Refractive Index Difference Research Articles

SPR Biosensor Sensor principle and application progress

SPR Biosensor, full name Surface Plasmon Resonance Biosensor, is an instrument used to detect biomolecular interactions. It has the advantages of high sensitivity, high selectivity and real-time to monitor the interaction between substances in real time by optical principle. The working principle of SPR biosensor is based on surface plasmon resonance effect. When there is a certain refractive index difference between the metal surface and the medium, the incident light will be reflected and transmitted. When a biological molecule or chemical molecule binds to a metal surface, it changes the refractive index of the surface, which causes the Angle and intensity of the reflected light to change. By monitoring the changes in reflected light, the binding process and properties of substances can be obtained. SPR biosensors can be widely used in biomedical fields, such as drug screening, disease diagnosis, protein interaction research and so on. Its simple principle, high sensitivity and strong real-time performance make it one of the indispensable tools in modern biological science research. The development direction of SPR biosensor mainly includes improving sensitivity and selectivity, expanding application field, reducing cost and so on. At present, many improved technologies and methods have emerged, such as the introduction of nanomaterials, microfluidic technology, etc., to improve the performance and practicality of sensors. In conclusion, SPR biosensor is an important bioanalytical instrument with broad application prospects and plays an important role in biomedical research and clinical diagnosis.

Tri-band and high FOM THz metamaterial absorber for food/agricultural safety sensing applications

Multi-band based terahertz metamaterial absorber is of great importance in current research and applications because of its ability to achieve multi-band absorption of electromagnetic waves and multi-point matching of detection material information. In this paper, a three-band terahertz metamaterial absorber based on metal split-opening ring is proposed, which produces harp peaks with high Q values due to the resonant response of the metal resonator matched with the surface lattice resonance. By optimizing the structure parameters, the Q-factor is as high as 528 and the FOM value is 153.2, which is better than the FOM of the currently reported absorbers. The sensing performance of absorber as refractive index sensor and thickness sensor is studied, and the results show that it can be used for refractive index sensing and thickness sensing detection of analytes. Finally, five pesticides were simulated and tested. The maximum frequency shift of the absorber was 16ghz when the refractive index changed by 0.02 steps, which proved its ability to recognize different pesticides. The detection of proline solutions of 2–10 g/100 ml proves that the absorber could detect analytes with a refractive index difference of 0.003. These results show that the absorber has high sensitivity, high Q factor, ultra-high FOM, and polarization-insensitive characteristics, which can be used for detecting food/agricultural safety testing and other fields.

Moisture modulated refractive index difference of engineered pore interface for indoor temperature and humidity regulation

Regulation of indoor environments like temperature and humidity consumes enormous energy and brings environmental crises. Therefore, the development of energy-free approaches is critical as it simultaneously improves living comfort and decreases the carbon footprint. Here we report a moisture-modulated strategy to access switchable thermal regulation by tuning solar radiative scattering through manipulation of the refractive index difference (Δn) of a porous surface. This approach is based on a double-layered film containing an upper porous polymer layer and a lower photothermal layer. Via moisture absorption and evaporation, the film performs a reversible thermal switching between solar heating and radiative cooling, allowing efficient space temperature manipulation in the range from + 12.0 to − 8.0 °C. Besides, the moisture-modulated characteristic also offers an opportunity for solar dehumidification by automatically absorbing ambient moisture while mitigating temperature rise. This work bridges a thermal nexus between moisture with solar radiation, while providing a guideline for energy-free indoor environment manipulation.

A regularization algorithm of dynamic light scattering for estimating the particle size distribution of dual-substance mixture in water

Dynamic light scattering (DLS) is a nondestructive, well-established technique for the size characterization of proteins, nanoparticles, polymers, and colloidal dispersions. However, current DLS techniques are only applied to particle groups of single composition due to the limitation of their inversion algorithm. In this study, we propose a particle size distribution inversion algorithm based on the Tikhnonov regularization method that can be applied to the dual-substance particle mixture. The algorithm retrieves the particle size distributions of two substances, respectively, by taking advantage of their refractive index differences. The simulation results reveal that the algorithm has excellent accuracy and stability when the scattering angle is 30°. Instead of the original identity matrix, the first-order difference matrix and second-order difference matrix are used as the regular matrix when utilizing the Tikhnonov algorithm, which obviously improves the anti-interference, accuracy, and stability of the algorithm. Furthermore, the inversion of particle size distribution is carried out at a 0.01%–1% noise level, which shows that the algorithm has an available antinoise ability. Finally, experimental particle size measurements for a mixture of polystyrene beads and toner particles demonstrate that the proposed algorithm is superior to the traditional Tikhnonov algorithm in applicability and accuracy.

