Changes In Optical Intensity Research Articles

Plastic Optical Fiber as Water-Level Sensor

This research presents a low-cost sensor for measuring liquid levels using plastic optical fibers (POF). The sensor reduces the scattering-based optical losses in the fiber, which increase linearly with the liquid height. A U-bent fiber probe and photodetector are used to detect the change in optical intensity. The U-bent probe serves as a test probe for measuring the liquid level. The voltage response difference of the photodetector provides liquid level measurement. This study demonstrates the sensor's responsiveness to liquid level fluctuations above 55 cm at varying temperatures. Sensitivity levels of 1.4 and 3.3 mV/mm were achieved for water level fluctuations below and above 45 cm, respectively. Furthermore, the sensor demonstrated consistently stable responsiveness over multiple cycles.

T-shaped silicon waveguide coupled with a micro-ring resonator-based Fano resonance modulator.

Fano resonance has an asymmetric and sharp resonance peak near the resonance wavelength, enhancing optical modulation performance. Here, a Fano resonant silicon optical modulator with a micro-ring resonator (MRR) coupled with a T-shaped waveguide is designed. Compared with an MRR modulator, a Fano resonance-based modulator has a smaller wavelength range of changes in optical intensity (from 0a.u. to 1a.u.). Under the condition of achieving the same light intensity change, Fano resonance only needs to shift the wavelength by 0.07 times compared with MRR. By optimizing the doping section and the Fano resonance line shape, the modulation depth of the Fano modulator is 12.44dB, and an insertion loss of 0.41dB is obtained. Moreover, it improves the modulation linearity. This modulator provides a new idea, to the best of our knowledge, for the single-cavity Fano resonance modulator.

Application of additional high-frequency modulation to reduce influence of residual amplitude modulation LiNbO3 phase modulator on fiber optical gyroscope signal

Residual amplitude modulation in LiNbO3 phase modulator is one of the key factors that limit the accuracy of high-sensitive fiber-optical sensors. A fiber-optical gyroscope is an angular velocity sensor whose sensitivity is better than 0.001 °/h. Optical light intensity changes after phase modulator is a reason for wrong phase difference that introduces an error in the angular velocity signal. Most existing residual amplitude modulation suppression methods are based on reduction of back reflections between an optical fiber and integrated optical waveguide, absorbing groove to suppress or reduce reflection on the bottom face, and algorithmic compensation. In this paper, new approach to reduce residual amplitude modulation in LiNbO3 for fiber optical gyroscope application is presented. Method feature is an application of additional differential signal modulation with uniform amplitude distribution in the input signal voltage range of the phase modulator. The proposed method allows to suppress residual amplitude modulation of the multifunctional integrated optical circuit phase modulator more than 3 times using additional triangle signal modulation with the frequency f = 200.09 MHz and power P = 36 dBm. This method is suitable for improving fiber optical gyroscope accuracy. Moreover, it could be applied for any fiber-optic sensors based on LiNbO3 phase modulator. The paper will be of interest to specialists in the field of highly sensitive fiber optical sensors, fiber, and integrated optics.

Urinary Tract Infections Impair Adult Hippocampal Neurogenesis.

