Remote plasmonic refractive index sensor based on MIM waveguide periodic structure

A refractive-index-sensitive plasmonic waveguide, whose transmission characteristics could be controlled remotely by a rake-like switch design, is theoretically studied in the reported work. The distance from the remote control unit to the bus waveguide is more than 0.25 μm, and it still possesses great efficiency even when the distance is increased to 0.535 μm. The switch basically contains two main sections. The first is on the bottom and next to the bus waveguide which functions as a plasmonic resonator that can induce localized surface plasmon resonance (LSPR) and restrict wave propagation at corresponding resonant frequency. The second is on the top and far away from the bus waveguide which functions as a remote controller that can modulate LSPR frequency in the first section. The refractive-index-dependent transmission spectra of this filter were simulated using finite-difference time-domain method. The results have shown that even at a distance as far as 0.5 μm, the ON/OFF switching of the wave propagation in a bus waveguide can still be modulated by adjusting the refractive index of a remote rectangular controller. With only 0.08 difference in refractive index, it could be obtained an on–off switching ratio of 18.7, 20.4 and 25.7 respectively for different waveguides at visible and near infrared wavelength, which shows great potential applications in refractive index sensors and remote-controllable band-stop filters.

Lattice plasmon resonances (LPRs), which originate from the plasmonic-photonic coupling in gold or silver nanoparticle arrays, possess ultra-narrow linewidth by suppressing the radiative damping and provide the possibility to develop the plasmonic sensors with high figure of merit (FOM). However, the plasmonic-photonic coupling is greatly suppressed when the nanoparticles are immobilized on substrates because the diffraction orders are cut off at the nanoparticle-substrate interfaces. Here, we develop the rational design of LPR structures for the high-performance, on-chip plasmonic sensors based on both orthogonal and parallel coupling. Our finite-difference time-domain simulations in the core/shell SiO2/Au nanocylinder arrays (NCAs) reveal that new modes of localized surface plasmon resonances (LSPRs) show up when the aspect ratio of the NCAs is increased. The height-induced LSPRs couple with the superstrate diffraction orders to generate the robust LPRs in asymmetric environment. The high wavelength sensitivity and narrow linewidth in these LPRs lead to the plasmonic sensors with high FOM and high signal-to-noise ratio (SNR). Wide working wavelengths from visible to near-infrared are also achieved by tuning the parameters of the NCAs. Moreover, the wide detection range of refractive index is obtained in the parallel LPR structure. The electromagnetic field distributions in the NCAs demonstrate the height-enabled tunability of the plasmonic “hot spots” at the sub-nanoparticles resolution and the coupling between these “hot spots” with the superstrate diffraction waves, which are responsible for the high performance LPRs-based on-chip refractive index sensors.

Using optical sensors to transform light-matter interaction into optical signal has become more and more popular. This is especially true for the fields that require ultrafast responsibility and remote sensing, such as environmental monitoring, food analysis and medical diagnosis. Among numerous optical sensors, plasmonic nanosensors are of great promise due to their spectral tunability and good adaptability to modern nanobiotechnologies. Localized surface plasmon resonance (LSPR) is the electromagnetic resonance of conducting electrons on metal surface, and it is very sensitive to the variation of environmental refractive index. The LSPR is considered as a useful sensing parameter that provides very good biochemical information. The SPR absorption peak also can be adjusted by changing the nano structure on the LSPR biological sensor chip. In this study, Finite-Difference Time- Domain (FDTD) was applied to simulate the LSPR absorption peak. Four model parameters were modified to study the LSPR sensing sensitivity: (a) the incident light wavelength, (b) the diameter of nanoparticle, (c) the spacing among nanoparticles, and (d) the height of nanoparticle. The simulation results show that 860nm is the best wavelength for the LSPR adsorption measurement. The optimal diameter of nanoparticle is 150nm, and the nanoparticle spacing is 90nm. Higher nanoparticle height provides higher sensitivity, but it also depends on the process capability. The FDTD simulation can be a useful tool to design a LSPR nanoparticle biosensor.

