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Nanoscale temperature sensor based on Fano resonance in metal–insulator–metal waveguide
Optics Communications 384 (2017) 85–88
Contents lists available at ScienceDirect
Optics Communications journal homepage: www.elsevier.com/locate/optcom
Nanoscale temperature sensor based on Fano resonance in metal– insulator–metal waveguide
crossmark
⁎
Yan Kong , Qi Wei, Cheng Liu, Shouyu Wang Department of Optoelectronic Information Science and Technology, School of Science, Jiangnan University, Wuxi, Jiangsu 214122, China
A R T I C L E I N F O
A BS T RAC T
Keyword: Temperature sensor Fano resonance Metal–insulator–metal waveguide Plasmonics
In order to realize temperature measurements with high sensitivity using compact structure, a nanoscale metal– insulator–metal waveguide based sensor combining with Fano resonance is proposed in this paper. Sealed ethanol in resonant cavity is adopted to further improve sensing performance. Additionally, dual resonant cavity based configuration is designed to generate a Fano-based sharp and asymmetric spectrum, providing high figure of merit in measurements. Moreover, structural parameters are optimized considering both transmission rate and spectral peak width. Certified by numerical calculation, sensitivity of 0.36 nm/°C is acquired with the optimized structure, indicating the designed sensor can play an important role in the nano-integrated plasmonic devices for high-accurate temperature detection.
1. Introduction As plasmonics has been proposed as a means of overcoming the diffraction limit [1], thus it has wide applications [2–12], especially in extraordinary optical transmission [13] and subwavelength imaging [14,15], etc. Additionally, since surface plasmon wave has good localization ability and high local field intensity, the extremely high sensitivity is particularly suitable for sensing. Commercial surface plasmon resonance sensors have become the gold standard for labelfree and real-time sensing considering their high accuracy and extensive application scope [16]. However, in measurements, bulk optical elements as prisms are still needed, limiting device potential for miniaturization. While nanoscale plasmonic structures provide another opportunity in designing nano-integrated sensors. Similar to surface plasmon resonance based sensing, they are also sensitive to local refractive index changing. Surface modulated grating and metasurfaces were proposed for refractive index sensing [17–24]. Guo et al. proposed a hybrid plasmonic optical resonance spectral biosensor based on metal-dielectric nanohole array [25]. Dong et al. designed metallic metamaterial structure to obtain higher sensitivity [26]. Wen et al. proposed surface plasmon polariton launching grating based tunable refractive index sensor [27]. Compared to these complicated metasurfaces and nanoscale patterns, waveguide based structures become another option for refractive index sensing considering their simple configurations and fabrications. Moreover, because surface plasmon polariton wave can reach longer propagation length in waveguides leading to larger sensing surfaces, sensors can obtain better overall
⁎
Corresponding author. E-mail address: [email protected] (Y. Kong).
http://dx.doi.org/10.1016/j.optcom.2016.09.041
0030-4018/ © 2016 Elsevier B.V. All rights reserved.
sensitivity compared to those based on single-interface structure [28]. Interference based sensing was reported with multi-channel waveguides with simple design and high accuracy [29,30]. While resonant cavity introduced in waveguide is another sensing tactic and they are widely available as these designs often have simple structures and high sensitivity in refractive index measurements [31,32]. Refractive index sensing is often applied for distinguishing materials. Moreover, it can also be extended into other fields as biological and medical detections, because molecular interaction induced local refractive index changing can be tracked by spectral shifting [33–35]. Besides, temperature sensing can also be realized from refractive index measurements [36]. Waveguide based devices were widely used for temperature detection [37–40]. Additionally, in order to further improve their sensing ability, surface plasmon based techniques were adopted. Srivastava et al. proposed highly sensitive temperature sensor based on photonic crystal surface plasmon waveguides [41]. Kong et al. proposed temperature sensor consisting of both metal–insulator– metal waveguides and resonators [42]. However, due to the low gradient in temperature coefficient of refractive index of air and glass which are the often used temperature sensing materials, the sensitivity of these proposed sensors is limited. In addition, sensing performance also depends on spectral shapes: sharper spectral configuration leading to higher figure of merit (FOM) always provides high-accurate and robust measurement. Different approaches such as cavity resonance [43–46] were proposed to generate such sharp spectral profile, however, these complicated modifications only provide limited improvements in sensing.