Simple SummaryUrinary tract infections are associated with features of cognitive decline and memory deficits, where the underlying correlation or mechanism is still not clear. In this study, we investigate the effect of urinary tract infections on cognitive functions in rodents and whether it is associated with adult hippocampal neurogenesis, a process that is detrimental for memory formation. We have shown that urinary tract infection affects the time spent exploring a novel arm in the Y-maze test. This was accompanied with a decrease in the proliferation of neural stem cells at an early time point post infection and a persistent decrease in neurogenesis at a later time point (34 days). We also detected decreased levels of neurotrophic factors important for neurogenesis and an elevated expression of interleukin 1β in the hippocampus. Treatment with either anti-inflammatory drugs or anti-biotics does not recover proliferation of neural stem cells. Here, we present hippocampal neurogenesis as a possible contributor to cognitive changes associated with urinary tract infections. Given the significant increase in urinary tract infection occurrence, it is important to address some of the detrimental effects that such an infection can have at the level of the brain.Previous studies have suggested a link between urinary tract infections (UTIs) and cognitive impairment. One possible contributing factor for UTI-induced cognitive changes that has not yet been investigated is a potential alteration in hippocampal neurogenesis. In this study, we aim to investigate the effect of UTI on brain plasticity by specifically examining alterations in neurogenesis. Adult male Sprague Dawley rats received an intra-urethral injection of an Escherichia coli (E. coli) clinical isolate (108 CFU/mL). We found that rats with a UTI (CFU/mL ≥ 105) had reduced proliferation of neural stem cells (NSCs) at an early time point post infection (day 4) and neurogenesis at a later time point (day 34). This was associated with the decreased expression in mRNA of BDNF, NGF, and FGF2, and elevated expression of IL-1β in the hippocampus at 6 h post infection, but with no changes in optical intensity of the microglia and astrocytes. In addition, infected rats spent less time exploring a novel arm in the Y-maze test. Treatment with an anti-inflammatory drug did not revert the effect on NSCs, while treatment with antibiotics further decreased the basal level of their proliferation. This study presents novel findings on the impact of urinary tract infections on hippocampal neurogenesis that could be correlated with cognitive impairment.

Photoacoustic Enhancement of Ferricyanide-Treated Silver Chalcogenide-Coated Gold Nanorods.

Plasmonic gold nanorods (AuNRs) are often employed as photoacoustic (PA) contrast agents due to their ease of synthesis, functionalization, and biocompatibility. These materials can produce activatable signals in response to a change in optical absorbance intensity or absorbance wavelength. Here, we report a surprising finding: Ag2S/Se-coated AuNRs have a ~40-fold PA enhancement upon addition of an oxidant but with no change in absorption spectra. We then study the mechanism underlying this enhancement. Electron micrographs and absorption spectra show good colloidal stability and retention of the core-shell structure after potassium hexacyanoferrate(III) (HCF) addition, ruling out aggregation and morphology-induced PA enhancement. X-ray diffraction data showed no changes, ruling out crystallographic phase changes upon HCF addition, thus leading to induced PA enhancement. Attenuated total reflectance-Fourier transform infrared spectroscopy and zeta potential analysis suggest that PA enhancement is driven by the irreversible displacement of hexadecyltrimethylammonium bromide with HCF. This is further confirmed using elemental mapping with energy-dispersive X-ray analysis. PA characterization after HCF addition showed a four-fold increase in the Grüneisen parameter (Γ), thus resulting in PA enhancement. The PA enhancement is not seen in uncoated AuNRs or spherical particles. Two possible mechanisms for PA enhancement are proposed: first, the photo-induced redox heating at the Ag2S/Se shell-HCF interface, resulting in an increase in temperature-dependent Γ, and second, an enhanced electrostriction response due to HCF adsorption on a layered plasmonic nanoparticle surface, resulting in a high thermal expansion coefficient (β) that is directly proportional to Γ.

Titanate nanotubes: Effect of rare earth insertion, thermal treatment and their optical properties

Titanate nanotubes (TiNTs) were synthesized by the microwave-assisted alkaline hydrothermal method, ionically exchanged with rare earth ions (RE) (La3+, Ce4+, Pr3+, Nd3+, Er3+, and Yb3+) (RE-TiNTs), and subjected to thermal treatment. The thermal treatment aimed at structural and morphological changes in the nanotubes in order to generate differentiated optical properties. The RE-TiNTs displayed significant changes in optical absorption and PL intensity compared to the NaTiNTs, which correlated with the temperature of treatment. The PL spectra of the samples was related to the morphological and structural changes of the TiNTs intercalated with RE, indicating that the RE insertion together with the existing oxygen vacancies directly influence the PL emission. The optimization/engineering of the optical properties of the produced nanomaterials could enable their use in applications in optoelectronics and photonics, such as photoluminescent devices, displays, and lasers.

