Sensitive Refractive Index Sensor Research Articles

Surface phonon resonance: A new mechanism for enhancing photonic spin Hall effect and refractive index sensor

Abstract Metal-based surface plasmon resonance (SPR) plays an important role in enhancing the photonic spin Hall effect (SHE) and developing sensitive optical sensors. However, the very large negative permittivities of metals limit their applications beyond the near-infrared regime. In this work, we theoretically present a new mechanism to enhance the photonic SHE by taking advantage of SiC-supported surface phonon resonance (SPhR) in the mid-infrared regime. The transverse displacement of photonic SHE is very sensitive to the wavelength of incident light and the thickness of SiC layer. Under the optimal parameter setup, the calculated largest transverse displacement of SiC-based SPhR structure reaches up to 163.8 μm, which is much larger than the condition of SPR. Moreover, a NO2 gas sensor based on the SPhR-enhanced photonic SHE is theoretically proposed with the superior sensing performance. Both the intensity and angle sensitivity of this sensor can be effectively manipulated by varying the damping rate of SiC. The results may provide a promising paradigm to enhance the photonic SHE in the mid-infrared region and open up new opportunity of highly sensitive refractive index sensors.

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-Q-factor multiple Fano resonance for sensitive refractive index sensors based on all-dielectric metasurface

High-Q-factor multiple Fano resonance for sensitive refractive index sensors based on all-dielectric metasurface

Highly Sensitive Refractive Index Sensor based on Silicon Nitride Strip Waveguide Directional Coupler

We propose a refractive index sensor, based on grating-assisted directional coupler, by comprising two coupled asymmetric strip waveguides with a top-loaded grating structure. We have studied variation of the sensitivity with the waveguide parameters to optimize the design of the sensor. The proposed sensor is an on-chip device with a high refractive index sensitivity of 104nm/RIU with $ \pm $ 140 nm fabrication tolerance, which is more than two times higher than the reported work, and the sensor can also achieve the ultrahigh sensitivity 105nm/RIU with the fabrication tolerance $ \pm $ 13nm. The sensor has large dynamic range from refractive index 1.0 to 1.55. We have also studied the propagation loss due to side wall roughness of the strip waveguide and found that it does not significantly affect sensor performance.

Adaptive peak extraction algorithm assisted fiber cavity ring‐down spectroscopy measurement system for refractive index sensing

AbstractThe article presents a dual‐optimized adaptive algorithm based on continuous wavelet transform and derivative precise peak capture is developed for fiber cavity ring‐down spectroscopy. Adaptive spectral signal processing is achieved so that peak selection blindness can be effectively solved. To verify the performance of the dual‐optimized adaptive algorithm, a highly sensitive refractive index sensor using a bandgap fiber‐based linear fiber cavity is demonstrated. The developed dual‐optimized adaptive algorithm is compared with the conventional maximum extraction algorithm, and the results show that the dual‐optimized adaptive algorithm has a better performance in suppressing noise and processing superimposed peaks. A stable enhancement factor of 5 is obtained, indicating that the newly developed dual‐optimized adaptive algorithm can generate a high‐quality cavity ring‐down spectrum for applications including refractive index sensors, biosensors, strain gauges, and pressure sensors.

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.

Anisotropic medium sensing controlled by bound states in the continuum in polarization-independent metasurfaces.

Bound states in the continuum (BICs) with infinite quality factor (Q-factor) and significant field enhancement pave the way for realizing highly sensitive optical sensors with enhanced light-matter interactions on the nanoscale. However, current optical sensing methods are difficult to discriminate between isotropic and anisotropic media from resonance spectral lines, resulting in optical sensing methods still being limited to isotropic media. In this work, we demonstrate that BICs can be realized by modulating the period of structural units to convert BICs to QBICs without changing their space group symmetry, and propose a polarization-independent metasurfaces-based realization of highly sensitive refractive index sensors for isotropic and anisotropic media as well as discrimination. We propose a metasurface of tetrameric silicon nanoboxes with C4 symmetry as structural units to achieve the conversion of BICs to QBICs by modulating the period of structural units without changing the geometry of the structure. Two QBICs modes dominated by electric toroidal dipole and magnetic toroidal dipole are identified by multipolar decomposition and electromagnetic distribution calculations. Meanwhile, we realize the refractive index detection and resolution of isotropic and anisotropic media based on polarization-independent metasurfaces combined with isotropic and anisotropic media layers. Our work provides what we believe to be a new method for realizing the fast resolution and refractive index optical sensing of isotropic and anisotropic media, and offers new ideas for the design and application of polarization-independent metasurfaces.

Optically Manipulated Micromirrors for Precise Excitation of WGM Microlasers

AbstractWhispering gallery mode microlasers are highly sensitive refractive index sensors widely explored for biophotonic and biomedical applications. Microlaser excitation and collection of the emitted light typically utilize microscope objectives at normal incidence, limiting the choice of the oscillation plane of the modes. Here, a platform that enables the excitation of microlasers from various directions using an optically manipulated micromirror is presented. The scheme enables precise sensing of the environment surrounding the microlasers along different well‐controlled planes. The capability of the platform to perform a time‐resolved experiment of dynamic sensing using a polystyrene probe bead orbiting the microlaser is further demonstrated.

