Polarization-sensitive perfect absorbers at
near-infrared wavelengths
Lijun Meng,1,2 Ding Zhao,1 Qiang Li,1 and Min Qiu,1,3,*
1
State Key Laboratory of Modern Optical Instrumentation, Department of Optical Engineering, Zhejiang University,
Hangzhou 310027, China
2
Department of Physics, Zhejiang University, Hangzhou 310027, China
3
School of Information and Communication Technology, Royal Institute of Technology (KTH), Electrum 229, 164 40
Kista, Sweden
*
[email protected]
Abstract: Three different types of polarization-sensitive perfect absorbers
are designed and numerically investigated. The bottle-like and the cup-like
absorbers are narrowband absorbers, which strongly absorb light of a specific
polarization and reflect almost all light of another polarization. By varying
the geometric parameters, their absorption peaks can be tuned from 1300 nm
to 2300 nm and 700 nm to 1400 nm, respectively. The broadband absorber is
polarization-sensitive as well, exhibiting an average absorption efficiency of
88% over a wide range of wavelength (700-2300 nm). The proposed
absorbers may have potential applications in polarization detectors,
polarizers etc.
©2012 Optical Society of America
OCIS codes: (250.5403) Plasmonics; (310.6628) Subwavelength structures, nanostructures;
(240.5440) Polarization-selective devices.
References and links
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15.
T. V. Teperik, F. J. Garcia de Abajo, A. G. Borisov, M. Abdelsalam, P. N. Bartlett, Y. Sugawara, and J. J.
Baumberg, “Omnidirectional absorption in nanostructured metal surfaces,” Nat. Photonics 2(5), 299–301 (2008).
N. Liu, M. Mesch, T. Weiss, M. Hentschel, and H. Giessen, “Infrared perfect absorber and its application as
plasmonic sensor,” Nano Lett. 10(7), 2342–2348 (2010).
K. Aydin, V. E. Ferry, R. M. Briggs, and H. A. Atwater, “Broadband polarization-independent resonant light
absorption using ultrathin plasmonic super absorbers,” Nat Commun 2, 517 (2011).
V. G. Kravets, S. Neubeck, A. N. Grigorenko, and A. F. Kravets, “Plasmonic blackbody: strong absorption of light
by metal nanoparticles embedded in a dielectric matrix,” Phys. Rev. B 81(16), 165401 (2010).
J. Hao, J. Wang, X. Liu, W. J. Padilla, L. Zhou, and M. Qiu, “High performance optical absorber based on a
plasmonic metamaterial,” Appl. Phys. Lett. 96(25), 251104 (2010).
J. Wang, Y. Chen, J. Hao, M. Yan, and M. Qiu, “Shape-dependent absorption characteristics of three-layered
metamaterial absorbers at near-infrared,” J. Appl. Phys. 109(7), 074510 (2011).
J. Wang, Y. Chen, X. Chen, J. Hao, M. Yan, and M. Qiu, “Photothermal reshaping of gold nanoparticles in a
plasmonic absorber,” Opt. Express 19(15), 14726–14734 (2011).
X. Chen, Y. Chen, M. Yan, and M. Qiu, “Nanosecond photothermal effects in plasmonic nanostructures,” ACS
Nano 6(3), 2550–2557 (2012).
A. Polyakov, S. Cabrini, S. Dhuey, B. Harteneck, P. J. Schuck, and H. A. Padmore, “Plasmonic light trapping in
nanostructured metal surfaces,” Appl. Phys. Lett. 98(20), 203104 (2011).
V. G. Kravets, F. Schedin, and A. N. Grigorenko, “Plasmonic blackbody: almost complete absorption of light in
nanostructured metallic coatings,” Phys. Rev. B 78(20), 205405 (2008).
J. Hao, Y. Yuan, L. Ran, T. Jiang, J. A. Kong, C. T. Chan, and L. Zhou, “Manipulating electromagnetic wave
polarizations by anisotropic metamaterials,” Phys. Rev. Lett. 99(6), 063908 (2007).
H. Tao, C. M. Bingham, D. Pilon, K. B. Fan, A. C. Strikwerda, D. Shrekenhamer, W. J. Padilla, X. Zhang, and R.
D. Averitt, “A dual band terahertz metamaterial absorber,” J. Phys. D Appl. Phys. 43(22), 225102 (2010).
Y. Ma, Q. Chen, J. Grant, S. C. Saha, A. Khalid, and D. R. S. Cumming, “A terahertz polarization insensitive dual
band metamaterial absorber,” Opt. Lett. 36(6), 945–947 (2011).