Method for a deflection-type refractometer measuring the fringe shift by using linear Fresnelzone plates.

This study describes the design and performance of a deflection-type refractometer based on measuring the fringe shift from the Fresnel diffraction pattern to solve some major limitations of conventional differential refractometers, such as measurement range, resolution, zero balancing, and monitoring analysis. The refractometer apparatus comprises a coherent light source, linear Fresnel zone plate, measuring cell, and image capture device mounted on a movable platform. The distance measurement unit is configured to detect fringe deflection due to the difference in refractive index between the sample and the reference. To achieve this, distance measurements with an accuracy of a few nanometers by using the local frequency method and fringe shift measurement method are quite feasible. The uncertainty in this technique is determined by the smallest change in the longitudinal displacement of the image for which the CCD camera can detect a change in pixel position. The refractive index is obtained with a highly extended measurement range of at least ±0.4R I U and precision of the order of 2×10-4 R I U. A numerical comparison between computer simulation of the diffraction patterns that occur when the linear Fresnel zone plate is illuminated by a plane light traveling parallel to the z axis.

Nanoplasmonic Au:CuO thin films functionalized with APTES to enhance the sensitivity of gas sensors

Carbon monoxide (CO) is a highly flammable and toxic gas to humans and animals, that’s why its detection and monitoring are crucial. A promising technique to develop a robust and cheap gas sensor, operating at room temperature, is Localized Surface Plasmon Resonance (LSPR) sensing. However, LSPR sensing of inorganic gas molecules, such as CO, is challenging due to their extremely small differences in refractive indices. In this work, a nanoplasmonic thin film, composed of Au NPs semi-embedded in a CuO matrix (Au:CuO) was functionalized with a silane self-assembled monolayer (APTES molecule) that enhanced the sensitivity of the film to a mixture of CO (50 ppm) in Argon. Three different concentrations of APTES (0.1 %, 1.0 %, and 5.0 %) were silanized on Au:CuO thin film surface, and all the functionalized Au:CuO thin films showed better sensing results than bare Au:CuO thin film. The functionalized Au:CuO thin film with 0.1 % of APTES revealed the best sensing characteristics. Its sensitivity was almost 3 times higher than that of the unmodified Au:CuO thin film. Au:CuO thin films functionalized with APTES are potentially relevant to developing sensitive and selective LSPR sensors for the detection of inorganic gases such as CO, in harsh environments.

Multi-step-index fiber with a large number of weakly coupled OAM mode groups for IM/DD systems in data centers: design, fabrication, and characterization

Mode division multiplexing (MDM) technique based on weakly coupled few-mode fibers (FMF) is promising to enhance the capacity of short-reach transmission. We design and fabricate a multi-step-index FMF (MSIF), which supports weakly coupled first-order radial orbital angular momentum mode group (OAMl,1 MG) for MDM transmission. We use three layers of core to regulate the minimum effective refractive index difference (min|Δn eff |) between OAMl,1 MG and the adjacent MGs. In experiments, we demonstrate that the fabricated MSIF can support up to OAM6,1 with the interferometric method, and the loss measured by an optical time-domain reflectometer (OTDR) can achieve <0.5 dB/km for the OAMl,1 with an order from |l| = 0 to |l| = 6. The inter-mode-group cross talk (XT) is tested by the power measurement, and the system-level XT after 20 km fiber transmission in the worst case is about −11.1 dB.

Anti-resonance fiber propagating 86 orbital angular momentum modes with high purity for a long distance

Future advances in information transmission technology require better capacities for fiber optics communication. As a new degree of freedom, the orbital angular momentum (OAM) has attracted extensive attention in the field of mode division multiplexing. Herein, an anti-resonance fiber (ARF) is designed with three different materials, SF11, LaSF09, and SiO2, for the negative curvature tube. Systematic analysis and optimization are carried out to determine the number of layers of the negative curvature tubes in the cladding, the number of second-layer cladding tubes, and thickness of the annular area. The finite element analysis software COMSOL is utilized to calculate the effective refractive index difference, dispersion, limiting loss, and other characteristics. The ARF can stably transmit 86 OAM modes in the wavelength range between 1.2 and 2.0[Formula: see text][Formula: see text]m, and the minimum refractive index difference is greater than [Formula: see text], which effectively reduces the mode abridgment. The nonlinear coefficients of the HE[Formula: see text] mode and the OAM purity of HE[Formula: see text] mode are 0.34[Formula: see text]km[Formula: see text][Formula: see text]⋅[Formula: see text]W[Formula: see text] and 99.43%, respectively, thus facilitating stable transmission of OAM modes for a long transmission distance. The anti-resonance fiber has significant application potential in long-distance network information transmission, relay communication, and other communication areas.