Optics Communications 384 (2017) 85–88
Y. Kong et al.
shifting, besides, measuring accuracy and sensitivity are determined by both transmittance and spectral shape, higher transmittance leads to larger signal to noise ratio, and narrower spectral width provides higher FOM for temperature sensing. It is worth noting that both transmittance and spectral shape can be modulated by adjusting dual resonance cavities. In order to quantitatively analyze the effect of structural design on sensing capability, moreover, to prove the optimal design has both high sensitivity and signal to noise ratio, spectral shapes with various structural parameters are calculated shown in Fig. 2. Fig. 2(A) and (B) shows spectra with different sizes of upper cavity, indicating size changes of upper cavity only shift spectral positions, while less influence on transmission rates. However, compared to influences from upper cavity, the design of lower cavity has obvious impact on both transmission rates and spectral shapes, as illustrated in Fig. 2(C) and (D). Larger height h generates higher transmission, while expands spectral width, which is similar to effects of length l. Considering both signal to noise ratio and sensitivity of the temperature sensor, size of the cavity is designed as 300 nm (l)×160 nm (h). Besides, gap size between air channel and upper cavity also shows obvious influence on spectral shape. Though small gap size is able to obtain higher transmission rate, spectral width is severely expanded which is not fit for high sensitive measurements as shown in Fig. 2(E). Thus, to balance the trade-off between transmission rates and spectral width, the gap is chosen as 20 nm in the optimal design. Fig. 2(F) indicates the interval Δ between upper and lower cavities can also modulate transmission rates, according to numerical calculation, an exactly opposite dual resonator structure is preferred for optimal design. Based on above quantitative analysis, in the proposed design, H and L are set as 500 nm and 580 nm, respectively, l is 300 nm and h is 160 nm, g is set as 20 nm and Δ is 0. It is believed the optimal temperature sensor has both high measuring sensitivity and signal to noise ratio since it possesses the spectrum with high transmission rate and rather narrow peak width. In following, the sensing performance of the nanoscale device is applied in temperature detection simulated by FEM. As environmental temperature varies, ethanol refractive index changing modulates spectral shapes and positions, as shown in Fig. 3(A). Since spectral transmittance drops sharply from peak to
Here, in order to acquire miniature temperature sensor with high sensitivity and FOM, a nanoscale Fano resonance based device composed of metal–insulator–metal (MIM) waveguide is designed in this paper. The temperature sensor has advantages as simple configuration and low cost. Since it works as a plasmonic sensor, high sensitivity can be acquired in temperature measurements. To further improve its sensing performance, ethanol is chosen as temperature sensitive material which can be sealed in the resonant cavity [47–50]. Additionally, dual resonant cavity based structure [51–57] is designed to generate a Fano-based sharp and asymmetric spectrum, providing high FOM in measurements. Moreover, considering both transmission rate and spectral peak width, structural details are quantitatively analyzed in order to obtain an optimal sensor design. Certified by numerical simulation based on the finite element method (FEM), the optimized temperature sensor yields sensitivity of 0.36 nm/°C with high figure of merit, indicating it can act as an important nanointegrated plasmonic device for high-accurate temperature detection. 2. Prototype design and sensing analysis The nanoscale temperature sensor is based on MIM waveguide owning air channel of w=50 m with two additional cavities embedded in the silver layer shown in Fig. 1(A) and (B). The upper cavity with height H=500 nm and length L=580 nm is filled with ethanol, and it acts as temperature sensitive material with refractive index n=1.360843.94×10−4(T−T0), T0 is room temperature as 20 °C. In addition, there is a gap g of 20 nm between cavity and air channel. The upper cavity functions as spectral continuous state generator, while the lower cavity owns height of h=160 nm and length of l=300 nm exhibiting as spectral discrete state generator. Thus extremely sharp asymmetric spectral shape is generated according to interference of both continuous and discrete states. Fig. 1(C) shows calculated spectrum performed by FEM. Moreover, Fig. 1(D) presents Hz distribution with wavelength λ of 1150 nm, and Fig. 1(E) and (F) show Hz distribution with wavelength λ of 1211 nm and 1238 nm corresponding to valley and peak transmission in asymmetric spectrum, respectively. In Fig. 1(C) to (F), temperature T is set as 20 °C. Since temperature sensing is completely according to spectral
Fig. 1. (A) and (B) structure of the proposed nanoscale temperature sensor. (C) Transmission spectrum. Hz distribution with wavelength λ of (D) 1150 nm, (E) 1211 nm and (F) 1238 nm, respectively.
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Optics Communications 384 (2017) 85–88
Y. Kong et al.
Fig. 2. Spectral shapes with various structural parameters as (A) height of upper cavity H; (B) length of upper cavity L; (C) height of lower cavity h; (D) length of upper cavity l; (E) gap size between air channel and upper cavity g; and (F) interval between dual cavities Δ.
valley, the asymmetric spectral shape induced by Fano resonance is capable of retrieving high sensitive temperature measurements. Moreover, according to linear fitting, sensitivity of the proposed temperature sensor is 0.36 nm/°C with R-square of 0.99981 indicating that the resonance wavelength varies linearly with temperature variation as shown in Fig. 3(B). Compared with works of reported optical temperature sensors [37–42], its sensing performance is obviously improved since temperature sensitive ethanol sealed in resonant cavity is adopted. Additionally, compared to those designs with ethanol, the proposed structure can reach extremely high temperature sensitivity with the same order in near-infrared band as [47–50]. Table 1 lists comparison of the performance of the reported temperature sensors. Additionally, to better evaluate sensing performance of the nanoscale device, figure of merit (FOM) is calculated, which is defined as FOM=max|(ΔI/ΔT)/I|. ΔI/ΔT is the relative intensity changing at fixed wavelength induced by a temperature change ΔT. Fig. 3(C) depicts the calculated FOM at different wavelengths when temperature changes form −120 °C to 60 °C. FOM of the structure increases from 1.26 to 2.73 and then decreases to 0.47, which means this sensor is more sensitive at range from −60 C to −20 °C. The numerical calculation on sensing performance proves that the proposed nanoscale structure can measure environmental temperature with high sensitivity. Moreover,
Table 1 Comparison of the performance of the reported temperature sensors. Ref.
Sensor type
Sensitivity
[37] [38] [39] [40] [41] [42] [47] [48] [49] [50]
Waveguide Waveguide Waveguide Waveguide SPP waveguide SPP waveguide SPP waveguide SPP waveguide SPP waveguide SPP waveguide
0.0590 nm/°C 0.073 nm/°C 0.0639 nm/°C 0.0591 nm/°C 0.066 nm/°C 0.12 nm/°C 1.36 nm/°C 0.51 nm/°C 0.65 nm/°C 0.664 nm/°C
with with with with
ethanol ethanol ethanol ethanol
as spectral peak with high transmission rate is applied for temperature sensing, it can maintain a high signal to noise ratio in measurements. 3. Conclusions In summary, a nanoscale temperature sensor based on Fano resonance in MIM waveguide consisting of double resonance cavities is proposed. Ethanol is sealed in one resonance cavity to enhance
Fig. 3. (A) Spectral shapes with temperature variations. (B) Linear fitting between spectral peak and temperature. (C) FOM of the proposed nanoscale temperature sensor.
