Refractive Index Difference Research Articles

WHITE SPOT LESIONS: DIAGNOSIS AND TREATMENT METHODS

White spot lesions are early caries lesions with a milky white opaque appearance, clearly distinguishable from the surrounding intact enamel due to the difference in refractive index between the intact enamel and the demineralized area. Diagnosing these lesions and treating them early prevents the excessive loss of material in the dental tissue that will occur as the caries progresses. This review is mainly focusing on, the development, diagnosis and management of the white spot lesions.

Fundamental spatial mode high power 808 nm double trench wide ridge waveguide laser

—Lasers operating at a wavelength of 808 nm, with watt-level output power and high beam quality in the fundamental spatial mode, have garnered significant attention due to their potential applications across various fields. Transverse optical confinement in double trench ridge waveguide lasers is determined by the width of the ridge and the refractive index difference between the ridge and trench. In this study, we have designed and fabricated a wide ridge laser operating at 808 nm with high power output and stable fundamental spatial mode based on this principle. The fundamental spatial mode operation was successfully achieved with an 8 μm ridge waveguide laser, producing an impressive output power of 1.3 W. The device exhibits a stable far-field as the current was increased from 0.3 A to 1.8 A. The laser's output power exhibits a 14% reduction with an increase in temperature of 80 °C, demonstrating a decrease rate of only 1.25 mW/°C and a wavelength variation rate of 0.22 nm/°C, indicating low sensitivity to temperature changes.

Contactless and nondestructive evaluation of residual stress distribution in modified and pure HDPE materials using a novel terahertz method and line-scan thermographic technique

Optical-stress properties were always studied at the elastic stage and at wavelengths shorter than terahertz (THz) radiation. Until present, the relationship between plastic strain and refractive index has not been fully understood. In this work, a novel THz method and line-scan thermographic technique are used for quantitative evaluation of the residual stress in the pure HDPE, as well as in the HDPE mixed with 5% by weight of wastepaper plus 5% by weight of chopped basalt as fillers. A new theory considering both influences from the sample thickness and the refractive index difference is proposed, thus allowing to improve the measurement accuracy. For the first time, the stress-optic constant and thermal diffusivity have been applied to characterize the residual stress.. The experiments suggest that, after stretching, the initial isotropic material transits into a material with highly anisotropic optical properties in THz band. This observation is useful when describing the conventional bi-refringence phenomenon. Finally, the residual stress distribution was calculated based on the proposed techniques.

Phase-change behavior of RuSbTe thin film for photonic applications with amplitude-only modulation.

Ge2Sb2Te5 (GST), the most mature phase-change materials (PCM), functions as a recoding layer in nonvolatile memory and optical discs by contrasting the physical properties upon phase transition between amorphous and crystalline phases. However, GST faces challenges such as a large extinction coefficient (k) and low thermal stability of the amorphous phase. In this study, we introduce RuSbTe as a new PCM to address the GST concerns. Notably, the crystallization temperature of the amorphous RuSbTe is approximately 350 °C, significantly higher than GST. A one-order-of-magnitude increase in the resistivity contrast was observed upon phase transition. The crystalline (0.35-0.50eV) and amorphous (0.26-0.37eV) phases exhibit relatively small band gap values, resulting in substantial k. Although RuSbTe demonstrates a k difference of approximately 1 upon crystallization at the telecommunications C-band, the refractive index (n) difference is negligible. Unlike GST, which induces both phase retardation and amplitude modulation in its optical switch device, RuSbTe exhibits amplitude-only modulation. This study suggests that RuSbTe has the potential to enable new photonic computing devices that can independently control the phase and amplitude. Combining RuSbTe with phase-only modulators could open avenues for advanced applications.

Ultra-high sensitivity weak magnetic field detecting magnetic fluid surface plasmon resonance sensor based on a single-hole fiber

An ultra-high sensitivity weak magnetic field detecting magnetic fluid surface plasmon resonance (SPR) sensor based on a single-hole fiber (SHF) is proposed for detecting weak magnetic fields. The sensor is constructed with a single-hole fiber in which an exclusive air hole in the cladding is embedded with a metal wire and filled with a magnetic fluid (MF) to enhance the magnetic field sensitivity. The effects of the structural parameters, embedded metals, and refractive index difference between the core and cladding on the magnetic field sensitivity and peak loss are investigated and optimized. The sensitivity, resolution, figure of merit (FOM), and other characteristics of the sensor are analyzed systematically. The numerical results reveal a maximum magnetic field sensitivity of 451,000 pm/mT and FOM of 15.03 mT-1. The ultra-high magnetic field sensitivity renders the sensor capable of detecting weak magnetic fields at the pT level for the first time, in addition to a detection range from 3.5 mT to 17 mT. The SHF-SPR magnetic field sensor featuring high accuracy, simple structure, and ease of filling has immense potential in applications such as mineral resource exploration as well as geological and environmental assessment.