Plasmonic MIM waveguide based FR sensors for refractive index sensing of human hemoglobin

Localized surface plasmon resonance (LSPR) gas sensitivity is introduced as a new parameter to evaluate the performance of plasmonic gas sensors. A model is proposed to consider the plasmonic sensors' surface sensitivity and plasmon decay length and correlate the LSPR response, measured upon gas exchange, with an equivalent refractive index change consistent with adsorbed gas layers. To demonstrate the applicability of this new parameter, ellipsoidal gold nanoparticles (NPs) arranged in densely packed hexagonal lattices were fabricated. The main advantages of these sensors are the small and tunable interparticle gaps (18-29 nm) between nanoparticles (diameters: 72-88 nm), with their robust and scalable fabrication technology that allows the well-ordered arrangement to be maintained on a large (cm2 range) area. The LSPR response of the sensors was tested using an LSPR sensing system by switching the gas atmosphere between inorganic gases, namely He/Ar and Ar/CO2, at constant pressure and room temperature. It was shown that this newly proposed parameter can be generally used for benchmarking plasmonic gas sensors and is independent of the type and pressure of the tested gases for a sensor structure. Furthermore, it resolves the apparent disagreement when comparing the response of plasmonic sensors tested in liquids and gases.

Plasmonic metal nanostructures are promising for chemical and biological sensor applications due to their high spectral sensitivity, defined as the relative shift in resonance wavelength with respect to the refractive index changes of the surroundings. In this work, the refractive index sensitivity (RI sensitivity) of one kind of core-shell nanostructure was studied, in which the gold nanobipyramid (AuBP) core was sheltered by the Au-Ag alloy shell. We investigated the dependence of the RI sensitivity and the figure of merit (FOM) of the localized surface plasmon resonance (LSPR) on the geometry and the composition of the nanostructures. Theoretical consideration on the LSPR revealed that the RI sensitivity of the nanostructures is determined by the bulk plasma wavelength, dielectric properties of the alloy and the geometrical parameters. To quantitatively explore the dependence of the RI sensitivity on the metal compositions and the aspect ratios of the nanostructures, the frequency-related dielectric properties of the alloy were calculated using the Drude-critical points model (DCPM). Then the calculated dielectric data were applied in the finite difference time domain (FDTD) solutions to simulate the optical spectra of the alloy nanostructures with various Ag concentrations. Experimentally, a series of fabrication processes were also carried out for the growth of a homogeneous Au-Ag alloy nanoshell on the surface of AuBPs using a wet-chemical method. The measured RI sensitivities agree well with the values predicted from FDTD simulations, indicating the availability, credibility and feasibility of the modelled dielectric data of the alloy. The DCPM and FDTD simulations can be combined to calculate the dielectric properties and forecast the sensitivity properties of the Au-Ag alloyed nanostructures with varying concentrations.