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[26] Z. Dong, H. Liu, J. Cao, T. Li, S. Wang, S. Zhu, X. Zhang, Enhanced sensing performance by the plasmonic analog of electromagnetically induced transparency in active metamaterials, Appl. Phys. Lett. 97 (2010) 114101. [27] Q. Wen, X. Han, C. Hu, J. Zhang, Non-spectroscopic surface plasmon sensor with a tunable sensitivity, Appl. Phys. Lett. 106 (2015) 031113. [28] W. Wong, O. Krupin, F. Adikan, P. Berini, Optimization of long-range surface plasmon waveguides for attenuation-based biosensing, J. Lightw. Technol. 33 (2015) 3234–3242. [29] H. Mulder, A. Ymeti, V. Subramaniam, J. Kanger, Size-selective detection in integrated optical interferometric biosensors, Opt. Express 20 (2012) 20934–20950. [30] Y. Ming, Z. Wu, H. Wu, F. Xu, Y. Lu, Surface plasmon interferometer based on wedge metal waveguide and its sensing applications, IEEE Photon. J. 4 (2012) 291–299. [31] M. Alam, F. Bahrami, J. Aitchison, M. Mojahedi, Analysis and optimization of hybrid plasmonic waveguide as a platform for biosensing, IEEE Photon. J. 6 (2014) 3700110. [32] X. Jin, X. Huang, J. Tao, X. Lin, Q. Zhang, A novel nanometeric plasmonic refractive index sensor, IEEE Trans. Nanotechnol. 9 (2010) 134–137. [33] Y. Lu, Y. Liu, S. Zhang, S. Wang, S. Zhang, X. Zhang, Aptamer-based plasmonic sensor array for discrimination of proteins and cells with the naked eye, Anal. Chem. 85 (2013) 6571–6574. [34] J. Cao, C. Feng, Y. Liu, S. Wang, F. Liu, Highly sensitive and rapid bacteria detection using molecular beacon–Au nanoparticles hybrid nanoprobes, Biosens. Bioelectron. 57 (2014) 1–2. [35] F. Zhao, Q. Xie, M. Xu, S. Wang, J. Zhou, F. Liu, RNA aptamer based electrochemical biosensor for sensitive and selective detection of cAMP, Biosens.Bioelectron. 66 (2015) 238–243. [36] J. Homola, S.S. Yee, G. Gauglitz, Surface plasmon resonance sensors: review, Sens. Actuators B: Chem. 54 (1999) 3–15. [37] H. Wang, H. Meng, R. Xiong, Q. Wang, B. Huang, X. Zhang, W. Yu, C. Tan, X. Huang, Simultaneous measurement of refractive index and temperature based on asymmetric structures modal interference, Opt. Commun. 364 (2016) 191–194. [38] J. Fan, J. Zhang, P. Lu, M. Tian, J. Xu, D. Liu, A single-mode fiber sensor based on core-offset inter-modal interferometer, Opt. Commun. 320 (2014) 33–37. [39] P. Lu, Q. Chen, asymmetrical fiber Mach–Zehnder interferometer for simultaneous measurement of axial strain and temperatures, IEEE Photon. J. 2 (2010) 942–953. [40] X. Dong, L. Su, P. Shum, Y. Chung, C.C. Chan, Wavelength-selective all-fiber filter based on a single long-period fiber grating and a misaligned splicing point, Opt. Commun. 258 (2006) 159–163. [41] T. Srivastava, R. Das, R. Jha, Highly sensitive plasmonic temperature sensor based on photonic crystal surface plasmon waveguide, Plasmonics 8 (2013) 515–521. [42] Y. Kong, P. Qiu, Q. Wei, Q. Wei, S. Wang, W. Qian, Refractive index and temperature nanosensor with plasmonic waveguide system, Opt. Commun. 371 (2016) 132–137. [43] Y. Xie, Y. Huang, H. Che, W. Zhao, W. Xu, X. Li, J. Li, Theoretical investigation of a plasmonic sensor based on a metal–insulator–metal waveguide with a side-coupled nanodisk resonator, J. Nanophoton. 9 (2015) 093099. [44] X. Lin, X. Huang, Tooth-shaped plasmonic waveguide filters with nanometeric sizes, Opt. Lett. 33 (2009) 2874–2876. [45] T. Wu, Y. Liu, Z. Yu, Y. Peng, C. Shu, H. Ye, The sensing characteristics of plasmonic waveguide with a ring resonator, Opt. express 22 (2014) 7669–7677. [46] Y. Gao, Z. Xin, B. Zeng, Q. Gan, X. Cheng, F. Bartoli, Plasmonic interferometric sensor arrays for high-performance label-free biomolecular detection, Lab Chip 13 (2013) 4755–4764. [47] T. Wu, Y. Liu, Z. Yu, Y. Peng, C. Shu, H. Ye, The sensing characteristics of plasmonic waveguide with a ring resonator, Opt. Express 22 (2014) 7669–7677. [48] T. Wu, Y. Liu, Z. Yu, Y. Peng, C. Shu, H. He, The sensing characteristics of plasmonic waveguide with a single defect, Opt. Commun. 323 (2014) 44–48. [49] T. Wu, Y. Liu, Z. Yu, H. Ye, Y. Peng, C. Shu, C. Yang, W. Zhang, H. He, A nanometeric temperature sensor based on plasmonic waveguide with an ethanolsealed rectangular cavity, Opt. Commun. 339 (2015) 1–6. [50] L. Xiao, F. Wang, R. Liang, S. Zou, M. Hu, A high-sensitivity refractive-index sensor based on plasmonic waveguides asymmetrically coupled with a nanodisk resonator, Chin. Phys. Lett. 32 (2015) 070701. [51] J. Chen, Z. Li, J. Li, Q. Gong, Compact and high-resolution plasmonic wavelength demultiplexers based on Fano interference, Opt. Express 19 (2011) 9976–9985. [52] X. Piao, S. Yu, N. Park, Control of Fano asymmetry in plasmon induced transparency and its application to plasmonic waveguide modulator, Opt. Express 20 (2012) 18994–18999. [53] B. Zhang, L. Wang, H. Li, X. Zhai, S. Xia, Two kinds of double Fano resonances induced by an asymmetric MIM waveguide structure, J. Opt. 18 (2016) 065001. [54] Z. Chen, L. Yu, L. Wang, G. Duan, Y. Zhao, J. Xiao, A refractive index nanosensor based on fano resonance in the plasmonic waveguide system, IEEE Photon. Technol. Lett. 27 (2015) 1695–1698. [55] Z. Chen, H. Li, S. Zhan, H. Xu, Sensing characteristics based on Fano resonance in rectangular ring waveguide, Opt. Commun. 356 (2015) 373–377. [56] Z. Chen, X. Cao, X. Song, L. Wang, L. Yu, Side-coupled cavity-induced Fano resonance and its application in nanosensor, Plasmonics 11 (2016) 307–313. [57] J. Qi, Z. Chen, J. Chen, Y. Li, W. Qiang, J. Xu, Q. Sun, Independently tunable double Fano resonances in asymmetric MIM waveguide structure, Opt. Express 22 (2014) 14688–14695.
