Spectral routing techniques have attracted plenty of research attention for the past decades, as they enable light manipulation in both the frequency domain and the spatial domain, which is crucial for applications in on-chip spectroscopy, optical switching, and modern communications. Here, we demonstrate an ultra-compact asymmetric nanoplasmonic router for communication bands that routes O and C bands to opposite positions. The nanorouter consists of two uneven grooves that create bidirectional scattered optical fields, utilizing the interference between different optical modes inside the grooves. A broadband spectrum exceeding 100 nm and a maximum extinction ratio of 31 dB are achieved, providing new opportunities for nanophotonic color routing solutions and extensions to other areas such as imaging sensors and spectral measurements.

Manipulation of light at the nanoscale has emerged as a crucial topic in nanophotonics due to its remarkable applications in optical communication,1,2 spectroscopy,3,4 biosensing,5–7 and metrology.8 Among the numerous approaches, the employment of plasmonic nanoantennas has been widely investigated since the import of surface plasmon polaritons (SPPs) can confine and enhance light at a subwavelength scale.9 By carefully engineering the geometry and material composition of nanoantennas, their plasmonic resonances can be customized, offering additional control over the localization, enhancement, and manipulation of electromagnetic fields. Directional light control,10,11 cloaking,12–14 spectral sorting of optical signals,15 fluorescence enhancement,16,17 and color routing18 have been demonstrated by plasmonic nanoantennas.

By sorting different colors in different directions, color routing is a crucial technique for photovoltaics,19 high-resolution color imaging,20,21 and on-chip spectroscopy.22,23 Various SPP-based on-chip color routers have been successfully demonstrated in several precisely designed nanoantennas,24 which utilize wavelength-dependent plasmonic resonance to achieve the desired color routing capabilities, enabling selective excitation of SPPs for different colors. One approach exploits asymmetric multi-element antennas, achieving wavelength-selective routing by introducing asymmetry in structure or material composition, leading to interference between excited modes,25–27 e.g., three gold nanodisks of varying sizes25 or a pair of nanometallic disks composed of Ag and Au.26 However, this method often requires intricate designs and complex collective geometries, which can increase the fabrication complexity and challenge the precise control of the individual element phases. To provide more flexibility for wavefront control, metasurfaces consisting of nanoantenna arrays are proposed to offer selective directional routing according to wavelengths.18,20,28,29 However, the relatively large dimensions of multi-element antennas and metasurfaces pose challenges in fabrication, prompting the exploration of single-element antennas with multiple-mode responses.30–33 For instance, the V-shaped metallic nanoantenna utilizes the Fano interference between the dipole mode and quadrupole mode, achieving unidirectional scattering with an extinction ratio of 15 dB.31 Nevertheless, plasmonic nanorouters based on multi-mode coupling with single-element antennas have predominantly been utilized for the visible spectra.32,33 Researchers have developed new techniques to fulfill the requirement for color routing in telecommunication’s O- and C-bands. They have combined a rod-shaped aperture antenna (nanoslit) with narrowband resonance and a circular patch antenna (nanodisk) with broadband resonance into a subwavelength nanoparticle, which has proven to be novel and effective.30 While this compact solution has achieved bidirectional scattering at 1310 and 1510 nm wavelengths by utilizing Fano resonances, however, the experimental directivity is only 3 and 4 for 1310 and 1550 nm, respectively. In addition, the small size of the nanoantenna increases fabrication complexity, and the spectral band of this antenna needs to be further broadened to support extensive data and signal transmission.

In this paper, a single-element nanoantenna that consists of two adjacent asymmetrical grooves for the communication band is proposed to switch the direction of the SPP excitation under different incident wavelengths. The unidirectionality of SPPs is achieved by the mode interference between different modes inside the grooves. We numerically and experimentally demonstrate that two critical communication wavelengths, 1310 and 1550 nm, can propagate in the opposite direction. The maximum extinction ratio in two directions can be achieved at 26 and 31 dB at wavelengths of 1310 and 1610 nm. At a wavelength of 1550 nm, the extinction ratio is 18 dB, which also exhibits an excellent extinction effect. The bandwidth is 100–140 nm, covering the entire O and C bands, which can be used as a coarse wavelength-division device for high-capacity communication. Furthermore, the resonance spectra are fine-tuned by carefully adjusting the structure widths to apply to specific application scenarios. The device can be used as an optical demultiplexer in two-dimensional photonic integration, enabling applications in optical communication, spectral imaging, and biosensing.