Proof-of-concept of a miniature pressure sensor based on coupled optical WGMs excited in a dielectric microsphere

Optical whispering-gallery mode (WGM) resonators retain increased interest as a key element in various high-resolution sensing and spectroscopic devices in modern optoelectronic, optofluidic and Lab-on-chip technologies. As a theoretical proof-of-concept, we present a new miniature pressure sensor based on coupled WGMs optically excited in a dielectric microsphere placed near a flexible reflective membrane which acts as an ambient pressure sensing element. WGMs are excited by free-space coupling of incoming optical radiation to a spherical microparticle. The distinctive feature of proposed sensor is double WGM excitation by forward and backward propagating radiation upon reflection from a membrane that causes WGMs interference in particle volume. Unlike known WGM-sensors, the proposed design utilize not the resonant frequency shift but the changes in optical intensity of resulting field established in the microsphere which carries information about the exact position of pressure-loaded membrane. The sensitivity of the proposed sensor strongly depends on the quality factor of the working resonance, as well as geometrical and mechanical parameters of flexible reflecting membrane. Important advantages of the proposed sensor are its miniature design and the absence of a mechanical contact of pressure-sensitive element with WGM resonator.

Investigation of the Crystallization Characteristics of Intermediate States in Ge2Sb2Te5 Thin Films Induced by Nanosecond Multi-Pulsed Laser Irradiation.

Laser pulses can be utilized to induce intermediate states of phase change materials between amorphous and crystalline phases, making phase change materials attractive and applicable for multi-level storage applications. In this paper, intermediate states of Ge2Sb2Te5 thin films induced via employing a nanosecond multi-pulse laser with different energy and pulse duration were performed by Raman spectroscopy, reflection measurement and thermal simulations. Upon laser-crystallized Ge2Sb2Te5 films, optical functions change drastically, leading to distinguishable reflectivity contrasts of intermediate states between amorphous and crystalline phases due to different crystallinity. The changes in optical intensity for laser-crystallized Ge2Sb2Te5 are also accompanied by micro-structure evolution, since high-energy and longer pulses result in higher-level intermediate states (corresponding to high reflection intensity) and largely contribute to the formation of stronger Raman peaks. By employing thermal analysis, we further demonstrated that the variations of both laser fluence and pulse duration play decisive roles in the degree of crystallinity of Ge2Sb2Te5 films. Laser fluence is mainly responsible for the variations in crystallization temperature, while the varying pulse duration has a great impact on the crystallization time. The present study offers a deeper understanding of the crystallization characteristic of phase change material Ge2Sb2Te5.

Distributed optical fiber sensing system based on bidirectional sensing structure and filtering effect of unbalanced Mach–Zehnder interferometer

A distributed optical fiber sensing (DOFS) system based on a bidirectional sensing structure and filtering effect of an unbalanced Mach–Zehnder (M-Z) interferometer is proposed and demonstrated. Unlike the M-Z interferometric DOFS system, in this system, the sensing fiber is not in the interferometer, but in series with the interferometer. The M-Z interferometer is employed to only convert the optical phase fluctuation caused by an external disturbance acting on the sensing fiber into the optical intensity change due to its comb filtering effect. Disturbance location can be realized by cross-correlating the two output signals of the sensing system and obtaining their time difference. Experimental results show that the location error is less than 5 m for the 5.7 km-long sensing fiber. The system is feasible in disturbance detection, accurate and repeatable in location results. The detection sensitivity is adjustable by changing the arm length difference of the M-Z interferometer and the frequency response is wideband.

Quantifying the performance of perovskite retinomorphic sensors

Perovskite retinomorphic sensors (PRSs) produce an output voltage in response to changes in optical intensity, but not to constant illumination. While these devices have been demonstrated experimentally, there does not yet exist a robust quantitative model for their behaviour. In this report, we derive a simple relationship between output voltage and optical power density in response to a step-change in illumination intensity. From this model we derive a parameter , which can serve as a proxy for PRS performance. We outline a simple strategy to extract from device data and demonstrate this technique on two sets of experimental data. We evaluate a maximum = 5.3 × 10−4 cm mW−1/2. We approximate that a target value of = 1 cm mW−1/2 would be adequate for most commercial applications and discuss some optimization strategies that could be followed to increase .

