Wavelength Monitoring Research Articles

Advancing Glucose Monitoring: A Near-Infrared Device for Continuous Invasive Assessment

Diabetes is a chronic disease that affects millions of people worldwide, with the number of newly diagnosed cases continuing to rise at an alarming rate. Patients diagnosed with diabetes require routine monitoring of their blood glucose levels, which is commonly done through invasive and minimally invasive techniques. However, these methods are often painful, prone to infection, and costly in the long run. Therefore, it is necessary to develop non-invasive, pain-free, affordable glucose monitoring techniques. Near-infrared spectroscopy has emerged as a promising technique among the non-invasive techniques for glucose monitoring, with several studies reporting its efficacy in detecting glucose concentration. This study designed and developed a near-infrared system based on an 1150nm wavelength for continuous non-invasive glucose monitoring. The system gave the output voltages that vary with increased glucose concentrations. It was ascertained from the Clark error grid analysis that the glucose concentration falls within region A and region B. This implies that the device is suitable for measuring glucose concentration non-invasively. As per Bland Altman's analysis, the majority of the data points were within both limits of agreement except one data point that was outside the upper limit of agreement, indicating 93% degree of accuracy, and the residual plot indicates that the regression model for the system is appropriate for predicting non-invasive glucose measurements.

Large optoelectronic chromatic dispersion in PN-type silicon photodiodes and photovoltaic cells.

Optoelectronic chromatic dispersion (OED) is a significant source of effective chromatic dispersion in photodiodes. We present an experimental and theoretical study of OED in PN-type Si photodiodes and photovoltaic cells and report on a very large effective chromatic dispersion in these devices. As measured with the modulation phase-shift technique at a frequency of 4 kHz for these slow devices, the OED spectral sensitivity for a commercial Si photodiode is approx. 0.02 deg/nm in the 720-850 nm wavelength band and increases to 0.25 deg/nm at λ = 1µm. For a Si photovoltaic cell, the OED is approx. 0.09 deg/nm in this spectral region. These values translate into an effective chromatic dispersion parameter of approx. 1012ps/(n m ×k m) for these sub-millimeter device lengths, which is over eight orders of magnitude larger than high-dispersion materials such as chalcogenide glass. The enormous dispersion in these sub-millimeter sized silicon-based devices can be utilized for on-chip optoelectronic sensors such as wavelength monitoring and spectroscopy. The substantial OED of photovoltaic cells can be utilized for the characterization and optimization and new applications for optical sensing with these self-powered devices.

Optical fiber surface plasmon resonance sensor using electroless-plated gold film for thrombin detection.

This paper describes the simple and label-free detection of thrombin using optical fiber surface plasmon resonance (SPR) sensors based on gold films prepared by the cost-effective method of electroless plating. The plating conditions for simultaneously obtaining gold film on cylindrical core and end surfaces of anoptical fiber suitable for measurement were optimized. The fabricated sensor exhibited a linear refractive index sensitivity of 2150 nm/RIU and 7.136 (a.u.)/RIU in the refractive index of 1.3329-1.3605 interrogated by resonance wavelength and amplitude methods respectively and a single wavelength monitoring method was proposed to investigate the sensing performance of this sensor. Polyadenine diblock and thiolated thrombin aptamers were immobilized on gold nanoparticles and gold films respectively to implement asandwich optical fiber assay for thrombin. The developed optical fiber SPR sensors were successfully used in the determination of thrombin down to 0.56 nM over a wide range from 2 to 100 nM and showed good selectivity for thrombin, which indicated their potential clinical applications for biomedical samples.

Highly Luminescent Lanthanide Metal‐Organic Frameworks with Tunable Color for Nanomolar Detection of Iron(III), Ofloxacin and Gossypol and Anti‐counterfeiting Applications

