High Sensitivity Refractive Index Sensor Research Articles

Fano Resonance-Associated Plasmonic Circular Dichroism in a Multiple-Dipole Interaction Born–Kuhn Model

Plasmon chirality has garnered significant interest in sensing application due to its strong electromagnetic field localization and highly tunable optical properties. Understanding the effects of mode coupling in chiral structures on chiral optical activity is particularly important for advancing this field. In this work, we numerically investigate the circular dichroism (CD) of elliptical nanodisk dimers arranged in an up-and-down configuration with a specific rotation angle. By adjusting the inter-particle distance and geometric parameters, we introduce the coupling between dipole and electric hexapole modes, forming an extended Born–Kuhn model that achieves strong CD. Our findings show that the coupling of dipole modes with electric hexapole modes in elliptical nanodisks can also show obvious Fano resonance and a strong CD effect, and the structure with the largest Fano asymmetry factor shows the highest CD. In addition, CD spectroscopy is highly sensitive to changes in the refractive index of the surrounding medium, especially in the visible and near-infrared regions, highlighting its potential for application in high-sensitivity refractive index sensors.

Borophene and Phase Change Material-based Integrated Multilayered High-Sensitive Refractive Index Sensor for Infrared Frequency Spectrum

Borophene and Phase Change Material-based Integrated Multilayered High-Sensitive Refractive Index Sensor for Infrared Frequency Spectrum

High-Sensitivity Refractive Index Sensor with Dual-Channel Based on Surface Plasmon Resonance Photonic Crystal Fiber.

In order to achieve a high-precision synchronous detection of two different refractive index (RI) analytes, a D-type surface plasmon resonance (SPR) photonic crystal fiber (PCF) RI sensor based on two channels is designed in this paper. The sensor uses a D-shaped planar region of the PCF and a large circular air hole below the core as the sensing channels. Surface plasmon resonance is induced by applying a coating of gold film on the surface. The full-vector finite-element method (FEM) is used to optimize the structural parameters of the optical fiber, and the sensing characteristics are studied, including wavelength sensitivity, RI resolution, full width at half maximum (FWHM), figure of merit (FOM), and signal-to-noise ratio (SNR). The results show that the channel 1 (Ch 1) can achieve RI detection of 1.36-1.39 in the wavelength range of 1500-2600 nm, and the channel 2 (Ch 2) can achieve RI detection of 1.46-1.57 in the wavelength range of 2100-3000 nm. The two sensing channels can detect independently or simultaneously measure two analytes with different RIs. The maximum wavelength sensitivity of the sensor can reach 30,000 nm/RIU in Channel 1 and 9900 nm/RIU in Channel 2. The RI resolutions of the two channels are 3.54 × 10-6 RIU and 10.88 × 10-6 RIU, respectively. Therefore, the sensor realizes dual-channel high- and low-RI synchronous detection in the ultra-long wavelength band from near-infrared to mid-infrared and achieves an ultra-wide RI detection range and ultra-high wavelength sensitivity. The sensor has a wide application prospect in the fields of chemical detection, biomedical sensing, and water environment monitoring.

High-sensitive refractive index sensor based on the long-period gratings inscribed in the tapered fiber at dispersion turning point

We demonstrated the fabrication of long-period fiber gratings (LPFGs) in the tapered single-mode fiber by CO2 laser. The phase-matching curves of the LPFGs inscribed in the tapered fiber with different waist diameters have been studied theoretically and experimentally. When the waist diameter of the tapered fiber decreased from 90 μm to 22 μm, the slope of the phase-matching curve changed dramatically. The refractive index sensitivity can be increased by inscribing the LPFGs in the tapered fiber around the dispersion turning point. A maximum refractive index sensitivity of 21702.78 nm/RIU has been achieved in the range of 1.445–1.457 for the LPFG inscribed in the tapered fiber with a waist diameter of 50 μm. This kind of LPFGs inscribing in the tapered fiber may be a good candidate for the development of refractive index based chemical and biological sensors.

High sensitivity refractive index sensors with different no-core fiber diameters

We investigate refractive index (RI) sensors using no-core fibers with diameters of 250 µm, 125 µm, and 62.5 µm. Experiments show that RI sensors with sizes of 62.5 µm and 250 µm are more sensitive than those with a diameter of 125 µm. The maximum RI sensitivity was 4886 nm/RIU. The RI sensor has a high sensitivity, a wide measurement range, and is insensitive to temperature, making it well-suited for a variety of practical applications.

