Refractive Index Sensitivity Research Articles

Highly sensitive liquid refractive index sensor based on a polymer two-mode ridge waveguide interferometer

In this paper, we propose and experimentally demonstrate a highly sensitive liquid refractive index (RI) sensor based on a two-mode interferometer (TMI) formed with a polymer ridge waveguide. Compared with the rectangular waveguide TMI sensor, our proposed ridge waveguide TMI sensor enables a higher waveguide sensitivity and hence device sensitivity. Our experimental results show that the fabricated ridge waveguide TMI sensor achieves a sensitivity of 6980.62 nm/RIU, indicating a significant improvement over the fabricated rectangular waveguide TMI sensor with almost identical dimensions; the latter exhibits a sensitivity of 3753.81 nm/RIU. Our proposed sensor is simple in structure but has high sensitivity and low cost.

Simultaneous measurement of temperature and refractive index based on fiber optic Fabry–Pérot cavity in batteries

Abstract A Fabry-Pérot (FP) sensor for simultaneous measurement of refractive index and temperature of an all-fiber synchronous liquid based on the Vernier effect is proposed, special application for internal monitoring of lithium-ion battery electrolytes. The theoretical model of high sensitivity cascade Fabry-Pérot interferometer (PFPI) is established, the sensitivity amplification mechanism of PFPI is analyzed in detail, the perfect matching scheme for measuring the refractive index of the electrolyte inside the battery is designed according to the matching conditions of the optical path, and the corresponding sensors for simultaneous measurement of the temperature and the refractive index are fabricated. The experimental results show that the sensor has a maximum refractive index sensitivity of 15391.5033 nm/RIU, a good linear fit, and can effectively monitor the refractive index change of the electrolyte by 10-4 orders of magnitude during normal charging and discharging of lithium-ion batteries. Compared to traditional epoxy adhesive bonded or laser processed FP sensors, this all-fibre optic structure not only improves temperature and corrosion resistance, but also significantly reduces temperature cross-sensitivity. Its small size and excellent resistance to high temperature and corrosion ensure the sensor's excellent response and broad application prospects in monitoring the refractive index of the electrolyte in 18650 lithium-ion batteries, which provides effective technical support for monitoring the health status of batteries and detecting early safety issues.

Multi-scenario refractive index sensor based on merging BIC in an all-dielectric metasurface

In recent years, bound states in the continuum (BICs) in the all-dielectric metasurfaces have attracted considerable attention due to the low radiation loss and large quality factor (Q-factor). In this study, we design a highly sensitive refractive index sensor working in multi-scenario based on merging quasi-BIC in the silicon nitride metasurface. By adjusting the thickness of the metasurface and keeping the structural symmetry, nine BICs distributed in momentum space form the merging BIC at the Γ point with significantly enhanced Q-factor. The transmission spectra of the metasurface sensor disperse with the refractive index in multi-scenario. The modulation depth of the Fano resonance spectrum can exceed 99.9%. The sensitivity and figure of merit of the refractive index sensor based on the merging quasi-BIC can reach 41.35 nm/RIU and 13,389.1 RIU-1 for gas, 59.05 nm/RIU and 8,415.9 RIU-1 for blood, and 66.08 nm/RIU and 8,845.8 RIU-1 for cerebrospinal fluid, respectively. Furthermore, we investigate the influence of the structural deviations on the Q-factor, which of the merging quasi-BIC maintains higher than that of the isolated quasi-BIC. Our work offers a method for designing high-sensitivity sensors working in multi-scenarios, which may hold significant potential for enhancing device performance in gas and biological detection.

Highly sensitive photonic spin Hall effect sensor with graphene-coated surface exciton polariton structure

The photonic spin Hall effect (PSHE) in a graphene-coated surface exciton polariton (SEP) structure is investigated in this work. The transverse shift of 32.95λ0 (17.53 μm) is achieved with the optimum graphene-coated SEP structure in the gaseous environment under λ0 = 532 nm illumination, which provides a 2.46-fold improvement compared to the optimum conventional SEP structure. The transverse shift is further improved to 76.39λ0 (i.e., 40.64 μm) with the graphene-coated long-range SEP (LRSEP) in the aqueous environment. Refractive index sensors based on the enhanced PSHE are proposed for sensing applications in the gaseous and aqueous environment, respectively, which possess the bulk refractive index sensitivities of 24424.4λ0 (12993.78 µm) 1/RIU (RIU: refractive index unit) and 57336.6λ0 (30503.1 µm) 1/RIU. The combination of SEP (LRSEP) and graphene layers provides a promising approach for enhancing the transverse shift of PSHE, and may find potential applications in gas sensing, chemical sensing, and biosensing base on the enhanced PSHE.

