Peak Wavelength Shift Research Articles

Fabry-Perot Interferometric High-Temperature Sensing Up to 1200 °C Based on a Silica Glass Photonic Crystal Fiber.

A Fabry-Perot interferometric sensor for temperature measurement was fabricated based on a silica glass solid-core photonic crystal fiber with a central air-bore. By splicing a stub of photonic crystal fiber to a standard single-mode fiber, an intrinsic Fabry-Perot cavity was formed inside the photonic crystal fiber. Sensing experiment results show that the sensor can work stably for a consecutive 24 h under temperatures up to 1100 °C, and the short-term operation temperature can reach as high as 1200 °C (<30 min). In the measurement range of 300–1200 °C, the temperature sensitivity of the peak wavelength shift can reach as high as 15.61 pm/°C, with a linearity of 99.76%. The presented interferometric sensor is compact in size and possesses advantages such as an extended working range and high sensitivity, showing promising application prospects.

Stimulus responsive hydrogel-coated etched fiber Bragg grating for carcinogenic chromium (VI) sensing

This paper proposes a chemo-mechanical-optical sensing approach for the detection of carcinogenic chromium (VI) metal ion using an etched fiber Bragg grating (FBG) coated with stimulus responsive hydrogel. Hydrogel synthesized from the blends of (3-acrylamidopropyl)—trimethylammonium chloride, which is highly responsive to chromium ions suffers a volume change when placed in Cr solution. When the proposed sensor system is exposed to various concentrations of Cr (VI) ion solution, FBG peak shifts due to the mechanical strain induced by the swelling of the hydrogel. The peak shift is correlated with the concentration of the Cr (VI) metal ion. Due to the reduction in the cladding diameter of FBG, wastage of swelling force due to hydrogel on FBG is lowered and utilized for more wavelength peak shift of FBG resulting in the increase in the sensitivity. The resolution of the sensor system is found to be 0.072 ppb. Trace amounts of chromium (VI) ion as low as 10 ppb can be sensed by this method. The sensor has shown good sensitivity, selectivity, and repeatability. The salient features of the sensors are its compact size, light weight, and adoptability for remote monitoring.

Fabrication of Au nanoparticles on poly(vinylpyrrolidone) nanowires exhibiting reversible frequency change of localized surface plasmon resonance

Au nanoparticles (NPs) are formed on gel nanowires (NWs) based on poly(vinylpyrrolidone) (PVP) via photoreduction in a HAuCl4-containing MeOH solution. The particle size and number density of the Au NPs increase with the photoreduction time. At a photoreduction time of 15 min, the surfaces of the PVP NWs are almost completely covered by Au NPs. The hybrid material exhibited visible optical absorption based on the localized surface plasmon resonance (LSPR) of the Au NPs. The peak LSPR absorption wavelength under dry conditions red-shifted slightly as the particle size and number density increased owing to increased coupling of the plasmonic bands of each particle. In water, the LSPR wavelength is blue-shifted compared with under dry conditions because of an increase in the interparticle distance between the Au NPs owing to the swelling of the PVP gel NWs; this causes a decrease of the plasmonic coupling of the particles. The absorption peak wavelength shifts reversibly when the hybrid NWs is alternately exposed to either air or water because the distance between the Au NPs is altered in response to the volume change of PVP gel during swelling and drying.

Methods for Hyperspectral Microscope Calibration and Spectra Normalization from Images of Bacteria Cells