Design of photonic crystal fiber supporting 190 orbital angular momentum modes with low nonlinearity coefficient

A new photonic crystal fiber is proposed for the transmission of more orbital angular momentum modes with a rectangular air hole arrangement to increase the cladding air-filling rate. The results reveal that the fiber can support 190 orbital angular momentum modes in the C+L band, with the topological charge ordering up to 48, and the effective refractive index difference between adjacent eigenmodes is above 10−3. The effective mode area of all the eigenmodes is larger than 208.02 μm2, the nonlinearity coefficient is less than 0.43 W−1∙km−1, the confinement loss reaches up to 10−12-10−8 dB/m, the dispersion is flat and the minimum dispersion change is 3.15 ps∙nm−1∙km−1, with mode purity greater than 97.4%. Compared to existing typical orbital angular momentum transmission photonic crystal fibers, this fiber can support more orbital angular momentum modes for most purposes with lower nonlinearity coefficient, higher mode purity, better propagation characteristics but simpler structure. The highest nonlinearity coefficient is reduced by at least 0.3 W−1∙km−1 compared to existing typical orbital angular momentum transmission photonic crystal fibers. The effect of fabrication errors on the transmission quality of orbital angular momentum modes is also discussed, and the results reveal that the effect on mode transmission quality is small at 1–2% variations of air holes. Therefore, this photonic crystal fiber is promising in high-capacity communication systems.

Incorporating boron carbide into fused silica imparts multiple mechanisms to facilitate vat photopolymerization

Rapid manufacturing of complex-shaped ceramic components has long been a pressing issue in the aerospace industry. Recent progress in this direction takes advantage of additive manufacturing, by employing vat photopolymerization (VPP) followed by sintering. Here we demonstrate a new recipe/protocol that enables the VPP route to deliver silica products of high relative density as well as high strength. This is achieved by incorporating 2.5 wt% of boron carbide (B4C) into the fused silica slurry, which offers beneficial effects in multiple fronts. During the VPP process, the added black B4C, together with the refractive index difference between the two components in the mixture, effectively increased the light absorbance. Upon sintering, the boron oxide produced by the oxidation of B4C played the role of a sintering aid. The boron oxide also helped to suppress the crystallization of the amorphous silica and therefore the formation of cracks. As a result, the overall quality (forming precision, density, strength and dielectric constant) of the product surpasses by far those prepared previously via VPP-sintering. In particular, the flexural strength reached 60.7 MPa, a factor of 2.5 better than the previously reported highest value. Extending the success above further, we have manufactured a complex-structured silica radome, as a demonstration of the high-quality products achievable for practical applications.

A low crosstalk seven-core five-mode fiber for high density transmission and large capacity communication

We propose a seven-core five-mode fiber with air hole-assisted and high refractive index ring structure, and it can be fabricated by the stack-and-draw technique. The air hole auxiliary structure can significantly restrain the energy coupling between cores, and the high refractive index ring structure can meet the requirements of low intra-core crosstalk (XT) by improving the effective refractive index difference (Δn eff ) between adjacent modes. Through analyzing the influence of the number and arrangement of air holes on inter-core XT and effective mode field area (A eff ), it can be achieved the results that the inter-core XT is less than −44 dB/100 km and all the A eff values of LP modes are greater than 100 μm2 in the seven-core five-mode fiber when the wavelength is 1550 nm and the bending radius (R) is 80 mm. At the same time, the Δn eff between LP21 and LP02 mode can be controlled to 1.3 × 10−3 by adjusting the parameters of the high refractive index ring. In addition, the relative core multiplexing factor (RCMF) of the seven-core five-mode fiber is as high as 88.34. The simulation results show that the seven-core five-mode fiber has high spatial density and is suitable for the communication system with multi-channel and long-distance transmission.

