Evanescent Field Research Articles

UV photosensitized N-CQDs@In2O3 ordered porous film elaborated optical fiber acetone gas sensor with ppb-level at room temperature

An optical fiber acetone gas sensor based on N-CQDs@In2O3 porous ordered thin film is proposed. The probe adopts the hollow malposition structure (HMS) to excite the evanescent field on the surface of hollow-core fiber (HCF). N-CQDs@In2O3 porous and ordered thin film was formed on the surface of optical fiber after calcining polystyrene (PS) microspheres at high temperature. The experimental results reveal the ultraviolet (UV) sensitization function for the proposed sensor at room temperature. The enhanced sensitivity is 7.1 pm/ppm, which is ∼5.9 times of the spiritual density of unsensitized sensor. In addition, the sensor has a limit of detection (LOD) of 500 ppb and excellent time response characteristics (response time 6.2 s and recovery time 7.1 s). The sensitization mechanism of N-CQDs to In2O3 is explained by the results of the universal density function (DFT). The frontier electron orbital studies show that N-CQDs@In2O3 has more abundant electron clouds. The good moisture resistance enables its stable performance in humid environment. UV sensitization is an effective way to improve the sensitivity of optical fiber gas sensor, which is of great significance for detecting the acetone gas with ultra-low concentration.

Sensing of lactose by graphitic carbon nitride/magnetic chitosan composites with surface plasmon resonance method

A simple technique was used to create a composite material made of graphitic carbon nitride supported on magnetic chitosan (g-C3N4/MNP/CS). This substance was employed in the structure of a surface plasmon resonance (SPR) lactose biosensor as a modifier for a thin layer of gold and as a support for the covalent stabilization of cellobiose dehydrogenase. The Finite-Difference Time-Domain (FDTD) approach was used to mimic the sensor's evanescent field in order to examine the SPR behavior. Additionally XRD and SEM techniques were used to examine the shape of MNPs/CS/g-C3N4 and the intended sensor's SPR behavior. It can be used in the food industry, with a detection limit of 5 μM and a linear range of 0.01–100 mM‏ The biosensor is extremely sensitive, demonstrating its accuracy in lactose detection.

Coupling package and WGM resonator filled with Terfenol-D for magnetic field sensing and tuning

In this work, we proposed a whispering gallery mode (WGM) resonator filled with Terfenol-D (WGMRFT), which could be applied to magnetic field sensing and tuning. We used a hollow quartz rod to fabricate the resonator, and then filled it with Terfenol-D to create a magnetic field-sensitive device. The WGM of the resonator were excited using a tapered fiber evanescent field. As the external magnetic field increased, the WGM resonant spectrum of the resonator shifted toward the short wavelength direction. The sensitivity of the resonator is −3.05 pm/mT. The structure has many advantages, such as simple structure, low cost and easy operation. In addition, we have demonstrated a resonator coupling and packaging device, using this device to adjust the coupling state of the resonator within a certain range. The package demonstrated good repeatability and reversibility in magnetic field measurement experiments. This lays the foundation for the application of millimeter-scale large WGM resonators.

Surface plasmonic Au nanoparticles assisted CuO nanorods for broadband diverse ultrafast pulse generation

In virtue of the local surface plasmon resonance (LSPR) properties of metal nanoparticles to enhance the nonlinear optical response of the material, we successfully embed small-size Au nanoparticles into CuO nanorods. Then, theoretical and experimental methods verify that the assistance of ultrafast plasma response enhances the light-matter interaction. The LSPR characteristics and evanescent field distribution of the Au-CuO saturable absorber on the tapered fiber are studied by the finite element simulation method (FEM). By utilizing the Z-scan technology and twin-balanced detector system, excellent nonlinear optical (NLO) properties of the Au-CuO nanorods are demonstrated. Subsequently, depending on the remarkable nonlinear saturable absorption effect of Au-CuO, multiple operating states such as Q-switched, conventional soliton, double-subpulse soliton cluster, and noise-like pulse mode-locking are achieved in the erbium-doped fiber ring cavity at 1.5 μm. In addition, dual-wavelength mode-locking pulses with the center wavelengths of 1031 nm and 1035 nm are realized in the ytterbium-doped fiber ring cavity. This work describes an effective strategy to improve the NLO properties of CuO nanorods and indicates the great potential of Au-CuO in pulsed fiber lasers, opening a path for its application in ultrafast photonics and optoelectronics.