temperature sensing ability. Moreover, in order to further increase its sensitivity, structure optimization is introduced for seeking optimal configuration to balance the trade-off between transmission rate and spectral peak width. With numerical simulations according to FEM, it proves the optimized temperature sensor has sensitivity of 0.36 nm/°C with high FOM. Due to its high sensitivity and integration potentials, we believe the proposed temperature sensor can be widely available in the nano-integrated plasmonic devices for high-accurate temperature detection. Acknowledgements Authors thank Aihui Sun and Wei Yu for 3-D Figure plotting and proof reading. This work was supported by the Natural Science Foundation of Jiangsu Province of China [Grant numbers BK20130162, BK20130116, BK2012548]; and the Fundamental Research Funds for the Central Universities [Grant number JUSRP115A14]. References [1] E. Ozbay, Plasmonics: merging photonics and electronics at nanoscale dimensions, Science 311 (2006) 189–193. [2] W. Cai, J. White, M. Brongersma, Compact, high-speed and power-efficient electrooptic plasmonic modulators, Nano Lett. 9 (2009) 4403–4411. [3] W. Dickson, G. Wurtz, P. Evans, R. Pollard, A. Zayats, Electronically controlled surface plasmon dispersion and optical transmission through metallic hole arrays using liquid crystal, Nano Lett. 8 (2008) 281–286. [4] C. Smith, N. Stenger, A. Kristensen, N. Mortensen, S. Bozhevolnyi, Gap and channeled plasmons in tapered grooves: a review, Nanoscale 7 (2015) 9355–9386. [5] D. Gramotnev, S. Bozhevolnyi, Nanofocusing of electromagnetic radiation, Nat. Photon. 8 (2014) 14–23. [6] V. Zenin, Z. Han, V. Volkov, K. Leosson, I. Radko, S. Bozhevolnyi, Directional coupling in long-range dielectricloaded plasmonic waveguides, Opt. Express 21 (2013) 8799–8807. [7] F. Lu, Z. Wang, Z. Tian, A. Xu, An efficient and ultra-broadband unidirectional optical coupler for wide incidence angles, Opt. Commun. 379 (2016) 1–5. [8] F. Lou, D. Dai, L. Wosinski, Ultracompact polarization beam splitter based on a dielectric-hybrid plasmonic-dielectric coupler, Opt. Lett. 37 (2012) 3372–3374. [9] L. Zhu, Z. Xiong, W. Yu, X. Tian, Y. Kong, C. Liu, S. Wang, Polarization-controlled tunable multi-focal plasmonic lens, Plasmonics (2016). http://dx.doi.org/10.1007/ s11468-016-0225-2. [10] T. Liu, S. Wang, Orbital angular momentum-controlled tunable directional plasmonic coupler, IEEE Photon. Technol. Lett. 28 (2016) 91–94. [11] S. Do, J. Park, B. Hwang, S. Lee, B. Ju, K. Choi, Plasmonic color filter and its fabrication for large-area applications, Adv. Opt. Mater. 1 (2013) 133–138. [12] K. Wen, Y. Hu, L. Chen, J. Zhou, M. He, L. Lei, Z. Meng, Tunable multimode plasmonic filter based on side-coupled ring-groove joint resonator, Plasmonics (2016). http://dx.doi.org/10.1007/s11468-016-0281-7. [13] T. Ebbesen, H. Lezec, H. Ghaemi, T. Thio, P. Wolff, Extraordinary optical transmission through sub-wavelength hole arrays, Nature 391 (1998) 667–669. [14] N. Fang, H. Lee, C. Sun, X. Zhang, Sub-diffraction-limited optical imaging with a silver superlens, Science 308 (2005) 534–537. [15] Z. Liu, H. Lee, Y. Xiong, C. Sun, X. Zhan, Far-field optical hyperlens magnifying sub-diffraction-limited objects, Science 315 (2007) 1686. [16] 〈https://www.biacore.com/lifesciences/index.html〉. [17] X. Wu, J. Zhang, J. Chen, C. Zhao, Q. Gong, Refractive index sensor based on surface-plasmon interference, Opt. Lett. 34 (2009) 392–394. [18] Z. Kang, H. Zhang, H. Lu, H. Hom, Double-layered metal nano-strip antennas for sensing applications, Plasmonics 8 (2013) 289–294. [19] M. Ren, C. Pan, Q. Li, W. Cai, X. Zhang, Q. Wu, S. Fan, J. Xu, Isotropic spiral plasmonic metamaterial for sensing large refractive index change, Opt. Lett. 38 (2013) 3133–3136. [20] Y. Gu, Q. Li, J. Xiao, K. Wu, G. Wang, Plasmonic metamaterials for ultrasensitive refractive index sensing at near infrared, J. Appl. Phys. 109 (2011) 023104. [21] P. Mandal, H-shape plasmonic metasurface as refractive index sensor, Plasmonics 10 (2015) 439–445. [22] L. Nien, B. Chao, J. Li, C. Hsueh, Optimized sensitivity and electric field enhancement by controlling localized surface plasmon resonances for bowtie nanoring nanoantenna arrays, Plasmonics 10 (2015) 553–561. [23] Q. Wei, P. Qiu, C. Liu, Y. Kong, S. Wang, Plasmonic interference-based refractive index sensor designed with spectral analysis and structure optimization, Plasmonics (2016). http://dx.doi.org/10.1007/s11468-016-0343-x. [24] J. Chen, Z. Li, S. Yue, J. Xiao, Q. Gong, Plasmon-induced transparency in asymmetric T-shape single slit, Nano Lett. 12 (2012) 2494–2498. [25] H. Guo, J. Guo, Hybrid plasmon photonic crystal resonance grating for integrated spectrometer biosensor, Opt. Lett. 40 (2015) 249–252.