Fiber-tip-integrated High-sensitivity Refractive Index and High-precision Liquid Level Sensor Based on Surface Plasmon Resonance

Fiber-tip-integrated High-sensitivity Refractive Index and High-precision Liquid Level Sensor Based on Surface Plasmon Resonance

A high sensitivity refractive index sensor based on microstructure fiber with simple structure and SPR effect

A novel dual-side polished photonic crystal fiber (PCF) based surface plasmon resonance (SPR) polarization filtering and refractive index (RI) sensor is presented in this paper. The cladding of PCF was composed of eight air holes and the outer surface was dual-sided polished and coated with gold film. Finite element method (FEM) was used for the simulation and design of the proposed sensor. Simulation results showed that sensor performance was better in analytes ranging from 1.33 to 1.42 RI. The wavelength and amplitude sensitivities at resonance wavelengths of 1269 and 995 nm were 27400 nm/RIU and −100.43 RIU−1 for an analyte of 1.42 and 1.41 RI, respectively, along with a spectral resolution of 3.64×10−6 RIU. Maximum loss of 52806 dB/m was obtained for an analyte of 1.41 RI towards Y-Polarization (Y-P). An extinction ratio of −105.374 dB was obtained using a fiber transferring length of 2 mm to achieve better polarization filtering effects. The proposed sensor is made of same size air holes which is easy to fabricate, cost effective, and shows better sensitivity and polarization filtering effects than several other sensors. It is expected that the sensor is suitable for wide RI detection range and capable of providing excellent polarization effect. The proposed sensor can be used for various applications including environmental detection, chemical sensing, biosensors, and pharmaceutical inspection.

High-sensitivity refractive index sensor based on strong localized surface plasmon resonance.

This study proposes two types of composite structures based on gold nano circular and nano square rings on a gold thin film for plasmonic refractive index sensing. The finite-difference time-domain method was used for simulation and analysis. The nano square ring composite structure showed superior performance, with five surface plasmon resonance modes, and a peak sensitivity and figure of merit in a liquid environment of 1600nm/RIU and 86R I U -1, respectively. The sensing performances of localized surface plasmon resonance modes of both structures are superior to those of the propagating surface plasmon resonance modes. The proposed composite structures can provide a reference for refractive index sensing and have broad application prospects in bio-chemistry.

Quasi-bound states in the continuum in a metal nanograting metasurface for a high figure-of-merit refractive index sensor.

In this work, we investigate the bound states in the continuum (BICs) in a gold nanograting metal-insulator-metal metasurface structure at oblique angles of incidence. The nanograting metasurface consists of a gold nanograting patterned on a silicon dioxide dielectric film deposited on a thick gold film supported by a substrate. With rigorous full-wave finite difference time domain simulations, two bound states in the continuum are revealed upon transverse magnetic wave angular incidence. One BIC is formed by the interference between the surface plasmon polariton mode of the gold nanograting and the FP cavity mode. Another BIC mode is formed by the interference between the metal-dielectric hybrid structure guided mode resonance mode and the FP cavity mode. While true BIC modes cannot be observed, quasi-BIC modes are investigated at angles of incidence slightly off from the corresponding true BIC angles. It is shown that quasi-BIC modes can suppress radiation loss, resulting in narrow resonance spectral linewidths and high quality-factors. The quasi-BIC mode associated with the surface plasmon polariton mode is investigated for refractive index sensing. As a result, a high sensitivity refractive index sensor with a large figure-of-merit of 364 has been obtained.

Temperature-insensitive high-sensitivity refractive index sensor based on a thinned helical fiber grating with an intermediate period.

A temperature-insensitive high-sensitivity refractive index sensor is proposed and experimentally demonstrated, which is based on utilization of a thinned helical fiber grating but with an intermediate period (THFGIP). Attributed to the reduced diameter and an intermediate period of the grating, the proposed sensor has a high surrounding refractive-index (SRI) sensitivity and a low temperature sensitivity. The average SRI sensitivity of the proposed sensor is up to 829.9 nm/RIU in the range of 1.3410-1.4480 RIU. Moreover, unlike the traditional sensitivity-enhancement method by increasing the waveguide dispersion factor, here the waveguide dispersion factor at the resonant wavelength was decreased by reducing the diameter of the fiber grating and as a result, the crosstalk effect due to the temperature change can be further suppressed. The proposed temperature-insensitive SRI sensor has the superiorities of simple structure, ease fabrication, and low cost, which could be found more potential applications in the SRI sensing fields.

