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High-sensitivity refractive index sensor with tunable detection range based on dual-core resonance effect in gold-coated photonic crystal fibers
摘要： A high-sensitivity refractive index (RI) sensor with wide tunable detection range based on the dual-core resonance of photonic crystal fibers are presented and studied by the finite element method. A cladding air hole coated with gold film is designed as the microfluidic channel for surface plasmon resonance sensing. The channel filled with liquid analyte acts as a defective core. The directional energy coupling between the fiber core and the defective core which determines the sensing performance is greatly influenced by both the RI of the filled liquid and the structural parameters. Numerical results show that the sensitivity of the sensor increases with the increase of the diameter of the analyte channel, and the RI detection range decreases with the increase of this diameter. So we tune the detection range by adjusting the diameter of the analyte channel to meet specific measurement requirements. As the diameter increases from 1.5 μm to 2.4 μm, the detection range shrinks from 1.45–1.62 to 1.45–1.48, both with the high spectral sensitivity 10 392 nm/RIU and 25 040 nm/RIU, respectively. The sensor with wide adjustable detection range shows great advantages in the field of biochemical, chemistry and environmental detection.
关键词： refractive index sensor,photonic crystal fiber,wide detection range,surface plasmon resonance,high-sensitivity
更新于2025-09-09 09:28:46
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Multiple Fano Resonance Based Optical Refractive Index Sensor Composed Of Micro-Cavity and Micro-Structure
摘要： A multiple Fano resonance based optical refractive index sensor composed of micro-cavity and micro-structure is designed. The multiple Fano resonances, generated by the interference between the multiple resonant peaks produced by the micro-cavity and the continuous background produced by the micro-structure, can reach high sensitivity in refractive index measurement. Besides, the micro-cavity con?guration obviously reduces the energy loss, thus effectively increasing the ?gure of merit. Adjusted by the micro-cavity thickness and the micro-structure con?guration, multiple Fano resonances can be generated potential for refractive index sensing: the sensitivity of 831 nm/RIU and the ?gure of merit of ～600 can be reached according to a single Fano resonance; moreover, spectral interval between double Fano resonances can also be used for refractive index sensing with the sensitivity of 194 nm/RIU but signi?cantly reducing the error due to the environmental changes. Considering the advantages as high sensitivity, narrow Fano resonant peak, high ?gure of merit and ease of integration, as well as its potential in environmental error reduction, the proposed multiple Fano resonance based optical refractive index sensor is expected to provide new tactics for optical refractive index sensing.
关键词： Refractive index sensor,micro-structures,micro-cavity,multiple Fano resonance
更新于2025-09-09 09:28:46
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Label-Free Digital Holo-tomographic Microscopy Reveals Virus-Induced Cytopathic Effects in Live Cells
摘要： Cytopathic effects (CPEs) are a hallmark of infections. CPEs are difficult to observe due to phototoxicity from classical light microscopy. We report distinct patterns of virus infections in live cells using digital holo-tomographic microscopy (DHTM). DHTM is label-free and records the phase shift of low-energy light passing through the specimen on a transparent surface with minimal perturbation. DHTM measures the refractive index (RI) and computes the refractive index gradient (RIG), unveiling optical heterogeneity in cells. We find that vaccinia virus (VACV), herpes simplex virus (HSV), and rhinovirus (RV) infections progressively and distinctly increased RIG. VACV infection, but not HSV and RV infections, induced oscillations of cell volume, while all three viruses altered cytoplasmic membrane dynamics and induced apoptotic features akin to those caused by the chemical compound staurosporine. In sum, we introduce DHTM for quantitative label-free microscopy in infection research and uncover virus type-specific changes and CPE in living cells with minimal interference.