Simulation studies to understand sensitivity and timing characteristics of an optical property modulation-based radiation detection concept for PET

The concept of using the modulation mechanisms of a material’s optical properties for annihilation photon detection has been proposed as a potential method to significantly improve the coincidence time resolution (CTR) of positron emission tomography detectors. However, the possibility of detecting individual 511 keV photons with largely improved CTR using the proposed detection method has not yet been demonstrated, either experimentally or theoretically. In addition, the underlying physical picture of the optical modulation effects induced by annihilation photons has not been fully understood. In this work, we perform simulation studies including generation of the annihilation photon-induced ionization energy deposition trajectory, estimation of the charge carrier cascade time and temporal variance, simulation of the distribution of ionization-induced charge carrier density, and calculation of the strength of the modulation of two optical parameters: the absorption coefficient and the refractive index, as well as evaluation of the resulting optical intensity and phase change experienced by a probe laser beam. Our simulation results show that the average absorption coefficient modulation induced by individual 511 keV photon interactions is around 0.04 cm−1, and the average refractive index change is 3.6 × 10−5, leading to modulations in the probe laser intensity of around 0.1% and phase modulation of around 0.05 radians. We have also found that the ionization process induced by a single 511 keV photon interaction occurs within 2.3 ps with a temporal variance of 0.4 ps. The fundamental limit on CTR using the optical property modulation-based detection mechanism is estimated to be around 1.2 ps full width at half maximum. Our simulation results indicate that with proper experiment design, it is possible to detect the ionization produced by an individual 511 keV photon with significantly improved CTR using the optical property modulation-based detection concept.

Low and High-Frequency Electro-Hydrodynamic Patterns in Nematic Liquid Crystal Aligned Using Dual Layer Alignment Produced by Nanofiber

The optical properties and electro-hydrodynamics (EHD) patterns of 4-methoxybenzylidene-4-butylaniline (MBBA) which is parallel oriented by nanofibers has been observed. The alignment of the liquid crystals was made using polyvinyl alcohol (PVA) nanofiber by used modified electrospinning. Electrospinning method was modified using two commercial copper (Cu) printed circuit board (PCB) as a gap collector. These planar samples area is 20 mm x 25 mm. The optical characteristic of these samples was studied by using an optical polarizing microscope. The optical intensity changes by a rotation of crossed polarizers are observed. When an electric field was applied to these samples, the electrohydrodynamic (EHD) pattern was observed. At the low till high frequency, by increasing the voltage, the patterns were formed such as Williams domain (WD), fluctuating Williams domain (FWD), grid patterns (GP) and dynamic scattering Mode (DSM).

Rewritable Optical Memory Based on Sign Switching of Magnetoresistance

AbstractDiscovering ways to control magnetic states by light is very attractive for prospective applications of optical–magnetic sensing and recording. Although several studies have demonstrated the light‐induced switching of magnetization, the magnetoresistance effect was seldom thought to depend on light illumination. A light‐induced magnetoresistance sign switching the resulting writable optical memory are described. A practical method is developed to form a p‐n junction at the interface of a p‐type amorphous carbon film and a quasi‐2D electron gas on an SrTiO3 surface. When illuminated, the as‐formed junction exhibits a clear transition from positive to negative magnetoresistance. A change of optical intensity influences the response time, but not the final value of the negative magnetoresistance. It is also found that, after a light pulse, the negative magnetoresistance state tends to persist, indicating a longstanding memory for an optical signal. This points to a new direction for studying light‐induced magnetoresistance switching, which could lead to the development of new memory devices.

Non-reciprocal biasing for performance enhancement of the resonant fiber gyroscope with ‘Reflector’ using In-line Faraday rotators: Design, analysis and characterization

Abstract Resonant fiber optic gyroscopes use highly expensive narrow linewidth lasers and complex lock-in detection methods since they measure changes in the beat frequency due to angular rotations. In our recent work, a novel resonant gyroscope with an embedded “reflector” was proposed along with a proof-of-principle demonstration. Our resonant gyroscope unconventionally utilizes the changes in optical intensity to measure angular velocity. In this work, a novel method of providing nonreciprocal bias has been designed and implemented using fiber pigtailed Faraday rotators to increase the gyroscope’s sensitivity. We have also created an in-line reflector within the resonator using thin film deposition, in order to stabilize and enhance the reflectance. Unlike earlier, we now use standard single mode fibers and a custom designed, feedback stabilized polarization controller to obtain a bias stability of 10.8 deg/h. Our all-fiber configuration shows enhanced performance and a shot noise limited sensitivity of 0.2 deg/h, indicating the potential for tactical grade performance (0.1–30 deg/h) at much reduced costs. The gyroscope’s performance in terms of sensitivity to Kerr nonlinear effects, ambient thermal changes and backscattering have also been analyzed and discussed in detail.