Directional optical scattering can be achieved by an asymmetric structure, including the asymmetric shape and materials.34,35 Figure 1(a) shows the schematic of the proposed nanoantenna, which consists of two adjacent asymmetric nanogrooves seated in a gold film deposited on a glass substrate. By adding an asymmetric resonant groove to the nanoantenna, multiple modes inside the grooves can be excited. The anti-phase of different modes can be implemented when the parameter optimization has been done, leading to constructive interference in one direction and destructive interference in the opposite direction to form unidirectional propagation of SPPs. In addition, the contribution modes inside the grooves are wavelength-dependent, which impacts the summation of SPP components at different wavelengths and thus forms bidirectional transmission, which can also be regarded as color routing (for details, see model analysis in the supplementary material). In this work, the parameters are optimized by the 2D finite-difference time-domain (FDTD) method to achieve bidirectional SPPs under 1310 and 1550 nm, which is significant for optical communication, LiDAR, and optical computing. The calculated range is 40 × 6 µm2 with a mesh accuracy of 5 nm. The thickness of the Au film is 300 nm. The widths and depths of the grooves are set to w1 = w2 = w = 700 nm, h1 = 280 nm, and h2 = 210 nm, and the length of the grooves is L = 30 µm. The p-polarized plane wave with a broadband wavelength of 1100–1700 nm impinges on the nanoantenna from the air side. SPPs are launched along the interface between the Au film and air, perpendicular to the long axis of the grooves. The electric field amplitude distributions |E| are shown in Figs. 1(b) and 1(c) for the wavelengths of 1310 and 1550 nm. Both field distributions exhibit near perfect unipolarity, demonstrating excellent spectral routing for two critical communication wavelengths. The efficiency of SPPs, defined as the ratio of the propagating SPP power to the incident power, is 19.8% at 1310 nm for left-propagating SPPs (in the −x direction) and 25.6% at 1550 nm for right-propagating SPPs (in the +x direction).

FIG. 1.

Color routing by a single-element antenna. (a) Schematic diagram of a single nanoantenna composed of two adjacent asymmetric nanogrooves; the inset figure indicates the widths and depths of the grooves. (b) and (c) Simulated electric field distributions |E| at wavelengths of (b) 1310 nm and (c) 1550 nm, respectively.

FIG. 1.

Color routing by a single-element antenna. (a) Schematic diagram of a single nanoantenna composed of two adjacent asymmetric nanogrooves; the inset figure indicates the widths and depths of the grooves. (b) and (c) Simulated electric field distributions |E| at wavelengths of (b) 1310 nm and (c) 1550 nm, respectively.