关键词： tomography,virus infection,apoptosis,herpes simplex virus,live-cell microscopy,membrane blebbing,cell volume,refractive index,cell contraction,rhinovirus,label-free microscopy,vaccinia virus
更新于2025-09-09 09:28:46
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Measurement of In-fiber Refractive Index Change Using a Mach-Zehnder Interferometer
摘要： We report, for the first time, the use of a fiber optic Mach-Zehnder interferometer to measure core refractive index changes written by an ultrafast laser irradiation. The core-offset interferometer was constructed by splicing a slightly misaligned stub of standard single mode fiber between lead-in and lead-out optical fibers. When the core refractive index of an in-fiber interferometer is altered, it changes the phase of the core light. Since the phase of light propagating in the cladding (reference arm) remains unchanged, the transmission fringe pattern of the interferometer observes a spectral shift. The spectral shift was used to quantify the effective core refractive index change in a standard single mode fiber. Measurement of effective refractive index changes as high as 0.01356 and as low as 0.000475 are reported in this work.
关键词： effective refractive index change,fiber-optic sensor,ultrafast laser,Mach-Zehnder interferometer,in-fiber refractive index measurement
更新于2025-09-04 15:30:14
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Influence factors and adjusting method of refractive indices of solid media
摘要： It is of great significance to explore changing behavior and adjustment method of the refractive index. Expression of the refractive index, which was derived from the electron-cloud conductor model, contains the equivalent volume V of the electron clouds and the molecular density ρ. The expression shows that the refractive index increases with V and ρ. Based on this expression, main factors influencing the refractive index of solid medium are analyzed and summarized: the Nephelauxetic Effect, number of bonding electrons in the molecule, chemical bond property, number of nonbonding electrons in outermost layer of the molecule, and molecular density of the medium (electromagnetic wave factor is not considered). The relationship between the refractive index and the Nephelauxetic Effect is established. The calculations show that the Nephelauxetic Effect helps to increase the refractive index. Some viewpoints related to the Nephelauxetic Effect are supplemented. Characteristics of the solid medium that has a high refractive index are proposed: (1) Covalent bond component is high, and number of covalent bonds in one molecule is large. (2) Periodic number is as large as possible without increasing the ionic bond component. (3) Molecular density is high. According to these characteristics, method of adjusting the refractive index is discussed, and the results are consistent with the real situations.
关键词： Refractive index,Nephelauxetic Effect,influence factors,adjustment method
更新于2025-09-04 15:30:14
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A novel use of etched multi-mode fibre as magnetic field sensor
摘要： In this study, an optical fibre magnetic field sensor is experimentally demonstrated using chemical etched multimode fibre sandwiched between two single mode fibres. The obtained result of the magnetic field and refractive index response shows that the decreasing fibre diameter in the sensing region plays an important role to enhance the sensitivity of the device. The magnetic field sensing is based on a tunable refractive index (RI) property of magnetic fluid infiltrated into the capillary tube. The sensing system is verified by testing RI of different concentrations of sodium chloride (NaCl) solution before sealing in capillary tube. Experimental results show that the sensor with taper fibre diameter of 45?μm has relatively high magnetic field sensitivity of ～ 0.993?dB/mT ranging from 0 to 6?mT. The proposed devices find potential applications in magnetic field sensing.
关键词： optical fibre magnetic field sensor,sensitivity,chemical etched multimode fibre,refractive index,magnetic fluid
更新于2025-09-04 15:30:14
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Temperature-independent refractive index sensor based on fiber Bragg grating and spherical-shape structure
摘要： A fiber-optic refractive index (RI) sensor consisting of a fiber Bragg grating (FBG) spliced in downstream of a spherical-shape structure in a single-mode fiber (SMF) is proposed and experimentally demonstrated. The cladding modes with different effective refractive indices can be efficiently excited by the spherical-shape structure. By measuring the difference of the wavelength shifts between the reflected cladding Bragg mode and the core mode, we have achieved a maximum sensitivity of 2.87 nm/RIU with range of the RI from 1.357 to 1.458. When the temperature changes from 25 °C to 225 °C, the relative wavelength shift between the cladding mode and the core mode has no significant changes, which indicates that this fiber-optic sensor allows for temperature-independent RI measurement.