Hump-shaped seven-core fiber-based WaveFlex biosensor for rapid detection of glyphosate pesticides in real food samples.

At present, pesticides are widely used in the cultivation of crops. Glyphosate is widely used in many pesticides. Glyphosate ingestion can cause a series of health problems. Therefore, this paper proposes to use localized surface plasmon resonance (LSPR) technology to develop a WaveFlex biosensor (plasma wave-based optical fiber sensor) to detect glyphosate concentration in pesticides. The evanescent field is improved by using the fusion of seven-core fiber and single-mode fiber and the tapering of the sensing area to improve the sensing performance. The gold nanoparticles (AuNPs) are used to excite the LSPR effect. Multi-walled carbon nanotubes (MWCNTs) and cerium oxide nanorods (CeO2-NRs) are used to increase the surface area and promote the adhesion of the enzyme. The sensitivity of the sensor is 137.7 pm/µM in the range of 0-60 µM glyphosate concentration, and the limit of detection (LoD) is 1.94 µM, which has good performance in compared to the existing biosensors. Subsequently, the sensor was tested for reusability, reproducibility, selectivity, stability, and excellent results were obtained. Finally, the sensor is tested on real samples, and the results show that it can be applied in practical applications. The test findings demonstrate that the sensor has a great deal of potential for use in glyphosate content detection in food samples.

Humidity sensing by tailoring light absorption of SiO2/bromophenol blue (BPB) thin film on optical fiber

The fabrication of an evanescent wave fiber optic humidity sensor based on bromophenol blue (BPB) doped SiO2 thin film was demonstrated, modulating in light intensity. The sensing film was coated on a fiber core via a single-step dip coating method, followed by sol-gel processing of the precursor. A good exponential relationship was established between output light intensity and relative humidity. The sensor exhibited a high sensitivity and fast response and recovery, as well as low hysteresis, good stability and repeatability. Adsorption of ambient water triggered a ring-opening reaction of BPB, which enhanced light absorption of the sensing film significantly and affected the transmission of the evanescent wave.

Evanescent Field Applicator for Contactless Microwave Breast Diagnostics in Air

Evanescent Field Applicator for Contactless Microwave Breast Diagnostics in Air

Investigation of Structural, Electronic, and Optical Characteristics of a Novel Perovskite Halide, Mg3AsCl3, for Electronic Applications

In the present research article, the structural, electronic, and optical characteristics of a novel perovskite halide, Mg3AsCl3, for a broad range of applications are thoroughly investigated. The characteristics of Mg3AsCl3 perovskite are investigated via the use of the generalized gradient approximation (GGA), Perdew–Burke–Ernzerhof and Heyd–Scuseria–Ernzerhof (HSE06) functionals, which are employed in conjunction with the linear combination of atomic orbital calculator. The structural, electrical, and optical characteristics of the material are investigated using density‐functional theory. In this study of the electronic characteristics, it is found that Mg3AsCl3 exhibits an indirect energy bandgap of 2.49 eV with GGA and 3.54 eV with HSE06. The complex band structure exhibits characteristics that indicate the presence of evanescent waves, which are characterized by a layer separation of 5 Å. The report in this research presents reflectivity values of 0.06328 and 0.02971 with GGA and HSE06 functionals, respectively. The reported values of the extinction coefficient are 3.36487 × 10−5 and 2.07389 × 10−5 calculated with GGA and HSE06 functionals. The value reported for the real dielectric function Re[ε] is 2.79625 with GGA and 2.00658 with HSE06. Overall, in these findings, an overview is given that Mg3AsCl3 holds potential as a candidate for use in a wide range of electronic device applications.