Close modal

The bidirectional propagation of SPP is demonstrated experimentally using a home-built short-wave infrared leakage radiation microscope (LRM),36 as shown in Fig. 2(a). The sample is illuminated by a collimated p-polarized Gaussian laser beam (NKT supercontinuum laser, EXW-12, SuperK-SELECT) with a beam diameter of D = 1.22λ/N.A., where N.A. = 0.5, perpendicular to the sample plane. The incident wavelength ranges from 1100 to 1700 nm. A polarizer (Thorlabs, LPNIR100-MP2) and half-wave plate (Thorlabs, AHWP10M-1600) are used to change the polarization direction without changing the intensity of the incident beam. The excited SPPs are routed along the +x/−x direction and collected by two gratings, and then, the leakage SPPs are collected by an objective (40×, NA = 0.75) from the glass side. The signal is subsequently imaged on a charge-coupled device (CCD, Allied Goldeye, G-130 SWIR) camera. The Au film with a titanium adhesion layer is deposited by the Sputter (PRO Line PVD 75) with a thickness of 40 nm. The thickness of the Au film in the experiment is ∼308 nm. The sputtering power is set to 150 W, with a deposition rate of 2 Å/S for Cr and 3.93 Å/S for Au. The process is carried out in an argon (Ar) atmosphere at a pressure of 3 mTorr. The asymmetric nanogrooves and two gratings for decoupling SPPs are milled on the Au film using focused ion beam (FIB) system (Helios G4 UX). The nanogrooves are fabricated with an ion beam current of 21 pA and an accelerating voltage of 30 kV, while the gratings are fabricated with an ion beam current of 770 pA and an accelerating voltage of 30 kV. Figures 2(b) and 2(c) are the SEM images of the fabricated structure. The two gratings with four periods are 25 µm away from the nanorouter. The period and duty cycle of the gratings are 1.25 µm and 0.5, respectively. Figure 2(c) displays the cross-sectional view of the structure with the measured geometry parameter w = 678 nm (smaller than the designed value of 700 nm), L = 30 µm, h1 = 276 nm, and h2 = 214 nm, which is similar to the design. The depth of the etching is not very uniform, mainly depending on the quality of the Au deposition and the process of FIB. The method of chemical synthesis can achieve a single crystal Au film with good smoothness. In addition, the use of EBL (Electron Beam Lithography) and dry etching process technology with higher resolution and precision is also a method to improve the straightness and integrity of the asymmetric groove (see the supplementary material for an analysis of the effect of defects on experimental results). The effective device size is only approximated at 1.4 × 4 µm2, which is defined as the width of the entire grooves and the diameter of the Gaussian beam.

FIG. 2.

Color routing of SPPs in the communication band. (a) Schematic of the optical setup for the leakage radiation microscope (LRM). (b) and (c) Top view and cross section of the SEM image of the experimental sample, respectively. (d) and (e) CCD images of the SPP excitation for the sample at wavelengths of 1310 and 1550 nm, respectively. The white arrow in (d) indicates the polarization direction of the incident Gaussian beam.

FIG. 2.

Color routing of SPPs in the communication band. (a) Schematic of the optical setup for the leakage radiation microscope (LRM). (b) and (c) Top view and cross section of the SEM image of the experimental sample, respectively. (d) and (e) CCD images of the SPP excitation for the sample at wavelengths of 1310 and 1550 nm, respectively. The white arrow in (d) indicates the polarization direction of the incident Gaussian beam.

Close modal

The scattered SPPs from the two gratings are captured by the CCD at wavelengths of 1310 and 1550 nm, as shown in Figs. 2(d) and 2(e), respectively. The white double arrow in Fig. 2(d) indicates the polarization direction of the incident Gaussian beam. At 1310 nm, only the grating in the −x direction is illuminated, while the grating in the +x direction is dark, demonstrating superior unidirectionality experimentally. The situation is reversed at 1550 nm, presenting bidirectional routing for the two essential telecommunication wavelengths. Both images are captured under the same incident and acquisition conditions.

To investigate the wavelength-dependent behavior of SPP excitation experimentally, we captured CCD images with wavelengths of incident light ranging from 1100 to 1700 nm at an interval of 5 nm. Several illustrated wavelengths with a 100 nm interval are depicted in Figs. 3(a)3(f), demonstrating that the propagation of SPPs varies with wavelengths. The coupling phase and amplitude of the gap modes inside the nanoantennas change with wavelength, leading to a change in the scattered SPPs. To quantify experimental data, the extinction ratio (ER) is defined as ER = 10 log(Il/Ir), where Il and Ir are the integrated intensity of SPPs in the yellow dashed squares in Fig. 3(d). It is worth noting that the integrated region may influence the experimental ERs (detailed in the supplementary material). The ERs vary with the wavelengths, as calculated in Fig. 3(g). The blue circles represent the actual experimental results, while the orange solid curve shows the fitted results by the smoothing spline model with a smoothing parameter of 0.0001. The wavelength for the inversion direction is 1470 nm, where the ER is equal to 0. From 1110 to 1470 nm, the leftward SPP intensity is stronger than that of the rightward, while the situation is reversed from 1470 to 1700 nm. The maximum ER in both directions can be achieved at 27 and 31 dB at wavelengths of 1310 and 1610 nm, respectively. At a wavelength of 1550 nm, |ER| = 18 db, which still shows a large usable ER. An effective directional SPP excitation is defined as ER10, at which point, the SPPs can effectively propagate unidirectionally to the right and left, respectively. In this case, the bandwidths for left and right directional launching reach about 100 and 140 nm, respectively, as indicated by the solid line in Fig. 3(g). Compared to nanorouters based on single-element nanoantennas or multi-element antennas experimentally demonstrated before,26,31,35,37,38 our work achieves relatively broadband directional scattering at two different resonant bands and a high extinction ratio simultaneously. The leftward propagating SPPs cover the O band, and the rightward propagating SPPs cover the C band, which can be used as a broadband plasmonic demultiplexer. The broadband characteristic of the device may have implications for future high-capacity communication applications.