88
Contents lists available at ScienceDirect
Optics Communications journal homepage: www.elsevier.com/locate/optcom
Nanoscale temperature sensor based on Fano resonance in metal– insulator–metal waveguide
crossmark
⁎
Yan Kong , Qi Wei, Cheng Liu, Shouyu Wang Department of Optoelectronic Information Science and Technology, School of Science, Jiangnan University, Wuxi, Jiangsu 214122, China
A R T I C L E I N F O
A BS T RAC T
Keyword: Temperature sensor Fano resonance Metal–insulator–metal waveguide Plasmonics
In order to realize temperature measurements with high sensitivity using compact structure, a nanoscale metal– insulator–metal waveguide based sensor combining with Fano resonance is proposed in this paper. Sealed ethanol in resonant cavity is adopted to further improve sensing performance. Additionally, dual resonant cavity based configuration is designed to generate a Fano-based sharp and asymmetric spectrum, providing high figure of merit in measurements. Moreover, structural parameters are optimized considering both transmission rate and spectral peak width. Certified by numerical calculation, sensitivity of 0.36 nm/°C is acquired with the optimized structure, indicating the designed sensor can play an important role in the nano-integrated plasmonic devices for high-accurate temperature detection.
1. Introduction As plasmonics has been proposed as a means of overcoming the diffraction limit [1], thus it has wide applications [2–12], especially in extraordinary optical transmission [13] and subwavelength imaging [14,15], etc. Additionally, since surface plasmon wave has good localization ability and high local field intensity, the extremely high sensitivity is particularly suitable for sensing. Commercial surface plasmon resonance sensors have become the gold standard for labelfree and real-time sensing considering their high accuracy and extensive application scope [16]. However, in measurements, bulk optical elements as prisms are still needed, limiting device potential for miniaturization. While nanoscale plasmonic structures provide another opportunity in designing nano-integrated sensors. Similar to surface plasmon resonance based sensing, they are also sensitive to local refractive index changing. Surface modulated grating and metasurfaces were proposed for refractive index sensing [17–24]. Guo et al. proposed a hybrid plasmonic optical resonance spectral biosensor based on metal-dielectric nanohole array [25]. Dong et al. designed metallic metamaterial structure to obtain higher sensitivity [26]. Wen et al. proposed surface plasmon polariton launching grating based tunable refractive index sensor [27]. Compared to these complicated metasurfaces and nanoscale patterns, waveguide based structures become another option for refractive index sensing considering their simple configurations and fabrications. Moreover, because surface plasmon polariton wave can reach longer propagation length in waveguides leading to larger sensing surfaces, sensors can obtain better overall
⁎
Corresponding author. E-mail address: [email protected] (Y. Kong).
http://dx.doi.org/10.1016/j.optcom.2016.09.041
0030-4018/ © 2016 Elsevier B.V. All rights reserved.
sensitivity compared to those based on single-interface structure [28]. Interference based sensing was reported with multi-channel waveguides with simple design and high accuracy [29,30]. While resonant cavity introduced in waveguide is another sensing tactic and they are widely available as these designs often have simple structures and high sensitivity in refractive index measurements [31,32]. Refractive index sensing is often applied for distinguishing materials. Moreover, it can also be extended into other fields as biological and medical detections, because molecular interaction induced local refractive index changing can be tracked by spectral shifting [33–35]. Besides, temperature sensing can also be realized from refractive index measurements [36]. Waveguide based devices were widely used for temperature detection [37–40]. Additionally, in order to further improve their sensing ability, surface plasmon based techniques were adopted. Srivastava et al. proposed highly sensitive temperature sensor based on photonic crystal surface plasmon waveguides [41]. Kong et al. proposed temperature sensor consisting of both metal–insulator– metal waveguides and resonators [42]. However, due to the low gradient in temperature coefficient of refractive index of air and glass which are the often used temperature sensing materials, the sensitivity of these proposed sensors is limited. In addition, sensing performance also depends on spectral shapes: sharper spectral configuration leading to higher figure of merit (FOM) always provides high-accurate and robust measurement. Different approaches such as cavity resonance [43–46] were proposed to generate such sharp spectral profile, however, these complicated modifications only provide limited improvements in sensing.