Highly sensitive temperature and refractive index sensor based on no-core fiber cascaded with a balloon-shaped bent single-mode fiber

A highly sensitive temperature and refractive index (RI) sensor based on no-core fiber (NCF) cascaded with a balloon-shaped bent single-mode fiber (BSBSF) is proposed and demonstrated. The NCF can excite higher-order modes which will be concentrated and transmitted into the BSBSF due to the characteristic of self-imaging effect. The BSBSF has an excellent temperature performance due to the high thermo-optical coefficient and thermal expansion coefficient of the polymer coating. The NCF and BSBSF are both conducive to the excitation of higher-order modes, which induces the sensitivity of the sensor with an efficiency improvement. The experimental results show that the maximum temperature sensitivity is −3.19nm/∘C in the range of 22°C–83°C, which is the highest temperature sensitivity in the cascaded BSBSF structure to our best knowledge. In addition, the maximum RI sensitivity is 232.16 nm/RIU when the RI changes from 1.3234 to 1.3512. Compared with other cascaded BSBSF structures, this sensor has a higher temperature sensitivity and can be applicated in the prospects of food, biology, and environmental monitoring.

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.

Highly Sensitive Surface Plasmon Resonance Refractive Index Sensor Based on D-Shaped Dual‑Core Photonic Crystal Fiber with ITO Film

Highly Sensitive Surface Plasmon Resonance Refractive Index Sensor Based on D-Shaped Dual‑Core Photonic Crystal Fiber with ITO Film

Ultrahigh Sensitivity Refractive Index Sensor Based on Double-Side Polished Photonic Crystal Fiber with Zigzag Gold Film

Ultrahigh Sensitivity Refractive Index Sensor Based on Double-Side Polished Photonic Crystal Fiber with Zigzag Gold Film

Ultrahigh Sensitivity Refractive Index Sensor Based on Surface Plasmon Resonance Effect of Double-Ring Hollow-Core Anti-Resonant Fiber

Ultrahigh Sensitivity Refractive Index Sensor Based on Surface Plasmon Resonance Effect of Double-Ring Hollow-Core Anti-Resonant Fiber

Sensitive and Compact Evanescent-Waveguide Optical Detector for Sugar Sensing in Commercial Beverages.

This work presents a compact and sensitive refractive index sensor able to evaluate the concentration of an analyte in a sample. Its working principle leverages on the changes in the optical absorption features introduced by the sample itself on the evanescent waves of a light beam. The device's high compactness is achieved by embedding the sample-light interaction site and the detector in a 1 cm2 glass substrate, thanks to microelectronics technologies. High sensitivity is obtained by employing a low-noise p-i-n hydrogenated amorphous silicon junction, whose manufacture process requires only four UV lithographic steps on a glass substrate, thus ensuring low production costs. The system's capabilities are investigated by sensing the sugar content in three commercial beverages. Sensitivities of 32, 53 and 80 pA/% and limits of detection of 47, 29 and 18 ppm are achieved. The above performance is comparable with state-of-the-art results available in the literature, where more complex optical setups, expensive instrumentation and bulky devices are used.

Enhanced refractive index sensing using a surface plasmon resonance sensor with heterostructure

This article aims to enhance the sensitivity of a surface plasmon resonance sensor for refractive index sensing in the visible region using a low refractive index prism. The proposed sensing system is ultrasensitive and employs an angular interrogation method for measuring reflected intensity. The bimetallic layers and two-dimensional heterostructure are utilized to increase sensitivity. Black phosphorus is utilized as an analyte-interacting layer due to its sp3 hybridized puckered structure, high charge carrier density, indirect bandgap and larger surface area for attachment of analyte. To optimize the sensor structure and architecture based on its sensitivity and figure of merit, a comprehensive analysis is performed. The proposed sensor achieves the best possible sensitivity of 345.83°/RIU, detection accuracy of 0.132 Deg−1 and figure of merit of 45.74/RIU. This work enables to design a highly sensitive refractive index sensor useful to sense small sized analyte. The proposed research work provides new dimension to develop highly sensitive refractive index sensor for biomolecule or biochemical sensing.

Highly sensitive refractive index and magnetic field sensor based on long-period fiber grating inscribed in tapered optical fiber

A refractive index (RI) and magnetic field sensor based on tapered long period fiber grating (LPFG) is proposed. We prepared two different periods of LPFGs (LPFG1 and LPFG2) using high-frequency CO2 laser point by point method on tapered single-mode fiber. Firstly, LPFG1 is used to measure the RI of sodium chloride solution. LPFG1 is immersed in sodium chloride solutions with different RI to measure the sensitivity of LPFG to RI. The experimental results indicate that LPFG1 is particularly sensitive to changes in environmental RI, with a sensitivity of 381.820 nm/RIU. Due to the special sensitivity of tapered LPFG to environmental RI, in order to eliminate the influence of residual sodium chloride on the surface of LPFG1 on magnetic field measurement, we use LPFG2 with similar parameters to measure the environmental magnetic field. LPFG2 was encapsulated in a glass capillary tube filled with the magnetic fluid (MF). After the environmental magnetic field changed, the RI of MF changed, causing the resonance peak wavelength of LPFG2 to drift. We measured the magnetic field using LPFG2 within the magnetic field range of 0.66 mT to 20 mT. Only in the magnetic field range of 1.95 mT to 4.6 mT, good linear fitting was achieved, with a magnetic field sensitivity of 1.242 nm/mT and a fitting coefficient of 0.9852. The experimental results indicate that LPFG inscribed in tapered optical fiber has high sensitivity to environmental RI and magnetic field. The sensor has a simple structure, small volume, easy production, and high sensitivity, which has certain practical application prospects.

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.

Highly sensitive refractive index sensor based on TiO2/Ag films coated D-type photonic crystal fibers

Highly sensitive refractive index sensor based on TiO2/Ag films coated D-type photonic crystal fibers

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.