Plastic fiber optic sensor for continuous liquid level monitoring

The study demonstrates the development of a novel low-cost plastic optical fiber (POF) based sensor for liquid level measurement. The sensor works on the principle of reduction in scattering-based optical losses (in contrast to the increase in optical losses for evanescent wave-based sensing) in a straight decladded fiber with an increase in the liquid level due to refractive index changes in the medium surrounding the fiber. A compact optical setup is developed in-house consisting of two U-bent fiber probes coupled to a single LED on one end and two photodetectors on the other ends to measure the optical intensity changes. One of the U-bent probes is decladded over the length of the fiber to act as a test probe to measure the liquid level, while the other probe acts as a reference to compensate for the light intensity fluctuations due to light source instability and ambient conditions. The difference in voltage responses of the two photodetectors gives a measure for liquid level. We have investigated the fiber optic level sensor response to rising and falling liquid levels over 55 cm in presence of aqueous liquids of different refractive index values (1.33 to 1.38) and 95% ethanol as well as DI water at various temperatures from 16 °C up to 70 °C. A level sensitivity of 1.4 and 3.3 mV/mm for water level changes was obtained for the liquid level below and above 45 cm respectively. In addition, the fiber optic level sensor shows a stable and reproducible response over several cycles of 30 min duration at different liquid levels. The results demonstrate that this fiber optic level sensor is not only easy-to-make, cost-effective and robust but also offers sensitive, stable and reproducible instantaneous level measurements.

Water-Soluble Perylene Diimide for Highly Sensitive and Repeatable Metal Ion Detection with Novel Logic Gate Operation

In this paper, we report a synthesised water soluble perylene derivative, N,N′-di(2-aspartic acid)-perylene-3,4,9,10-tetracarboxylic diimide (PASP), for highly sensitive and repeatable detection of copper (Cu2+) and aluminium ions (Al3+) and novel logic gate operation. In the presence of metal ions, a dramatic decrease in PASP optical intensity was induced based on the strong interaction between terminal carboxy groups and the metal ions. Detection limits of 0.22 and 0.24 μM were respectively obtained at physiological pH. The signals could be recovered upon the addition of ethylenediaminetetraacetate (EDTA) and P2O74−, which competed for Cu2+ and Al3+ in the PASP-CuII and PASP-AlIII systems and induced their dissociation as secondary sensors for anions. At least four detection cycles were performed with a high recovery efficiency. Based on these phenomena, a novel three-level logic gate (OR-IMP-OR) was performed for smart signal readout with metal ions (Cu2+ and Al3+) and anions (EDTA and P2O74−) as input signals, and the relative change of optical intensity of PASP as output signal. Furthermore, the prepared PASP molecule also responded sensitively to Cu2+ and Al3+ in 10 % diluted serum medium.

Resonant Scattering Effect on the Soft X-Ray Line Emission from the Hot Interstellar Medium. I. Galactic Bulges

Abstract Diffuse soft X-ray line emission is commonly used to trace the thermal and chemical properties of the hot interstellar medium, as well as its content, in nearby galaxies. Although resonant-line scattering complicates the interpretation of the emission, it also offers an opportunity to measure the kinematics of the medium. We have implemented a direct Monte Carlo simulation scheme that enables us to account for the resonant scattering (RS) effect in the medium, in principle, with arbitrary spatial, thermal, chemical, and kinematic distributions. Here we apply this scheme via dimensionless calculation to an isothermal, chemically uniform, and spherically symmetric medium with a radial density distribution characterized by a β-model. This application simultaneously accounts for both optical depth-dependent spatial distortion and intensity change of the resonant-line emission due to the scattering, consistent with previous calculations. We further apply the modeling scheme to the O vii and O viii emission line complex observed in the XMM-Newton RGS spectrum of the M31 bulge. This modeling, although with various limitations due to its simplicity, shows that the RS could indeed account for much of the spatial distortion of the emission, as well as the relative intensities of the lines, especially the large forbidden-to-resonant-line ratio of the O vii Heα triplet. We estimate the isotropic turbulence Mach number of the medium in M31 as ∼0.17 for the first time and the line-emitting gas temperature as ∼2.3 × 106 K. We conclude that the RS may in general play an important role in shaping the soft X-ray spectra of diffuse hot gas in normal galaxies.

