Wavelength Monitoring Research Articles

Plasmonic Fiber-Optic Refractometers Based on a High Q-Factor Amplitude Interrogation

A nano-scale gold-coated tilted fiber Bragg grating sensor with clear surface plasmon resonance is proposed and experimentally demonstrated. The transmission spectrum of the sensor provides a fine comb of narrowband resonances that overlap with the broader absorption of the surface plasmon and thus provides a unique tool to measure small shifts of the plasmon and identify the changes of the surrounding refractive index (SRI) with high accuracy. Meanwhile, our proposed sensor provides an amplitude interrogation method for SRI measurement, which is much simpler and cost-effective than the traditional wavelength monitoring. Experimental results obtained in sucrose solutions with different refractive indices ranging from 1.3330 to 1.3410 show that the sensitivities of our proposed sensor are 450 nm/RIU and 2040 dB/RIU by using the wavelength and amplitude interrogation methods, respectively. Furthermore, the Q-factor of amplitude interrogation signal has been increased from $\sim 70$ to $\sim 6000$ by using the narrowband cladding resonance instead of broader SPR absorption.

Monitoring of the laser wavelength in modern fiber-optic communication systems using dual photodetectors

Fiber-optic communication systems enable very fast access to large amounts of data for all users of the information and communication systems. Monitoring and control of such fiber-optic systems is of crucial importance for the very large data rate traffic over the internet. DWDM systems have become a standard in order to maximize utilization of existing resources of the fiber-optic systems. These systems use large number of laser light sources with adjacent wavelengths and therefore constant monitoring and control of all lasers in the system is of vital importance. There are different methods for the determination of the lasers wavelength such as optical spectrometers with a monochromator or Fabry-Perot interferometers. In this paper a simple and cost effective solution for laser wavelength monitoring in DWDM L-band with two different photodetectors is presented. Different sensitivities of Ge and InGaAs photodiodes in the L-band were used for implementation of a simple and accurate sensing system for the monochromatic light source wavelength measurement and monitoring. By illuminating simultaneously both photodiodes with the help of the fiber-optic coupler and corresponding signal processing, a wavelength dependent signal was obtained. While the distance between two adjacent channels in DWDM systems is around 0.8 nm, measurement accuracy achieved using proposed method was around ±0.4 nm. Compared to channel spacing in DWDM systems, acquired accuracy is considered sufficient for monitoring of the laser wavelength.

Pulse oximetry optical sensor using oxygen-bound haemoglobin.

In this paper we report a unique approach to measuring oxygen saturation levels by utilising the wavelength of the haemoglobin instead of the conventional absorption difference. Two experiments are set up to measure the wavelength of the haemoglobin bound to oxygen at different oxygen saturation levels with the help of a spectrometer. We report a unique low cost and robust wavelength monitoring SpO2 sensor that measures the SpO2 by using the colour of the blood and not the absorption difference of oxyhaemoglobin and deoxyhaemoglobin. With use of a spectrometer, we show that the wavelength of the oxygen-bound haemoglobin has a relation to the oxygen saturation level. The proposed device is designed and experimentally implemented with a colour sensor to measure the SpO2 level of the blood.

Fano-resonance-based ultra-high-resolution ratio-metric wavelength monitor on silicon.

An integrated ultra-high-resolution ratio-metric wavelength monitor (RMWM) with compact size based on slope tunable Fano resonance is demonstrated on silicon. The Fano resonance is generated by adding an asymmetric microring inside and coupling with the outer ring to produce a nonlinear phase shift. The slope tunability is achieved by controlling the microheaters to adjust the phase condition. Two asymmetric embedded microring resonators (AEMR) are functioned as edge filters and designed to achieve an "X-type" spectral response in a particular wavelength range. An ultra-high resolution of 0.8 pm in a 0.47 nm wide wavelength range is experimentally demonstrated. This device could be applied in on-chip high-sensitivity wavelength monitoring sensing.

Choosing the probe radiation wavelengths for noninvasive monitoring of haemoglobin in blood

The goal of our study was to estimate the accuracy of measuring the blood haemoglobin concentration by means of the pulse CO-oximetry, depending on the probe radiation wavelength. Revealing the combinations of wavelengths, optimal for minimising the measurement error, will allow the formulation of requirements to the instruments for noninvasive assessment of haemoglobin concentration, applicable in wide clinical practice. To solve this problem, we examined a group of haematological patients in the Haematology Department of the Samara State Medical University Clinic with the aim to compare the results obtained using the experimental multiwave system for noninvasive haemoglobin concentration assessment and the results of the clinical blood analysis.