Influence of black phosphorus structural variations for soliton and noise-like pulse generations in an erbium-doped fiber laser

We demonstrate black phosphorus (BP) with structural variations of layers (Ls) and quantum dots (QDs) blended with polydimethylsiloxane (PDMS) spin-coated tapered fiber as a light absorbing material for conventional soliton (CS) and noise-like pulse (NLP) generations. Interaction of the evanescent field leads BP materials to exhibit saturable absorption characteristics, with measured modulation depths of 3.50% and 2.12%, respectively. When integrated into an erbium-doped fiber laser cavity, both saturable absorbers (SAs) generated CS pulses initially with durations of 836 fs (BPLs/PDMS-SA) and 1.11 ps (BPQDs/PDMS-SA). At higher pump powers, the pulses switched to NLP with double-scale autocorrelation traces of 283 fs spike on 50 ps pedestal (BPLs/PDMS-SA) and 184 fs spike on 65 ps pedestal (BPQSs/PDMS-SA) due to the optical limiting properties of BP materials. These versatile findings facilitate the potential opportunities of BP-based photonic devices for next generation of ultrafast fiber laser technology with compact and dual functionality.

Converting evanescent waves into propagating waves by hyper-hemi-microsphere.

Hyper-hemi-microspheres (HHMS) have shown promise in enhancing super-resolution imaging when combined with conventional optical microscopy. To offer actionable guidance for optimizing HHMS and hold broad applicability in the field of super-resolution imaging, the mechanism underpinning the enhanced imaging facilitated by HHMS is revealed by deriving the conversion and transmission conditions for evanescent waves. This is achieved by elucidating the intricate interplay between evanescent wave conversion and factors including refractive index, thickness, and surroundings of HHMS. Using the finite-difference time-domain (FDTD) method, influences of various HHMS properties on the conversion and transmission process are analyzed in detail. To fully harness the potential of HHMS in super-resolution imaging, the immersion conditions are elucidated.

Time Refraction and Time Reflection above Critical Angle for Total Internal Reflection.

We study the time reflection and time refraction of waves caused by a spatial interface with a medium undergoing a sudden temporal change in permittivity. We show that monochromatic waves are transformed into a pulse by the permittivity change, and that time reflection is enhanced at the vicinity of the critical angle for total internal reflection. In this regime, we find that the evanescent field is transformed into a propagating pulse by the sudden change in permittivity. These effects display enhancement of the time reflection and high sensitivity near the critical angle, paving the way to experiments on time reflection and photonic time crystals at optical frequencies.

Vector magnetic field sensor based on coreless D-shaped fiber and magnetic fluid.

A vector magnetic field sensor based on a ferrofluid-encapsulated coreless D-shaped fiber is proposed and demonstrated. The core of the singlemode fiber (SMF) is completely removed by fiber polishing technology, and the remaining part transformed into a multimode interference (MMI) waveguide. The exposed side-polishing plane enable the evanescent field to interact with surrounding magnetic fluid (MF). Relying on the non-circularly symmetric geometry of the coreless D-shaped fiber and the MF refractive index modulation by the orientation and intensity of the applied magnetic field, vector magnetic field sensing is achieved. The magnetic field response characteristics of the coreless D-shaped fibers with different residual thicknesses (RTs) are investigated. The experimental results show that a reduced RT yields enhanced sensitivity, and the magnetic field intensity sensitivity reaches -0.231 nm/mT and -0.483 dB/mT at a RT of 42.7 µm. The developed coreless D-shaped fiber sensor exclusively utilizes SMF, thereby offering a cost-effective scheme for the fabrication of vector magnetic field sensors.

Graphene Thermal Infrared Emitters Integrated into Silicon Photonic Waveguides.

Cost-efficient and easily integrable broadband mid-infrared (mid-IR) sources would significantly enhance the application space of photonic integrated circuits (PICs). Thermal incandescent sources are superior to other common mid-IR emitters based on semiconductor materials in terms of PIC compatibility, manufacturing costs, and bandwidth. Ideal thermal emitters would radiate directly into the desired modes of the PIC waveguides via near-field coupling and would be stable at very high temperatures. Graphene is a semimetallic two-dimensional material with comparable emissivity to thin metallic thermal emitters. It allows maximum coupling into waveguides by placing it directly into their evanescent fields. Here, we demonstrate graphene mid-IR emitters integrated with photonic waveguides that couple directly into the fundamental mode of silicon waveguides designed to work in the so-called "fingerprint region" relevant for gas sensing. High broadband emission intensity is observed at the waveguide-integrated graphene emitter. The emission at the output grating couplers confirms successful coupling into the waveguide mode. Thermal simulations predict emitter temperatures up to 1000 °C, where the blackbody radiation covers the mid-IR region. A coupling efficiency η, defined as the light emitted into the waveguide divided by the total emission, of up to 68% is estimated, superior to data published for other waveguide-integrated emitters.