High sensitivity refractive index sensor based on double peanut-shaped and etched multimode fiber structures

A fiber optic refractive index (RI) sensor based on an etched multimode fiber (MMF) with a double peanut-shaped structure is proposed and experimentally demonstrated. The sensor consists of two peanut-shaped and a section of etched MMF tapered fiber structure. The excitation of the fundamental mode to higher-order modes is facilitated by using the beam splitting/coupling effect of the double peanut-shaped and etched taper structures, and the higher-order modes can be excited into an evanescent field. In the sensing medium, the stronger the evanescent field, the stronger the energy shock between the fiber and the sensing environment. Experimental results showed that the sensitivity was 326.52 nm/RUI and 823.91 nm/RUI when the etched waist taper diameter was 51.92 μm and the glycerol solution index ranged from 1.3395 to 1.3945 and 1.3945 to 1.4200, respectively. Compared to the MMF sensor structure without etching, the RI sensitivity is improved by about 2 times. In addition, the temperature characteristics of the sensor were investigated over a range of 30 °C–100 °C, and the results showed a maximum temperature sensitivity of only 30.24 pm °m−1. The sensor structure has a low-temperature sensitivity and the temperature effect on the RI measurement results is negligible within the allowable error range. The sensor has the advantages of simple fabrication, wide measurement range, good stability, low cost, and compact structure, which has potential application value in the field of RI detection.

High-sensitivity refractive index sensor based on defective modes of an 8-fold quasi-periodic photonic crystal

The refractive index sensing performance of the 8-fold quasi-periodic photonic crystal (QPhC) defect modes is studied. The proposed QPhC structure consists of the silicon columns immersed in a free-flowing liquid environment to enable real-time detection. The refractive index sensitivity of 982 nm/RIU, and a detection limit of 4.82×10−5 are achieved at the near-infrared wavelength. The influence of protein's thickness attached by the central dielectric column on the resonant wavelength is investigated. For the optimized radius of the central column r = 375 nm, the Q value of the resonant peak exceeds 4.9×104, and a slight variation of protein's thickness less than 1 nm attached by the micro-cavity can be distinguished. The spatial field distributions of the multiple defect modes and the corresponding sensitivity are analyzed and explained.

High angular sensitivity refractive index sensors based on 1D single-defect magneto-optical photonic crystals

Strong localization and enhancement of fields may arise in the defect layer of an 1D single-defect magneto-optical photonic crystal (1DSDMOPC), which has been applied to design and fabricate several types of optical devices. In this work, we demonstrate numerically that, for the case that a linearly polarized light is normally incident on a selected 1DSDMOPC, rotation angle induced by polar linear magneto-optical Kerr effect may strongly depend on refractive index of the fluid encountered by the transmission, which indicates that 1DSDMOPC is promising to be applied as a refractive index sensor based on Kerr angle detection. Furthermore, it is shown that sensitivity and detection range of the sensor can be adjusted by either modifying refractive index of the dielectric layers or altering number of layers of the 1DSDMOPC. An angular sensitivity in the order of 104 °/RIU is inferred, a value much larger than both the one usually encountered in photonic crystal sensors and the surface plasmon resonance based sensors (the angular sensitivity usually in the order of 101 or 102 °/RIU). Our work may provide a new possible way to design and manufacture high angular sensitivity sensors by using 1DSDMOPCs.

High-Sensitivity and Wide Detection-Range Refractive-Index Sensor Based on Amplitude Change in Slotted Photonic Crystal Nanobeam Cavity

High Q-factor is essential for the realization of high sensitivity photonic crystal-based sensors. The Q-factor is usually optimized for a specific refractive-index (RI) value of the ambient background. However, a small change in the RI reduces the Q value, and therefore limits the performance of the sensor to a narrow RI range. Here, we report a high-sensitivity RI sensor with a wide detection-range based on amplitude change of the fundamental mode in slotted photonic crystal nanobeam cavity. Both wavelength and amplitude sensitivity of 333 nm/RIU and 188/RIU are realized in the RI range from 1.3 to 1.6, respectively. To the best of our knowledge, this represents the widest sensing range ever reported in photonic crystal cavities. Owing to the wide sensing range and the insignificance of the Q value, this approach would find applications in various research areas in integrated lab-on-chip systems for optofluidic- and bio-sensing applications.

High Sensitivity and Wide Range Refractive Index Sensor Based on Surface Plasmon Resonance Photonic Crystal Fiber.