Abstract. Hyperspectral microscope images (HMIs) have previously shown promise as a means for rapid and early detection of foodborne bacteria at the cellular level. System calibration and data normalization are critical for comparing information obtained from HMIs collected with multiple instruments and system parameters. Here, we implement a wavelength and radiometric calibration for spectral data obtained from a hyperspectral microscope, assess the spatial uniformity of HMIs, and show the need to normalize data from single-cell regions of interest (ROIs). A hyperspectral microscope with a tungsten halogen light source, acousto-optical tunable filter, and electron multiplying camera with variable gain and exposure time settings were used. HMIs were collected at additional gain settings of 0%, 1.6%, 3.5%, and 5.1% along with ten exposure time settings between 100 and 1000 ms with both calibration lamps. Wavelength peak shift started to occur at an exposure time of 600 ms for 1.6% gain, at 400 ms for 3.5% gain, and at 200 ms for 5.1% gain. HMIs of , Typhimurium, and cells were collected to assess spectral data normalcy and the need for preprocessing spectra from single bacteria cells. Spatial characteristics of cells were assessed by HMIs of a glass slide with a micrometer for determining pixel size from the field of view. HMIs were preprocessed by normalizing cell spectra to the light source and applying multiplicative scatter correction. Data normalcy was assessed on both the raw and preprocessed data sets. Preprocessing the data was found to reduce the cell-to-cell variation associated with a single-cell ROI method, while outliers were detected and verified through HMIs as physically different from other cells. Keywords: Bacteria, Calibration, Food safety, Hyperspectral microscope, Pathogen.

Plasmonic Coupling Effects on the Refractive Index Sensitivities of Plane Au-Nanosphere-Cluster Sensors

Plasmonic coupling effects (between neighboring components) are able to red shift the peak wavelengths of dipolar-localized surface plasmon resonances (LSPRs) and increase the corresponding refractive index sensitivity of nanoparticle sensors. The coupling effects on plane Au-nanosphere-cluster (including nanosphere dimer, trimer, pentamer, and heptamer) sensors are numerically investigated by finite element method (FEM). We found that the coupling does not violate the quadratic response characteristics of LSPR peak wavelengths, hence the linear responses of the sensitivities to the bulk refractive index of Au cluster sensors. Yet, for nanosphere dimer sensors, they contribute to the exponential decrease of sensitivities with their gap distances, which follow the universal plasmon ruler behavior. The amplitude of their fractional sensitivity shift is revealed to be bulk refractive index independent, which is different from that of their fractional LSPR peak wavelength shift. These are analytically explained well in terms of an effective nanoparticle model. The present work also gives an upper sensitivity limit for Au nanosphere dimer systems and provides a method to estimate the interparticle separation between the two component nanospheres of the dimer.

Measurement of strains by optical fiber Bragg grating sensors embedded into polymer composite material

This paper presents the experimental results of strain measurements made by the fiber Bragg grating sensors embedded into polymer composite materials (PCMs). A series of performed experiments are described to demonstrate the capability of fiber optic sensors to measure strains in the case of their pronounced gradient distribution within the material, under compression and tension, at cyclic variation of strains with time and at different temperatures. A measuring technique is presented, and the results of strain measurements during the process of preparation of PCM including measurements of residual process-induced strains are discussed.The results of strain measurements made by fiber optic strain sensors (FOSS) are compared with the results of numerical modeling based on the finite element method and independent measurement data obtained with the use of a digital optical system Vic-3D and other experimental devices. The comparison made shows good agreement between the results obtained by the experimental methods and numerical simulation.The results of numerical computations demonstrate that the embedment of optical fibers in a PCM introduces perturbations in the strain distribution pattern in the vicinity of optical fibers but practically does not cause changes in the value of the strain tensor component measured by the FOSS. The conclusions about applicability range of FOSS embedded into PCM were made based upon the numerical simulation. The interrelation model between Bragg wavelength peak shift and the strain of the optical fiber in the fiber Bragg grating area for the sensor that is not affected by the environment is proposed.

Femtosecond laser induced photoluminescence enhancement of TGA-capped CdTe quantum dots

In this paper, we demonstrate a technique of femtosecond laser induced enhancement in the photoluminescence efficiency of TGA-capped CdTe quantum dot/water colloid. The average laser power required is of the order of few W/cm2 and the time required is few tens of minutes. This process results in stable quantum dots with negligible shift in the PL peak wavelength.