Local Refractive Index Sensitivity of Localized Surface Plasmon Resonance Biosensors

Local Refractive Index Sensitivity of Localized Surface Plasmon Resonance Biosensors

Regulation and Liquid Sensing of Electromagnetically Induced Transparency-like Phenomena Implemented in a SNAP Microresonator.

Optical microresonators supporting whispering-gallery modes (WGMs) have become a versatile platform for achieving electromagnetically induced transparency-like (EIT-like) phenomena. We theoretically and experimentally demonstrated the tunable coupled-mode induced transparency based on the surface nanoscale axial photonics (SNAP) microresonator. Single-EIT-like and double-EIT-like (DEIT-like) effects with one or more transparent windows are achieved due to dense mode families and tunable resonant frequencies. The experimental results can be well-fitted by the coupled mode theory. An automatically adjustable EIT-like effect is discovered by immersing the sensing region of the SNAP microresonator into an aqueous environment. The sharp lineshape and high slope of the transparent window allow us to achieve a liquid refractive index sensitivity of 2058.8 pm/RIU. Furthermore, we investigated a displacement sensing phenomenon by monitoring changes in the slope of the transparent window. We believe that the above results pave the way for multi-channel all-optical switching devices, multi-channel optical communications, and biochemical sensing processing.

Double-slot micro-ring resonators with trapezoidal subwavelength grating as ultra-sensitive biochemical sensors

Silicon-based refractive index sensors are of significance in the detection of gases, biological substances and chemical compounds. Among these, optical microcavities can confine the optical field to the micrometre-scale region, and possess the advantages of high Q factor, small size and easy integration. In this paper, a trapezoidal subwavelength grating (SWG) is introduced into a slot micro-ring resonator, and the mode splitting is employed to enrich the supported standing wave modes and optimize the spatial profiles of the resonant modes. The modes’ Q factor is improved and the high sensitivity and low detection limit is achieved. The optimal trapezoidal subwavelength grating double slot micro-ring resonator (T-SWGDSMRR) structure is obtained by designing the structural parameters and analyzing their effects on the sensing performance parameters and spectral characteristics. The T-SWGDSMRR, designed for detecting the glucose solution, demonstrated a low detection limit of 3.3×10−5 RIU and an ultra-high Q factor of up to 100825, accompanied by a refractive index sensitivity of 424 nm/RIU. Finally, a cascaded double micro-ring sensor is proposed using the vernier effect, through cascading the T-SWGDSMRR with a referential ring, the sensitivity is enhanced to 12828 nm/RIU, and the limit of detection is 3.12×10−6 RIU.

Highly Sensitive Gas Pressure Sensing with Temperature Monitoring Using a Slightly Tapered Fiber with an Inner Micro-Cavity and a Micro-Channel.

A highly sensitive optical fiber gas pressure sensor with temperature monitoring is proposed and demonstrated. It is based on a slightly tapered fiber with an inner micro-cavity forming an in-fiber Mach-Zehnder interferometer (MZI), and a micro-channel is drilled into the lateral wall of the in-fiber micro-cavity using a femtosecond laser to allow gas to flow in. Due to the dependence of the refractive index (RI) of air inside the micro-cavity on its gas pressure and the high RI sensitivity of the MZI, the device is extremely sensitive to gas pressure. To prevent fiber breakage, the MZI is housed in a silicate capillary tube with an air inlet. Multiple modes are excited by slightly tapering the inner micro-cavity, and the resonance dips in the sensor's transmission spectrum feature different linear gas pressure and temperature responses, so a sensitivity matrix algorithm can be used to achieve simultaneous demodulation of two parameters, thus resolving the temperature crosstalk. As expected, the experimental results demonstrated the reliability of the matrix algorithm, with pressure sensitivity reaching up to ~-12.967 nm/MPa and temperature sensitivity of ~89 pm/°C. The features of robust mechanical strength and high air pressure sensitivity with temperature monitoring imply that the proposed sensor has good practical and application prospects.