关键词： Refractive index sensor,Temperature-independent,Spherical-shape structure,Fiber Bragg grating
更新于2025-09-04 15:30:14
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Simultaneous measurement of refractive index and temperature based on a long period fiber grating inscribed in a photonic crystal fiber with an electric-arc discharge
摘要： A novel fiber sensor composed by two single mode fibers and long period fiber grating based on a photonic crystal fiber prepared by periodic discharge heating has been experimentally investigated to measure refractive index and temperature. A Mach-Zehnder interferometer was formed due to the presence of two fusion spliced collapsed regions in the photonic crystal fiber. The resonance dip and interference pattern were differently influenced by the ambient disturbance, so the dual-parameters were simultaneously measured by analyzing the characteristics of transmission spectrum. After the experimental measurements, refractive index and temperature sensitivities of 117.28 nm/RIU and (cid:1)86.29 pm/(cid:3)C were realized. Therefore, the reported sensor with advantages of easy fabrication, simple structure, and small size has the potential for simultaneous refractive index and temperature measurements involving biochemical sensing applications.
关键词： simultaneous measurement,photonic crystal fiber,refractive index and temperature,Long period fiber grating
更新于2025-09-04 15:30:14
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Synthesis and characterization of thianthrene-containing preimidized soluble polyimide resins and the derived films with high refractive indices and good optical transparency
摘要： A series of organo-soluble polyimide (PI) resins were prepared from a newly designed and synthesized aromatic thianthrene-containing diamine, 2,7-bis(3-aminophenoxy)thianthrene (APOT) and various aromatic dianhydrides via a one-step high temperature polycondensation procedure with N-methyl-2-pyrrolidone (NMP) as the solvent. The derived PI resins were soluble in polar aprotic solvents, including NMP and N,N-dimethylacetamide (DMAc). For comparison, several unsoluble sulfur-containing PIs were prepared from another para-substituted thianthrene-containing diamine, 2,7-bis(4-aminophenylenesulfanyl)thianthrene (APTT) and aromatic dianhydrides by a two-step polycondensation procedure via poly(amic acid) (PAA) precursors at elevated temperatures as high as 300 °C. Flexible and tough PI films with the tensile strength higher than 88 MPa were successfully cast from the APOT-PI resin solution at a relatively low curing temperature of 250 °C. The meta-substituted molecular skeleton in the APOT- PIs endowed the films good optical transparency with the transmittance higher than 83% at a thickness around 10 um, which was apparently higher than those of the para-substituted APTT-PI analogues. The sulfur-rich thianthrene moiety with high molar refraction endowed the APOT-PI films high refractive indices up to 1.7147 at 632.8 nm and low birefringence in the range of 0.0064–0.0133. In addition, the PI films showed good thermal stability with the glass transition temperatures (Tg) higher than 198.3 °C and 5% weight loss temperatures higher than 510 °C in nitrogen.
关键词： Thermal properties,High refractive index,Polyimide,Optical properties,Thianthrene
更新于2025-09-04 15:30:14
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The Effects of Hydrostatic Pressure on the Surface Plasmon Resonance of Gold Nanocrystals
摘要： The surface plasmon resonances of gold nanospheres and nanorods have been measured as a function of hydrostatic pressure up to 17 GPa in methanol-ethanol 4:1 solvent and up to 10 GPa in paraffin. Both the sphere resonance and the longitudinal rod resonance exhibit redshifts while the transverse rod mode shows an extremely weak redshift or blueshift depending on the nanorod aspect ratio. Solidification of the solvent around 11 GPa causes some aggregation of the particles, readily identified through broadening of the SP band and further redshifting. Loading and unloading cycles show only minimal hysteresis in the spectra if the pressure remains below 11 GPa. The surface plasmon shifts are the result of two competing effects. Compression of the conduction electrons in the metals increases the bulk plasma frequency, which causes a blueshift. However, the increase in the solvent density under hydrostatic load leads to an increase in the solvent refractive index, which in turn leads to a redshift. We find that after accounting for the solvent contribution, we can spectroscopically determine the bulk modulus of the gold nanoparticles with a precision of 10%. The value obtained of K0 = 190 GPa is significantly higher than the value for bulk gold (167 GPa). Furthermore, we show that pressure-induced solidification causes a significant broadening and anomalous shift of the surface plasmon band that we attribute to aggregation and nanorod deformation.
关键词： optical absorption,refractive index,hydrostatic pressure,surface plasmon resonance,bulk modulus,gold nanoparticles
更新于2025-09-04 15:30:14