Narrowing of band gap and decrease in dielectric loss in La1-xSrxMnO3 for x = 0.0, 0.1, and 0.2 manganite nanoparticles

Polycrystalline compounds of lanthanum strontium manganite (La1-xSrxMnO3, LSMO) are widely used in electronic storage devices due to their minimal losses and electronic charge transport properties. In this study, we investigated how varying substitutions of Sr2+ for values of x = 0.0, 0.1, and 0.2 affected the tuning of the optical band gap and dielectric losses in La1-xSrxMnO3 nanoparticles. Synthesized samples were structurally analyzed via X-ray diffraction. A rhombohedral R3¯c crystal structure was confirmed for all prepared samples; crystallite size ranging from 15 nm to 20 nm was estimated along with other lattice parameters. Polygonal or hexagonal-like morphology was revealed by field emission scanning electron microscopy, with a moderate size distribution of nanoparticles affected by thinner grain boundaries in doped LSMO. Energy dispersive spectroscopy was employed to confirm the elemental composition of each compound, and the infrared spectrum indicated bonding in the fingerprint region It was observed that there was a significant reduction in the optical band gap, which was measured using ultraviolet spectrometer absorption data. The band gap decreased from 4.34 eV to 4.11 eV. This reduction was found to be related to the difference in refractive index, which was calculated using both Moss and Herve–Vandamme relations. In parallel, frequency-dependent dielectric analysis revealed that frequency was proportional to the increase in Sr content, inversely affecting dielectric loss. Moreover, the AC conductivity of the prepared samples increased with the rise in Sr content, as described by Johnscher’s universal power law in the region of high frequency.

Customized linear refractive index GRIN prepared by rapid sintering of multilayer chalcogenide glass powders

AbstractGradient refractive index (GRIN) lenses have recently become a hot topic in compact imaging and achromaticity. Current research focuses on exploiting GRIN materials and upgrading the preparation technology. In this study, infrared (IR) GRIN materials were successfully prepared by spark plasma sintering of multilayer chalcogenide glass (ChGs) powders. ChGs powders were derived from the Ge20Se80‐xTex series glasses (x = 0–28 mol%) with a maximum refractive index difference (Δn) of 0.25. The similar glass transition temperatures (ΔTg < 10°C) promote efficient sintering of multilayer powders. Six‐, eight‐, and ten‐layer powders of different compositions were rapidly sintered with a thickness of 600, 300, and 200 µm per layer, respectively. Such tiny layer thickness enables the GRIN materials to exhibit nearly linear refractive index variation. Energy dispersive spectroscopy line scans well characterized the gradient variation of GRIN. The maximum deviation of the refractive index gradient from the fitted target line was only ± 0.016 for the 10‐layer GRIN. The sintered GRIN shows excellent IR transparency, which is of great interest for mid‐wave and long‐wave infrared imaging.

Performance of Ce:YAG-MgO composite ceramics as high-power LED phosphor densified by non-reactive sintering

A novel white light converter has been successfully synthesized using a non-reactive sintering process to afford a fully densified Ce:YAG-MgO composite ceramic phosphor with high wavelength conversion efficiency under excitation at 450 nm. The composite obtained by HIP (hot isostatic pressing) treatment at 1080 ºC has no residual pores and the XRD (X-ray diffraction) analysis shows that there are no secondary phases other than Ce:YAG and MgO, moreover, the EDS (Energy-dispersive X-ray spectroscopy) analysis indicates no interdiffusion at the Ce:YAG-MgO contact interface. The thermal conductivity of 5–7.5 wt% Ce:YAG-added MgO composites is over 40 W/mK, nearly reaching the theoretical value. Due to the synergetic effect of “the difference in refractive index between MgO and Ce:YAG” and “MgO matrix with strong birefringence”, the excitation light (450 nm) is multiply scattered inside the composite medium, which provides efficient excitation even in a thin medium, resulting in the photoluminescence intensity that is 2.6 times higher than that of transparent Ce:YAG ceramics. This innovative white light converter combines a highly thermal conductive MgO matrix and Ce:YAG phosphor with high emission intensity.

Graphene‐based transparent and tunable plus‐shaped refractive index sensor for detecting waterborne bacteria

AbstractWaterborne bacteria cause many dangerous diseases as well as several health‐related issues hence detection of them is a global challenge today. A plus‐shaped graphene sensor to detect waterborne bacteria is presented in this paper. The detection mechanism is based upon the refractive index difference between waterborne bacteria sample and pure water which causes a change in resonance peak in the transmittance graph. The use of graphene material increases the sensitivity and also gives the tuning behavior by changing its potential. The effect of various parameters such as sensitivity (S), Q factor, figure of merit (FOM), and detection limit are discussed in the paper. The maximum values Q factor and FOM are 13.46 and 4.03 RIU−1 respectively. The minimum detection limit is 0.277 RIU. The proposed sensor exhibits the highest sensitivity of 255 GHz/RIU at the optimum condition which is comparably higher than previously published papers on biosensors. The proposed design with its highest sensitivity and good detection parameters can be helpful in detecting waterborne bacteria.