M. K. Hedayati, M. Javaherirahim, B. Mozooni, R. Abdelaziz, A. Tavassolizadeh, V. S. K. Chakravadhanula, V.
Zaporojtchenko, T. Strunkus, F. Faupel, and M. Elbahri, “Design of a perfect black absorber at visible frequencies
using plasmonic metamaterials,” Adv. Mater. 23(45), 5410–5414 (2011).
K. Iwaszczuk, A. C. Strikwerda, K. Fan, X. Zhang, R. D. Averitt, and P. U. Jepsen, “Flexible metamaterial
absorbers for stealth applications at terahertz frequencies,” Opt. Express 20(1), 635–643 (2012).
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16. X. Liu, T. Starr, A. F. Starr, and W. J. Padilla, “Infrared spatial and frequency selective metamaterial with
near-unity absorbance,” Phys. Rev. Lett. 104(20), 207403 (2010).
17. N. I. Landy, S. Sajuyigbe, J. J. Mock, D. R. Smith, and W. J. Padilla, “Perfect metamaterial absorber,” Phys. Rev.
Lett. 100(20), 207402 (2008).
18. D. Y. Shchegolkov, A. K. Azad, J. F. O'Hara, and E. I. Simakov, “Perfect subwavelength fishnetlike
metamaterial-based film terahertz absorbers,” Phys. Rev. B 82(20), 205117 (2010).
19. X. Shen, T. J. Cui, J. Zhao, H. F. Ma, W. X. Jiang, and H. Li, “Polarization-independent wide-angle triple-band
metamaterial absorber,” Opt. Express 19(10), 9401–9407 (2011).
20. X. Liu, T. Tyler, T. Starr, A. F. Starr, N. M. Jokerst, and W. J. Padilla, “Taming the blackbody with infrared
metamaterials as selective thermal emitters,” Phys. Rev. Lett. 107(4), 045901 (2011).
21. Y. Gong, X. Liu, H. Lu, L. Wang, and G. Wang, “Perfect absorber supported by optical Tamm states in plasmonic
waveguide,” Opt. Express 19(19), 18393–18398 (2011).
22. M. Pu, C. Hu, M. Wang, C. Huang, Z. Zhao, C. Wang, Q. Feng, and X. Luo, “Design principles for infrared
wide-angle perfect absorber based on plasmonic structure,” Opt. Express 19(18), 17413–17420 (2011).
23. J. Hao, L. Zhou, and M. Qiu, “Nearly total absorption of light and heat generation by plasmonic metamaterials,”
Phys. Rev. B 83(16), 165107 (2011).
24. B. Zhang, Y. Zhao, Q. Hao, B. Kiraly, I. C. Khoo, S. Chen, and T. J. Huang, “Polarization-independent dual-band
infrared perfect absorber based on a metal-dielectric-metal elliptical nanodisk array,” Opt. Express 19(16),
15221–15228 (2011).
25. C. Hu, Z. Zhao, X. Chen, and X. Luo, “Realizing near-perfect absorption at visible frequencies,” Opt. Express
17(13), 11039–11044 (2009).
26. E. Popov, D. Maystre, R. C. McPhedran, M. Nevière, M. C. Hutley, and G. H. Derrick, “Total absorption of
unpolarized light by crossed gratings,” Opt. Express 16(9), 6146–6155 (2008).
27. C. Wu, Y. Avitzour, and G. Shvets, “Ultra-thin, wide-angle perfect absorber for infrared frequencies, “Proc. SPIE,
Proceedings of Metamaterials: Fundamentals and Applications, San Diego, CA, August 10-14 (2008).
28. J. Le Perchec, P. Quémerais, A. Barbara, and T. López-Ríos, “Why metallic surfaces with grooves a few
nanometers deep and wide may strongly absorb visible light,” Phys. Rev. Lett. 100(6), 066408 (2008).
29. A. Sundaramurthy, K. B. Crozier, G. S. Kino, D. P. Fromm, P. J. Schuck, and W. E. Moerner, “Field enhancement
and gap-dependent resonance in a system of two opposing tip-to-tip Au nanotriangles,” Phys. Rev. B 72(16),
165409 (2005).
