Highly Sensitive Plasmonic Sensor with a Coupled Split-Square-Ring Resonator

Highly Sensitive Plasmonic Sensor with a Coupled Split-Square-Ring Resonator | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Highly Sensitive Plasmonic Sensor with a Coupled Split-Square-Ring Resonator Jiajun Wu, Jinhua Li, Yuan Ma, Youqiao Ma This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2270072/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract A novel design for a highly-sensitive plasmonic sensor, consisting of metal-insulator-metal (MIM) waveguide with a coupled split-square-ring resonator, is presented and studied by two-dimensional (2D) finite-difference time-domain (FDTD) method in this paper. The simulation results show that the proposed sensor possesses a refractive index (RI) sensitivity up to 2040 nm/RIU with optimized structural parameters. In addition, a temperature sensitivity of −1.2 nm/◦C is determined. Numerical calculations indicate that the sensing performance can still be further improved via optimization of the structure. The compact waveguide structure may find important applications in areas of sensing and integrated circuits. Surface Plasmon MIM waveguide Resonator Temperature sensing RI Sensing Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Surface plasmon polaritons (SPPs) are mixed-excited states formed by the interaction of free electrons and photons on local metal surface, which possess potential capability to overcome the typical diffraction limit [1]. The field intensity of SPPs wave decreases exponentially with the increasing distance from dielectric-metal interface, giving rise to the highly confined mode confinement which is measured in nano-meter or subwavelength scale [2]. SPPs are considered as one of the promising ways to develop nano-photonic devices and have been extensively explored for applications in integrated circuits [3-5]. In addition, plasmonic nanostructures are also competitive candidates for designing refractive index (RI) sensors owing to their local field enhancement and relatively high sensitivity [6]. In recent years, several types of plasmonic sensors, based on the metal–insulator–metal (MIM) or insulator–metal–insulator (IMI) configurations, have been proposed and investigated [7-9]. The IMI structures support the well-known long-range SPPs (LRSPPs) waveguide modes with relatively low propagation loss, which in turn can improve the sensing accuracy [10]. However, they cannot realize the subwavelength field localization, limiting the improvement in sensitivity. On the other hand, the MIM structures with nanoscale confined fields have been widely used in biosensing applications, offering pathways to explore mutli-functionality in metallic nanostructures [11]. Various MIM-based sensing structures have recently been both numerically and experimentally designed and demonstrated [12-14]. By introducing different sensing materials within the structures, the effective indices of MIM or cavity modes change accordingly, giving rise to shifts in wavelength, which provides the basis for realization of sensing scheme. For example, H. Bahri et al. proposed a high-sensitive sensor using MIM waveguide coupled with a rectangular cavity with Fano resonance, which shows a sensitivity of 3010 nm/RIU [12]. In 2020, L. Hajshahvaladi et al. investigated a tunable plasmonic refractive index sensor with a sensitivity of 2160 nm/RIU based on a nano ring- shaped resonator [13]. In [14] S. Shen designed a MIM waveguide-based sensor consisting of two triangle stubs and side-coupled with an eight-like resonant cavity. The RI sensitivity of the device was measured to be 6000 nm/RIU [14]. Although the MIM-based sensing configurations have been widely investigated over the past decade, it is still believed that finding new realizable schemes to further enhance the sensing performance remains highly desired. Herein, in this work we investigate in simulation a robust MIM waveguide-based plasmonic sensor that comprises a side-coupled split-square-ring resonator, in which the effective indices of cavity modes change accordingly with resonating characteristics, thus offering flexibility in enhancing sensing performance by geometric optimization. The numerical results show that with proper geometrical parameters, a refractive index sensitivity of 2040nm/RIU and a temperature sensitivity of 1.2nm/℃ can be achieved. The paper is organized as follows: In section 2, the structure and basic considerations are briefly introduced. In section 3, the transmission characteristics of proposed structure are studied using the finite-difference time-domain (FDTD) method. In section 4, the refractive index and temperature plasmonic sensors based on proposed structure are investigated. Finally, the conclusions are discussed in section 5. 2. Structure and Considerations The schematic view of proposed structure is shown in Fig. 1 (a), which consists of a MIM waveguide and a side-coupled split-square-ring resonator. All the physical parameters and coordinate system are given in the figure. The material filled within the MIM waveguide and split-square-ring resonator is assumed as air, while the silver (Ag) is selected as the plasmonic material due to its relatively small Ohmic loss compared to other noble metals. The frequency-dependent complex relative permittivity of Ag ( ε m ) can be expressed by the Drude model [15]: where 𝜀 ∞ represents the permittivity at infinite angular frequency, 𝜔 𝑝 is the plasma frequency, 𝜔 and 𝛾 are the angular frequency of incident light and collision frequency of electron, respectively. The parameters of Drude model are set as 𝜀 ∞ = 3.7, 𝜔 𝑝 = 1.38 × 10 16 rad/s and 𝛾 = 2.7 × 10 13 rad/s. Furthermore, in order to support the fundamental SPPs mode with optimized trade-off between the mode confinement and propagation length, which correspond to the effective index and mode loss as shown in Fig. 1 (b), respectively, the width of the bus waveguide is fixed as w = 50 nm throughout this work. In this paper, the characteristics of our design are investigated numerically by utilizing a two-dimensional finite-difference time-domain (2D-FDTD) method with Perfectly Matched Layer (PML) boundary conditions to absorb the scattered outgoing field radiations. Convergence tests were also done to ensure the meshing and boundaries have minimal effect on the solutions. A TM-polarized beam (i.e. E y ≠ 0) is assumed to excite the SPPs waveguide mode from the input port, which then interacts with split-square-ring resonator forming cavity modes. The transmission can be calculated by T = P out / P in , where P in and P out are incident power and transmitted power, respectively. 