FIG. 3.

Wavelength dependence of the SPP excitation. (a)–(f) Measured direct images of the scattered SPPs for different wavelengths. The white arrow in (a) indicates the polarization of the incident Gaussian beam. The yellow dashed squares in (d) represent the SPP intensity integration area for evaluating the extinction ratio. (g) Extinction ratio as a function of wavelength. The blue circles represent the experimental data, and the red solid line indicates the fitting result. The black dashed lines indicate the effective wavelength ranges for left and right directional SPP excitation, which is when ER=10dB.

FIG. 3.

Wavelength dependence of the SPP excitation. (a)–(f) Measured direct images of the scattered SPPs for different wavelengths. The white arrow in (a) indicates the polarization of the incident Gaussian beam. The yellow dashed squares in (d) represent the SPP intensity integration area for evaluating the extinction ratio. (g) Extinction ratio as a function of wavelength. The blue circles represent the experimental data, and the red solid line indicates the fitting result. The black dashed lines indicate the effective wavelength ranges for left and right directional SPP excitation, which is when ER=10dB.

Close modal

The excitation and regulation of SPP modes primarily depend on the plasmonic materials used and the geometric parameters of the nanoantennas. By carefully designing the width of the grooves, it is possible to manipulate the specific wavelength ranges at which resonance takes place.39 By changing the width of the nanogrooves, the amplitude, phase, and number of modes inside the nanogrooves can be altered, enabling the corresponding response wavelength ranges to be tuned in two directions. This allows for a degree of control over the operating wavelengths, enabling adjustments to be made according to specific requirements. As the widths of the nanogrooves have been set to w = 600, 650, 700, 750, and 800 nm, while the depths remain the same as above, the resonance peak redshifts, as shown in Fig. 4(a), for the adjustment of the operating spectral bands for the two output directions. It is worth noting that the resonance peak is reduced with the change in widths and can be optimized by adjusting the depths of both nanogrooves. This is attributed to the phase difference between the modes, which depends on the depths of the nanogrooves. The corresponding experimental results have also been demonstrated, as shown in Fig. 4(b). The curves are similar to the simulation results. The discrepancy in the experimental and simulated extinction ratios arises from variations in the depth, shape, and smoothness of the grooves. The width of the actual fabrication is also smaller than that of the simulation, resulting in a resonance peak shorter than that of the simulation.

FIG. 4.

Resonance peak tuned by the widths of the nanogrooves. (a) Simulated and (b) experimental ERs vary in wavelengths from 1100 to 1700 nm with the designed groove widths of 600, 650, 700, 750, and 800 nm. The circles in (b) represent the experimental data, and the solid lines indicate the fitting results.

FIG. 4.

Resonance peak tuned by the widths of the nanogrooves. (a) Simulated and (b) experimental ERs vary in wavelengths from 1100 to 1700 nm with the designed groove widths of 600, 650, 700, 750, and 800 nm. The circles in (b) represent the experimental data, and the solid lines indicate the fitting results.