30. D. P. Fromm, A. Sundaramurthy, P. J. Schuck, G. Kino, and W. E. Moerner, “Gap-dependent optical coupling of
single ‘bowtie’ nanoantennas resonant in the visible,” Nano Lett. 4(5), 957–961 (2004).
31. K.-H. Su, Q.-H. Wei, X. Zhang, J. J. Mock, D. R. Smith, and S. Schultz, “Interparticle coupling effects on plasmon
resonances of nanogold particles,” Nano Lett. 3(8), 1087–1090 (2003).
32. S. W. Zhang, H. T. Liu, and G. G. Mu, “Electromagnetic enhancement by a single nano-groove in metallic
substrate,” J. Opt. Soc. Am. A 27(7), 1555–1560 (2010).
33. D. R. Smith, S. Schultz, P. Markos, and C. M. Soukoulis, “Determination of effective permittivity and permeability
of metamaterials from reflection and transmission coefficients,” Phys. Rev. B 65(19), 195104 (2002).
34. N. L. Landy, C. M. Bingham, T. Tyler, N. Jokerst, D. R. Smith, and W. J. Padilla, “Design, theory, and
measurement of a polarization-sensitive absorber for terahertz imaging,” Phys. Rev. B 79(12), 125104 (2009).
1. Introduction
From gigahertz to visible regime, metal surfaces are usually high efficient reflectors, which can
be utilized as mirrors. However, micro or nanostructured surfaces may become high-efficiency
absorbers, which have aroused significant interest and attracted tremendous theoretical and
experimental studies over the past few years. Many metallic nanostructures with either
polarization-insensitive or polarization-sensitive absorption have been proposed and some
promising applications have been discussed [1–28].
At visible and near-infrared regime, for polarization-insensitive absorption, T. V. Teperik et
al [1] showed that total omnidirectional absorption of light can be achieved using the
mesoporous gold surfaces. N. Liu et al [2] experimentally investigated a wide-angle perfect
absorber at 1600 nm and utilized it as plasmonic sensor for refractive index sensing. K. Aydin
et al [3] proposed an absorber consisting of a metal-insulator-metal stack, where the top silver
film is nanostructured into crossed trapezoidal arrays. The absorber yielded
polarization-independent light absorption over the entire visible spectrum (400-700 nm), which
has the potential to improve the efficiency of solar cells. V. G. Kravets et al [4] theoretically and
experimentally studied a thin nanostructured layer with silver nanoparticles in a dielectric
matrix, which possesses wide-angle, polarization-independent, and high absorption over a wide
optical wavelength range (240-850 nm). In recent work, our group has also fabricated and
characterized ultrathin, wide-angle, subwavelength high performance metamaterial absorbers
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around the near-infrared wavelength near 1550 nm [5,6]. Further, we studied the photothermal
effects arising in the structures and considered utilizing it to reshape the gold nanoparticles [7,
8].
For polarization-sensitive absorption, A. Polyakov et al [9] experimentally demonstrated an
array of rectangular trenches in gold to form a subwavelength grating, which can strongly
concentrate the polarized incident light. The effect can be used for generation of laser
harmonics or polarization switch. V. G. Kravets et al [10] designed and investigated composite
deep metallic gratings, which strongly absorb the light with electric field perpendicular to the
gratings, while behave as good reflectors for the other polarized light.
In this paper, three different types of metallic nanostructures are presented and numerically
investigated. First, a bottle-like narrowband absorber is presented, originating from the gap
plasmon resonance, whose resonant peak can be tuned from 1300 nm to 2300 nm. Then a
cup-like narrowband absorber is discussed, which is simple to fabricate. Its resonant peak can
also be varied through a broad spectral range from 700 nm to 1400 nm. Finally a broadband
absorber is investigated, and numerical simulations show that the average absorption efficiency
is over 88% from 700 nm to 2300 nm. All three absorbers are high-performance and
polarization-sensitive at near-infrared range, so they can be used as polarization detectors or
reflective polarizers to manipulate the polarization of electromagnetic wave [11].