3. Optimization of geometric parameters To reveal the distinct characteristics of proposed structure, Fig. 2 (a) shows the transmission spectra for three types of cavity-coupled configurations, which are denoted as the case 1 (i.e. the individual rectangular-ring-coupled structure), case 2 (i.e. case 1 combined with a cut cavity) and case 3 (i.e. the proposed split-square-ring-coupled structure), respectively, as shown in the inset of Fig. 2 (a). In the simulation, the structural parameters of a , b , d , h, s, l and g are set as a = 20 nm, b = 40 nm, d = 50 nm, h = 200 nm , s = 300 nm , l = 100 nm and g = 10 nm, respectively. From Fig. 2 (a) one can see that there is obvious discrepancy of resonant properties for three cases. For example, a strong resonant dip appears at a wavelength of 1350 nm for case 1, which is a typical property of well-known notch filter, while there are three completely different transmission dips for proposed structure (i.e. case 3) within the same wavelength range. In order to better understand the underlying mechanism, it is useful to visualize the field distributions. The contour profiles of normalized electric fields corresponding to the resonant modes of D 1 at λ = 1141nm, D 2 at λ = 1346 nm and D 3 at λ = 2030 nm in x-y plane were investigated in the whole simulation domain and are summarized in Figs. 2 (b-d). From Figs. 2 (b-d) one can clearly find that the SPPs modes are coupled to the cavity modes at the corresponding resonant wavelengths, due to the destructive interference between the initial SPPs wave and that coupled from the resonator to the bus waveguide, thus giving rise to the low transmission. The results are consistent with the transmission spectrum in Fig.2. (a). From Figs. 2 (b-d) one can also find that the electromagnetic fields are highly localized inside the cavity, suggesting great promise for developing highly sensitive sensors by introducing the sensing medium (i.e. refractive index varied or temperature-dependent) into the cavity. Before studying the sensing properties, the transmission characteristics of the proposed structure are quantitatively investigated by varying the structural parameters. The structural parameters are optimized by varying parameters within a certain range and determined for structures achieving the desired sensing performance. Fig. 3 shows the transmission spectra for structures with different value of g . In the simulation, the other structural parameters are set as a = 20 nm, b = 40 nm, d = 50 nm, h = 200 nm , s = 300 nm and l = 100 nm From Fig. 3, it is clear that the transmission dips remain unchanged, while exhibit significant enhancements in transmittance as the value of g increases. These phenomena are physically reasonable because the coupling efficiency between the bus waveguide and resonator gradually weakens with the increase of g , or in other words, more power directly transmits through the bus waveguide, giving rise to the enhance transmission at the resonant wavelengths. Since a strong coupling is required for sensors to achieve high accuracy, the value of g is set as g = 10 nm in the following discussion. The other key parameters affecting the transmission characteristics are a , b and d , as they modify the electric field pattern within the cavity. Fig. 4 (a) depicts the resonance wavelength as a function of a . The parameters used in the simulation are b = 40 nm, d = 50 nm, h = 200 nm , s = 300 nm , l = 100 nm and g = 10 nm. As can be seen that the value of a has an insignificant influence on the resonant dip related to D2, which is reasonable since the field is almost located within the outside square cavity as shown in Fig. 2(c). On the contrary, the power located within the outside square cavity increases with the increase of a , leading to the higher effective indices for the resonant modes of D1 and D3, thus their resonant wavelengths exhibit the obvious blue-shifts, as depicted in Fig. 4(a). Fig. 4 (b) shows that the transmission spectra for structures with parameter of b varying from 20 nm to 60 nm. The other parameters are selected as a = 20 nm, d = 50 nm, h = 200 nm , s = 300 nm , l = 100 nm and g = 10 nm. From Fig. 4 (b) it is found that the resonant dips D1 and D3 experience red-shifts as the value of b increases. This is because the effective refractive index of cavity mode within the split-square-ring resonator decreases with the increase of b , thus giving rise to the increased resonant wavelength. On the other hand, the resonant dip D2 does not change significantly which is because of the fact that the power distributed within the central rectangular cavity is very small. The same phenomena are expected for structures with the decreased value of d , as shown in Fig. 4 (c). Considering the sensing accuracy (i.e. the half-wave width) and structural integration, the parameters of a , b and d are chosen as a = 20 nm, b = 40 nm and d = 50 nm, respectively. 4. Potential design of refractive index and temperature sensors As discussed above, if the SPPs wave is coupled into the split-square-ring resonator, the resonant wavelength is affected by the refractive index ( n ) distributed within the resonator, thus offering the potential for developing plasmonic refractive index sensor. As an example, Fig. 5 (a) gives the transmission spectra for n ranges from 1 to 1.05 with a step of 0.01 with structural parameters of a = 20 nm, b = 40 nm, d = 50 nm, h = 200 nm , s = 300 nm , l = 100 nm and g = 10 nm As can be seen, all resonant dips shift toward larger wavelength as n increases, indicating that the variations of refractive index can be monitored by measuring the shift of the valley wavelength. The variations of resonant wavelength as a function of n for dips D1, D2 and D3 are shown in Fig. 5 (b). From Fig. 5 (b) one can see that the positions of the resonant wavelengths vary approximately linearly with n . From it one can also find that the slope of resonant wavelength shift for dip D3 is higher than those for dips D1 and D2. For example, the estimated sensitivities for dips D1, D2 and D3 are 1125 nm/RIU, 1325nm/RIU and 2040 nm/RIU, respectively. Here the RI sensitivity is defined as where 𝛥𝜆 and 𝛥𝑛 are the variations of resonant wavelength and RI, respectively. To illustrate the improved sensing performance of proposed structure, the comparison with several recently published results [16-19] are