Temperature and RI sensing based on micro-structured optical fiber surface plasmon resonance

In this paper, we propose a surface plasmon resonance sensor based on micro-structured optical fiber capable of simultaneous sensing of a liquid refractive index and temperature. The fiber structure comprises four large air holes, with side polishing and rectangular groove processing on one side without air holes. Ag film and α-Fe2O3 film are coated inside the rectangular groove for refractive index sensing. Au film is coated on the inner walls of the two side air holes and filled with polydimethylsiloxane (PDMS) for temperature sensing. The results show that the sensor can achieve sensing of two parameters in two polarization directions. With a refractive index ranging from 1.35 to 1.42 and temperature ranging from 10°C to 100°C, the maximum refractive index sensitivity reaches 28225.7 nm/RIU and the maximum temperature sensitivity reaches −3.64nm/∘C. The sensor features simple structure, easy implementation, and high sensitivity, making it applicable in fields such as biosensing, chemical sensing, and environmental monitoring.

Numerical Investigation of a Highly Sensitive Plasmonic Refractive Index Sensor for the Detection of Breast and Cervical Cancer Biomarkers

Numerical Investigation of a Highly Sensitive Plasmonic Refractive Index Sensor for the Detection of Breast and Cervical Cancer Biomarkers

Design and performance of a dual-band plasmonic perfect absorber for infrared refractive index sensing

In this study, we introduce what we believe is an innovative design for a plasmonic perfect absorber (PPA) that is based on half-cut disk resonator metamaterials. This design exhibits remarkable stability and versatility, demonstrating effective functionality across a wide range of incident angles for both transverse electric (TE) and transverse magnetic (TM) polarization. The distinct operational characteristics of the PPA are highlighted by the presence of two corresponding absorption peaks at wavelengths of 870 and 1599 nm, where it achieves outstanding maximum absorption rates of 98.99% and 97.5%, respectively. The design’s ultra-narrow resonance peaks are indicative of its high-quality factors, which are vital for enhancing sensitivity in plasmonic sensory applications. This characteristic renders our PPA an exceptional candidate for refractive index (RI) sensing, where precision is critical. The dual-band perfect absorber (PA)-based sensor demonstrates significant RI sensitivity, with values approximately equal to 365 nm/RIU at the first absorption peak and 733 nm/RIU at the second. Our findings elucidate the exceptional potential inherent in this novel dual-band perfect absorber design. The versatility and efficiency across varied applications not only contribute to the existing body of knowledge but also pave the way for future advancements in plasmonic sensor technologies and metamaterial research.

High-Sensitivity Refractive Index Sensing Based on an SNPNS Composite Structure

In this paper, we design and demonstrate an all-fiber-sensitive refractive index (RI) sensor based on the Mach–Zehnder interferometer (MZI). It is constructed by splicing two no-core fibers (NCFs) and a photonic crystal fiber (PCF) between two single-mode fibers (SMFs) to obtain an SMF–NCF–PCF–NCF–SMF composite structure (SNPNS). A study of the effect of varying PCF lengths on the RI reveals that the shorter the length, the higher the sensitivity. The maximum RI sensitivity of 176.9 nm/RIU is attained within the RI range of 1.3365–1.3767 when the PCF length in the SNPNS structure is 3 cm. Meanwhile, the sensor exhibits a high stability in water, with an RSD of only 0.0019% for the interference trough over a duration of two hours. This proposed sensing structure offers the advantages of a large extinction ratio, small size, low temperature sensitivity, and simple fabrication, exhibiting a great potential in RI measurements.

High-Q fano resonance metasurface sensor for refractive index and methane gas concentration measurement

High-quality-factor Fano resonances excited by metasurfaces have been playing an important role in the field of optical sensing. A high-performance sensor for refractive index and methane concentration measurement is designed and prepared in this paper. The symmetry of the structure is broken by altering the size of the rectangular holes in the tetramer, resulting fano resonance Q-factor of 34176 and modulation depth of 100%. The finite-difference time-domain (FDTD) method is used to simulate the structure. The results show that the refractive index and methane concentration sensitivity are 325 nm/RIU and −1.44 nm/%, respectively. The FOM can achieve 10156 RIU−1. Furthermore, experiments are carried out on the gas application of the structure and the sensitivity of methane concentration is −1.03 nm/%. Therefore, the proposed metasurface has more practical and feasible significance in background refractive index and gas environment monitoring.