Close modal

In conclusion, we have numerically and experimentally demonstrated a broadband compact color router operated at telecommunication wavelengths by utilizing a nanoantenna with two adjacent asymmetric nanogrooves. The broadband spectrum exceeds 100 nm, which covers the entire O and C bands. The device can be integrated with other devices that can be used as a compact coarse wavelength division device for an ultra-high-capacity communication system. The maximum extinction ratio can be achieved is 31 dB. The ER at two critical telecommunication wavelengths is 26 and 18 dB. The characteristics of the inversion of SPP launch provide a new degree of freedom to realize bidirectional routing, which has highly directional and wavelength-selective properties, allowing the spectral response to be tailored through geometry adjustments. In particular, the efficient area for completing the color routing is a mere 1.4 × 4 µm2, defined as the width of the entire grooves and the diameter of the Gaussian beam. Our results can open the way to the use of flat-optical broadband color routers in wavelength division multiplexing systems, two-dimensional spectroscopy, and plasmonic biosensors.

See the supplementary material for more details on the mode analysis, as well as the influence of integration area and fabricated defects.

This work was supported by the National Key R&D Program of China (No. 2023YFB2805), National Natural Science Foundation of China (Nos. 62275259 and 12204309), Program of Shanghai Academic Research Leader (No. 22XD1404300), and Youth Innovation Promotion Association of the Chinese Academy of Sciences (No. 2021232).

The authors have no conflicts to disclose.

Xianghua Liu: Writing – original draft (equal); Writing – review & editing (equal). Ang Li: Resources (equal). Chenyang Liu: Resources (equal). Nengyang Zhao: Resources (equal). Jiahao Peng: Resources (equal). Fengyuan Gan: Writing – review & editing (equal). Xinrui Lei: Writing – review & editing (equal). Ruxue Wang: Formal analysis (equal); Writing – review & editing (equal). Aimin Wu: Funding acquisition (equal); Writing – review & editing (equal).