summarized in in Table 1. Table 1 A comparison of some recent reported plasmonic refractive index sensors Reference Sensitivity (nm/RIU) The range of working wavelength (nm) [16] 1261.67 600-1000 [17] 1295 2402 [18] 1535 2200–2300 [19] 1550 1500-1700 This study 2040 2000–2200 Finally, the proposed structure also possesses capabilities in measuring the temperature if introducing a high thermal-optical material (i.e. PDMS) within the resonator. As the temperature coefficient of PDMS is 4.5 × 10 −4 , therefore the relationship between the RI (i.e. ) and ambient temperature ( ) can be described as [20]: Under the influence of temperature changing from 10 ℃to 100 ℃, the transmission spectra of the structure is shown in Fig. 6 (a). It is evident that the dips perform blue-shift as rises. Moreover, the wavelength of dip D3 possesses the largest blue-shift with the increase of temperature, resulting in the maximum temperature sensitivity of 1.2 nm/℃, which is much higher than other reported devices, as compared and shown in Table 2. Here the temperature sensitivity is defined as where 𝛥𝜆 and 𝛥 T are the variations of resonant wavelength and temperature, respectively. Table 2 A comparison of some recent reported plasmonic temperature sensors Reference Absolute temperature sensitivity (nm/◦C) The range of working wavelength (nm) [21] -4 1100-1300 [22] 0.45 1200-1500 [23] 0.8 1900-2200 [24] 1.48 2800-3200 [25] 0.059 1500–1600 This study 1.2 2600 – 3000 5. Conclusion In summary, we have proposed and theoretically investigated a plasmonic sensor based on the metal-insulator-metal waveguide coupled with a split-square-ring resonator. The transmission characteristics of the device are systematically analysed by using FDTD method. With the optimized structural parameters, the simulation results show that the RI and temperature sensitivity could reach up to 2040 nm/RIU and 1.2 nm/℃, respectively. Comparisons with other plasmonic configurations further reveal the superior sensing properties of our structure. We believe that the remarkable sensing capacity and compact architecture show a great promise for future development of miniaturized plasmonic sensors. Declarations Ethical Approval Not applicable Competing Interest The authors declare no competing interests. Author ’s Contributions Jiajun Wu designed the structures, performed the numerical simulations and wrote the manuscript. Youqiao Ma supervised the project, participated in analysis of the results and reviewed the manuscript. Jinhua Li and Yuan Ma participated in analysis of the results and reviewed the manuscript. Funding This work was supported by the start-up foundation for introducing talent of Nanjing University of Information Science and Technology (NUIST), the National Natural Science Foundation of China (Grant nos. 11605090), the Natural Science Foundation of the Jiangsu Province (BK20191396). Availability of Data and Material All the data and materials are in the manuscript. References D. K. Gramotnev, S. I. Bozhevolnyi, Nature Photon. 4 , 83-91 (2010). P. Berini, I. D. Leon, Nature Photon. 6 , 16-24 (2012). J. J. Zhang, H. C. Zhang, X. X. Gao, L. P. Zhang, L. Y. Niu, P. H. He, T. J. Cui, Sci. Bull. 64 , 843-855 (2019). M. Fukuda, Y. Tonooka, T. Inoue, M. Ota, Solid State Electron. 156 , 33-40 (2019). Y. Q. Ma, B. Liu, Z. Q. Huang, J. H. Li, Z. H. Han, D. Wu, J. Zhou, Y. Ma, Q. Wu, H. Maeda, Nanoscale 14 , 428-432 (2022). E. Mauriz, Sensors 20 , 4745 (2020). N. L. Kazanskiy, S. N. Khonina, M. A. Butt, Physica E Low Dimens. Syst. Nanostruct. 117 , 113798 (2020). Z. K. Liang, Y. Wen, Z. Zhang, Z. H. Liang, Z. F. Xu, Y. S. Lin, Results Phys. 15 , 102602 (2019). M. A. Butt, A. Kaźmierczak, N. L. Kazanskiy, S. N. Khonina, Electronics, 10 , 1419 (2021). J. W. Mu, W. P. Huang, J. Light. Technol. 27 , 436-439 (2009). K. Q. Le, Q, M. Ngo, T. K. Nguyen. IEEE J. Sel. Top. Quantum Electron. 23 , 388-393 (2016). H. Bahri, S. Mouetsi, A. Hocini, H. B. Salah, Opt. Quantum Electron. 53 , 332 (2021). L. Hajshahvaladi, H. Kaatuzian, M. Danaie, Y. Karimi, Opt. Quantum Electron. 54 , 51 (2022). S. M. Shen, S. C. She, Z. Y. Wang, Q. L. Tan, J. J. Xiong, W. D. Zhang, Opt. Commun. 495 , 127087 (2021). P. B. Johnson, R. W. Christy, Phys. Rev. B 6, 4370-4379 (1972). Zhu J, Li N. MIM waveguide structure consisting of a semicircular resonant cavity coupled with a key-shaped resonant cavity[J]. Optics express, 2020, 28(14): 19978-19987. M. Rahmatiyar, M. Afsahi, M. Danaie, Plasmonics 15, 2169-2176 (2020). S. Gaur, R. Zafar, D. Somwanshi, ICRAIE 16933034 , 1-4 (2016). Su H, Yan S, Yang X, et al. Sensing features of the Fano resonance in an MIM waveguide coupled with an elliptical ring resonant cavity[J]. Applied Sciences, 2020, 10(15): 5096. Z. Zhu, L. Liu, Z. Liu, Y. Zhang, Y. Zhang, Opt. Lett. 42 , 2948-2951 (2017). Zhu J, Lou J. High-sensitivity Fano resonance temperature sensor in MIM waveguides coupled with a polydimethylsiloxane-sealed semi-square ring resonator[J]. Results in Physics, 2020, 18: 103183. Zhu J, Jin G. Detecting the temperature of ethanol based on Fano resonance spectra obtained using a metal-insulator-metal waveguide with SiO 2 branches[J]. Optical Materials Express, 2021, 11(9): 2787-2799. Yang X, Hua E, Su H, et al. A nanostructure with defect based on Fano resonance for application on refractive-index and temperature sensing[J]. Sensors, 2020, 20(15): 4125. Liu P, Yan S, Ren Y, et al. A MIM Waveguide Structure of a High-Performance Refractive Index and Temperature Sensor Based on Fano Resonance[J]. Applied Sciences, 2021, 11(22): 10629. H. Wang, H. Meng, R. Xiong, Q. Wang, B. Huang, X. Zhang, W. Yu, C. Tan, X. Huang, Opt. Commun. 364 , 191-194 (2016). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2270072","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":151910981,"identity":"1e52a611-cbd5-4e5a-997b-697a56dd5e34","order_by":0,"name":"Jiajun Wu","email":"","orcid":"","institution":"Nanjing University of Information Science and Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jiajun","middleName":"","lastName":"Wu","suffix":""},{"id":151910982,"identity":"d86ffc95-9715-4138-a7e0-317cdd313dfa","order_by":1,"name":"Jinhua Li","email":"","orcid":"","institution":"Nanjing University of Information Science and Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jinhua","middleName":"","lastName":"Li","suffix":""},{"id":151910983,"identity":"4130049d-9492-4fef-8174-e75440623f5e","order_by":2,"name":"Yuan Ma","email":"","orcid":"","institution":"Dalhousie University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yuan","middleName":"","lastName":"Ma","suffix":""},{"id":151910984,"identity":"cea7bacf-d18d-4e6b-ab9c-ebaf7a21ebb0","order_by":3,"name":"Youqiao Ma","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/UlEQVRIiWNgGAWjYPACCQYGZuaDDz42gDiMjQeI08LOlmw4swHEYmwgRgsQ8POYSfOCtTAw4NWi237G8DFPmYU8PzNbsrHtDps63fbDQFtqbKJxaTE7k2NszHNOwnBmM/PBx7ln0iTMziQCtRxLy23ApeVADtA9bRKMGw4DbcltOyxhdgCohbHhMG4t59+AtdhvOAz0iyVIy/mHBLTcgNiSCNbCCNJyg5AtN54VG845J5E8sxkYyL1taZLbbgBtScDnl/PJGx+8Kauz7ec/fPDBzzYbfrPz6Q8ffKixwamFgYHDgIGBDV0wAadyEGB/gEXLKBgFo2AUjAIkAAAPHmAm1MWaoQAAAABJRU5ErkJggg==","orcid":"","institution":"Nanjing University of Information Science and Technology","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Youqiao","middleName":"","lastName":"Ma","suffix":""}],"badges":[],"createdAt":"2022-11-14 03:59:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2270072/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2270072/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":29144818,"identity":"cfbcb330-12fe-4b29-862e-0b8407773342","added_by":"auto","created_at":"2022-11-16 16:01:52","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":228629,"visible":true,"origin":"","legend":"\u003cp\u003e(a)Two-dimensional (2D)sketch diagram of proposed structure. (b) Dependence of effective index on wavelength for structures with different value of \u003cem\u003ew\u003c/em\u003e. Inset: Dependence of mode loss on wavelength for structures with different value of \u003cem\u003ew\u003c/em\u003e.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-2270072/v1/995ef2e275ceb0abc555d796.png"},{"id":29144817,"identity":"446c4712-f890-46a2-b20f-e16fbb228d71","added_by":"auto","created_at":"2022-11-16 16:01:52","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":472496,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Transmission spectra for structures with different resonators of case 1, case 2 and case 3. Contour profiles of normalized electric fields related to resonant modes of (b) D\u003csub\u003e1\u003c/sub\u003e at\u003cem\u003e l\u003c/em\u003e = 1141 nm, (c) D\u003csub\u003e2\u003c/sub\u003e at\u003cem\u003e l\u003c/em\u003e = 1346nm and (d) D\u003csub\u003e3\u003c/sub\u003e at\u003cem\u003e l\u003c/em\u003e = 2030 nm. \u0026nbsp;\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-2270072/v1/cdbd1f9ecfbde5476426c908.png"},{"id":29145564,"identity":"f89c9217-ca39-498e-b85a-f780899f8a67","added_by":"auto","created_at":"2022-11-16 16:09:52","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":234003,"visible":true,"origin":"","legend":"\u003cp\u003eTransmission spectra of proposed structure with different value of \u003cem\u003eg\u003c/em\u003e.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-2270072/v1/cfada490c29a0d6479de6c42.png"},{"id":29144819,"identity":"bda3aecd-da73-4626-8c97-036b525e54fc","added_by":"auto","created_at":"2022-11-16 16:01:52","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":654610,"visible":true,"origin":"","legend":"\u003cp\u003eTransmission spectra of proposed structure with different value of (a) \u003cem\u003ea\u003c/em\u003e, (b) \u003cem\u003eb\u003c/em\u003e and (c) \u003cem\u003ed\u003c/em\u003e.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-2270072/v1/e5d61080bb7f9a89f43ef5fe.png"},{"id":29144820,"identity":"0ea54e34-3a39-4fa3-9280-2281090aec7c","added_by":"auto","created_at":"2022-11-16 16:01:52","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":458765,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Transmission spectra of proposed structure with different value of \u003cem\u003en\u003c/em\u003e. (b) Dip wavelength plotted against \u003cem\u003en\u003c/em\u003e for dips D1, D2 and D3.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-2270072/v1/ed05818291a101d997021433.png"},{"id":29145908,"identity":"05cb4602-dccd-432e-8c02-275dae5a3015","added_by":"auto","created_at":"2022-11-16 16:17:52","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":426001,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Transmission spectra of proposed structure at different ambient temperature. (b) Dip wavelength plotted against \u003cem\u003eT \u003c/em\u003efor dips D1, D2 and D3.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-2270072/v1/e19539040e7c10382c2d6779.png"},{"id":30502356,"identity":"98f0e899-460c-421a-8ed0-2db9045a8284","added_by":"auto","created_at":"2022-12-19 07:29:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1548625,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2270072/v1/d419ada2-f79a-4b93-83b3-a28b4f3a119f.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Highly Sensitive Plasmonic Sensor with a Coupled Split-Square-Ring Resonator","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eSurface plasmon polaritons (SPPs) are mixed-excited states formed by the interaction of free electrons and photons on local metal surface, which possess potential capability to overcome the typical diffraction limit [1]. The field intensity of SPPs wave decreases exponentially with the increasing distance from dielectric-metal interface, giving rise to the highly confined mode confinement which is measured in nano-meter or subwavelength scale [2]. SPPs are considered as one of the promising ways to develop nano-photonic devices and have been extensively explored for applications in integrated circuits [3-5]. In addition, plasmonic nanostructures are also competitive candidates for designing refractive index (RI) sensors owing to their local field enhancement and relatively high sensitivity [6]. \u003c/p\u003e\n\u003cp\u003eIn recent years, several types of plasmonic sensors, based on the metal\u0026ndash;insulator\u0026ndash;metal (MIM) or insulator\u0026ndash;metal\u0026ndash;insulator (IMI) configurations, have been proposed and investigated [7-9]. The IMI structures support the well-known long-range SPPs (LRSPPs) waveguide modes with relatively low propagation loss, which in turn can improve the sensing accuracy [10]. However, they cannot realize the subwavelength field localization, limiting the improvement in sensitivity. On the other hand, the MIM structures with nanoscale confined fields have been widely used in biosensing applications, offering pathways to explore mutli-functionality in metallic nanostructures [11]. Various MIM-based sensing structures have recently been both numerically and experimentally designed and demonstrated [12-14]. By introducing different sensing materials within the structures, the effective indices of MIM or cavity modes change accordingly, giving rise to shifts in wavelength, which provides the basis for realization of sensing scheme. For example, H. Bahri et al. proposed a high-sensitive sensor using MIM waveguide coupled with a rectangular cavity with Fano resonance, which shows a sensitivity of 3010 nm/RIU [12]. In 2020, L. Hajshahvaladi et al. investigated a tunable plasmonic refractive index sensor with a sensitivity of 2160 nm/RIU based on a nano ring- shaped resonator [13]. In [14] S. Shen designed a MIM waveguide-based sensor consisting of two triangle stubs and side-coupled with an eight-like resonant cavity. The RI sensitivity of the device was measured to be 6000 nm/RIU [14]. Although the MIM-based sensing configurations have been widely investigated over the past decade, it is still believed that finding new realizable schemes to further enhance the sensing performance remains highly desired.