In this work, a plasmonic sensor established on metal-insulator-metal waveguide configuration is proposed and numerically investigated for biosensing applications. The spectral and sensing characteristics of the device are examined via the two-dimensional finite element method. Sensitivity (Sbulk) and figure of merit (FOM) are two important parameters that are considered to determine the device performance. The Sbulk of the device is considered as a ratio between the change in resonance wavelength and change in the ambient refractive index. Whereas FOM is the ratio of Sbulk to full width at half maximum. The Sbulk and FOM offered by the device are ~825.7 nm/RIU and ~13.14, respectively. This work can provide a guideline for the realization of highly sensitive plasmonic sensing devices. Full Text: PDF ReferencesN.L. Kazanskiy, S.N. Khonina, M.A. Butt, "Plasmonic sensors based on Metal-insulator-metal waveguides for refractive index sensing applications: A brief review", Physica E: Low-dimensional systems and Nanostructures 117, 113798 (2020). CrossRef D. Xiang, W. Li, "MIM plasmonic waveguide splitter with tooth-shaped structures", Journal of Modern Optics 61, 222-226 (2014). CrossRef M.A. Butt, S.N. Khonina, N.L. Kazanskiy, "Ultra-short lossless plasmonic power splitter design based on metal–insulator–metal waveguide", Laser Physics 30, 016201 (2020). CrossRef J. Park, S. Lee, B. Lee, "Polarization Singularities in the Metal-Insulator-Metal Surface Plasmon Polariton Waveguide", IEEE Journal of Quantum Electronics 46, 1577-1581 (2010). CrossRef M. T. Hill, M. Marell, E. S. P. Leong, B. Smalbrugge, Y. Zhu, M. Sun, P. J. V. Veldhoven, E. J. Geluk, F. Karouta, Y-S. Oei, R. Notzel, C-Z. Ning, M. K. Smit, "Lasing in metal-insulator-metal sub-wavelength plasmonic waveguides", Optics Express 17, 11107-11112 (2009). CrossRef A. Udupi, S. K. Madhava, "Plasmonic Coupler and Multiplexer/Demultiplexer Based on Nano-Groove-Arrays", Plasmonics 16, 1685-1692 (2021). CrossRef Y-F. C. Chau, C-T. C. Chao, H-P. Chiang, "Ultra-broad bandgap metal-insulator-metal waveguide filter with symmetrical stubs and defects", Results in Physics 17, 103116 (2020). CrossRef H. Bahri, S. Mouetsi, A. Hocini, H.B. Salah, "A high sensitive sensor using MIM waveguide coupled with a rectangular cavity with Fano resonance", Optical and Quantum Electronics 53, 332 (2021). CrossRef S.N. Khonina, N.L. Kazanskiy, M.A. Butt, A. Kazmierczak, R. Piramidowicz, "Plasmonic sensor based on metal-insulator-metal waveguide square ring cavity filled with functional material for the detection of CO2 gas", Optics Express 29, 16584 (2021). CrossRef M.A. Butt, S.N. Khonina, N.L. Kazanskiy, "Plasmonics: A Necessity in the Field of Sensing-A Review (Invited)", Fiber and Integrated Optics 40, 14-47 (2021). CrossRef M.A. Butt, A. Kazmierczak, N.L. Kazanskiy, S.N. Khonina, "Metal-Insulator-Metal Waveguide-Based Racetrack Integrated Circular Cavity for Refractive Index Sensing Application", Electronics 10, 1419 (2021). CrossRef N.L. Kazanskiy, S.N. Khonina, M.A. Butt, A. Kazmierczak, R. Piramidowicz, "A Numerical Investigation of a Plasmonic Sensor Based on a Metal-Insulator-Metal Waveguide for Simultaneous Detection of Biological Analytes and Ambient Temperature", Nanomaterials 11, 2551 (2021). CrossRef I. Tathfif, A.A. Yaseer, K.S. Rashid, R.H. Sagor, "Metal-insulator-metal waveguide-based optical pressure sensor embedded with arrays of silver nanorods", Optics Express 29, 32365-32376 (2021). CrossRef P.D. Sia, "Overview of Drude-Lorentz type models and their applications", Nanoscale Syst. Math. Model. Theory Appl. 3, 1-13 (2014) CrossRef M.A. Butt, N.L. Kazanskiy, "Nanoblocks embedded in L-shaped nanocavity of a plasmonic sensor for best sensor performance", Optica Applicata LI, 109-120 (2021). CrossRef S. Khani, M. Hayati, "An ultra-high sensitive plasmonic refractive index sensor using an elliptical resonator and MIM waveguide", Superlattices and Microstructures 156, 106970 (2021). CrossRef F. Chen, J. Li, "Refractive index and temperature sensing based on defect resonator coupled with a MIM waveguide", Modern Physics Letters B 33, 1950017 (2019). CrossRef M. Rahmatiyar, M. Danaie, M. Afsahi, "Employment of cascaded coupled resonators for resolution enhancement in plasmonic refractive index sensors", Optical and Quantum Electronics 52, 153 (2020). CrossRef M.A. Butt, S.N. Khonina, N.L. Kazanskiy, "A multichannel metallic dual nano-wall square split-ring resonator: design analysis and applications", Laser Physics Letters 16, 126201 (2019). CrossRef

This work proposed a multiple mode Fano resonance-based refractive index sensor with high sensitivity that is a rarely investigated structure. The designed device consists of a metal–insulator–metal (MIM) waveguide with two rectangular stubs side-coupled with an elliptical resonator embedded with an air path in the resonator and several metal defects set in the bus waveguide. We systematically studied three types of sensor structures employing the finite element method. Results show that the surface plasmon mode’s splitting is affected by the geometry of the sensor. We found that the transmittance dips and peaks can dramatically change by adding the dual air stubs, and the light–matter interaction can effectively enhance by embedding an air path in the resonator and the metal defects in the bus waveguide. The double air stubs and an air path contribute to the cavity plasmon resonance, and the metal defects facilitate the gap plasmon resonance in the proposed plasmonic sensor, resulting in remarkable characteristics compared with those of plasmonic sensors. The high sensitivity of 2600 nm/RIU and 1200 nm/RIU can simultaneously achieve in mode 1 and mode 2 of the proposed type 3 structure, which considerably raises the sensitivity by 216.67% for mode 1 and 133.33% for mode 2 compared to its regular counterpart, i.e., type 2 structure. The designed sensing structure can detect the material’s refractive index in a wide range of gas, liquids, and biomaterials (e.g., hemoglobin concentration).