Optics Communications 384 (2017) 85–88
Y. Kong et al.
shifting, besides, measuring accuracy and sensitivity are determined by both transmittance and spectral shape, higher transmittance leads to larger signal to noise ratio, and narrower spectral width provides higher FOM for temperature sensing. It is worth noting that both transmittance and spectral shape can be modulated by adjusting dual resonance cavities. In order to quantitatively analyze the effect of structural design on sensing capability, moreover, to prove the optimal design has both high sensitivity and signal to noise ratio, spectral shapes with various structural parameters are calculated shown in Fig. 2. Fig. 2(A) and (B) shows spectra with different sizes of upper cavity, indicating size changes of upper cavity only shift spectral positions, while less influence on transmission rates. However, compared to influences from upper cavity, the design of lower cavity has obvious impact on both transmission rates and spectral shapes, as illustrated in Fig. 2(C) and (D). Larger height h generates higher transmission, while expands spectral width, which is similar to effects of length l. Considering both signal to noise ratio and sensitivity of the temperature sensor, size of the cavity is designed as 300 nm (l)×160 nm (h). Besides, gap size between air channel and upper cavity also shows obvious influence on spectral shape. Though small gap size is able to obtain higher transmission rate, spectral width is severely expanded which is not fit for high sensitive measurements as shown in Fig. 2(E). Thus, to balance the trade-off between transmission rates and spectral width, the gap is chosen as 20 nm in the optimal design. Fig. 2(F) indicates the interval Δ between upper and lower cavities can also modulate transmission rates, according to numerical calculation, an exactly opposite dual resonator structure is preferred for optimal design. Based on above quantitative analysis, in the proposed design, H and L are set as 500 nm and 580 nm, respectively, l is 300 nm and h is 160 nm, g is set as 20 nm and Δ is 0. It is believed the optimal temperature sensor has both high measuring sensitivity and signal to noise ratio since it possesses the spectrum with high transmission rate and rather narrow peak width. In following, the sensing performance of the nanoscale device is applied in temperature detection simulated by FEM. As environmental temperature varies, ethanol refractive index changing modulates spectral shapes and positions, as shown in Fig. 3(A). Since spectral transmittance drops sharply from peak to
Here, in order to acquire miniature temperature sensor with high sensitivity and FOM, a nanoscale Fano resonance based device composed of metal–insulator–metal (MIM) waveguide is designed in this paper. The temperature sensor has advantages as simple configuration and low cost. Since it works as a plasmonic sensor, high sensitivity can be acquired in temperature measurements. To further improve its sensing performance, ethanol is chosen as temperature sensitive material which can be sealed in the resonant cavity [47–50]. Additionally, dual resonant cavity based structure [51–57] is designed to generate a Fano-based sharp and asymmetric spectrum, providing high FOM in measurements. Moreover, considering both transmission rate and spectral peak width, structural details are quantitatively analyzed in order to obtain an optimal sensor design. Certified by numerical simulation based on the finite element method (FEM), the optimized temperature sensor yields sensitivity of 0.36 nm/°C with high figure of merit, indicating it can act as an important nanointegrated plasmonic device for high-accurate temperature detection. 2. Prototype design and sensing analysis The nanoscale temperature sensor is based on MIM waveguide owning air channel of w=50 m with two additional cavities embedded in the silver layer shown in Fig. 1(A) and (B). The upper cavity with height H=500 nm and length L=580 nm is filled with ethanol, and it acts as temperature sensitive material with refractive index n=1.360843.94×10−4(T−T0), T0 is room temperature as 20 °C. In addition, there is a gap g of 20 nm between cavity and air channel. The upper cavity functions as spectral continuous state generator, while the lower cavity owns height of h=160 nm and length of l=300 nm exhibiting as spectral discrete state generator. Thus extremely sharp asymmetric spectral shape is generated according to interference of both continuous and discrete states. Fig. 1(C) shows calculated spectrum performed by FEM. Moreover, Fig. 1(D) presents Hz distribution with wavelength λ of 1150 nm, and Fig. 1(E) and (F) show Hz distribution with wavelength λ of 1211 nm and 1238 nm corresponding to valley and peak transmission in asymmetric spectrum, respectively. In Fig. 1(C) to (F), temperature T is set as 20 °C. Since temperature sensing is completely according to spectral
Fig. 1. (A) and (B) structure of the proposed nanoscale temperature sensor. (C) Transmission spectrum. Hz distribution with wavelength λ of (D) 1150 nm, (E) 1211 nm and (F) 1238 nm, respectively.
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Fig. 2. Spectral shapes with various structural parameters as (A) height of upper cavity H; (B) length of upper cavity L; (C) height of lower cavity h; (D) length of upper cavity l; (E) gap size between air channel and upper cavity g; and (F) interval between dual cavities Δ.
valley, the asymmetric spectral shape induced by Fano resonance is capable of retrieving high sensitive temperature measurements. Moreover, according to linear fitting, sensitivity of the proposed temperature sensor is 0.36 nm/°C with R-square of 0.99981 indicating that the resonance wavelength varies linearly with temperature variation as shown in Fig. 3(B). Compared with works of reported optical temperature sensors [37–42], its sensing performance is obviously improved since temperature sensitive ethanol sealed in resonant cavity is adopted. Additionally, compared to those designs with ethanol, the proposed structure can reach extremely high temperature sensitivity with the same order in near-infrared band as [47–50]. Table 1 lists comparison of the performance of the reported temperature sensors. Additionally, to better evaluate sensing performance of the nanoscale device, figure of merit (FOM) is calculated, which is defined as FOM=max|(ΔI/ΔT)/I|. ΔI/ΔT is the relative intensity changing at fixed wavelength induced by a temperature change ΔT. Fig. 3(C) depicts the calculated FOM at different wavelengths when temperature changes form −120 °C to 60 °C. FOM of the structure increases from 1.26 to 2.73 and then decreases to 0.47, which means this sensor is more sensitive at range from −60 C to −20 °C. The numerical calculation on sensing performance proves that the proposed nanoscale structure can measure environmental temperature with high sensitivity. Moreover,
Table 1 Comparison of the performance of the reported temperature sensors. Ref.
Sensor type
Sensitivity
[37] [38] [39] [40] [41] [42] [47] [48] [49] [50]
Waveguide Waveguide Waveguide Waveguide SPP waveguide SPP waveguide SPP waveguide SPP waveguide SPP waveguide SPP waveguide
0.0590 nm/°C 0.073 nm/°C 0.0639 nm/°C 0.0591 nm/°C 0.066 nm/°C 0.12 nm/°C 1.36 nm/°C 0.51 nm/°C 0.65 nm/°C 0.664 nm/°C
with with with with
ethanol ethanol ethanol ethanol
as spectral peak with high transmission rate is applied for temperature sensing, it can maintain a high signal to noise ratio in measurements. 3. Conclusions In summary, a nanoscale temperature sensor based on Fano resonance in MIM waveguide consisting of double resonance cavities is proposed. Ethanol is sealed in one resonance cavity to enhance
Fig. 3. (A) Spectral shapes with temperature variations. (B) Linear fitting between spectral peak and temperature. (C) FOM of the proposed nanoscale temperature sensor.