\u003c/p\u003e\n\u003cp\u003eHerein, in this work we investigate in simulation a robust MIM waveguide-based plasmonic sensor that comprises a side-coupled split-square-ring resonator, in which the effective indices of cavity modes change accordingly with resonating characteristics, thus offering flexibility in enhancing sensing performance by geometric optimization. The numerical results show that with proper geometrical parameters, a refractive index sensitivity of 2040nm/RIU and a temperature sensitivity of 1.2nm/℃ can be achieved. The paper is organized as follows: In section 2, the structure and basic considerations are briefly introduced. In section 3, the transmission characteristics of proposed structure are studied using the finite-difference time-domain (FDTD) method. In section 4, the refractive index and temperature plasmonic sensors based on proposed structure are investigated. Finally, the conclusions are discussed in section 5.\u003c/p\u003e"},{"header":"2. Structure and Considerations","content":"\u003cp\u003eThe schematic view of proposed structure is shown in Fig. 1 (a), which consists of a MIM waveguide and a side-coupled\u0026nbsp;split-square-ring resonator.\u0026nbsp;All the physical parameters and coordinate system are given in the figure. The\u0026nbsp;material filled within the MIM waveguide and\u0026nbsp;split-square-ring\u0026nbsp;resonator is assumed as air, while\u0026nbsp;the silver (Ag) is selected as the plasmonic material due to its relatively small Ohmic loss compared to other noble metals.\u0026nbsp;The frequency-dependent complex relative permittivity of Ag (\u003cem\u003e\u0026epsilon;\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e) can be expressed by the Drude model [15]:\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cimg 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iUFhQWwDxgVjw1/PxVTjk478ek/RSUv8owDwWic+8xePEEfi61M9i1DuWTooItaWpn9UZ+Mk0CPAuGXh6M2tmp75gtgn/aOQMT7nrWzzYO6R/9xYJ36urm3e+bxGtNDerBs5tnUMw7T9Uf1oY/LpiejUlWPS9daqms5zCexFgLGG3erZ0r3KYG3A0dA+1K/N/3CiBYiZvD2QLCCJn5rcpKkLyqOFlwWH/OYWFPIgbfLliMhIHThGdJAfnUR6FuclIe0+opt9Sf1Nc3wCjDEWKMbn3BNPPJaknwoZs+Q3EiLomUOtIGjzifCYq297H59zL8JhJDDXq9ioc5i4MKTd+eutVWFIGu55tA5Rv5TZy2uk/qaVwCgBxtzcXBzNk/TkydydG/sjeY+tNiM5nyQtMBEKLKAswu8IdSF8Vx3e0W7LfB0BxlUE99LFKcZ5StCz0GGQR4Q2ZXPP0vnG3IgwGPXmrBUt9EoeQNq2kSdcEDLULUx7wigiZGlb8wBF2QYJSKBP4PaiBSxZ0JcuLn2U665WwbLUmKwrybvuSgADG+M64rGIKOHeXhgVBXlvAxEy4iqOgBg15qP1q22MYENItIE5mxBhQvoaIs5G2rqlvrVszyVwZQKKln97l4U9CxCLR3UJP2MAsPCxsGEQeJobfYp8Rp3M85oEYoBbw0prq3FtvXx1e6MnMkaM7JxwipehJ5BSDgKgCob0Vjwxa45T8y55zT1I1LqlPhyZ0+QxIhKTV89rU/P2XAJ3JqBoaXqfRYonupHFpsli0UeMAEaEp9neQrwoExNJYIZAFSU9A804x7j2xEIVLRjUNowY2SpKeuM9wqrnTUk51LPXhgiMNcdefrXdrZCbYkDZCfFQ9URi0vSOaaeipUfHaxL4SuC/mSYRCUjgcgTiPWzfzUhDIxZ6hrIa762iJYJiarsl8Y/KIU1PZKQt7XGtCMh9PSE3VUbSIsg452/UW5tye33RlutnCdyVgKLlrj1vu29BIGKgJxYAkPieWKiipbdNstTIzuVT43uiJOVQ1xEhkPtGRUCEXs/r0w6atox4lHrbae297ec2rzbezxKQwMeHosVRIIELE1gqStaIhWyDTHlxgnVElOSeeoyImCun3sP5WhEQZrRvLtQy2Eri3rVbyxE8S8TSXL2Ml8BVCShartqztksCM56UGFwMbe89k7xMOmVEY6S5/1GYEy0RJb13QPCsjIiIWo+0b8TTUtsUIQebKc9JLYP699pQ6/ToPByWiKVH+RgngSsTeLzaXLnltk0CNyDw6J2ViJKeaIkXZe7dDOK5Pwa+hxSjH+GBka+hipKewUcwcW8vrubTO6+Cohffu1YFFkKF+lE27ewJu5SR9s29uNsrM9f2yCN5eZTAVQkoWq7as7ZLAh8fn2IixjBP8BhitiIwxBEneecFw5xrxM8Z4WxpzG2JxLiTZwQOeSMI+Mu3mPLuTOoYwdITDHMdnDLXelrCjfpNcUgZpA3fuXr14hFI5DG6BdbLy2sSuDIBRcuVe9e2SeDfH0+MxyKGEbERIYDBxDBXI40xTvwjiPGUIEbmwlQ5uY8yq/cHsRERkzQjxwiKEdFC/rmPNlVOvbKTdrSMNq/0z5b2tnn6WQJXJKBouWKv2iYJvJBAvC0Y8LsFxApiD0G2NuDFiZhcm4f3SeAuBBQtd+lp2ymBJxHAI4OHZMl20pOq8JZs6/sveJzWBNjFyzW1BbUmX++RwFUJKFqu2rO2SwIvJIDBRbTcSbjEy0Kb14QqWNwWWkPQe+5IQNFyx163zRJ4AgG8DTHkbBWt9T48oWq7Z5l3edjWmfpK+FShiBVECmIHD1VeTJ5K73UJSOA/AoqW/1h4JgEJ7EAAg4whn/tG0Q5FvS2LvIeCaBn1kuSFZL5thIAxSEACywkoWpazMqUEJCABCUhAAm8koGh5I3yLloAEJCABCUhgOQFFy3JWppSABCQgAQlI4I0EFC1vhG/REpCABCQgAQksJ6BoWc7KlBKQgAQkIAEJvJGAouWN8C1aAhKQgAQkIIHlBBQty1mZUgISkIAEJCCBNxJQtLwRvkVLQAISkIAEJLCcgKJlOStTSkACEpCABCTwRgKKljfCt2gJSEACEpCABJYT+B9ci/4NEHQlZAAAAABJRU5ErkJggg==\" height=\"90\" width=\"557\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere\u0026nbsp;𝜀\u003csub\u003e\u0026infin;\u0026nbsp;\u003c/sub\u003erepresents the permittivity at infinite angular frequency,\u0026nbsp;𝜔\u003csub\u003e𝑝\u003c/sub\u003e is the plasma frequency, 𝜔 and 𝛾 are the angular frequency of incident light and collision frequency of electron, respectively. The parameters of Drude model are set as 𝜀\u003csub\u003e\u0026infin;\u0026nbsp;\u003c/sub\u003e= 3.7,\u0026nbsp;𝜔\u003csub\u003e𝑝\u003c/sub\u003e = 1.38 \u0026times; 10\u003csup\u003e16\u0026nbsp;\u003c/sup\u003erad/s and\u0026nbsp;𝛾 =\u0026nbsp;2.7 \u0026times; 10\u003csup\u003e13\u003c/sup\u003e rad/s. Furthermore, in order to support the fundamental SPPs mode with optimized trade-off between the mode confinement and propagation length, which correspond to the effective index and mode loss as shown in Fig. 1 (b), respectively, the width of the bus waveguide is fixed as \u003cem\u003ew\u003c/em\u003e = 50 nm throughout this work.\u003c/p\u003e\n\u003cp\u003eIn this paper, the characteristics of our design are investigated numerically by utilizing a two-dimensional finite-difference time-domain (2D-FDTD) method with Perfectly Matched Layer (PML) boundary conditions to absorb the scattered outgoing field radiations. Convergence tests were also done to ensure the meshing and boundaries have minimal effect on the solutions. A TM-polarized beam (i.e. \u003cem\u003eE\u003csub\u003ey\u003c/sub\u003e\u003c/em\u003e \u0026ne; 0) is assumed to excite the SPPs waveguide mode from the input port, which then interacts with split-square-ring resonator forming cavity modes. The transmission can be calculated by \u003cem\u003eT\u003c/em\u003e = \u003cem\u003eP\u003csub\u003eout\u003c/sub\u003e\u0026nbsp;\u003c/em\u003e/ \u003cem\u003eP\u003csub\u003ein\u003c/sub\u003e\u003c/em\u003e, where \u003cem\u003eP\u003csub\u003ein\u003c/sub\u003e\u003c/em\u003e and \u003cem\u003eP\u003csub\u003eout\u003c/sub\u003e\u003c/em\u003e are incident power and transmitted power, respectively.