Dual planer PCF-SPR sensor based on Au-TiO2 composite nanostructure

A novel dual planer type PCF-SPR sensor based on Au-TiO2 composite nanostructure is proposed for the first time. In this sensor, a novel PCF structure was designed. The structure is composed of air holes of various diameters. A layer of nanogold film was platted on TiO2 nanopillar to form Au-TiO2 composite nanopillar. Then the Au-TiO2 composite nanopillar was embedded into the PCF. The geometrical parameters such as PCF air hole diameters, gold layer thickness, and TiO2 cylinder diameter were optimized, utilizing the finite-element method(FEM), and the performance of the optimized sensor was significantly improved. The maximum sensitivity was 30,000 nm RIU−1 in the refractive index range of 1.37–1.41. Unlike traditional array and planar structures, we have achieved high sensitivity refractive index sensing in PCF by using a single composite nanopillar. Due to its high sensitivity, the proposed PCF-SPR sensor is expected to find applications in biomolecular detection and chemical quantity detection.

Highly sensitive one-dimensional Dielectric-Superconductor photonic crystal structure for low temperature sensing applications

The work proposed in this paper investigates the design and simulation of low temperature refractive-index (RI) sensor using one-dimensional photonic crystal (1D-PhC) structure. The bilayer stack is created using dielectric and superconductor materials. The dielectric material is assumed to be air and the superconductor considered is YaBa2Cu3O7. Compared to superconductor material, air’s RI is hardly affected by the temperature. The parameter perceived by the suggested sensor for precise temperature measurement in the region of 10 K to 90 K is thought to be the superconductor’s RI, which is a function of temperature. To the best of our knowledge, the structural characteristics have been precisely adjusted to increase sensor efficiency to a level never before seen in published research. According to the findings, the temperature sensitivity of 1.524 nm/K and the maximum RI sensitivity of 1079.42 nm/RIU are found in the proposed structure. Applications for bio-sensing are a good fit for the suggested sensing device.

High-sensitivity and wide-range refractive index sensing based on the envelope spectrum of the subwavelength grating waveguide racetrack microring resonator.

Integrated microring resonators (MRRs) on silicon on insulator (SOI) are attractive candidates for excellent performance sensing systems. In this work, a novel, to the best of our knowledge, subwavelength grating waveguide racetrack microring resonator (SWGW-RMRR) on SOI with high-sensitivity and wide-range refractive index (RI) sensing is proposed and demonstrated experimentally. Owing to the exceptional evanescence field of the Bloch mode for the SWGW, the SWGW-RMRR provides highly sensitive RI sensing. Meanwhile, the SWGW-RMRR makes the free of free spectral range (FSR) limitation on the detection range (DR) by monitoring the envelope spectrum. By combining the advantages of the evanescent field and envelope spectrum, a SWGW-RMRR sensor has been demonstrated with a RI sensitivity of 860.8 nm/RIU, a limit of the detection value of 1.9 × 10-5 RIU, and a wide range of detection range. The measured Q-factor of the SWGW-RMRRs with an 88.8 µm total cavity length is 6200. This work can successfully realize high-sensitivity and wide-range RI sensing, showing the promising applications of silicon photonics sensors on chips.

Sandwich Layer-Modified Ω-Shaped Fiber-Optic LSPR Enables the Development of an Aptasensor for a Cytosensing-Photothermal Therapy Circuit.