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[26] Z. Dong, H. Liu, J. Cao, T. Li, S. Wang, S. Zhu, X. Zhang, Enhanced sensing performance by the plasmonic analog of electromagnetically induced transparency in active metamaterials, Appl. Phys. Lett. 97 (2010) 114101. [27] Q. Wen, X. Han, C. Hu, J. Zhang, Non-spectroscopic surface plasmon sensor with a tunable sensitivity, Appl. Phys. Lett. 106 (2015) 031113. [28] W. Wong, O. Krupin, F. Adikan, P. Berini, Optimization of long-range surface plasmon waveguides for attenuation-based biosensing, J. Lightw. Technol. 33 (2015) 3234–3242. [29] H. Mulder, A. Ymeti, V. Subramaniam, J. Kanger, Size-selective detection in integrated optical interferometric biosensors, Opt. Express 20 (2012) 20934–20950. [30] Y. Ming, Z. Wu, H. Wu, F. Xu, Y. Lu, Surface plasmon interferometer based on wedge metal waveguide and its sensing applications, IEEE Photon. J. 4 (2012) 291–299. [31] M. Alam, F. Bahrami, J. Aitchison, M. Mojahedi, Analysis and optimization of hybrid plasmonic waveguide as a platform for biosensing, IEEE Photon. J. 6 (2014) 3700110. [32] X. Jin, X. Huang, J. Tao, X. Lin, Q. Zhang, A novel nanometeric plasmonic refractive index sensor, IEEE Trans. Nanotechnol. 9 (2010) 134–137. [33] Y. Lu, Y. Liu, S. Zhang, S. Wang, S. Zhang, X. Zhang, Aptamer-based plasmonic sensor array for discrimination of proteins and cells with the naked eye, Anal. Chem. 85 (2013) 6571–6574. [34] J. Cao, C. Feng, Y. Liu, S. Wang, F. Liu, Highly sensitive and rapid bacteria detection using molecular beacon–Au nanoparticles hybrid nanoprobes, Biosens. Bioelectron. 57 (2014) 1–2. [35] F. Zhao, Q. Xie, M. Xu, S. Wang, J. Zhou, F. Liu, RNA aptamer based electrochemical biosensor for sensitive and selective detection of cAMP, Biosens.Bioelectron. 66 (2015) 238–243. [36] J. Homola, S.S. Yee, G. Gauglitz, Surface plasmon resonance sensors: review, Sens. Actuators B: Chem. 54 (1999) 3–15. [37] H. Wang, H. Meng, R. Xiong, Q. Wang, B. Huang, X. Zhang, W. Yu, C. Tan, X. Huang, Simultaneous measurement of refractive index and temperature based on asymmetric structures modal interference, Opt. Commun. 364 (2016) 191–194. [38] J. Fan, J. Zhang, P. Lu, M. Tian, J. Xu, D. Liu, A single-mode fiber sensor based on core-offset inter-modal interferometer, Opt. Commun. 320 (2014) 33–37. [39] P. Lu, Q. Chen, asymmetrical fiber Mach–Zehnder interferometer for simultaneous measurement of axial strain and temperatures, IEEE Photon. J. 2 (2010) 942–953. [40] X. Dong, L. Su, P. Shum, Y. Chung, C.C. Chan, Wavelength-selective all-fiber filter based on a single long-period fiber grating and a misaligned splicing point, Opt. Commun. 258 (2006) 159–163. [41] T. Srivastava, R. Das, R. Jha, Highly sensitive plasmonic temperature sensor based on photonic crystal surface plasmon waveguide, Plasmonics 8 (2013) 515–521. [42] Y. Kong, P. Qiu, Q. Wei, Q. Wei, S. Wang, W. Qian, Refractive index and temperature nanosensor with plasmonic waveguide system, Opt. Commun. 371 (2016) 132–137. [43] Y. Xie, Y. Huang, H. Che, W. Zhao, W. Xu, X. Li, J. Li, Theoretical investigation of a plasmonic sensor based on a metal–insulator–metal waveguide with a side-coupled nanodisk resonator, J. Nanophoton. 9 (2015) 093099. [44] X. Lin, X. Huang, Tooth-shaped plasmonic waveguide filters with nanometeric sizes, Opt. Lett. 33 (2009) 2874–2876. [45] T. Wu, Y. Liu, Z. Yu, Y. Peng, C. Shu, H. Ye, The sensing characteristics of plasmonic waveguide with a ring resonator, Opt. express 22 (2014) 7669–7677. [46] Y. Gao, Z. Xin, B. Zeng, Q. Gan, X. Cheng, F. Bartoli, Plasmonic interferometric sensor arrays for high-performance label-free biomolecular detection, Lab Chip 13 (2013) 4755–4764. [47] T. Wu, Y. Liu, Z. Yu, Y. Peng, C. Shu, H. Ye, The sensing characteristics of plasmonic waveguide with a ring resonator, Opt. Express 22 (2014) 7669–7677. [48] T. Wu, Y. Liu, Z. Yu, Y. Peng, C. Shu, H. He, The sensing characteristics of plasmonic waveguide with a single defect, Opt. Commun. 323 (2014) 44–48. [49] T. Wu, Y. Liu, Z. Yu, H. Ye, Y. Peng, C. Shu, C. Yang, W. Zhang, H. He, A nanometeric temperature sensor based on plasmonic waveguide with an ethanolsealed rectangular cavity, Opt. Commun. 339 (2015) 1–6. [50] L. Xiao, F. Wang, R. Liang, S. Zou, M. Hu, A high-sensitivity refractive-index sensor based on plasmonic waveguides asymmetrically coupled with a nanodisk resonator, Chin. Phys. Lett. 32 (2015) 070701. [51] J. Chen, Z. Li, J. Li, Q. Gong, Compact and high-resolution plasmonic wavelength demultiplexers based on Fano interference, Opt. Express 19 (2011) 9976–9985. [52] X. Piao, S. Yu, N. Park, Control of Fano asymmetry in plasmon induced transparency and its application to plasmonic waveguide modulator, Opt. Express 20 (2012) 18994–18999. [53] B. Zhang, L. Wang, H. Li, X. Zhai, S. Xia, Two kinds of double Fano resonances induced by an asymmetric MIM waveguide structure, J. Opt. 18 (2016) 065001. [54] Z. Chen, L. Yu, L. Wang, G. Duan, Y. Zhao, J. Xiao, A refractive index nanosensor based on fano resonance in the plasmonic waveguide system, IEEE Photon. Technol. Lett. 27 (2015) 1695–1698. [55] Z. Chen, H. Li, S. Zhan, H. Xu, Sensing characteristics based on Fano resonance in rectangular ring waveguide, Opt. Commun. 356 (2015) 373–377. [56] Z. Chen, X. Cao, X. Song, L. Wang, L. Yu, Side-coupled cavity-induced Fano resonance and its application in nanosensor, Plasmonics 11 (2016) 307–313. [57] J. Qi, Z. Chen, J. Chen, Y. Li, W. Qiang, J. Xu, Q. Sun, Independently tunable double Fano resonances in asymmetric MIM waveguide structure, Opt. Express 22 (2014) 14688–14695.