Based on a metal-insulator-metal (MIM) waveguide with a side-coupled nanodisk cavity, the sensor using the surface plasmon polaritons (SPPs) refractive index is investigated and studied numerically. The finite-difference time-domain (FDTD) method is used to simulate the performance of the sensor. The numerical simulation result indicates that all the resonance wavelengths in the transmission characteristic of the structure have a linear relationship with the refractive index of the cavity. Furthermore, the sensitivities of the sensor in this paper for the refractive index can be achieved as high as 1320 nm RIU for the mode1, 812.5 nm RIU for the mode2, 600 nm RIU for the mode3, respectively. Besides, the influences of the structural parameters on the transmission characteristic and the sensing characteristic are also studied in detail by the FDTD method. The sensor with compact and simple structure not only can be used to measure the temperature based on the linear relation between the refractive index and temperature, but also has many potential applications in optical networks on chip and On-chip sensor networks.

Surface Plasma resonance (SPR) sensors combined with biological receptors are widely used in biosensors. Due to limitations of measurement techniques, small-scale, low accuracy, and sensitivity to the refractive index of solution in traditional SPR prism sensor arise. As a consequence, it is difficult to launch commercial production of SPR sensors. The theory of localized surface plasmon resonance (LSPR) developed based on SPR theory has stronger coupling ability to near-field photons. Based on the LSPR sensing theory, we propose a submicron-sized golden-disk and graphene composite structure. By varying the thickness and diameter of the array disk, the performance of the LSPR sensor can be optimized. A graphene layer sandwiched between the golden-disk and the silver film can prevent the latter from oxidizing. Symmetrical design enables high-low concentration of dual-channel distributed sensing. As the fixed light source, we use a 632.8-nm laser. A golden nano-disk with 45 nm thickness and 70 nm radius is designed, using a finite difference time domain (FDTD) simulation system. When the incident angle is 42°, the figure of merit (FOM) reaches 8826, and the measurable refractive index range reaches 0.2317.

Biomolecular detection using Localized Surface Plasmon Resonances (LSPR) has been extensively investigated because these techniques enable label-free detection. The high-density metal nanopatterns with tunable LSPR characteristics have been used as refractive index sensing because LSPR property is highly sensitive to refractive index change of surroundings. Meanwhile, Colloidal lithography is a robust method for fabricating regularly ordered nanostructures in a controlled and reproducible way using spontaneous assembly of colloidal particles. In this study, nanopatterns on UV-curable polymer were prepared via colloidal lithography. Then, metallic nanograil arrays with high density were fabricated by sputtering noble metals such as gold and subsequent removal of residual polymers and colloidal particles. From Finite-Difference Time-Domain Method (FDTD) simulations and reflectance spectra, we found that multiple dipolar plasmon modes were induced by gold nanograil arrays and each mode was closely related with structural parameters. LSPR characteristics of gold nanograil arrays could be tuned by varying the fabrication conditions to obtain optimal structures for LSPR sensing. Sensing behavior of gold nanograil arrays was tested by applying various solvents with different refractive indices and measuring the variations of LSPR dips. Finally, gold nanograil arrays as LSPR sensors were integrated in optofluidic devices and used to achieve real-time label-free monitoring of biomolecules.