Low crosstalk six-core five-mode fiber with high refractive index rings and air trench

A novel six-core five-mode fiber composed of an air trench and high refractive index ring is proposed in this paper. Numerical analysis shows that the fiber can stably transmit five LP modes in the C + L band. The effective refractive index difference of the five LP modes at 1.55 μm is more significant than 1.4 × 10-3, which is conducive to the independent transmission of the modes. The inter-core crosstalk of the fiber is less than -95 (dB / 100km). Therefore, the fiber can be well used to build a large-capacity optical fiber transmission system.

Interactive calculation of light refraction and caustics using a graphics processor

While modern rendering systems are effective at modeling complex light paths in complex environments, rendering refractive caustics still takes a long time. Caustics are light patterns that occur when light is refracted and reflected from a surface. Due to the sharp density distribution of these mirror events, rendering algorithms mainly rely on direct sampling of the bidirectional scattering distribution function on these surfaces to plot trajectories. This requires many calculations. Photonic maps are also used. However, there are problems limiting the applicability of caustic maps. Since each photon in the photon buffer must be processed, therefore, one has to choose between a strongly underestimated caustic sampling and a large decrease in speed in order to use a sufficient number of photons for caustics in order to obtain high-quality images. Complex mirror interactions cause oversampling in bright focal areas, while other areas of the caustic map remain under-selected and noisy. At the same time, speed takes precedence over realism in most interactive applications. However, the desire to improve the quality of graphics prompted the development of various fast approximations for realistic lighting. This paper presents a combined method for visualizing refraction of light and caustics using reverse integration for illumination and direct integration for viewing rays. An approach is used for simultaneous propagation of light and for tracking rays in volume and, therefore, it does not require storing data of an intermediate volume of illumination. In the implementation of the method, the distance between the light planes is set to one voxel, which provides at least one sample per voxel for all orientations. The method does not use preliminary calculations; all rendering parameters can be changed interactively. As a result, using the proposed method, it is possible to create plausible approximations of complex phenomena such as refractions and caustics. The effect of refraction on the shadow is shown. Complex light patterns are demonstrated due to the curved geometry of the objects. The visualization results show the importance of refraction for the appearance of transparent objects. For example, distortions caused by refraction and refraction at the interface between media. The difference in refractive indices between individual media causes a complex interaction between light and shadow areas. It is shown how refraction and caustics improve the visualization of functionally defined objects by providing additional information about shape and location.

Enantioselective control in chiral crystallization of ethylenediamine sulfate using optical trapping with circularly polarized laser beams.

In this study, we conducted successful experiments on ethylenediamine sulfate (EDS), an organic compound, to investigate its enantioselectivity in chiral crystallization. We employed optical trapping with circularly polarized laser beams, using a continuous wave laser at 1064nm. By focusing the laser at the air-solution interface of a heavy water-saturated EDS solution, the formation of sub-micrometer-sized chiral EDS crystals was verified. Two generated enantiomorphs (d-crystal and l-crystal) were identified by the rotating analyzer method. The enantioselectivity in the chiral crystallization of EDS was assessed through 30 to 60 times experiments conducted under various conditions of laser powers and polarization modes, utilizing the count of generated crystals for each enantiomorph in the evaluation. Circularly polarized lasers at a specific power created an imbalance in the generation probability of the enantiomorphs, resulting in crystal enantiomeric excess values of 23% and -30%. The enantioselectivity mechanism was explored from two perspectives: refractive index differences of two enantiomorphs and 3D helical optical forces. Study of the thermodynamic mechanism was insufficient to explain the outcomes. Conversely, the 3D helical optical force mechanism revealed that the forces acting on EDS clusters in solution induced helical fluid motion, driving EDS nucleation, with the helicity of fluid motion determining the crystal's chirality. This approach will present new insights into chirality in industrial and research fields, with potential applications in regard to improving optical resolution and addressing the origin of homochirality.

