低交叉干扰深亚波长等离子体金属/绝缘体/金属波导交叉连接器

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"Low cross-talk, deep subwavelength plasmonic metal/insulator/metal waveguide intersections with broadband tunability" 本文提出了一种低交叉干扰、深亚波长的等离子体金属/绝缘体/金属波导交叉连接器设计，旨在解决在微纳光子集成电路中的通信效率和干扰问题。该设计基于金属/绝缘体/金属腔体和波导结构，通过有限差分时间域（Finite-Difference Time-Domain, FDTD）方法分别研究了孤立腔体模式、波导模式以及腔体和波导模式的组合。交叉连接器的关键特性在于其利用了共振隧穿效应和奇波导模的截止频率。共振隧穿是指电磁能量通过一个薄绝缘层时发生的非局域传输现象，这在本设计中提高了信号的传输效率。而奇波导模的截止频率决定了能有效传输的光波长范围，低于该频率的模式将被阻止，从而有效地消除交叉干扰，确保信号在不同波导间的独立传输。此外，该结构具有587纳米的宽带可调性，这是通过调节腔体内空气隙的厚度来实现的。这种宽带调谐能力为光子集成电路的微型化和各种传感应用提供了可能。通过调整空气隙的尺寸，可以改变腔体的谐振频率，从而适应不同的光谱范围，适应性强，灵活性高。在微纳尺度下，传统的光学组件由于尺寸限制常常面临高交叉干扰和低传输效率的问题。而等离子体光学因其能够在深亚波长尺度上操纵光的能力，成为了解决这些问题的有力工具。等离子体金属/绝缘体/金属波导结构利用金属材料的表面等离子体共振，能够有效压缩光的传播路径，同时增强局部电磁场强度，因此在光子集成、光通信和光传感等领域具有广阔的应用前景。这项研究提出的新型等离子体交叉连接器不仅降低了交叉干扰，提高了传输效率，还具备宽带调谐能力，这为未来构建更复杂、性能更优的微纳光子系统奠定了基础。通过精细调控结构参数，可以进一步优化其性能，满足不同应用场景的需求。

Low cross-talk, deep subwavelength plasmonic

metal/insulator/metal waveguide intersections

with broadband tunability

Tae-Woo Lee, Da Eun Lee, Young Jin Lee, and Soon-Hong Kwon*

Department of Physics, Chung-Ang University, Seoul 06974, South Korea

*Corresponding author: soonhong.kwon@gmail.com

Received July 31, 2016; revised September 28, 2016; accepted October 2, 2016;

posted October 4, 2016 (Doc. ID 272935); published October 26, 2016

We suggest a low cross-talk plasmonic cross-connector based on a metal/insulator/metal cavity and waveguides.

We separately investigate the isolated cavity mode, the waveguide mode, and the combination of cavity and wave-

guide modes using a finite-different time-domain method. Due to resonant tunneling and the cutoff frequency of

the odd waveguide mode, our proposed structure achieves a high throughput transmission ratio and eliminates

cross-talk. Furthermore, the proposed structure has a broadband tunability of 587 nm, which can be achieved by

modulating the cavity air gap thickness. This structure enables the miniaturization of photonic integrated circuits

OCIS codes: (250.5403) Plasmonics; (240.6680) Surface plasmons; (230.5750) Resonators; (230.7370)

Waveguides.

http://dx.doi.org/10.1364/PRJ.4.000272

1. INTRODUCTION

Surface plasmon polaritons (SPPs) are propagating collective

oscillations that are electromagnetic waves coupled with free

electrons between a dielectric and a metallic interface.

Compared to conventional optics, SPPs can manipulate light

beyond the subwavelength regime. This is because the field

confinement of SPPs overcomes the diffraction limit of light

near the surface plasmon frequency [1–15]. Recent studies

have demonstrated the application of plasmonic devices such

as optical switches [2,3], biochemical sensors [4,5], and

advanced displays [6,7]. Plasmonic waveguides [5,8–13] are

another example of plasmonic applications. Due to their sub-

wavelength mode confinement, SPP waveguides are among

the best candidates for compact photonic integrated circuits

(PICs). In SPP waveguides, the trade-off between the lateral

confinement and propagation length is determined by the

geometry. Metal/insulator/metal (MIM) waveguides are suit-

able for optical data transmission in PICs because of their

deep subwavelength modal area, strong confinement, and rel-

atively long propagation length [10–14]. In order to construct

more compact and less complex PICs, it is also necessary to

intersect waveguide devices [13,16–18]. In addition, for effi-

cient signal transduction, SPPs must be able to propagate

in a desired direction. Therefore, elimination of cross-talk

must be achieved.

In photonic crystal waveguides, low cross-talk structures

have been proposed based on the resonant tunneling and

mode symmetry [16,17]. Minimizing cross-talk in the metal slot

waveguides and dielectric ridge waveguides has also been

studied [13,18]. However, previous research was mostly lim-

ited in two-dimensional (2D) simulations, which cannot con-

sider radiation loss. Also, the previous crossing regions to

minimize cross-talk usually had a size of several micrometers

or at least a wavelength. Only a few three-dimensional (3D)

studies on low cross-talk cross-connecting waveguides with

deep subwavelength size have been reported [19].

In order to understand the transmission properties of con-

ventional cross-connected MIM waveguides, we investigated

the transmission properties of a system consisting of two

MIM waveguides that are orthogonally crossed, as shown in

Fig. 1(a). Each MIM waveguide consists of two silver strips

with a width of 290 nm and a thickness of 100 nm; these

are separated by an air gap with a size of 10 nm. In this

MIM structure, the SPP waveguide mode with a target wave-

length of 1550 nm (λ

) is tightly confined inside of the air gap

[side-view of Fig. 1(b)]. The cross-sectional physical mode

area is 290 nm × 10 nm, which is a deep subwavelength size

of 0.0012λ

. In this structure, when the SPP mode is injected

from one of the waveguides, as shown in the top-view of

Fig. 1(b), 53.4% of the mode energy transmits through the

junction to the straight arm waveguide and 46.6% of the mode

propagates to the two orthogonal waveguides. This large

cross-talk (46.6%) will lower the signal to the desired wave-

guide (i.e., the straight waveguide) and cause a large amount

of noise in unwanted waveguides (i.e., the orthogonal wave-

guides). The cross-talk can be suppressed by introducing a

cavity and using resonant tunneling and mode symmetry

[16,17]. In addition, the cutoff frequency of the waveguide

mode will prevent coupling with unwanted waveguides.

In this article, we propose a theoretical tunable cross-con-

nector, which transmits a signal into the desired waveguide

with low cross-talk using resonant tunneling and the sym-

metries of the cavity and waveguide modes. The transmitting

wavelength can be tuned over a broad spectral range (500 nm)

with a center wavelength of 1550 nm. This is done by adjusting

the air gap of the cavity placed at the waveguide intersection.

Broadband light is injected, and the transmitting signal and

272 Photon. Res. / Vol. 4, No. 6 / December 2016 Lee et al.

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