temperature sensing ability. Moreover, in order to further increase its sensitivity, structure optimization is introduced for seeking optimal configuration to balance the trade-off between transmission rate and spectral peak width. With numerical simulations according to FEM, it proves the optimized temperature sensor has sensitivity of 0.36 nm/°C with high FOM. Due to its high sensitivity and integration potentials, we believe the proposed temperature sensor can be widely available in the nano-integrated plasmonic devices for high-accurate temperature detection. Acknowledgements Authors thank Aihui Sun and Wei Yu for 3-D Figure plotting and proof reading. This work was supported by the Natural Science Foundation of Jiangsu Province of China [Grant numbers BK20130162, BK20130116, BK2012548]; and the Fundamental Research Funds for the Central Universities [Grant number JUSRP115A14]. References [1] E. Ozbay, Plasmonics: merging photonics and electronics at nanoscale dimensions, Science 311 (2006) 189–193. [2] W. Cai, J. White, M. Brongersma, Compact, high-speed and power-efficient electrooptic plasmonic modulators, Nano Lett. 9 (2009) 4403–4411. [3] W. Dickson, G. Wurtz, P. Evans, R. Pollard, A. Zayats, Electronically controlled surface plasmon dispersion and optical transmission through metallic hole arrays using liquid crystal, Nano Lett. 8 (2008) 281–286. [4] C. Smith, N. Stenger, A. Kristensen, N. Mortensen, S. Bozhevolnyi, Gap and channeled plasmons in tapered grooves: a review, Nanoscale 7 (2015) 9355–9386. [5] D. Gramotnev, S. Bozhevolnyi, Nanofocusing of electromagnetic radiation, Nat. Photon. 8 (2014) 14–23. [6] V. Zenin, Z. Han, V. Volkov, K. Leosson, I. Radko, S. Bozhevolnyi, Directional coupling in long-range dielectricloaded plasmonic waveguides, Opt. Express 21 (2013) 8799–8807. [7] F. Lu, Z. Wang, Z. Tian, A. Xu, An efficient and ultra-broadband unidirectional optical coupler for wide incidence angles, Opt. Commun. 379 (2016) 1–5. [8] F. Lou, D. Dai, L. Wosinski, Ultracompact polarization beam splitter based on a dielectric-hybrid plasmonic-dielectric coupler, Opt. Lett. 37 (2012) 3372–3374. [9] L. Zhu, Z. Xiong, W. Yu, X. Tian, Y. Kong, C. Liu, S. Wang, Polarization-controlled tunable multi-focal plasmonic lens, Plasmonics (2016). http://dx.doi.org/10.1007/ s11468-016-0225-2. [10] T. Liu, S. Wang, Orbital angular momentum-controlled tunable directional plasmonic coupler, IEEE Photon. Technol. Lett. 28 (2016) 91–94. [11] S. Do, J. Park, B. Hwang, S. Lee, B. Ju, K. Choi, Plasmonic color filter and its fabrication for large-area applications, Adv. Opt. Mater. 1 (2013) 133–138. [12] K. Wen, Y. Hu, L. Chen, J. Zhou, M. He, L. Lei, Z. Meng, Tunable multimode plasmonic filter based on side-coupled ring-groove joint resonator, Plasmonics (2016). http://dx.doi.org/10.1007/s11468-016-0281-7. [13] T. Ebbesen, H. Lezec, H. Ghaemi, T. Thio, P. Wolff, Extraordinary optical transmission through sub-wavelength hole arrays, Nature 391 (1998) 667–669. [14] N. Fang, H. Lee, C. Sun, X. Zhang, Sub-diffraction-limited optical imaging with a silver superlens, Science 308 (2005) 534–537. [15] Z. Liu, H. Lee, Y. Xiong, C. Sun, X. Zhan, Far-field optical hyperlens magnifying sub-diffraction-limited objects, Science 315 (2007) 1686. [16] 〈https://www.biacore.com/lifesciences/index.html〉. [17] X. Wu, J. Zhang, J. Chen, C. Zhao, Q. Gong, Refractive index sensor based on surface-plasmon interference, Opt. Lett. 34 (2009) 392–394. [18] Z. Kang, H. Zhang, H. Lu, H. Hom, Double-layered metal nano-strip antennas for sensing applications, Plasmonics 8 (2013) 289–294. [19] M. Ren, C. Pan, Q. Li, W. Cai, X. Zhang, Q. Wu, S. Fan, J. Xu, Isotropic spiral plasmonic metamaterial for sensing large refractive index change, Opt. Lett. 38 (2013) 3133–3136. [20] Y. Gu, Q. Li, J. Xiao, K. Wu, G. Wang, Plasmonic metamaterials for ultrasensitive refractive index sensing at near infrared, J. Appl. Phys. 109 (2011) 023104. [21] P. Mandal, H-shape plasmonic metasurface as refractive index sensor, Plasmonics 10 (2015) 439–445. [22] L. Nien, B. Chao, J. Li, C. Hsueh, Optimized sensitivity and electric field enhancement by controlling localized surface plasmon resonances for bowtie nanoring nanoantenna arrays, Plasmonics 10 (2015) 553–561. [23] Q. Wei, P. Qiu, C. Liu, Y. Kong, S. Wang, Plasmonic interference-based refractive index sensor designed with spectral analysis and structure optimization, Plasmonics (2016). http://dx.doi.org/10.1007/s11468-016-0343-x. [24] J. Chen, Z. Li, S. Yue, J. Xiao, Q. Gong, Plasmon-induced transparency in asymmetric T-shape single slit, Nano Lett. 12 (2012) 2494–2498. [25] H. Guo, J. Guo, Hybrid plasmon photonic crystal resonance grating for integrated spectrometer biosensor, Opt. Lett. 40 (2015) 249–252.
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