AbstractSolvothermal reaction of 5,5′‐(pyridine‐2,6‐diylbis(oxy))diisophthalic acid (H4L) with europium(III) or terbium(III) nitrates in acetonitrile‐water (1 : 1) at 120 °C gave rise to isostructural 2D coordination polymers, [Ln(HL)(H2O)3]∞ (NIIC‐1‐Eu and NIIC‐1‐Tb), the layers of which are composed by eight‐coordinated lanthanide(III) ions interconnected by triply deprotonated ligands HL3−. The layers are packed in the crystal without any specific intermolecular interactions between them, allowing the facile preparation of stable water suspensions, in which NIIC‐1‐Tb exhibited top‐performing sensing properties through luminescence quenching effect with exceptionally low detection limits towards Fe3+ (LOD 8.62 nM), ofloxacin (OFX) antibiotic (LOD 3.91 nM) and cotton phytotoxicant gossypol (LOD 2.27 nM). In addition to low detection limit and high selectivity, NIIC‐1‐Tb features fast sensing response (within 60–90 seconds), making it superior to other MOF‐based sensors for metal cations and organic toxicants. The photoluminescence quantum yield of NIIC‐1‐Tb was 93 %, one of the highest among lanthanide MOFs. Mixed‐metal coordination polymers NIIC‐1‐EuxTb1−x demonstrated efficient photoluminescence, the color of which could be modulated by the excitation wavelength and time delay for emission monitoring (within 1 millisecond). Furthermore, an original 2D QR‐coding scheme was designed for anti‐counterfeiting labeling of goods based on unique and tunable emission spectra of NIIC‐1‐Ln coordination polymers.

Highly Luminescent Lanthanide Metal-Organic Frameworks with Tunable Color for Nanomolar Detection of Iron(III), Ofloxacin and Gossypol and Anti-counterfeiting Applications.

Solvothermal reaction of 5,5'-(pyridine-2,6-diylbis(oxy))diisophthalic acid (H4 L) with europium(III) or terbium(III) nitrates in acetonitrile-water (1 : 1) at 120 °C gave rise to isostructural 2D coordination polymers, [Ln(HL)(H2 O)3 ]∞ (NIIC-1-Eu and NIIC-1-Tb), the layers of which are composed by eight-coordinated lanthanide(III) ions interconnected by triply deprotonated ligands HL3- . The layers are packed in the crystal without any specific intermolecular interactions between them, allowing the facile preparation of stable water suspensions, in which NIIC-1-Tb exhibited top-performing sensing properties through luminescence quenching effect with exceptionally low detection limits towards Fe3+ (LOD 8.62 nM), ofloxacin (OFX) antibiotic (LOD 3.91 nM) and cotton phytotoxicant gossypol (LOD 2.27 nM). In addition to low detection limit and high selectivity, NIIC-1-Tb features fast sensing response (within 60-90 seconds), making it superior to other MOF-based sensors for metal cations and organic toxicants. The photoluminescence quantum yield of NIIC-1-Tb was 93 %, one of the highest among lanthanide MOFs. Mixed-metal coordination polymers NIIC-1-Eux Tb1-x demonstrated efficient photoluminescence, the color of which could be modulated by the excitation wavelength and time delay for emission monitoring (within 1 millisecond). Furthermore, an original 2D QR-coding scheme was designed for anti-counterfeiting labeling of goods based on unique and tunable emission spectra of NIIC-1-Ln coordination polymers.

Tilted fiber Bragg grating surface plasmon resonance based optical fiber cadmium ion trace detection

A plasmonic tilted fiber Bragg grating (TFBG)-based sensor for the detection of cadmium ion (Cd2+) is proposed and demonstrated experimentally. The TFBG is coated with a thin gold film, where glutathione (GSH) can self-assemble on the gold coating to bond Cd2+ and form complexes. To enhance Cd2+ sensitivity, GSH-modified gold nanoparticles are used to amplify localized refractive index changes around TFBG surface, induced by Cd2+ concentration variations. The experimental results indicate a limit of detection of ∼0.06 nM, which is two orders better than reported fiber grating-based Cd2+ sensors. Additionally, the proposed TFBG sensor performs a wide dynamic range from 0.01 nM to 1000 nM for Cd2+ detections and temperature-compensated wavelength monitoring with Bragg resonance.