All‐Dielectric High‐Q Dynamically Tunable Transmissive Metasurfaces

AbstractActive metasurfaces, which are arrays of actively tunable resonant elements, can dynamically control the wavefront of the scattered light at a subwavelength scale. To date, most active metasurfaces that enable dynamic wavefront shaping operate in reflection. On the other hand, active metasurfaces operating in transmission are of considerable interest as they can readily be integrated with chip‐scale light sources, yielding ultra‐compact wavefront shaping devices. Here, designs for all‐dielectric low‐loss active metasurfaces which can dynamically manipulate the transmitted light wavefront in the near‐infrared wavelength range are reported. The active metasurfaces feature an array of amorphous silicon (a‐Si) pillars on a silica (SiO2) substate, which support resonances with quality factors (Q‐factors) as high as 9800. The high‐Q resonance dips observed in transmission can be transformed into transmission resonance peaks by positioning a‐Si pillar resonators at a prescribed distance from a crystalline Si substrate. The design of metasurface geometry with realistic interconnect architectures that enable thermo‐optic dynamic beam switching with switching times as low as 7.3 µs is reported. Beam switching is observed for refractive index differences between neighboring metasurface elements as low as 0.0026. It is shown that the metasurface structures with realistic interconnect architectures can be used for dynamic beam steering.

Observation of Visible Upconversion Luminescence of Soft Glass Multimode Fibers

This research investigates the visible upconversion luminescence which is induced by multiphoton absorption of soft glass fiber defects. The study of this phenomenon has thus far been restricted to standard silica fibers. We observed the emission of green and cyan light as a consequence of fiber material ionization. We investigate both the commercial ZBLAN step index and in-house-made tellurite nanostructured graded-index fibers. For the latter, the analysis of the luminescence signal permits us to determine the core and cladding refractive index difference. Upconversion luminescence is a powerful tool for characterizing soft glass fibers and a promising platform for innovative photonic technologies and mid-IR applications.

Remote-controllable refractive-index-sensitive plasmonic waveguide and rake-like switch: designs and FDTD simulations

A refractive-index-sensitive plasmonic waveguide, whose transmission characteristics could be controlled remotely by a rake-like switch design, is theoretically studied in the reported work. The distance from the remote control unit to the bus waveguide is more than 0.25 μm, and it still possesses great efficiency even when the distance is increased to 0.535 μm. The switch basically contains two main sections. The first is on the bottom and next to the bus waveguide which functions as a plasmonic resonator that can induce localized surface plasmon resonance (LSPR) and restrict wave propagation at corresponding resonant frequency. The second is on the top and far away from the bus waveguide which functions as a remote controller that can modulate LSPR frequency in the first section. The refractive-index-dependent transmission spectra of this filter were simulated using finite-difference time-domain method. The results have shown that even at a distance as far as 0.5 μm, the ON/OFF switching of the wave propagation in a bus waveguide can still be modulated by adjusting the refractive index of a remote rectangular controller. With only 0.08 difference in refractive index, it could be obtained an on–off switching ratio of 18.7, 20.4 and 25.7 respectively for different waveguides at visible and near infrared wavelength, which shows great potential applications in refractive index sensors and remote-controllable band-stop filters.

Design and fabrication of asymmetric Mach-Zehnder interferometers based on EpoClad and EpoCore strip waveguides

Integrated polymeric optical interferometers offer the possibility of developing sensors with low cost, scalability, and easy integration. Although they are not yet competitive with inorganic materials in terms of sensitivity, they have good biocompatibility in general, and suitable designs may provide sufficient sensitivity for biosensing. A new design for integrated Mach-Zehnder interferometers based on asymmetric arms with different widths has been proposed and experimentally demonstrated, avoiding the need for additional fabrication steps for an interaction window where biosamples are placed. The basic sensory principle is built upon the non-zero variation in the difference of the effective refractive index between the two arms due to their different dimensions, causing a phase variation in the output signal. In this work, we present a design optimization method and fabrication results by e-beam lithography for integrated asymmetric Mach-Zehnder interferometers based on strip waveguides made from EpoClad and EpoCore polymers. The operation wavelength was set to 650 nm. The optimization algorithm is based on open-source mode-solver simulations that return the optimal fabrication dimensions of the interferometer, avoiding high-order modes and enhancing single-mode confinement.

Comparative Analysis of Physicochemical Properties of Oils from Groundnut, Melon, Watermelon and Orange Seeds

This study analyzed and compared the physicochemical properties of oils produced from groundnut, melon, watermelon and orange seeds. The moisture content, saponification value, iodine value, peroxide value, acid value, free fatty acid, ester value, refractive index, viscosity, density, specific gravity, cloud point, pour point, flash point and fire point of the oils were analyzed. There were no significant differences in iodine value, peroxide value, refractive index, viscosity, specific gravity, cloud point, pour point, flash point and fire point, while there were significant differences in the moisture content, saponification value, acid value, free fatty acid, ester value, and density, The results revealed that these oils contain low fatty acid value and they are good sources of edible oil as they have low acid value. These oils also have great potentials as industrially promising oils, with their high saponification and iodine values, they will be good raw materials for bio-lubricant production and for a variety of industrial applications.