A micro S-shaped optical fiber temperature sensor based on dislocation fiber splice

We fabricated a simple, compact, and stable temperature sensor based on an S-shaped dislocated optical fiber. The dislocation optical fiber has two splice points, and we obtained the optimal parameters based on the theory and our experiment, such as the dislocation amount and length of the dislocation optical fiber. According to the relationship between the temperature and the peak wavelength shift, the temperature of the environment can be obtained. Then, we made this fiber a micro bending as S-shape between the two dislocation points, and the S-shaped micro bending part could release stress with the change in temperature and reduce the effect of stress on the temperature measurement. This structure could solve the problem of sensor distortion caused by the cross response of temperature and stress. We measured the S-shaped dislocation fiber sensor and the dislocation fiber without S-shape under the same environment and conditions, and the S-shaped dislocation fiber had the advantages of the stable reliability and good linearity.

Multiobjective optimization for a plasmonic nanoslit array sensor using Kriging models.

We propose an efficient multiobjective optimization approach for a plasmonic nanoslit array sensor using Kriging surrogate models. The universal Kriging models whose regression functions are zeroth-, first-, and second-order polynomials are adopted to estimate objective functions. The multiobjective extension of the genetic algorithm is used for Pareto optimal sensor geometry. The objective functions are the figure of merit defined as a ratio of peak wavelength shift at molecular adsorption and 3 dB bandwidth of transmission spectrum, and peak transmission power, respectively. The optical properties of a plasmonic slit sensor are investigated, such as transmission power, bandwidth, and peak shift, using the finite element method.

Detection of Refractive Index Change From the Critical Wavelength of an Etched Few Mode Fiber

A novel scheme for the detection of refractive index change based on the mode interference in a special few mode fiber (FMF) is proposed in this paper. The parameters and index profile of the FMF used in the measurement are specifically designed so that only LP01 and LP02 modes are transmitted within the operation wavelength, and the propagation constant difference Δβ between these two modes reaches maximum at critical wavelength (CWL). An inline Mach–Zehnder interferometric sensor for the detection of surrounding refractive index (SRI) is constructed by splicing FMF with two sections of conventional single mode fiber. We demonstrated at the first time that the CWL will change monotonically with the change of SRI in the measurement range of 1.316–1.439. The experimental sensitivity of the CWL increases with the increase of SRI. A sensitiviy of 140.626 ± 12.560 nm/RIU in the range of 1.316–1.383 and a maximum sensitivity of 2489.796 ± 190.179 nm/RIU in the range of 1.433–1.439 were obtained, respectively, in the experiment. At present parameters of the etched FMF, the limit of detection of the refractive index is 3.413 × 10–4 RIU in the SRI range of 1.316–1.383, and 1.928 × 10–5 RIU in the SRI range of 1.433–1.439, respectively. The detection of SRI via monitoring the shift of CWL is superior to the traditional detection method via monitoring merely the shift of peak or dip wavelength of the transmission spectrum, since the latter usually suffers from limited measurement range and multivalue problem because it is difficult to identify and follow one specific peak or dip from the transmission spectrum especially if the system needs to reset in practical application. The novel detection scheme based on monitoring the shift of the exclusive CWL of FMF is promising in practical applications.

CVD GROWTH and CHARACTERIZATION OF 2D TRANSITION METAL DICHALCOGENIDES, MoS2 and WS2

Two-dimensional transition metal dichalcogenides (TMDC), specifically molybdenum disulfide and tungsten disulfide have received significant attention as their direct bandgap exhibits a shift from indirect to direct as the layer goes to single molecular thickness (2D). Hence, they have high potential to pave way for novel optoelectronic devices. However, their structural and optical properties are still not completely understood, especially, spatial change of photoluminescence intensities, variations in excitons-trions, and shift in peak wavelengths in these 2D flake structures need further investigation. In this research work, after growing TMDCs using chemical vapor deposition technique, in addition to measuring micro Raman and photoluminescence spectra, we performed dark field microscopy measurements and photoluminescence mappings to identify grain boundaries and seeding particles. The results clearly show that the flakes, which look lie single-piece through the optical spectroscopy images, in fact, include grain boundaries, seeds and wrinkles. Photoluminescence maps reveal that emission occurs due to different mechanisms such as excitons and trions, depending on the locations on the flakes where the measurement is performed. Our results show that there are different routes that emission can occur and 2D TMDCs provide a rich variety of alternatives to realize novel photonic devices.