\u0026nbsp;\u003c/p\u003e"},{"header":"3. Optimization of geometric parameters","content":"\u003cp\u003eTo reveal the distinct characteristics of proposed structure, Fig. 2 (a) shows the transmission spectra for three types of cavity-coupled configurations, which are denoted as the case 1 (i.e. the individual rectangular-ring-coupled structure), case 2 (i.e. case 1 combined with a cut cavity) and case 3 (i.e. the proposed split-square-ring-coupled structure), respectively, as shown in the inset of Fig. 2 (a). In the simulation, the structural parameters of \u003cem\u003ea\u003c/em\u003e, \u003cem\u003eb\u003c/em\u003e, \u003cem\u003ed\u003c/em\u003e, \u003cem\u003eh, s, l\u0026nbsp;\u003c/em\u003eand \u003cem\u003eg\u003c/em\u003e are set as \u003cem\u003ea\u003c/em\u003e = 20 nm, \u003cem\u003eb\u003c/em\u003e = 40 nm, \u003cem\u003ed\u003c/em\u003e = 50 nm, \u003cem\u003eh =\u0026nbsp;\u003c/em\u003e200 nm\u003cem\u003e, s =\u0026nbsp;\u003c/em\u003e300\u003cem\u003e\u0026nbsp;\u003c/em\u003enm\u003cem\u003e, l =\u0026nbsp;\u003c/em\u003e100 nm\u003cem\u003e\u0026nbsp;\u003c/em\u003eand \u003cem\u003eg\u003c/em\u003e = 10 nm, respectively. From Fig. 2 (a) one can see that there is obvious discrepancy of resonant properties for three cases. For example, a strong resonant dip appears at a wavelength of 1350 nm for case 1, which is a typical property of well-known notch filter, while there are three completely different transmission dips for proposed structure (i.e. case 3) within the same wavelength range. \u0026nbsp;In order to better understand the underlying mechanism, it is useful to visualize the field distributions. The contour profiles of normalized electric fields corresponding to the resonant modes of D\u003csub\u003e1\u003c/sub\u003e at \u003cem\u003e\u0026lambda;\u0026nbsp;\u003c/em\u003e= 1141nm, D\u003csub\u003e2\u003c/sub\u003e at \u003cem\u003e\u0026lambda;\u003c/em\u003e = 1346 nm and D\u003csub\u003e3\u003c/sub\u003e at \u003cem\u003e\u0026lambda;\u003c/em\u003e = 2030 nm in x-y plane were investigated in the whole simulation domain and are summarized in Figs. 2 (b-d). From Figs. 2 (b-d) one can clearly find that the SPPs modes are coupled to the cavity modes at the corresponding resonant wavelengths, due to the destructive interference between the initial SPPs wave and that coupled from the resonator to the bus waveguide, thus giving rise to the low transmission. The results are consistent with the transmission spectrum in Fig.2. (a). From Figs. 2 (b-d) one can also find that the electromagnetic fields are highly localized inside the cavity, suggesting great promise for developing highly sensitive sensors by introducing the sensing medium (i.e. refractive index varied or temperature-dependent) into the cavity. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBefore studying the sensing properties, the transmission characteristics of the proposed structure are quantitatively investigated by varying the structural parameters. The structural parameters are optimized by varying parameters within a certain range and determined for structures achieving the desired sensing performance. Fig. 3 shows the transmission spectra for structures with different value of \u003cem\u003eg\u003c/em\u003e. In the simulation, the other structural parameters are set as \u003cem\u003ea\u003c/em\u003e = 20 nm, \u003cem\u003eb\u003c/em\u003e = 40 nm, \u003cem\u003ed\u003c/em\u003e = 50 nm, \u003cem\u003eh =\u0026nbsp;\u003c/em\u003e200 nm\u003cem\u003e, s =\u0026nbsp;\u003c/em\u003e300\u003cem\u003e\u0026nbsp;\u003c/em\u003enm\u003cem\u003e\u0026nbsp;\u003c/em\u003eand\u003cem\u003e\u0026nbsp;l =\u0026nbsp;\u003c/em\u003e100 nm From Fig. 3, it is clear that the transmission dips remain unchanged, while exhibit significant enhancements in transmittance as the value of \u003cem\u003eg\u003c/em\u003e increases. \u0026nbsp;These phenomena are physically reasonable because the coupling efficiency between the bus waveguide and resonator gradually weakens with the increase of \u003cem\u003eg\u003c/em\u003e, or in other words, more power directly transmits through the bus waveguide, giving rise to the enhance transmission at the resonant wavelengths. Since a strong coupling is required for sensors to achieve high accuracy, the value of \u003cem\u003eg\u003c/em\u003e is set as \u003cem\u003eg\u003c/em\u003e = 10 nm in the following discussion.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe other key parameters affecting the transmission characteristics are \u003cem\u003ea\u003c/em\u003e, \u003cem\u003eb\u003c/em\u003e and \u003cem\u003ed\u003c/em\u003e, as they modify the electric field pattern within the cavity. \u0026nbsp;Fig. 4 (a) depicts the resonance wavelength as a function of \u003cem\u003ea\u003c/em\u003e. The parameters used in the simulation are\u0026nbsp;\u003cem\u003eb\u003c/em\u003e = 40 nm, \u003cem\u003ed\u003c/em\u003e = 50 nm, \u003cem\u003eh =\u0026nbsp;\u003c/em\u003e200 nm\u003cem\u003e, s =\u0026nbsp;\u003c/em\u003e300\u003cem\u003e\u0026nbsp;\u003c/em\u003enm\u003cem\u003e, l =\u0026nbsp;\u003c/em\u003e100 nm\u003cem\u003e\u0026nbsp;\u003c/em\u003eand \u003cem\u003eg\u003c/em\u003e = 10 nm. As can be seen that the value of \u003cem\u003ea\u003c/em\u003e has an insignificant influence on the resonant dip related to D2, which is reasonable since the field is almost located within the outside square cavity as shown in Fig. 2(c). On the contrary, the power located within the outside square cavity increases with the increase of \u003cem\u003ea\u003c/em\u003e, leading to the higher effective indices for the resonant modes of D1 and D3, thus their resonant wavelengths exhibit the obvious blue-shifts, as depicted in Fig. 4(a). Fig. 4 (b) shows that the transmission spectra for structures with parameter of \u003cem\u003eb\u003c/em\u003e varying from 20 nm to 60 nm.\u0026nbsp;The other parameters are selected as \u003cem\u003ea\u003c/em\u003e = 20 nm, \u003cem\u003ed\u003c/em\u003e = 50 nm, \u003cem\u003eh =\u0026nbsp;\u003c/em\u003e200 nm\u003cem\u003e, s =\u0026nbsp;\u003c/em\u003e300\u003cem\u003e\u0026nbsp;\u003c/em\u003enm\u003cem\u003e, l =\u0026nbsp;\u003c/em\u003e100 nm\u003cem\u003e\u0026nbsp;\u003c/em\u003eand \u003cem\u003eg\u003c/em\u003e = 10 nm.