导致无法有效传播。数值模拟结果显示，前向透射率最高可达87%，透射对比度达到1250。" 这篇论文探讨的关键知识点包括： 1. **集成光学设备**：这是一种将光学元件集成在微小尺度上的技术，可以实现高效、紧凑的光信号处理。 2. **Tamm等离子体激元-极化子(TPP)**：Tamm等离子体激元是一种特殊的电磁模式，它出现在金属和介质界面，结合了等离子体振荡与晶格极化子。在这种情况下，它们被用来实现单向光传播。 3. **表面等离振子(SPP)**：SPP是金属表面的电子集体振荡，能够在金属和介质界面传播光，而不沿垂直方向传播。在本文中，SPP被TPP激发后用于后续的光传播。 4. **一维光子晶体(PhC)**：PhC是一种具有周期性结构的材料，其光子带隙特性能够阻止特定频率的光在其中传播，这里作为单向传输的潜在屏障。 5. **非对称激发**：波导结构的不对称设计是实现单向传播的关键，因为TPP只在PhC的一侧被激发，而在另一侧则不会，从而导致光的单向传输。 6. **法布里-珀罗(FP)共振**：FP共振是两面反射镜之间光的干涉现象，文中利用这种共振增强了TPP在介电层中的传播。 7. **单向传输**：这是研究的主要目标，通过以上机制，光被有效地限制在一个方向上传播，这对光学通信和光子集成电路有重要意义，可以防止信号的反向干扰。这些技术和概念的结合为设计新型光学器件提供了新的思路，尤其是对于提高光通信系统的性能和效率。

Optics Communications 430 (2019) 428–433

Contents lists available at ScienceDirect

Optics Communications

journal homepage: www.elsevier.com/locate/optcom

Efficient unidirectional light propagation realized via asymmetrically

exciting and transmitting Tamm plasmon-polaritons in a

metal–dielectric–metal waveguide

Yunqing Lu, Min Xu, Jiong Xu, Yilin Chen, Ji Xu, Jin Wang *

School of Electronic and Optical Engineering & College of Microelectronics, Nanjing University of Posts and Telecommunications, Nanjing 210023, China

A R T I C L E I N F O

Keywords:

Integrated optics device

Tamm plasmon-polaritons

Surface plasmons

Unidirectional transmission

A B S T R A C T

An efficient nanoscale unidirectional transmission device at telecommunication wavelength is proposed, which

is made up of a metal–dielectric–metal (MDM) waveguide. The waveguide core is asymmetric and comprises

of a one-dimensional photonic crystal (PhC), a thin Ag film and a dielectric layer in a sequential order. In this

waveguide structure, the PhC acts as a finite potential barrier and the unidirectional propagation is realized by

combining the photonic bandgap effect and the asymmetric excitations of Tamm plasmon polaritons (TPPs) on

two sides of the PhC. With respect to asymmetric excitation, the TPPs are only excited at the interface between

the PhC and the Ag core film, and not excited on the other facet of the PhC. Further, for the forward transmission,

the TPPs can penetrate the thin Ag core film and is then coupled to the surface plasmon-polaritons (SPPs) for

the following propagation, which is also enhanced in this work by utilizing the F–P resonance in the dielectric

layer. Differently, for the backward transmission, the TPPs cannot tunnel through the PhC because it is trapped

in the stopband of the PhC. The numerical simulations demonstrate that the maximum forward transmittance of

87% and a high transmission contrast ratio of 1250 are achieved.

1. Introduction

Optical unidirectional devices, in which optical signals are allowed

to propagate only in one direction, play key roles in all-optical signal

processing just as diodes in electric circuits and gained much attention

due to the great potential in many applications using integrated pho-

tonic circuits [1–5]. In the past, various schemes have been proposed

to demonstrate optical unidirectional transmission by utilizing nonlin-

ear materials [6], anisotropic materials [7,8], magneto-optical mate-

rials [9,10], angular momentum-biased metamaterials [11], metallic

and dielectric metamaterials [12,13], metal gratings [14,15], photonic

crystals [16,17], and so on. While these proposals could satisfy different

requirements, an efficient unidirectional transmission device for the

practical applications should possess the following key characteristics:

ultrasmall feature size, ultralow threshold power and high efficiency.

From the integration point of view, surface plasmon polaritons (SPPs)

can be utilized to realize nanoscale integrated photonic devices, due to

their unique ability of confining light into deep-subwavelength scale and

strong field reinforcement effect [18]. Not surprisingly, nonreciprocity

and unidirectional propagation of SPPs have recently attracted consider-

able attention and various optical unidirectional devices based on SPPs

Corresponding author.

E-mail addresses: luyq@njupt.edu.cn (Y. Lu), jinwang@njupt.edu.cn (J. Wang).

have been investigated [19–22], e.g., a silver film with a hyperbolic

air hole [19], a tunable all-optical plasmonic diode based on Fano

resonance [20], and an all-optical diode based on a plasmonic slot

waveguide [21].

Recently, another form of surface mode called Tamm plasmon

polaritons (TPPs) [23,24], have become a very interesting platform to

realize nanoscale integrated photonic devices. TPPs can strongly localize

the electric fields at the interface between a finite one-dimensional

(1D) photonic crystal (PhC) and a metal film. In such planar structures,

simple direct optical excitation of SPPs is impossible for the reason that

the dispersion of SPPs lies outside the light cone given by 𝑘 = 𝜔/c,

where 𝑘 is the wave vector of light and 𝜔 is the angular frequency. The

excitation of SPPs requires dispersion-compensating elements such as

prisms and diffraction gratings. In addition, the SPPs can only be excited

by TM polarized light [18]. In contrast to SPPs, because the dispersion

of TPPs is within the light cone, TPPs can be excited by both TE and

TM polarized light without any dispersion-matching devices [23], which

simplify the realization of TPP-based structures [25–27]. Furthermore,

coupling between TPPs and other resonant states, such as Fabry–Pérot

https://doi.org/10.1016/j.optcom.2018.08.067

Received 23 May 2018; Received in revised form 20 August 2018; Accepted 27 August 2018

Available online 5 September 2018

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