2. Bottle-like narrowband absorber
A bottle-like absorber consists of an array of dielectric ( SiO 2 ) strips embedded in gold, with
small air gaps on the top of the dielectric strips, as illustrated in Fig. 1(a). Figure 1(b) shows the
cross-section of a unit cell, where a and b represent, respectively, the width and the depth of the
air gaps, d and c denote the width and the thickness of the dielectric strips, respectively, and w is
the period. In our numerical simulations using the commercial software COMSOL
MULTIPHYSICS based on finite element method, the refractive index of the dielectric is 1.5,
the permittivity of gold is given by the Drude Model ε Au = 9 − ω p2 / (ω 2 + i ωγ ) with the
plasmon
ω p = 2π × 2.175 × 1015 s −1
frequency
γ = 2π × 1.5958 × 10 s
13
−1
and
the
collision
frequency
[7]. All materials are assumed to be nonmagnetic ( μ = μ0 ).
Fig. 1. (a) Schematic of the bottle-like absorber, the yellow region is gold and blue regions are
the dielectric. (b) Cross-section of a unit cell. The width and the depth of the air gap are
represented by a and b, respectively. c and d represent the thickness and the width of the
dielectric strip, respectively, and w is the period.
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Fig. 2. Dependence of absorption spectra on geometric parameters, if not particularly specified,
a = 5 nm, b = 10 nm, c = 60 nm, d = 60 nm, w = 600 nm. (a)-(c) are for p-polarized light. (d) is for
s- polarized light.
Gapped nanoparticles have been proved to be able to concentrate light and therefore cause
electric field enhancement in the gap at resonant wavelength [29–31]. In our absorber, the thin
layers of gold on the dielectric strips are structured to form small air gaps. Assume that a
p-polarized (electric field perpendicular to the gap) plane wave illuminates the structure at
normal incidence. Here an optimized set of parameters for a perfect absorber with resonant
wavelength near 1600 nm is used as a = 5 nm, b = 10 nm, c = 60 nm, d = 60 nm, and w = 600
nm. In the following simulations, if not particularly specified in the figure legends, the
geometric parameters always keep constant. To investigate the relationship between the
absorption spectra and the geometric parameters, the depth of the gap b, the width and the
thickness of the dielectric strip d and c are, respectively, varied while the other parameters
fixed. The results shown in Figs. 2(a)-2(c) demonstrate that resonant wavelength can be tuned
over a very broad spectral range via varying the relevant parameters. The absorption is always
above 97% for all different parameters. Figure 2(d) gives the absorbance for s-polarized normal
incident light. Compared with the nearly total absorption under p-polarized light, the structure
reflects almost all s-polarized light for the same wavelength range (average absorption is less
than 1.8%), illustrating that it’s highly polarization-selective. Numerical simulations have also
been carried out to extract the electric field distribution excited by the different polarized light
2
radiation. We utilize a formula EIF = E / E inc
2
to describe the electric intensity
enhancement [32], where E inc is the electric field of the incident wave and E is the total
electric field. Under normal incidence at the resonant wavelength, comparison between the
electric intensity enhancements under p- and s-polarized light radiations is shown in Fig. 3 to
verify the effect. The values of electric intensity enhancements are plotted on log scale. Note
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that the lack of obvious enhancement for the s-polarized light radiation is in sharp contrast to
the situation for the p-polarized.
Fig. 3. Comparison between the electric intensity enhancements under (a) p-polarized light
radiation and under (b) s-polarized light radiation at 1600 nm (plotted on log scale). Geometric
parameters: a = 5 nm, b = 10 nm, c = 60 nm, d = 60 nm, and w = 600 nm.
In order to reveal the underlying physics of the relationship between the geometric
parameters and the resonant wavelength, that is to answer why the resonant peaks can be tuned
through varying the geometric parameters, further simulations were performed. Figure 4 shows
the absorption efficiency and the electric intensity enhancement (plotted on log scale) in the
center of the gap as functions of incident wavelength. It is clear that the resonant wavelength is
achieved when the coupling strength is maximized. More numerical computations give similar
results. Different sets of b, c, and d correspond to different resonant wavelength to maximize
the electric field enhancement in the gap.
Fig. 4. Absorption and electric intensity enhancement (plotted on log scale) at the center of the
air gap as functions of incident wavelengths under p-polarized light radiation. The geometric
parameters are the same as those in Fig. 3.