High-sensitivity strain sensor with micron-scale imitation dumbbell structure based on differential temperature self-compensation

A micron-sized dumbbell-like -MZI structure has been developed using hydroxide flame melt taper and arc fusion discharge, with the dumbbell rod region prepared by melt taper drawing and the dumbbell sheet region prepared by arc fusion discharge. This structure has a sensitive light intensity response in the sensing field due to a double-order mode-field coupled excitation region. The geometrical parameters of the dumbbell-like system are optimized theoretically, and the feasibility of the microstructure to achieve high strain sensing sensitivity is analyzed. Experimental results show that the microstructure has a high strain sensing sensitivity of ∼ 0.074 dB/µε and a consistent temperature sensing sensitivity over the entire monitoring wavelength range. Therefore, a light intensity-dependent temperature self-compensation calculation is proposed to achieve a uniform light intensity-strain response for each characteristic peak in the monitored wavelength domain. Since the device has a significant advantage in light intensity modulation and is not affected by polarization light perturbations, it can be used as an alternative light intensity modulation device in optical communication networks and laser research. It can also be used as a probe for medical diagnostic testing based on its enhanced evanescent field properties.

Optoelectronic oscillator controlled by photodiode-based optoelectronic chromatic dispersion and FBG integration

High Optoelectronic Chromatic Dispersion in Ge PN-type photodetectors affects the output of the Optoelectronic Oscillator. This is utilized to achieve high sensitivity wavelength monitoring and strain sensing. The sensitivity is enhanced for higher oscillating mode numbers and lower cavity lengths.

Unsupervised real-world knowledge extraction via disentangled variational autoencoders for photon diagnostics

We present real-world data processing on measured electron time-of-flight data via neural networks. Specifically, the use of disentangled variational autoencoders on data from a diagnostic instrument for online wavelength monitoring at the free electron laser FLASH in Hamburg. Without a-priori knowledge the network is able to find representations of single-shot FEL spectra, which have a low signal-to-noise ratio. This reveals, in a directly human-interpretable way, crucial information about the photon properties. The central photon energy and the intensity as well as very detector-specific features are identified. The network is also capable of data cleaning, i.e. denoising, as well as the removal of artefacts. In the reconstruction, this allows for identification of signatures with very low intensity which are hardly recognisable in the raw data. In this particular case, the network enhances the quality of the diagnostic analysis at FLASH. However, this unsupervised method also has the potential to improve the analysis of other similar types of spectroscopy data.

High sensitivity trace carbon monoxide gas sensor based on endlessly single-mode photonic crystal fiber Sagnac interferometer

Abstract In this paper, a novel carbon monoxide (CO) gas sensor based on α-Fe2O3/MgO is presented and constructed. The endlessly single-mode photonic-crystal fibers (ESPCF) was sandwiched between the four-core fibers (FCF) to form the ESPCF-FCF-ESPCF structure, which was embedded it in the Sagnac loop to construct the Sagnac interferometer. The crystal structure, composition and morphology of α-Fe2O3/MgO sensing film were characterized by the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM), respectively. The results indicated that the α-Fe2O3/MgO sensing film was uniformly coated on the outside surface of two ESPCFs, with a thickness of about 1 μm. When these sensing films adsorbed CO, the monitoring wavelength showed blueshift and the maximum sensitivity was 99.42 pm/ppm. The response time and recovery time were respectively 90 s and 100 s respectively. The Sagnac fiber-optic sensor exhibt high sensitivity, good selectivity and strong stability, and it can effectively realize the monitoring of carbon monoxide.

1D Interferometric Rayleigh Scattering Velocimetry And Thermometry Using VIPA

One-dimensional interferometric Rayleigh scattering is applied to simultaneous measure velocity and temperature by using virtually imaged phased array. The Doppler shift of interferometric pattern was produced by flow velocity plus laser drifts. Online monitoring of the laser wavelength is achieved by adding an additional F-P etalon-based IRS system. Velocity measurements at a low flow rates show an accuracy of 10 m/s. The Rayleigh-Brillouin spectrum is function of pressure and temperature, and provides temperature diagnostics in isobaric flows. The different fringes of interferometric pattern represent different measurements in temperature fitting. This make it possible that one-time experiment but multi-times measurement. The instrument precision of temperature was 3.5% at 809K, which was contributed by the signal to noise ratio decrease at high temperature.