Preparation and Properties of Immiscible Poly(lactic acid)/Ethyl Cellulose Bioplastic Blends with Good Transparency and Optical Control by Drawing

In this study we prepared a poly(lactic acid)/ethyl cellulose (PLA/EC) bioplastic blend film by melt pressing after solvent casting and investigated the optical, thermal, and mechanical properties in relation to the structural changes revealed by various microscopies and scattering measurements. Despite the immiscibility of PLA and EC, the blend film exhibited good optical transparency due to the close match in their refractive indices. A second run of differential scanning calorimetry during heating revealed a decrease in the glass transition temperature () and melting point () of PLA with EC although EC had the higher values. Thermomechanical analysis suggested that these decreases were due to the negative pressure generated due to the suppression of PLA shrinkage below and above during cooling. Furthermore, ductile drawing of the blend film (70/30) at an optimal temperature of 70 °C above resulted in a uniform whitening near 100% strain. Delamination at the interface between the PLA matrix and EC domain led to the formation of micrometer-sized oriented voids, which enhanced the refractive index difference in the phase-separated structure, thereby scattering light and achieving the uniform and oriented white blend film.

Controllable reduction of absorbance and two-step reaction for 3D-printed SiC ceramics with micron-level periodic structure

Digital light processing (DLP) is increasingly widely used to manufacture high-precision complex structural ceramic components quickly and efficiently. However, due to the high absorbance of silicon carbide (SiC) micron fine powder and the high refractive index difference between the powder and the photosensitive resin, it is extremely challenging to DLP print SiC with high precision complex structure. Here, the surface of SiC powder was coated with SiO2 nano-layer of different thickness by controllable oxidation coating method, thus realizing the photocurable printing of SiC@SiO2 green bodies with structural precision up to 80 μm. Through the two-step reaction method of carbothermal reduction combined with gas-phase siliconizing (GSI), not only the SiO2 coated layer was effectively removed, but also the reaction-bonded silicon carbide (RB-SiC) ceramics with 80–300 μm periodic structure was successfully realized. Ultimately, the comprehensive performance of the RB-SiC samples is effectively improved by chemical vapor infiltration of silicon carbide (CVI-SiC). It is noteworthy that the maximum elastic modulus and hardness of the ultima SiC specimens (RB-SiC@CVI-SiC) are as high as 394.599 GPa and 50.241 GPa, respectively. Shockingly, the nanomechanical properties of postgenetic RB-SiC bound to initial α-SiC on the cross-section of ultima specimens were much higher than those of CVI-SiC on the surface. This study fills the gap that liquid-phase siliconizing (LSI) or pyrolysis process could not achieve high-performance SiC ceramics with micron-level periodic structure.

MIMO-free OAM-MDM transmission with a ring-core fiber recirculation loop

We experimentally demonstrate the record long-haul orbital angular momentum (OAM) mode-division multiplexed (MDM) transmission over 300-km assisted by a ring-core fiber (RCF) recirculating loop. The recirculation loop consisting of 50-km RCF is controlled mainly by two acousto-optic switches with opposite states, and the signals are cyclically transmitted in the single-span 50-km RCF to achieve long-haul transmission. The RCF features largely separated OAM mode groups, where the effective refractive index difference between adjacent high-order OAM mode groups is larger than 1.0 × 10-3. Due to the low-crosstalk feature of RCF incorporated into fiber optic links, multiple-input multiple-output (MIMO) equalization technology is not used in the OAM MDM system. We transmit 20-Gbit/s quadrature phase-shift keying signals over two high-order OAM modes, and the transmission performance is characterized. The measured average optical signal-to-noise ratio penalties at a bit-error rate of 1.5 × 10-2 are about 2 dB between single OAM mode transmission and OAM modes multiplexing transmission. The obtained experimental results indicate favorable OAM-based MDM transmission performance in a 300-km recirculating loop link.

Chalcogenide GRIN glasses with high refractive index and large refractive index difference for LWIR imaging.