\u0026nbsp;From Fig. 4 (b) it is found that\u0026nbsp;the resonant dips D1 and D3 experience red-shifts as the value of \u003cem\u003eb\u003c/em\u003e increases. This is because the effective refractive index of cavity mode within the split-square-ring resonator decreases with the increase of \u003cem\u003eb\u003c/em\u003e, thus giving rise to the increased resonant wavelength. On the other hand, the resonant dip D2 does not change significantly which is because of the fact that the power distributed within the central rectangular cavity is very small. The same phenomena are expected for structures with the decreased value of \u003cem\u003ed\u003c/em\u003e, as shown in Fig. 4 (c). Considering the sensing accuracy (i.e. the half-wave width) and structural integration, the parameters of\u003cem\u003e\u0026nbsp;a\u003c/em\u003e, \u003cem\u003eb\u003c/em\u003e and \u003cem\u003ed\u003c/em\u003e are chosen as \u003cem\u003ea\u003c/em\u003e = 20 nm, \u003cem\u003eb\u003c/em\u003e = 40 nm and \u003cem\u003ed\u003c/em\u003e = 50 nm, respectively.\u003c/p\u003e"},{"header":"4. Potential design of refractive index and temperature sensors","content":"\u003cp\u003eAs discussed above, if the SPPs wave is coupled into the split-square-ring resonator, the resonant wavelength is affected by the refractive index (\u003cem\u003en\u003c/em\u003e) distributed within the resonator, thus offering the potential for developing plasmonic refractive index sensor. As an example, Fig. 5 (a) gives the transmission spectra for \u003cem\u003en\u003c/em\u003e ranges from 1 to 1.05 with a step of 0.01 with structural parameters of \u003cem\u003ea\u003c/em\u003e = 20 nm, \u003cem\u003eb\u003c/em\u003e = 40 nm, \u003cem\u003ed\u003c/em\u003e = 50 nm, \u003cem\u003eh =\u0026nbsp;\u003c/em\u003e200 nm\u003cem\u003e, s =\u0026nbsp;\u003c/em\u003e300\u003cem\u003e\u0026nbsp;\u003c/em\u003enm\u003cem\u003e, l =\u0026nbsp;\u003c/em\u003e100 nm\u003cem\u003e\u0026nbsp;\u003c/em\u003eand \u003cem\u003eg\u003c/em\u003e = 10 nm \u0026nbsp;As can be seen, all resonant dips shift toward larger wavelength as \u003cem\u003en\u003c/em\u003e increases, indicating that the variations of refractive index can be monitored by measuring the shift of the valley wavelength. The variations of resonant wavelength as a function of \u003cem\u003en\u003c/em\u003e for dips D1, D2 and D3 are shown in Fig. 5 (b). From Fig. 5 (b) one can see that the positions of the resonant wavelengths vary approximately linearly with \u003cem\u003en\u003c/em\u003e. From it one can also find that the slope of resonant wavelength shift for dip D3 is higher than those for dips D1 and D2. For example, the estimated sensitivities for dips D1, D2 and D3 are 1125 nm/RIU, 1325nm/RIU and 2040 nm/RIU, respectively. Here the RI sensitivity is defined as\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"153\" height=\"98\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere 𝛥𝜆 and 𝛥𝑛 are the variations of resonant wavelength and RI, respectively. To illustrate the improved sensing performance of proposed structure, the comparison with several recently published results [16-19] are summarized in in Table 1. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1 A comparison of some recent reported plasmonic refractive index sensors\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellpadding=\"0\" cellspacing=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"27.272727272727273%\"\u003e\n \u003cp\u003e\u003cstrong\u003eReference\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"31.31313131313131%\"\u003e\n \u003cp\u003e\u003cstrong\u003eSensitivity (nm/RIU)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"41.41414141414141%\"\u003e\n \u003cp\u003e\u003cstrong\u003eThe range of working wavelength (nm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"27.272727272727273%\"\u003e\n \u003cp\u003e[16]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"31.31313131313131%\"\u003e\n \u003cp\u003e1261.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"41.41414141414141%\"\u003e\n \u003cp\u003e600-1000\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"27.272727272727273%\"\u003e\n \u003cp\u003e[17]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"31.31313131313131%\"\u003e\n \u003cp\u003e1295\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"41.41414141414141%\"\u003e\n \u003cp\u003e2402\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"27.272727272727273%\"\u003e\n \u003cp\u003e[18]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"31.31313131313131%\"\u003e\n \u003cp\u003e1535\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"41.41414141414141%\"\u003e\n \u003cp\u003e2200\u0026ndash;2300\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"27.272727272727273%\"\u003e\n \u003cp\u003e[19]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"31.31313131313131%\"\u003e\n \u003cp\u003e1550\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"41.41414141414141%\"\u003e\n \u003cp\u003e1500-1700\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"27.272727272727273%\"\u003e\n \u003cp\u003eThis study\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"31.31313131313131%\"\u003e\n \u003cp\u003e2040\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"41.41414141414141%\"\u003e\n \u003cp\u003e2000\u0026ndash;2200\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eFinally, the proposed structure also possesses capabilities in measuring the temperature if introducing a high thermal-optical material (i.e. PDMS) within the resonator.\u0026nbsp;As the temperature coefficient of PDMS is 4.5 \u0026times; 10\u003csup\u003e\u0026minus;4\u003c/sup\u003e, therefore the relationship between the RI (i.e. \u0026nbsp;) and ambient temperature ( ) can be described as [20]:\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"1004\" height=\"51\"\u003e\u003c/p\u003e\n\u003cp\u003eUnder the influence of temperature changing from 10 ℃to 100 ℃, the transmission spectra of the structure is shown in Fig. 6 (a). It is evident that the dips perform blue-shift as \u0026nbsp;rises. Moreover, the wavelength of dip D3 possesses the largest blue-shift with the increase of temperature, resulting in the maximum temperature sensitivity of 1.2 nm/℃, which is much higher than other reported devices, as compared and shown in Table 2. Here the temperature sensitivity is defined as\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"172\" height=\"89\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere\u0026nbsp;𝛥𝜆\u0026nbsp;and\u0026nbsp;𝛥\u003cem\u003eT\u003c/em\u003e are the variations of resonant wavelength and temperature, respectively.