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

1.
X.
Fang
,
H.
Ren
,
K.
Li
,
H.
Luan
,
Y.
Hua
,
Q.
Zhang
,
X.
Chen
, and
M.
Gu
, “
Nanophotonic manipulation of optical angular momentum for high-dimensional information optics
,”
Adv. Opt. Photonics
13
(
4
),
772
833
(
2021
).
2.
F.
Wang
,
Z.
Gong
,
X.
Hu
,
X.
Yang
,
H.
Yang
, and
Q.
Gong
, “
Nanoscale on-chip all-optical logic parity checker in integrated plasmonic circuits in optical communication range
,”
Sci. Rep.
6
(
1
),
24433
(
2016
).
3.
L.
Novotny
and
B.
Hecht
,
Principles of Nano-Optics
(
Cambridge University Press
,
2012
).
4.
P.
Anger
,
P.
Bharadwaj
, and
L.
Novotny
, “
Enhancement and quenching of single-molecule fluorescence
,”
Phys. Rev. Lett.
96
(
11
),
113002
(
2006
).
5.
H.
Altug
,
S.-H.
Oh
,
S. A.
Maier
, and
J.
Homola
, “
Advances and applications of nanophotonic biosensors
,”
Nat. Nanotechnol.
17
(
1
),
5
16
(
2022
).
6.
H.
Xu
,
E. J.
Bjerneld
,
M.
Käll
, and
L.
Börjesson
, “
Spectroscopy of single hemoglobin molecules by surface enhanced Raman scattering
,”
Phys. Rev. Lett.
83
(
21
),
4357
4360
(
1999
).
7.
J. N.
Anker
,
W. P.
Hall
,
O.
Lyandres
,
N. C.
Shah
,
J.
Zhao
, and
R. P.
Van Duyne
, “
Biosensing with plasmonic nanosensors
,”
Nat. Mater.
7
(
6
),
442
453
(
2008
).
8.
R.
Wang
et al, “
Directional imbalance of Bloch surface waves for ultrasensitive displacement metrology
,”
Nanoscale
13
(
25
),
11041
11050
(
2021
).
9.
L.
Novotny
and
N.
Van Hulst
, “
Antennas for light
,”
Nat. Photonics
5
(
2
),
83
90
(
2011
).
10.
N.
Li
,
Y.
Lai
,
S. H.
Lam
,
H.
Bai
,
L.
Shao
, and
J.
Wang
, “
Directional control of light with nanoantennas
,”
Adv. Opt. Mater.
9
(
1
),
2001081
(
2021
).
11.
H.
Nouri
and
T.
Pakizeh
, “
Spectrally-tunable directionality of compact optical nanoantennas
,”
Plasmonics
8
(
4
),
1633
1641
(
2013
).
12.
P.
Livreri
and
G.
Raimondi
, “
A novel plasmonic nanoantenna for high efficiency energy harvesting applications
,” in
2020 IEEE 20th Mediterranean Electrotechnical Conference (MELECON)
(
IEEE
,
2020
), pp.
193
196
.
13.
J.
Qi
,
T.
Kaiser
,
R.
Peuker
,
T.
Pertsch
,
F.
Lederer
, and
C.
Rockstuhl
, “
Highly resonant and directional optical nanoantennas
,”
J. Opt. Soc. Am. A
31
(
2
),
388
393
(
2014
).
14.
R.
Alaee
,
R.
Filter
,
D.
Lehr
,
F.
Lederer
, and
C.
Rockstuhl
, “
A generalized Kerker condition for highly directive nanoantennas
,”
Opt. Lett.
40
(
11
),
2645
2648
(
2015
).
15.
F. B.
Barho
et al, “
Highly doped semiconductor plasmonic nanoantenna arrays for polarization selective broadband surface-enhanced infrared absorption spectroscopy of vanillin
,”
Nanophotonics
7
(
2
),
507
516
(
2017
).
16.
C. R.
Simovski
,
M. S. M.
Mollaei
, and
P. M.
Voroshilov
, “
Fluorescence quenching by plasmonic nanoantennas
,”
Phys. Rev. B
101
(
24
),
245421
(
2020
).
17.
A.
Puchkova
,
C.
Vietz
,
E.
Pibiri
,
B.
Wünsch
,
M.
Sanz Paz
,
G. P.
Acuna
, and
P.
Tinnefeld
, “
DNA origami nanoantennas with over 5000-fold fluorescence enhancement and single-molecule detection at 25 μM
,”
Nano Lett.
15
(
12
),
8354
8359
(
2015
).
18.
M.
Barelli
,
A.
Mazzanti
,
M. C.
Giordano
,
G.
Della Valle
, and
F.
Buatier de Mongeot
, “
Color routing via cross-polarized detuned plasmonic nanoantennas in large-area metasurfaces
,”
Nano Lett.
20
(
6
),
4121
4128
(
2020
).
19.
W.
Zhang
,
M.
Anaya
,
G.
Lozano
,
M. E.
Calvo
,
M. B.
Johnston
,
H.
Míguez
, and
H. J.
Snaith
, “
Highly efficient perovskite solar cells with tunable structural color
,”
Nano Lett.
15
(
3
),
1698
1702
(
2015
).
20.
S.
Yun
,
S.
Roh
,
S.
Lee
,
H.
Park
,
M.
Lim
,
S.
Ahn
, and
H.