Gradient refractive index (GRIN) materials utilize an internally tailored refractive index in combination with the designed curvature of the optical element surface, providing the optical designer with additional freedom for correcting chromatic and spherical aberrations. In this paper, new GRIN materials suitable for the second (3-5 µm) and third (8-12 µm) atmospheric windows were successfully developed by the thermal diffusion method based on Ge20As20Se60-xTex series high refractive index glasses, where the maximum refractive index difference (Δn) at 4 µm and 10.6 µm were 0.281 and 0.277, respectively. The diffusion characteristics and refractive index distribution of the GRIN glass were analyzed by Raman characterization. Furthermore, the performance of GRIN singlet and homogeneous singlet in the LWIR band (8 µm, 10.6 µm (primary wavelength), 12 µm) was compared, and the results showed that the GRIN singlet had better chromatic aberration correction and unique dispersion characteristics.

Controllable hydrophilic/superhydrophobic patterned coatings for optical information encryption/decryption based on water-triggered opaque to translucent transition

Anti-counterfeiting technologies are crucial for securing the authenticity and proof of commodities, in which the optical information encryption/decryption has attracted extensive attention for its overriding advantages of visibility and convenience. Inspired by the unique transparency transformation phenomenon of Diphylleia grayi petals, a controllable hydrophilic/superhydrophobic patterned coating with water-triggered opaque to translucent transition is proposed through the construction of a superhydrophobic coating, subsequent air plasma etching under a mask, and final hydrophilic modification to introduce stable invisible patterns. The superhydrophobic region exhibits great water repellency with a water contact angle (WCA) at 157°, while the hydrophilic region quickly absorbs water with a WCA at 61°. The patterned coating presents an opaque state for the serious light scattering induced by the rough microstructure and large refractive index difference between the coating and air, while the hydrophilic patterns on the coating transform to translucent after water infiltration for the reduced roughness and close refractive indexes of the coating and water. The information revealing is rapid and reversible, and demonstrates heat and long-term stability and great reusability. The findings conceivably stand out as a new methodology to fabricate controllable superwettable coatings with optical information encryption/decryption capability for application in anti-counterfeiting.

AI aided microfluidic auto continuous separation and sorting of microspheres simultaneously based on their morphological and optical properties

We report a novel method of continuous online microsphere/particle separation and sorting that integrated techniques of microsphere-imaging, microfluidic chip, moving micro-object super-resolution analysis, and AI image recognition into a simple system. It is the first method with the ability to determine the size of moving micro-objects with nanoscale resolution and separate/sort them simultaneously according to their size, shape, and refractive index. In the experiment, the separation and sorting of polystyrene, silica, and PMMA microspheres from the mixture solutions of several different microspheres using a microfluidic device demonstrated that the sorting was accurate and highly efficient and could classify micro-objects with a nanoscale size difference of ∼ 10 nm and a refractive index difference of 10−5. The method is suitable for coupling with various micro-object separation/sorting instruments for different micro-object separations. It can also divide micro-objects either with or without coating.

Effect of femtosecond laser-assisted arcuate keratotomy versus toric intraocular lens implantation on correction of astigmatism in cataract surgery: a systematic review and meta-analysis.

To compare the efficacy of femtosecond laser-assisted arcuate keratotomy (FSAK) combined with non-toric intraocular lens (IOL) implantation versus Toric IOL (TIOL) implantation in correcting corneal astigmatism in cataract patients. Relevant literature was searched in databases including PubMed, Web of Science, Cochrane Central Register of Controlled Trials (CENTRAL), and SinoMed. Data from the included studies were extracted. A meta-analysis was conducted to compare the correction performance of FSAK combined with non-toric IOL implantation and TIOL implantation using postoperative refractive astigmatism, correction index, and uncorrected distance visual acuity (UDVA) outcomes. Publication bias assessment and sensitivity analysis were also performed. Five comparative studies were ultimately included in the meta-analysis. The TIOL group had smaller postoperative refractive astigmatism and a greater correction index compared to the FSAK group. The mean differences in postoperative refractive astigmatism and correction index between the two groups were - 0.19D (95% CI = 0.12 to 0.26, P < 0.01, I2 = 7%) and - 0.09 (95% CI = - 0.18 to 0.00, P = 0.04, I2 = 0%), respectively. We found no statistically significant difference in UDVA between the two groups (95% CI = - 0.01 to 0.11, P = 0.09, I2 = 70%). FSAK combined with non-toric IOL implantation was found to be less effective than TIOL implantation in correcting preoperative corneal astigmatism in cataract patients. The difference in the effectiveness of astigmatism correction between the two surgical methods seems to diminish, as the degree of preoperative corneal astigmatism decreases.