Insights into Photopolymerization at the Nanoscale Using Surface Plasmon Resonance Imaging.

Near-field photopolymerization (NFPP) driven by surface plasmon resonance has attracted increasing attention in nanofabrication. This interest comes from the nanometer-scale control of polymer thickness, due to the confinement of the evanescent wave within a highly restricted volume at the surface. In this study, a novel approach using a multi-spectral surface plasmon resonance instrument is presented that gives access to real-time images of polymer growth during NFPP with nanometer sensitivity. Using the plasmonic evanescent wave for both polymerization and real-time sensing, the influence of irradiance, concentration of dye, and initiator are investigated on the threshold energy and kinetics of NFPP. How oxygen inhibition in the near field strongly affects photopolymerization is highlighted, more than in the far field.

All-fiber light intensity sensor employing a three-core fiber taper integrated by magnetic fluids

An all-fiber optic light intensity sensor employing a three-core fiber (TCF) taper integrated by magnetic fluids (MFs) is proposed and fabricated. The three-beam interference and evanescent field characteristic of the TCF taper are combined with the laser-generated photothermal effect of the MFs for the first time. The effect of irradiation laser intensity on the interference spectrum of the proposed sensor is investigated experimentally. According to the experimental results, the interferential transmission spectrum is susceptible to the irradiation laser intensity. Under 473 nm laser irradiation, the maximum laser intensity sensitivity reaches −1.64425 nm/(mW/mm2). Moreover, the modal coupling processes of the TCF before and after tapering are investigated experimentally and by simulation. The proposed sensor is attractive because of its sensitive light response, simple structure, easy fabrication, and compact size. This work gives a significant reference for the manufacture and application of optically controlled microfluidic devices integrated by MFs.

Dynamic control of optical skyrmions in cylindrical waveguide

In recent times, the optical skyrmions have received an increasing amount of interest owing to its applications in optical manipulation, super-resolution imaging and microscopy, quantum technologies. However, few studies are focused on the dynamic control of optical skyrmions. It is found that Neel-type photonic skyrmions were discovered in evanescent electromagnetic waves. Here, we find the Bloch-type skyrmions in a three-dimensional cylindrical waveguide. By modulating the amplitude ratio of two incident vortex beams, the new types of skyrmions such as Twisted-type skyrmions and Planar-type skyrmions can be found. Further more, we have also achieved arbitrary modulation ratios of internal spin components. It is believed that our findings greatly enrich the types of photonic skyrmions and provide a method to freely control the photonic skyrmions.

A high Q-factor evanescent field fiber sensor coated with C-MWCNT for label-free HPV determination

A high Q-factor evanescent field fiber sensor is designed based on a fiber Bragg grating (FBG) coated with carboxylic multi-walled carbon nanotubes (C-MWCNT). In a high-reflectivity FBG, multiple cladding modes are stimulated as the forward-moving guided mode within the core of the multimode fiber is coupled to the FBG’s reverse-moving guided mode within the cladding. Our evanescent field fiber sensor is highly sensitive to the refractive index without altering the architecture of fiber or deviating from the conventional process of fabricating fiber gratings. The proposed sensor exhibits a full-width at half maximum (FWHM) of 78 pm and a Q-factor of 1.9 × 104 for its standard cladding-mode resonance, outperforming the majority of reported evanescent field fiber sensors in these parameters. Furthermore, by coating C-MWCNT on the fiber sensing surface, our sensor has been demonstrated to combine multiple functions into one, such as label-free determination of human papilloma virus (HPV) DNA sequences, the measurement of different concentrations, and mispairing discrimination. The sensor design put forward offers a compelling technique within the realm of optical fiber sensing for refractive index and label-free biomolecule detection.