Escherichia coli Fiber Sensors Using Concentrated Dielectrophoretic Force with Optical Defocusing Method.

A sensitive tapered optical fiber tip combined with dielectrophoretic (DEP) trapping was used for rapid and label-free detection of bacteria in water. The angular spectrum of the optical field at the fiber tip was changed with the surrounding refractive index (RI). By measuring far-field intensity change at the defocus plane, the intensity sensitivity was up to 95 200%/RIU (RI unit), and the detection limit was 5.2 × 10-6 RIU at 0.5% intensity stability. By applying an AC voltage to a Ti/Al coated fiber tip and an indium-tin-oxide glass, the DEP force effectively trapped the Escherichia coli ( E. coli) near the fiber tip. Those bacteria can be directly measured from optical intensity change due to the increase of surrounding RI. By immobilizing the antibody on the Ti/Al fiber tip, the tests for specific K12 bacteria and nonspecific BL21 bacteria verified the specificity. The antibody-immobilized Ti/Al coated fiber tip with DEP trapping can detect bacteria at a concentration about 100 CFU/mL.

Quantitative Detection in Lateral Flow Immunoassay Using Integrated Organic Optoelectronics

A low cost, disposable point-of-care (POC) diagnostic device with integrated organic optoelectronic devices has been investigated for quantitative detection. The diagnostic component consists of a lateral flow immunoassay (LFIA) paper-based biosensor that uses capillary action for transportation of fluids. The absence of external fluid pumps and the low cost of materials utilized make LFIA a simple, inexpensive POC diagnostic device. For detection, the LFIA was integrated with organic optoelectronics devices on thin plastic sheets as a step toward a fully integrated lab-on-chip device. Organic semiconductor devices are suited for this purpose as they can be formed on many types of substrates and can have relatively large active area. For the light emitting component, phosphorescent green emitting organic light emitting diodes (OLED) have been used owing to their high brightness, while for the light detector an organic photodiode (OPD) that absorbs at green wavelengths has been used. Quantitative measurements were performed using optical transmission mode through the LFIA strip that forms red test and control lines by accumulation of gold nanoparticles (AuNP). In this configuration, the amount of transmitted light decreases as AuNPs accumulate on the test line, which directly correlates with the analyte concentration. This change in optical intensity results in a corresponding change in the measured OPD photocurrent. Initial quantification was obtained for 5 levels of rotavirus analyte. OLEDs and OPDs fabricated on plastic substrates were integrated within the LFIA chip to measure the intensity of line formation over a period of 30 min.

Reversible Absorption and Emission Responses of Nile Blue and Azure A Derivatives in Extreme Acidic and Basic Conditions.

Oxazinium derivatives have recently played an important role in bioanalysis attributing to the distinguished properties, thus a detailed study of the structure-property relationship is especially significant. Herein, pH-sensitive optical properties of Nile Blue (1a), N-monoalkyl-Nile Blue (1b) and Azure A (1c) have been carried out in extreme acid and base conditions. Dyes 1a and 1c showed colorimetric changes by the protonation of nitrogen atom in strong acidic condition (pH<2.0), and dyes 1a-c exhibited colorimetric changes by equilibrium between amino and imide groups in very strong basic case (pH>7.6). Besides, their fluorescent properties were closed to ON-OFF and OFF-ON emissions at 640-820nm under strong acidic and basic conditions. Moreover, the absorption and emission properties were reversible, and there were no remarkable optical intensity changes of dyes 1a-c under subacidic and neutral solutions (pH=3.0-7.0). The (TD) DFT calculations were used to optimize the most stable structures of their corresponding protonated and deprotonated forms, and their absorption and emission properties were also explained. Their fluorescent properties nearly ON-OFF and OFF-ON in strong acidic and basic conditions at near-infrared region will give the possible application in pH detection for extreme conditions. Graphical abstract ᅟ.