The metastasis of cancer cells is a principal cause of morbidity and mortality in cancer. The combination of a cytosensor and photothermal therapy (PTT) cannot completely eliminate cancer cells at one time. Hence, this study aimed to design a localized surface plasmonic resonance (LSPR)-based aptasensor for a circuit of cytosensing-PTT (COCP). This was achieved by coating a novel sandwich layer of polydopamine/gold nanoparticles/polydopamine (PDA/AuNPs/PDA) around the Ω-shaped fiber-optic (Ω-FO). The short-wavelength peak of the sandwich layer with strong resonance exhibited a high refractive index sensitivity (RIS). The modification with the T-shaped aptamer endowed FO-LSPR with unique characteristics of time-dependent sensitivity enhancement behavior for a sensitive cytosensor with the lowest limit of detection (LOD) of 13 cells/mL. The long-wavelength resonance peak in the sandwich layer appears in the near-infrared region. Hence, the rate of increased localized temperature of FO-LSPR was 160 and 30-fold higher than that of the bare and PDA-coated FO, indicating strong photothermal conversion efficiency. After considering the localized temperature distribution around the FO under the flow environment, the FO-LSPR-enabled aptasensor killed 77.6% of cancer cells in simulated blood circulation after five cycles of COCP. The FO-LSPR-enabled aptasensor improved the efficiency of the cytosensor and PTT to effectively kill cancer cells, showing significant potential for application in inhibiting cancer metastasis.

Realization and optimization of the gold-mesoporous silica based bimodal surface plasmon resonance sensor with digital Gaussian filter

Abstract This work presented a novel biomdal surface plasmon resonance (BSPR) sensor with mesoporous silica film (MSF) and digital Gaussian filter. A modified Stöber solution growth approach was applied to prepare MSF film on the gold film. The conventional SPR sensor was coupled with a digital Gaussian filter to realize the BSPR sensor. After that, the Gaussian parameters were modified and the BSPR angular spectrum was obtained for further sensing experiments. Porosity and thickness of the MSF film were measured and calculated by means of a combination of simulation and measurement. The simulation results indicate that the refractive index (RI) sensitivity of the BSPR sensor could reach 75.11 deg/RIU which is 66.91% higher than the 45 deg/RIU of the conventional gold-MSF SPR sensor. Based on the experiments, the RI resolution of BSPR sensor was improved by 37.1% to 6.61 × 10−6 RIU, the limit of detection (LOD) for glucose was raised from 320 mg l−1 to 131 mg l−1, and the LOD for CTAB molecule was raised from 124.98 nM to 63.78 nM when compared to the gold-MSF SPR sensor.

High sensitivity metamaterial thin film: bio and thermal sensors based on Fano resonances and nematic liquid crystals

ABSTRACT In this research, a new sensor was designed that exhibits high biological and thermal sensitivities. It is suitable for use as a biosensor, a thermal sensor, or both simultaneously. This nanostructure sensor is based on two non-identical copper rings, which are dependent on two dielectric environments, and has been optimised to enhance sensitivity. To control and increase the sensitivity of the designed metamaterial, the E7 liquid crystal was used, which has a temperature-dependent refractive index. The optimised data indicate that the highest sensitivity for the structural parameters; R, dr and d are 70, 43 and 30 nm, respectively. This nanostructure demonstrates a refractive index sensitivity of 500 nm/RIU and a very high temperature sensitivity of 11 nm/K in the wavelength range of 500–1000 nanometres and a temperature range of 290–330 Kelvin. The second peak has the highest sensitivity to the refractive index and the third peak has the highest sensitivity to temperature. The high temperature sensitivity reported is at a 90-degree orientation angle of the liquid crystal director. Therefore, the simulation and optimisation of this ultra-thin film indicates that it can be suitable for use as a high-quality bio-thermal sensor with a high figure of merit.

Terahertz tunable quasi-bound state in the continuum metasurface with high sensitivity based on Dirac semimetal

We have proposed a novel tunable terahertz (THz) quasi-bound states in the continuum (BIC) metasurface based on Dirac semimetal (DS). By modifying the structural parameters of the DS resonator and disrupting the C4 symmetry to induce perturbations, we achieve the conversion of BIC to quasi-BIC with a high Q-factor, reaching up to 1291.3. Moreover, we conducted a systematic analysis of the electric field distribution and surface current density for both symmetric and asymmetric configurations to elucidate the formation mechanism of the quasi-BIC. Furthermore, by varying the Fermi energy of the DS within the range of 0.1–0.2eV, we achieved continuously tunable operation with the operating frequency ranging from 1.179 to 1.248 THz and the transmission from 21.18% to 96.87%. Most notably, we investigated the sensing performance of the device, finding that its refractive index sensitivity and figure of merit (FOM) are 0.301 THz/RIU and 143.3 RIU−1, respectively, highlighting its potential for high-sensitivity applications, particularly in material detection and biomedical diagnostics.