Controllable optical tweezer and spanner in evanescent fields via a single plasmonic metasurface

A dual-functional plasmonic metasurface is proposed to realize trapping and rotation of microparticles in evanescent fields by simply changing the polarization of incident light. The metasurface is constituted with subwavelength rectangular nanoslit that is perforated in an Au film on the glass substrate. Simulated near-field intensity distributions show that surface plasmon vortex with designed topological charge and focused point with enhanced intensity can be controllably generated in the center region of the designed metasurface by different circularly polarized lights. Calculated optical force and optical potential on a polystyrene sphere further demonstrate the good performances of rotating and trapping a microparticle with the generated vortex and focused surface plasmon polaritons. Moreover, two examples designed with different topological charges demonstrate the flexibility of these metasurfaces in tuning the rotation radius of microparticles. The advantages of the proposed metasurface in design flexibility, multifunctionality, and small size may provide new possibilities for applications of integrated optical manipulation devices and systems.

Investigation into the thermal noise propagation mechanism within composite materials for gravitational wave detection systems

The thermal transmission properties of polymer-based composites, commonly used in satellites, are crucial for high-precision thermal management applications. The study constructed the structures of polyimide polymers and polyimide/graphene interfaces based on molecular dynamics and fluctuation dissipation theorem. Optical parameters were determined through first-principles calculations, and the thermal transport from a microthermal source was simulated using Reverse Non-Equilibrium Molecular Dynamics (RNEMD) and the modified four-dimensional transfer matrix method (M4D-TMM). Simulations of polymers, interface structures, and interfacial thermal radiation models investigated the transmission dynamics of microthermal sources during heat transport. Findings showed that the differences in the temperature fields formed within the polymer from microthermal heat sources were less than 20 K for heat source inputs ranging from 0.002 W/m² to 20 GW/m². With a microthermal source, the heat diffusion was extensive, the heat transport was continuous, and the temperature field remained stable. At the level of the heat source up to the intermolecular energy level, the temperature field distribution showed significant instability, leading to nonlinear effects. Within the interface structure, the continuity of heat diffusion increased as the heat source intensified. The interface structure demonstrated enhanced temperature sensitivity and improved stability, with minimal fluctuations of only 0.59 %. The increase in heat flux perpendicular to the interface structure was ascribed to near-field radiative heat transfer. As the temperature difference decreased to less than 0.1 K, the influence of evanescent waves on radiative heat flux nearly disappeared. Phonon polaritons maintained temperature stability during thermal transport through micro- and nanoscale gaps. Integrating thermal conduction principles in polyimide polymers and interface structures with near-field thermal radiation provides a theoretical framework for high-precision thermal management in gravitational wave detection.

Integrated photodetectors embedded within fiber laser based on hybrid rGO:ZnO nanostructures

Online power monitoring is helpful in fiber-optic communication applications. This report introduced an innovative all-fiber photodetector based on the polished side of an arc-shaped fiber for the optical signals’ in situ measurements. For this purpose, a metal-semiconductor–metal photodetector was designed with multiple interdigitated metal fingers of gold electrodes. A waveguide structure containing polymethyl methacrylate (PMMA), graphene layers, and zinc oxide nanostructures was developed and covered over the arc-shaped fiber. Due to the PMMA’s refractive index (n = 1.4905), the evanescent field of propagating mode was drawn out of the core, thus increasing the light interaction with semiconductor nanostructures. To study the influence of graphene flakes on the optoelectrical behavior of zinc oxide nanostructures, a suspension of graphene oxide (GO) and ZnO nanorods was synthesized and transferred onto the PMMA thin film, which was deposited on the polished side of the arc-shaped fiber. The morphological analysis indicates the formation of ZnO nanorods with different orientations, and these nanorods have the potential to enhance incident photon trapping greatly. Upon photon exposure, the guiding photons in the fiber evanescently coupled with the deposited nanostructures, and the photoexcited electron–hole pairs were generated in the semiconductor material. Using applied voltage across the interdigitated electrodes, the generated excitons were separated and increased the photocurrent, which was monitored precisely by source-measure equipment. The optoelectrical properties of fabricated devices showed that incorporating graphene layers can improve the photon detection performance of the fabricated all-fiber photodetectors based on ZnO nanostructures.