We also utilized the effective medium theory to obtain the impendence Z and the refractive
index n of the absorber [33]. As shown in Fig. 5, both Z and n are complex numbers. At 1.6 μm
(as predicted by the vertical dashed line), Z = 0.84 + 0.02i, which is close to that of the free
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Z (ω ) − 1 2
) [34]. Meanwhile, since
Z (ω ) + 1
n = 0.52 + 8.15i, the large imaginary part of refractive index gives rise to a high absorption.
space. Therefore the reflection is very low, since R (ω ) = (
Fig. 5. Retrieved impedance Z and refractive index n. The geometric parameters are the same as
those in Fig. 3.
Fig. 6. Absorbance as functions of wavelengths and incident angles. (a) E⊥Syz (b) H⊥Syz (c)
E⊥Sxz (d) H⊥Sxz.
The absorption effect of this type of absorber is robust and highly polarization selective
even for non-normal incident radiation. As shown in Fig. 6, there is no obvious absorbance
within the simulated wavelength region in the cases of E⊥Sxz and H⊥Syz. However, when the
electric field is parallel to the xz plane, the structures strongly absorb the incident radiation at
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resonant wavelengths regardless of the incident planes. In the E⊥Syz case (incident plane is the
yz plane), even if the angle is up to 65°, the absorption remains 80%. It is similar to H⊥Sxz case
(incident plane is the xz plane), in which the absorption efficiency remains high while the
oblique incident angle becomes very large.
3. Cup-like narrowband absorber
Though the above type of structure possesses high performance and fine tunability, it’s fairly
difficult to fabricate. Thus more simple structure is desirable in practice. For this purpose,
another type of narrowband absorber is proposed.
As shown in Fig. 7(a), the absorber is composed of an array of nanoscale grooves with a
layer of dielectric on it. Figure 7(b) is its cross-section of a unit cell. The width and the depth of
the grooves are represented by a and H, respectively. The thickness of the dielectric is denoted
by d, and w is the period. When carefully designed, it can provide nearly total absorption at
resonant wavelength resulting from the destructive interference between light reflected from
the top surface and light from the bottom of the grooves. Furthermore, it is found that by
adjusting the thickness of the deposited dielectric, resonant peaks can also be tuned. Figure 8
shows the dependence of the absorption spectra on the groove depth H and the thickness of the
dielectric layer d with a = 20 nm, w = 600 nm under p-polarized (electric field perpendicular to
the grooves) normal light radiation.
(a)
(b)
z
p
s
a
y
x
H
d
d
w
Fig. 7. (a) Schematic of the cup-like absorber, the yellow region is gold and blue regions are the
dielectric. (b) Cross-section of a unit cell. a and H, respectively, represent the width and the
depth of the grooves, d denote the thickness of the deposited dielectric, and w is the period.
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Fig. 8. Dependence of absorption spectra on the geometric parameters under p-polarized light.
Here a = 20 nm, and w = 600 nm.
As the depth of the grooves or the thickness of the dielectric layer increases, the absorption
peaks are red-shifted. The structure still acts as a good reflector for s-polarized impinging light.
Figure 9 shows the excited electric intensity enhancements under different polarized light
radiation (plotted on log scale). In comparison with the significant field enhancement in the
groove under p-polarized light, the structure can hardly concentrate s-polarized light. In the
above simulations, the geometric parameters and the incident wavelength are the same as those
corresponding to the first peak in Fig. 8(a). This type of absorber is also robust and highly
polarization selective for non-normal radiation as well, which is verified by the Fig. 10, here H
= 100 nm and d = 90 nm. For either E⊥Syz or H⊥Sxz, the absorption remains over 85% when
the incident angle is up to 50° at the main resonant wavelength around 1350 nm.
Fig. 9. Comparison between electric intensity enhancements under (a) p-polarized light radiation
and under (b) s-polarized light radiation (plotted on log scale). Wavelength and geometric
parameters correspond to the first peak in Fig. 8(a).
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Fig. 10. Absorbance as functions of wavelengths and incident angles. (a) E⊥Syz (b) H⊥Syz (c)
E⊥Sxz (d) H⊥Sxz. Here H = 100 nm, d = 90 nm.
Though the refractive index of the dielectric above is chosen to be 1.5, further numerical
simulations show that for both the bottle-like and cup-like absorbers, absorption spectrum will
redshift when the value of refractive index is increased, but the high absorption is kept
unchanged.