Choo
, “
Highly efficient color separation and focusing in the sub-micron CMOS image sensor
,” in
2021 IEEE International Electron Devices Meeting (IEDM)
(
IEEE
,
2021
), pp.
30.1.1
30.1.4
.
21.
N.
Zhao
,
P. B.
Catrysse
, and
S.
Fan
, “
Perfect RGB-IR color routers for sub-wavelength size CMOS image sensor pixels
,”
Adv. Photonics Res.
2
(
3
),
2000048
(
2021
).
22.
Z.
Wang
,
S.
Yi
,
A.
Chen
,
M.
Zhou
,
T. S.
Luk
,
A.
James
,
J.
Nogan
,
W.
Ross
,
G.
Joe
,
A.
Shahsafi
,
K. X.
Wang
,
M. A.
Kats
, and
Z.
Yu
, “
Single-shot on-chip spectral sensors based on photonic crystal slabs
,”
Nat. Commun.
10
(
1
),
1020
(
2019
).
23.
J.
Bao
and
M. G.
Bawendi
, “
A colloidal quantum dot spectrometer
,”
Nature
523
(
7558
),
67
70
(
2015
).
24.
S.
Zhang
,
Z.
Ye
,
Y.
Wang
,
Y.
Park
,
G.
Bartal
,
M.
Mrejen
,
X.
Yin
, and
X.
Zhang
, “
Anti-Hermitian plasmon coupling of an array of gold thin-film antennas for controlling light at the nanoscale
,”
Phys. Rev. Lett.
109
(
19
),
193902
(
2012
).
25.
S. H.
Alavi Lavasani
and
T.
Pakizeh
, “
Color-switched directional ultracompact optical nanoantennas
,”
J. Opt. Soc. Am. B
29
(
6
),
1361
1366
(
2012
).
26.
T.
Shegai
,
S.
Chen
,
V. D.
Miljković
,
G.
Zengin
,
P.
Johansson
, and
M.
Käll
, “
A bimetallic nanoantenna for directional colour routing
,”
Nat. Commun.
2
(
1
),
481
(
2011
).
27.
T.
Shegai
,
P.
Johansson
,
C.
Langhammer
, and
M.
Käll
, “
Directional scattering and hydrogen sensing by bimetallic Pd–Au nanoantennas
,”
Nano Lett.
12
(
5
),
2464
2469
(
2012
).
28.
M. S.
Davis
,
W.
Zhu
,
T.
Xu
,
J. K.
Lee
,
H. J.
Lezec
, and
A.
Agrawal
, “
Aperiodic nanoplasmonic devices for directional colour filtering and sensing
,”
Nat. Commun.
8
(
1
),
1347
(
2017
).
29.
C.
Yan
,
K.-Y.
Yang
, and
O. J. F.
Martin
, “
Fano-resonance-assisted metasurface for color routing
,”
Light: Sci. Appl.
6
(
7
),
e17017
(
2017
).
30.
R.
Guo
,
M.
Decker
,
F.
Setzpfandt
,
I.
Staude
,
D. N.
Neshev
, and
Y. S.
Kivshar
, “
Plasmonic Fano nanoantennas for on-chip separation of wavelength-encoded optical signals
,”
Nano Lett.
15
(
5
),
3324
3328
(
2015
).
31.
D.
Vercruysse
et al, “
Unidirectional side scattering of light by a single-element nanoantenna
,”
Nano Lett.
13
(
8
),
3843
3849
(
2013
).
32.
X.
Zhuo
,
H. K.
Yip
,
X.
Cui
,
J.
Wang
, and
H.-Q.
Lin
, “
Colour routing with single silver nanorods
,”
Light: Sci. Appl.
8
(
1
),
39
(
2019
).
33.
T.
Coenen
,
F.
Bernal Arango
,
A.
Femius Koenderink
, and
A.
Polman
, “
Directional emission from a single plasmonic scatterer
,”
Nat. Commun.
5
(
1
),
3250
(
2014
).
34.
X.
Lei
,
R.
Wang
,
L.
Liu
,
C.
Xu
,
A.
Wu
, and
Q.
Zhan
, “
Multifunctional on-chip directional coupler for spectral and polarimetric routing of Bloch surface wave
,”
Nanophotonics
11
(
21
),
4627
4636
(
2022
).
35.
W.
Yao
et al, “
Efficient directional excitation of surface plasmons by a single-element nanoantenna
,”
Nano Lett.
15
(
5
),
3115
3121
(
2015
).
36.
E.
Descrovi
et al, “
Leakage radiation interference microscopy
,”
Opt. Lett.
38
(
17
),
3374
3376
(
2013
).
37.
Y. Y.
Tanaka
and
T.
Shimura
, “
Tridirectional polarization routing of light by a single triangular plasmonic nanoparticle
,”
Nano Lett.
17
(
5
),
3165
3170
(
2017
).
38.
R.
Kullock
,
M.
Ochs
,
P.
Grimm
,
M.
Emmerling
, and
B.
Hecht
, “
Electrically-driven Yagi-Uda antennas for light
,”
Nat. Commun.
11
(
1
),
115
(
2020
).
39.
J.
Yang
,
X.
Xiao
,
C.
Hu
,
W.
Zhang
,
S.
Zhou
, and
J.
Zhang
, “
Broadband surface plasmon polariton directional coupling via asymmetric optical slot nanoantenna pair
,”
Nano Lett.
14
(
2
),
704
709
(
2014
).