A tunable MEMS sub-wavelength surface plasmonic apparatus is proposed based on localized surface-plasmon resonance effects. Optical tunneling is obtained through Surface Plasmon Polaritons (SPP) and Localized Surface Plasmon (LSP) by using a periodic sub-wavelength narrow-grooved metal-dielectric-metal (MDM) composite structure. Only p-polarized light can excite the SPP and LSP resonantly. The excited LSP mode with a strong field enhancement at the incident side grooves, resonantly excites the LSP mode on the other side of the thin structure. Then, with matched radiative modes, photons are radiated and tunneled. Nano/micro electromechanical actuation of small elastic deformations makes it possible to dynamically tune the localized surface plasmons via shape changes. Numerical simulations based on the Finite-Difference Time-Domain (FDTD) method are carried out on sub-wavelength structures and the results discussed. The MDM concept provides a new method to achieve real-time, dynamic tunable control and manipulation of light transmission and reflection via LSP which is different from novel tunable SPP apparatus where refractive index modulation is obtained using a voltage-controlled liquid crystal or tunable spaced air-gapped micro-prisms 1-3 based on a convential SPP arrangement. This is important for the manipulation of LSP and plasmonic device design applications. Furthermore, a proposed Localized Surface Plasmon Resonance (LSPR) sensor mechanism with MDM-LSPR are demonstrated with numerical results. We believe that the MDM-LSPR is a novel principle for LSPR sensors in dielectric sensing for chemical or biologic applications which compares to current LSPR sensors with nano-particle LSPR and nanosphere lithography (NSL) 4-6 .

In this work, the device is integrated with two bus waveguides and three ring waveguides. The ring and the bus waveguide is designed with a width of 250nm and a height of 400nm is considered. The mid infrared wavelength of 1550nm is considered as an input source for the coupling of light from the bus waveguide to ring waveguide. The coupling between the three ring waveguides is also observed. The multimode coupling takes place in the configuration. The guided mode resonance at 1550nm is observed. The four ports are placed at the inputs and outputs of the bus waveguide. Here the three ring structure with the bus waveguide is analyzed for spectral properties, where quality factor is of main concern. If the structure has to be implemented for a lab-on-a-chip application, sensitivity plays an important role, which in turn is related to the quality factor. Hence the enhancement of the quality factor up to 3000 with three rings is achieved. Two rings are considered as sensing ring for various parameter analyses with one of the ring as reference ring. In the designed structure, the phase shift in the transmission spectrum is observed for the bio-sensing application. The sensor in the ring resonator is based on the refractive index change. The change in the refractive index of the surrounding medium will change the effective refractive index. Hence the effective refractive index along with the group index is monitored for the bio-sensing application. A thin layer on the surface of the waveguide is highly sensitive to refractive index change in the TM mode. The configuration is simulated using Lumerical FDTD as well as Lumerical Mode solutions. The integrated optical devices has a good platform in bio-sensing application, hence the designed configuration can be further incorporated for point of care device.

A new composite metal-insulator-metal (MIM) system consisting of exceptionally dense non-close-packed (NCP) arrays of gold or silver nanoparticles, porous anodic aluminum oxide (PAAO), and bulk aluminum substrate interacts strongly with visible light and may become a very useful component for optical applications. The proposed MIM structure can be synthesized using accessible lithography-free chemical and physical processes (anodization and capillary force assisted colloidal particle deposition) that are suitable for the low-cost production of specialized devices. Here, we present a systematic study to determine the essential MIM structure parameters (nanoparticle size and PAAO layer thickness) for localized surface plasmon resonance (LSPR) refractometric sensing. A performance comparison was done by recording the spectra of scattered light upon angled illumination in media with different refractive indices. A clear advantage for maximizing the signal to background ratio was observed in the case of 60 and 80 nm Au nanoparticles with a PAAO thickness in a narrow range between 300 and 375 nm. Sensitivity exceeding a 200 nm peak wavelength shift per refractive index unit was found for 60 nm Au nanoparticles on approximately 500-nm-thick PAAO. The experimental observations were supported by finite-difference time-domain (FDTD) simulations.

In this paper, a plasmonic switch based on metal-insulator-metal (MIM) waveguide structure is proposed, whose transmission characteristics can be remotely controlled by a rake switch design. The distance from the remote control unit to the bus waveguide is more than 1 um and still maintains a very high efficiency. The refractive-index-dependent transmission spectrum of this filter was simulated using the finite-difference time-domain method. The results show that the on/off switching of wave propagation in the bus waveguide can be achieved by changing the refractive index of the control unit 1 µm away from the bus waveguide. A change in refractive index of only 0.2 is required to simultaneously control the switching off and on of four waves in the waveguide in the visible band, with corresponding switching ratios of 40.5, 74.3, 48.6, and 15.1, showing great potential for applications in refractive index sensors and remotely controllable band stop filters.