It’s worth noting that the bottle-like absorber exhibits the tunable resonant peak ranging
from 1300 nm to 2300 nm, while the cup-like absorber exhibits the tunable resonant peak
ranging from 700 nm to 1400 nm, which theoretically implies that any polarized
electromagnetic wave with wavelength ranging from 700 nm to 2300 nm can be perfectly
absorbed using the designed absorbers.
4. Broadband absorber
In addition to the narrowband absorber, broadband absorber with high performance is also of
importance. Here a broadband absorber is demonstrated, and an average absorption efficiency
of 88% is achieved over a wide range of wavelengths (700-2300 nm) for p-polarized light.
In the inset of Fig. 11, (a) shows the 3D schematic, and (b) is the cross-section of the half of
a unit cell. Blue regions are the dielectric. For better performance, the refractive index is chosen
to be 1.75. Yellow region is gold. a = 100 nm, w = 80 nm, and H = 50 nm. In the simulations,
half a unit cell consists of 40 grooves, i. e, the width of half a unit is 40 × a = 4000 nm and the
depth of the deepest groove is 40 × H = 2000 nm. Note that, for visual convenience, we present
only the simplified structure in the insert in Fig. 11, in which half of a unit cell consists of three
grooves instead of 40 grooves. Figure 11 shows the absorption as a function of wavelengths
under p-polarized light. An average absorption efficiency of 88% is achieved. It is highly
polarization sensitive, reflecting more than 98% of incident s-polarized light.
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(a)
(b)
z
s
p
y
w
x
H
2H
3H
a
a
Fig. 11. Absorption under p-polarized light. Average absorption efficiency is over 88%. Every
half of a unit cell contains 40 grooves. In the Inset is the simplified structure. (a) is schematic of
the broadband absorber, the yellow region is gold and blue regions are the dielectric. (b) is
cross-section of half a unit cell. a = 100 nm, w = 80 nm, H = 50 nm.
Figure 12 shows the calculated impendence and refractive index using the effective medium
theory. In the simulated wavelength range, Im(n) is always large and Z average = 0.52 + 0.01i .
Z (ω ) − 1 2
) [34], we obtain that the average reflectivity R (ω ) is
Z (ω ) + 1
9.8%. Since the transmission here is very low, so the absorption is approximately
A (ω ) = 1 − R (ω ) . The obtained average absorption is thus 91%, which agrees well with the
numerical result (88%).
Using the formula R (ω ) = (
Fig. 12. Retrieved impendence and refractive index in the simulated region.
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Fig. 13. Absorbance as functions of wavelength and incident angle. (a) E⊥Syz (b) H⊥Syz (c)
E⊥Sxz (d) H⊥Sxz.
Figure 13 presents the absorbance as functions of wavelengths and incident angles. In sharp
contrast to the good reflection to the incident light for the H⊥Syz and E⊥Sxz cases, when
electric field is parallel to the xz plane i.e. perpendicular to the grooves, the structure strongly
absorbs the incident light over a wide angle range. When the incident angle is up to 60°, for the
E⊥Syz case, the absorbance remains over 75%. For the H⊥Sxz case, a much higher absorption
efficiency of 95% can be achieved.
5. Summary
In conclusion, we utilize the gap plasmon resonance to design the bottle-like absorber, where
the resonant wavelength can be tuned over nearly one thousand nanometers via varying the
embedded dielectric strip’s width, thickness or the depth of the gaps. Based on the destructive
interference, we also propose the cup-like absorber, which is simple to fabricate. It’s found that
just by depositing dielectrics with different thickness, the absorption peaks can be altered for a
range of hundreds of nanometers. Finally, by combining grooves with different depths and
carefully arranging its geometric and material parameters, a broadband absorber with an
average absorption efficiency of 88% (700-2300 nm) is presented. All three structures are
highly polarization selective, so they might have the potential to be used as polarization
detectors or reflective polarizers at near-infrared wavelengths.
Acknowledgments
This work is supported by the National Natural Science Foundation of China (Grant Nos.
61275030, 61235007 and 61205030), the Opened Fund of State Key Laboratory of Advanced
Optical Communication Systems and Networks, the Opened Fund of State Key Laboratory on
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Integrated Optoelectronics, the Fundamental Research Funds for the Central Universities
(2012QNA5003) and the Swedish Foundation for Strategic Research (SSF) and the Swedish
Research Council (VR). We thank Xingxing Chen, Hanmo Gong, Weichun Zhang, and Hang
Zhao for useful discussions.
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