In order to detect the refractive index (RI) of high refractive index materials such as trichlorobenzene and aniline in the near-infrared and mid-infrared spectra and expand the detection range of the refractive index, a surface plasmon resonance (SPR) photonic crystal fiber (PCF) sensor based on an elliptical sensing channel is proposed for high refractive index detection. The fiber core and the analyte channel are surrounded by two types of air holes with different sizes. When the surface plasmon resonance effect appears at the interface between the fiber core and the elliptical sensing layer, obvious resonance peaks appear in the near-infrared and mid-infrared bands. The full vector finite element method (FEM) is used to study the sensing characteristics of the sensor and the influence of structural parameters on the resonance peak. The results demonstrate that the sensor achieves detection in the refractive index range of 1.41-1.58, in the wavelength range of 1600-3200 nm. The average wavelength sensitivity is 9217.22 nm/RIU, and the refractive index resolution is 10.85 × 10-6 RIU. The proposed sensor realizes high refractive index detection in the near-infrared and mid-infrared bands, and obtains an ultra-wide detection range and higher sensitivity. The sensor has broad application prospects in chemical detection, biomedical sensing and other fields, and provides a theoretical reference for the design of a photonic crystal fiber surface plasmon resonance sensor.

High sensitivity and stability probe-type refractive index sensor based on an optical fiber metasurface

A specific probe-type sensor based on an optical fiber metasurface was proposed and simulated for refractive index (RI) sensing. In this work, a metasurface has been integrated with an optical fiber platform, which has huge potential applications in imaging, sensing, and communications. The designed RI sensor consists of stacking layers of Au and ZnO in a 2D structure deposited on the end face of commercial multimode optical fiber. The parameters and performance of the sensor structure are designed and simulated. The results show that the designed sensor structure can generate mode resonance and realize RI sensing. Numerical simulations reveal that when the pair of Au/ZnO layers is 4, the width of the nanopillars is 300 nm, the thickness of the Au layer is 45 nm, the thickness of ZnO layer is 40 nm, and the RI sensitivity of the designed sensor reaches 1415 nm/RIU. In addition, the high RI of Au/ZnO, along with its compatibility with the fiber core (SiO2), makes it a perfect candidate to realize a multifunctional device. It also is a the biocompatible material that can be functionalized easily and used to realize biosensing.

Temperature-insensitive high sensitivity refractive index sensor based on tapered no core fiber

This study fabricated an ultra-high refractive index (RI) sensor based on tapered no-core fiber (NCF) involving a simple inexpensive process. A splice section of NCF in the middle of single mode fiber was tapered to small diameters. The sensor was sensitive to the surrounding RI with a large measurement range of 1.3330–1.4437. The RI sensitivity differed with varying wavelengths, with a value of 41 916 nm/RIU at approximately 1550 nm, for the RI ranges of 1.4407–1.4437. It yielded a low temperature sensitivity of 8 pm °C−1, which indicates an ultra-low temperature cross-sensitivity. The proposed fiber optic RI sensor can be used in many fields such as medicine and biochemical applications.

High sensitivity photonic crystal fiber temperature and refractive index sensor based on surface plasmon resonance

High sensitivity photonic crystal fiber temperature and refractive index sensor based on surface plasmon resonance

High Sensitivity Refractive Index Sensor Based on D-Shaped Photonic Crystal Fiber Coated with Graphene-Silver Films

High Sensitivity Refractive Index Sensor Based on D-Shaped Photonic Crystal Fiber Coated with Graphene-Silver Films

Enhanced spin Hall effect of light in the PT-symmetric trilayer structure containing epsilon-near-zero materials

We systematically study the spin Hall effect of light (SHEL) in the parity-time (PT)-symmetric trilayer structure containing epsilon-near-zero (ENZ) materials, and design a high sensitivity refractive index sensor with an adjustable sensing range. It is revealed that the SHEL shift in the PT-symmetric trilayer structure is clearly enhanced, which is two orders of magnitude larger than that in the conventional sandwich structure containing ENZ materials. The enhancement of the SHEL shift is attributed to the fact that the change of reflection coefficient induced by the quasi-bound states in the continuum (quasi-BIC) in the former structure is smoother than that induced by the bound states in the continuum in the latter structure. It is further found that when the refractive index of the interlayer dielectric in the PT-symmetric structure is fixed, the SHEL shift is significantly enhanced near the quasi-BIC resonance angle determined by the gain-loss coefficient. Meanwhile, the SHEL shift enhanced by excitation of quasi-BIC is very sensitive to the gain-loss coefficient and the refractive index of the interlayer dielectric. Finally, we design a high sensitivity refractive index sensor with an adjustable sensing range based on the quasi-BIC-enhanced SHEL shift. These studies provide a pathway to enhance the SHEL and may open avenues for the application of optical sensors.