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2 A comparison of some recent reported plasmonic temperature sensors\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellpadding=\"0\" cellspacing=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"27.272727272727273%\"\u003e\n \u003cp\u003e\u003cstrong\u003eReference\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"31.31313131313131%\"\u003e\n \u003cp\u003e\u003cstrong\u003eAbsolute temperature sensitivity (nm/◦C)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"41.41414141414141%\"\u003e\n \u003cp\u003e\u003cstrong\u003eThe range of working wavelength (nm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"27.272727272727273%\"\u003e\n \u003cp\u003e[21]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"31.31313131313131%\"\u003e\n \u003cp\u003e-4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"41.41414141414141%\"\u003e\n \u003cp\u003e1100-1300\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"27.272727272727273%\"\u003e\n \u003cp\u003e[22]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"31.31313131313131%\"\u003e\n \u003cp\u003e0.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"41.41414141414141%\"\u003e\n \u003cp\u003e1200-1500\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"27.272727272727273%\"\u003e\n \u003cp\u003e[23]\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"31.31313131313131%\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"41.41414141414141%\"\u003e\n \u003cp\u003e1900-2200\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"27.272727272727273%\"\u003e\n \u003cp\u003e[24]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"31.31313131313131%\"\u003e\n \u003cp\u003e1.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"41.41414141414141%\"\u003e\n \u003cp\u003e2800-3200\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"27.272727272727273%\"\u003e\n \u003cp\u003e[25]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"31.31313131313131%\"\u003e\n \u003cp\u003e0.059\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"41.41414141414141%\"\u003e\n \u003cp\u003e1500\u0026ndash;1600\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"27.272727272727273%\"\u003e\n \u003cp\u003eThis study\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"31.31313131313131%\"\u003e\n \u003cp\u003e1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"41.41414141414141%\"\u003e\n \u003cp\u003e2600\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e3000\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eIn summary, we have proposed and theoretically investigated a plasmonic sensor based on the metal-insulator-metal waveguide coupled with a split-square-ring resonator. The transmission characteristics of the device are systematically analysed by using FDTD method. With the optimized structural parameters, the simulation results show that the RI and temperature sensitivity could reach up to 2040 nm/RIU and 1.2 nm/℃, respectively. Comparisons with other plasmonic configurations further reveal the superior sensing properties of our structure. We believe that the remarkable sensing capacity and compact architecture show a great promise for future development of miniaturized plasmonic sensors.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interest\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor\u003c/strong\u003e\u003cstrong\u003e\u0026rsquo;s\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJiajun Wu designed the structures, performed the numerical simulations and wrote the manuscript. Youqiao Ma supervised the project, participated in analysis of the results and reviewed the manuscript. Jinhua Li and Yuan Ma participated in analysis of the results and reviewed the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the start-up foundation for introducing talent of Nanjing University of Information Science and Technology (NUIST), the National Natural Science Foundation of China (Grant nos. 11605090), the Natural Science Foundation of the Jiangsu Province (BK20191396).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of Data and Material\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the data and materials are in the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eD. K. Gramotnev, S. I. Bozhevolnyi, Nature Photon. \u003cstrong\u003e4\u003c/strong\u003e, 83-91 (2010).\u003c/li\u003e\n \u003cli\u003eP. Berini, I. D. 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Commun. \u003cstrong\u003e364\u003c/strong\u003e, 191-194 (2016).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Surface Plasmon, MIM waveguide, Resonator, Temperature sensing, RI Sensing ","lastPublishedDoi":"10.21203/rs.3.rs-2270072/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2270072/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA novel design for a highly-sensitive plasmonic sensor, consisting of metal-insulator-metal (MIM) waveguide with a coupled split-square-ring resonator, is presented and studied by two-dimensional (2D) finite-difference time-domain (FDTD) method in this paper. The simulation results show that the proposed sensor possesses a refractive index (RI) sensitivity up to 2040 nm/RIU with optimized structural parameters. In addition, a temperature sensitivity of −1.2 nm/◦C is determined. Numerical calculations indicate that the sensing performance can still be further improved via optimization of the structure. The compact waveguide structure may find important applications in areas of sensing and integrated circuits.\u003c/p\u003e","manuscriptTitle":"Highly Sensitive Plasmonic Sensor with a Coupled Split-Square-Ring Resonator","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-11-16 16:01:47","doi":"10.21203/rs.3.rs-2270072/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"966e8bfe-0d6a-4912-bc9f-81a8af87034c","owner":[],"postedDate":"November 16th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2022-12-23T05:29:07+00:00","versionOfRecord":[],"versionCreatedAt":"2022-11-16 16:01:47","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2270072","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2270072","identity":"rs-2270072","version":["v1"]},"buildId":"rHA-KDH7Qsr4HCuvH75dn","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}