Optimal Design of Plasmonic Nanoslit Array Sensor Using Kriging Model

An efficient optimization approach is proposed to design plasmonic nanoslit array biosensor based on extraordinary optical transmission using Kriging surrogate models. The particle swarm optimization is adopted as a global optimization tool, which searches for optimal geometry with high sensitivity and narrow bandwidth. The design variables are the width and height of the slit, respectively, and objective function is a figure of merit defined as a ratio between peak wavelength shift and 3 dB bandwidth of optical transmission spectrum.

Thermal Analysis and Design of AlGaInP-based Light Emitting Diode Arrays

LED arrays with pixel numbers of 3×3, 4×4, and 5×5 have been studied in this paper in order to enhance the optical output power and decrease heat dissipation of an AlGaInP-based light emitting diode display device (pixel size of 280×280 μm) fabricated by micro-opto-electro-mechanical systems. Simulation results showed that the thermal resistances of the 3×3, 4×4, 5×5 arrays were 52°C/W, 69.7°C/W, and 84.3°C/W. The junction temperature was calculated by the peak wavelength shift method, which showed that the maximum value appears at the center pixel due to thermal crosstalk from neighboring pixels. The central temperature would be minimized with 40 μm pixel pitch and 150 μm substrate thickness as calculated by thermal modeling using finite element analysis. The modeling can be used to optimize parameters of highly integrated AlGaInP-based LED arrays fabricated by micro-opto-electro-mechanical systems technology.

Improvement of holographic sensing response in substrate-free acrylamide photopolymer.

A novel substrate-free acrylamide photopolymer was proposed to improve holographic sensing characterization. The diffraction spectrum response of reflection volume grating recorded in the medium was characterized for exploring the improvement of sensitivity. The compared result indicated that the response rate and sensitivity were evidently improved by absorption of double surface in substrate-free polymer. The thickness of the sample as a significant factor was discussed in detail experimentally. During the sensing process, the inhibition concentration and concentration constant of organic vapor were extracted to evaluate the significance of sample thickness. Simultaneously, optimization of thickness could be considered as an effective approach to improve the response rate of holographic sensing. The reversibility of a novel holographic sensor with double surface was demonstrated by recovery measurement. The swelling ratio indicated that the peak wavelength shift was attributed to the expansion of binder induced by absorption of organic vapor. Theoretically, the sensing physical mechanism and the dynamic swelling process were analyzed and simulated using a diffusional model with nonlocal response. These experimental results provide an effective strategy for improving the response of a holographic sensor and accelerate the development of the holographic optical element based on photopolymer.

Microwave-Assisted Synthesis of Unmodified Gold Nanoparticles for Colorimetric Detection of Dopamine

Unmodified gold nanoparticles (AuNPs) have been successfully synthesized by the chemical reduction of tetrachloride gold (III) ions ([AuCl4]-) in the presence of sodium citrate based on the rapid microwave−assisted approach. The diameter of the synthesized nanoparticles was found in the range of 16.50±2.75 nm. The AuNPs were characterized using UV−vis spectrophotometer, zeta potential analyzer and transmission electron microscope (TEM). The sodium citrate protected AuNPs were found to be selective and sensitive for the detection of dopamine. It was based on the aggregation change of the nanoparticles from random coil to hairpin structure upon the addition of dopamine concentration. The red shift of the plasmonic peak wavelength of AuNPs could be used for the detection of dopamine. The response to dopamine allows for a linear range from 10 to 125 mg⋅L-1 (R2 = 0.9804) with a limit of detection (LOD) at a signal to noise ratio of 3 of 12.85±1.38 mg⋅L-1. The colorimetric sensor was evaluated with 98.0−99.9% recovery of added dopamine in urine sample. The proposed sensor was successfully applied to the determination of dopamine in biological samples.