SOYBEAN YIELD FORECAST USING DUAL-POLARIMETRIC C-BAND SYNTHETIC APERTURE RADAR

Abstract. Crop yield forecast is important, but determining productivity is an on-going challenge for agricultural communities including policy makers. An increase in the number of satellites, improved temporal and spatial resolutions and more open data policies, are leading to wider interest by the agricultural sector in exploiting space-based data at moderate spatial resolutions (10–30 m) and varying wavelengths (optical and microwave) for crop yield monitoring. This study evaluated Sentinel-1 dual-polarimetric data to forecast soybean yields one month before the harvest at field scales over a site in central Argentina. Specifically, polarimetric features were extracted from the Sentinel-1 data using the M-Chi decomposition. An Artificial Neural Network (ANN) model was trained using a time series of the single-bounce and volume scattering parameters derived from M-Chi from stacks of data acquired during the growing season. To estimate soybean yield from the ANN model, an innovative iterative retrieval method was developed. This retrieval approach improved the accuracies of the soybean yield forecast delivering a final coefficient of determination (R2) of 0.81 with a root mean square error (RMSE) of 755.81 kg/ha and mean absolute error (MAE) of 581.65 kg/ha. These accuracies demonstrate a high potential of Synthetic Aperture Radar (SAR) data from Sentinel-1 for soybean yield forecast at field scales.

Femtometer-resolved wavelength monitor based on photodiode optoelectronic chromatic dispersion with RF phase-shift amplification.

The spectral sensitivity of photodiode-based optoelectronic chromatic dispersion is enhanced by phase-shift amplification using RF interferometry. With phase-shift amplification of G=4⋅104, a peak phase-shift sensitivity of Δθ = 27deg/pm is achieved, corresponding to a spectral resolution of Δλres = 1fm. This all-electronic solid-state technology can serve as an on-chip inexpensive technique for femtometer-resolved wavelength monitoring.

Up-/Downconversion Fluorescence Dual-Channel Probe Based on NaYF4: Yb/Er/Eu Nanoparticles for the Determination of Cu(II)

Copper ions [Cu(II)] are essential in many biological processes. Accurate determination of Cu(II) is of great significance for environment monitoring and diseases diagnosis. A dual-channel probe (DCP) with up/downconversion fluorescence is developed using a one-pot solvothermal method in this work. Yb(III), Er(III), and Eu(III) are doped into NaYF4 capped with ethylene imine polymer (PEI), that is, PEI-capped NaYF4: Yb(III), Er(III), and Eu(III) NPs (marked as PEI-capped NYF: Yb/Er/Eu NPs), forming the DCP to determine Cu(II) through the up- and downconversion fluorescence variations. The DCP is designed aiming to minimize mutual interference between the fluorescent signals. Under the optimized conditions, the up-/downconversion fluorescence performances of DCP are excellent, including a linear range for 30 nM–10 μM Cu(II) with the detection limits of 29.30, 18.23, and 26.04 nM (monitoring wavelengths of 545, 592, and 616 nm) as well as excellent selectivity to Cu(II). The mechanism of Cu(II) determination could be attributed to the quenching of up-/downconversion fluorescence because of the inner filter effect triggered by PEI–Cu(II) complexes. To illustrate the potential application of up-/downconversion fluorescence DCP, the concentration of Cu(II) in tap water is detected, and satisfactory results are acquired, indicating that the up-/downconversion fluorescence DCP has promising applications in the fields of food safety and environmental detection. More importantly, the proposed design idea is universal regarding the construction of other dual-channel probes for the detection of metal ions.

Filament-arrayed Bragg gratings for azimuthally resolved displacement sensing in single-mode fibers.

Filament arrays were inscribed off-axis in the core of standard single-mode telecommunication fiber, using femtosecond laser pulses. The flexible line-by-line writing formed uniform, parallel filaments, permitting Bragg grating sensing of the photoelastic response from inside of the narrow grating plane. Active monitoring of the Bragg resonance wavelength while driving a lateral fiber tip displacement directly informed on the fiber mechanics when coupled with opto-mechanical modelling. Overlaying of parallel and orthogonal gratings further provided a strongly contrasting azimuthal sensitivity, which paves the way for multi-dimensional displacement sensing with improved precision.