Design and analysis of ultra-large capacity heterogeneous nineteen-core seven-mode fiber

The multi-core few-mode fiber based on space division multiplexing technology is one of the critical ways to address the issue that the current single-mode fiber communication capacity has reached its maximum. However, the energy crosstalk between the cores is an important reason for the deterioration of signal quality. Consequently, this paper designs a nineteen-core seven-mode fiber with more transmission channels, and the auxiliary structures such as trench, high and low refractive index double rings, and air holes can effectively reduce intra-core crosstalk and inter-core crosstalk. After optimization, each core of the nineteen-core fiber can transmit seven LP modes, and the effective refractive index difference between adjacent modes is greater than or equal to 10−3. The optical fiber provides 228 transmission channels for the entire transmission system, the inter-core crosstalk of the highest order LP41 mode is lower than −30 dB/100 km at 1550 nm. Based on the above, the proposed optical fiber has excellent optical properties and can be applied to data centers, optical sensors, high-speed computer communication networks, and other applications.

Inverse design of deformed Sb2Se3 stripes in silicon waveguide for reconfigurable mode converters

Reconfigurable photonic devices integrated with silicon waveguides are important building blocks for future on-chip photonic circuits. In this paper, we focus on the mode order conversion in silicon waveguides with non-volatile reconfigurable capability. Deformed phase change material Sb2Se3 (antimony triselenide) stripes are introduced at the edges of the functional region to provide the refractive index difference required by mode conversions. The shapes of stripes are inversely designed by a gradient-based iterative optimization strategy with 57 (19) iterations for TE0-to-TE1 (TE0-to-TE2) mode converter. The footprint of the functional region is as compact as square center wavelength. In the crystalline phase, TE0-to-TE1 and TE0-to-TE2 mode conversions are realized with conversion efficiencies of 98.5% and 96.3% at a center wavelength of 1550 nm, respectively. While in the amorphous phase, the input TE0 mode directly passes through the functional region with efficiencies of 93.0% and 92.4%, respectively. The output mode can be reconfigured by changing the phase of Sb2Se3 stripes. Moreover, after introducing ±10 nm geometrical deviations to the perfect Sb2Se3 stripe design, corresponding red and blue shifts of conversion efficiency spectra can be observed, and the simulation results reflect the reasonable robustness of the proposed mode converters.

Mid-infrared supercontinuum generation of orbital angular momentum modes based on ring-core As2S3 photonic crystal fiber

In this paper, a wide supercontinuum of multi-order orbital angular momentum (OAM) modes is generated theoretically in the mid-infrared region based on a ring-core As2S3-based photonic crystal fiber (PCF). This PCF supports six OAM modes with two orders and exhibits an ultra-high effective refractive index difference of 10-2 between the vortex modes. After customizing the nonlinear coefficient and dispersion, all the supported OAM modes can be used for wide-band supercontinuum (>3100 nm) generation at low input pulse power of 1000 W. In particular, the supercontinuum of OAM1,1 mode covers a wavelength range from 2860 nm to 6120 nm at −40 dB level. This work has great potentials in the OAM-based mid-infrared source in optical communication and sensor systems.

A Ti: LiNbO3 optical waveguide sensor for measurement of intensive electric field

In this paper, a Ti: LN optical waveguide intensive electric field sensor without metal structure is designed and fabricated. By using the finite element simulation, the refractive index difference Δno and Δne of the waveguide are designed as 0.0105 and 0.0305 respectively when the prediffusion depth d is 5 μm, which results in the static operating point of the sensor is 86.4° when the length L is 45 mm and the prediffusion width w is 10 μm. The simulation results show that when the design of LN substrate is 6 mm (x) × 1 mm (y) × 45 mm (z), the ratio of the external and internal electric fields is 4.216, and the half-wave electric field is 10053 kV/m. The sensor is measured by the power-frequency electric field measurement system, and the half-wave electric field is about 10135 kV/m, and the maximum detectable electric field is about 3041 kV/m.

Compactly integrated polarization insensitive 24-channel variable optical attenuator arrays using silica-based

A 24-channel variable optical attenuator array with a compact size of 15 × 10 mm2 is demonstrated using silica-based waveguides with 2.0% refractive index difference. Asymmetric Mach-Zehnder structures are well optimized to achieve low polarization-dependent loss (PDL) and wide bandwidth. In addition, the power consumption is reduced by optimizing the trench structures. Experimental results show that the power consumption is 160 mW when the attenuation changes by 10 dB. Within the operating voltage range, the PDL is less than 0.7 dB, and the device can operate in the C+L band with a wavelength-dependent loss (WDL) of less than 0.9 dB.