Study on optical characteristic variations according to spectrum changes of RGBY multi-chip LEDs

Recently, various multi-chip LEDs have been developed as the efficiency of red, green, and blue LED chips is improved. RGBY multi-chip LEDs have a high color rendering index, but there is no research on the change of optical characteristics according to the peak wavelength, peak power and bandwidth of the spectrum. In this study, the spectra of commercially available RGBY LEDs are approximated by the Gaussian model and the effect of the spectral variations of red, green, blue and yellow regions on the color rendering indices was examined. CCT and CRI changes due to peak wavelength shift and change in full width at half maximum (FWHM) were simulated and a CRI higher than 98 at 2500 K to 6000 K color temperature range was resulted.

Temperature-dependent optical properties of lead selenide quantum dot polymer nanocomposites.

The optical properties of PbSe quantum dots (QDs) in AB9093 epoxy nanocomposite are examined with respect to temperature over a range of 0°C-80°C, a useful working range for many QD-based sensors and devices, and results are compared to QDs in toluene solution. A complete characterization of QD optical properties is provided as a function of temperature, including the absorption spectrum, first excitonic (1-s) absorption peak intensity and wavelength, fluorescence intensity, and peak wavelength. QD optical properties in toluene were found to be more sensitive to temperature as compared to those in AB9093. Interestingly, 1-s and fluorescence peak wavelength variation with temperature are reversed in AB9093 as compared to those in toluene solution. Results for the fluorescence properties of Lumogen F Red 305 dye in toluene are presented for comparison. The dye was found to have similar sensitivity to temperature to that of the QDs in terms of fluorescence peak wavelength shift, but the fluorescence peak intensity was far less variant. These results can be used to build a temperature sensor or as a guide to building other types of QD-based devices to be more robust against changes in ambient temperature.

Plasmonic detection of mercury via amalgam formation on surface-immobilized single Au nanorods

Au nanorods were used as plasmonic transducers for investigation of mercury detection through a mechanism of amalgam formation at the nanorod surfaces. Marked scattering color transitions and associated blue shifts of the surface plasmon resonance peak wavelengths (λmax) were measured in individual nanorods by darkfield microscopy upon chemical reduction of Hg(II). Such changes were related to compositional changes occurring as a result of Hg–Au amalgam formation as well as morphological changes in the nanorods’ aspect ratios. The plot of λmax shifts vs. Hg(II) concentration showed a linear response in the 10–100 nM concentration range. The sensitivity of the system was ascribed to the narrow width of single nanorod scattering spectra, which allowed accurate determination of peak shifts. The system displayed good selectivity as the optical response obtained for mercury was one order of magnitude higher than the response obtained with competitor ions. Analysis of mercury content in river and tap water were also performed and highlighted both the potential and limitation of the developed method for real sensing applications.

Synthesis and Characterization of Ni and Cu Doped ZnO

In this work pure and transition elements (Ni and Cu) doped Zinc Oxide is prepared. All the samples were prepared through chemical co-precipitation method, by using sulfates of metallic precursors. We have doped pure ZnO with Ni and Cu by 3% by weight concentration. Further the structural, Crystallite size and band gap approximation studies were performed by utilizing X-ray diffraction and spectroscopic techniques respectively. X-ray diffraction (XRD) result indicates that the sample possess a crystalline Wurtzite single phase. Crystallite size is in 19-30 nm range. PL characterization gives optical band gap that is 2.65-3.0 2 eV. FTIR gives the molecular band present in the samples. UV-Vis shows red shift in peak wavelength.

Improving Peak-Wavelength Method to Measure Junction Temperature by Dual-Wavelength LEDs

In this paper, the improvement of the method measuring the junction temperature of light-emitting diodes (LEDs) has been studied experimentally. A practical method is proposed with only three measurement procedures. With the consideration of indium (In) composition and blue shift, the method has a high applicability, which is practical for the LED chips vary from blue to green chips under different currents, including the packaged chips. On the other hand, according to the experimental and derived results, the junction-temperature difference and peak-wavelength shift in both blue-shift and red-shift fields show similar parabolic-like relations. To simplify the experimental processes, dual-wavelength LEDs were fabricated and measured instead of conventional single-wavelength LEDs.