Four-quadrant demodulation fiber sensor for wavelength monitoring of a wavelength phase-shifting interferometer

Four-quadrant demodulation fiber sensor for wavelength monitoring of a wavelength phase-shifting interferometer

Modified laser scanning technique in wavelength modulation spectroscopy for advanced TDLAS gas sensing

• Modified laser scanning technique, i.e. half-wave scan, allows the unique in-situ monitoring and regulation of laser wavelength in the TDLAS gas sensor. • Nonlinear half-wave scan can maintain the sensing stability with a minimized sampling rate beyond the conventional linear scan for data volume and time saving. • Minimum detecting limit of 3 ppm and measurement accuracy of 9.6 ppm @400 ppm in methane sensors. Tunable diode laser absorption spectroscopy (TDLAS) for trace gas sensing has been investigated widely. Conventional wavelength-modulation spectroscopy (WMS) in TDLAS usually involves linear triangle patterns for tunable laser scanning. Here, a novel modified laser scanning technique is proposed and experimentally demonstrated in the WMS-based TDLAS gas sensor. The half-wave scan is primarily introduced to drive the laser diode to cover 1/2 range of the Lorentz-like gas absorption line. By monitoring waveform derivation of second harmonics, real-time status of the laser output could be exhibited and the output wavelength constancy can be controlled. It is also verified that second harmonics feature basically linearly with wavelength drifts, allowing the in-situ regulation of laser wavelength stability. Moreover, the nonlinear half-wave scan is introduced and designs a nonlinear function across the scanning pattern. It enlarges the temporal window around strong absorption and consequently acquires additional valuable waveform data. With the limited sampling rate for TDLAS signal processing, by using the nonlinear half-wave scan, second harmonics fluctuate merely 1/3 of that in the conventional WMS-2f linear scan. The proposed modified laser scanning technique is employed in a methane sensor, realizing about 3 ppm minimum detection limit and 9.6 ppm measurement accuracy. This technique is beneficial and universal for real-time monitoring and in-situ control of laser sources and improvement in accuracy and stability for current WMS-based TDLAS gas detection.

Ultrathin sputtered silver films protected by ALD alumina: Comparison of in-situ investigation with ex-situ resistance and ellipsometric measurements

We compare in-situ transmittance and plasma emission spectra with ex-situ resistance and ellipsometric measurements performed on ultrathin silver films with thicknesses varying from 3 nm through 40 nm and on relatively thick layers up to 100 nm. We show that the transmittance broadband monitoring (BBM) of the growing silver layer allows for in-situ reliable estimation of the minimum thickness when the film becomes continuous. Moreover, a proper selection of the monitoring wavelength(s) renders the coalescence and percolation stages of the film growth clearly distinguishable. For our films deposited by magnetron sputtering on fused silica substrates, the minimum thickness when a film becomes continuous was found to be approximately 12 nm. The percolation threshold was determined as approximately 6 nm. The method of selective-wavelength transmittance BBM is practical, intuitive and hence may represent a useful tool enabling high-precision growth of ultrathin silver layers. Furthermore, we show here for the first time that ellipsometry is sensitive to the metal coalescence development. In particular, the ellipsometric analysis suggests that the percolation of silver sputtered films begins at the top of the growing layer and hence propagates towards the film bottom.

Selection of Materials for Double Layer Antireflection Coating of Silicon Solar Cell

In present work an attempt has been made to select material to design double layer antireflection coatings (DLARC) for silicon solar cell, theoretically. In this regard, silicon nitride (Si3N4) is used along with MgF2 and SiO2 to design DLARC to achieve zero reflectance over wide range of spectra. Reflection spectra for DLARC systems of MgF2/Si3N4 and SiO2/Si3N4 have been evaluated numerically using transfer matrix method (TMM). Further, reflectance for MgF2/Si3N4 is investigated at various monitoring wavelengths (o = 550, 600, 650 and 700 nm). Calculated reflectance has been used in PC1D simulator to study the effect of double layer antireflection coating on optical and electrical parameters of silicon solar cell. Simulation results shows, reduction in reflectance form > 30% down to zero in the wavelength range 500 – 700 nm with conversion efficiency 21.33% at 600 nm for MgF2/Si3N4.

Automated optical monitoring wavelength selection for thin-film filters.

In this paper we study the wavelength selection process for optical monitoring of thin film filters. We first discuss the technical limitations of monitoring systems as well as the criteria defining the sensitivity of different wavelengths to thickness errors. We then present an approach that considers the best monitoring wavelength for each individual layer with a monitoring strategy selection process that can be fully automated. We finally validate experimentally the proposed approach on several optical filters of increasing complexity. Optical interference filters with close to theoretical performances are demonstrated.