高分辨率波长监测新方法

高分辨率波长监测新方法

Effect of Eu2+ on the luminescence properties of Ba1.52−xZn0.2Li0.4SiO4:0.05Ce3+, 0.03Mn2+, xEu2+ phosphor

The Ba1.52−xZn0.2Li0.4SiO4:0.05Ce3+, 0.03Mn2+, xEu2+ phosphors are synthesized by a co-precipitation method. Luminescence properties and crystal structure of Ba1.52−xZn0.2Li0.4SiO4:0.05Ce3+, 0.03Mn2+, xEu2+ phosphors are investigated in this paper. Crystal phase, excitation and emission spectra of phosphors are analyzed by XRD and FL. Emission spectra of Ba1.52−xZn0.2Li0.4SiO4:0.05Ce3+, 0.03Mn2+, xEu2+ phosphor show three color bands with the peaks at about 400nm, 502nm and 600nm, respectively. CIE chromaticity coordinates calculated through corresponding emission spectra indicate that white light could be achieved by adjustment of the content of Ce3+, Mn2+ and Eu2+. An overlap of excitation spectra under various monitoring wavelengths demonstrates that three colors can be obtained simultaneously under near-UV excitation. Thus, Ba1.52−xZn0.2Li0.4SiO4:0.05Ce3+, 0.03Mn2+, xEu2+ can be considered as a potential candidate phosphor for near-UV white LED.

A wavelength selective application for an optical fiber surface plasmon resonance sensor

In this paper, a wavelength selective optical fiber surface plasmon resonance sensor, which provides a flexible detection capability, has been experimentally investigated. The light reflected from the sensor tip in response to flowing water and ethanol are monitored at several single wavelengths. The reflected light transient modulated by flowing solvent has an exponential form, which the change in magnitude and response time are dependent on the monitoring wavelength. Optimal wavelength best suited for measurement was determined by investigating the dynamic response curve. Rather than wavelength and angular interrogation methods commonly used in SPR measurement, this single wavelength monitoring scheme is a low-cost, flexible and reliable method.

Effect of Trace Fe3+ on Luminescent Properties of CaWO4: Pr3+ Phosphors

Abstract Fe3+ undoped and doped CaWO4: Pr3+ phosphors have been successfully synthesised by using the solid-state reaction method. The products were characterised by powder X-ray diffraction (XRD), photoluminescence (PL) and fluorescence lifetime testing techniques, respectively. The mean crystallite size (50.7 nm) of CaWO4: Pr3+ is obtained from powder XRD data. PL spectra of both Fe3+ undoped and doped CaWO4: Pr3+ phosphors exhibit excitation peaks at 214, 449, 474, and 487 nm under monitor wavelength at 651 nm, and emission peaks at 532, 558, 605, 621, 651, 691, 712, and 736 nm under blue light (λ em=487 nm) excitation. The effect of trace Fe3+ on luminescence properties of CaWO4: Pr3+ phosphor is studied by controlling the doping concentration of Fe3+. The results show that radioactive energy transfers from luminescence centre Pr3+ to quenching centre Fe3+ occurred in Fe3+ doped CaWO4: Pr3+ phosphors. With the increasing concentration of Fe3+, the energy transfer from Pr3+ to Fe3+ is enhanced, and the emission intensity of CaWO4: Pr3+ will be lower. The decay times (5.22 and 4.99 μs) are obtained for typical samples Ca0.995WO4: Pr3+ 0.005 and Ca0.99275WO4: Pr3+ 0.005, Fe3+ 0.00225, respectively. This work shows that nonferrous phosphors can improve the luminescent intensity of the phosphors.

Wide-range modulation and micro-identification of the plasmonic behaviour in gas phase-deposited silver nanoparticle arrays

The surface plasmon resonance properties of silver cluster-deposited multi-structured nanoparticle arrays are investigated for various substrate surfaces. A remarkable redshift from 396 to 572 nm is observed on Formvar film-decorated substrate with controlled particle coverage under in situ surface plasmon resonance wavelength monitoring. The redshift induced by the electromagnetic near-field couplings between the silver nanoparticles and the tuning of the local surface plasmon resonance wavelength in the nanoparticle arrays is found to be correlated to the fraction of closely spaced particle-pairs. Plasmonic ruler behaviour of the closely spaced particle-pair fraction is established and used as an indicator on a gradient silver nanoparticle micro-assembly for identifying the local surface plasmon resonance property in nanostructures. With a 473 nm laser probe, the featured surface plasmon resonance of the optimal nanoparticle assembly for surface-enhanced Raman scattering is found to be around 515 nm.

Resolution-improved in situ DNA hybridization detection based on microwave photonic interrogation.

In situ bio-sensing system based on microwave photonics filter (MPF) interrogation method with improved resolution is proposed and experimentally demonstrated. A microfiber Bragg grating (mFBG) is used as sensing probe for DNA hybridization detection. Different from the traditional wavelength monitoring technique, we use the frequency interrogation scheme for resolution-improved bio-sensing detection. Experimental results show that the frequency shift of MPF notch presents a linear response to the surrounding refractive index (SRI) change over the range of 1.33 to 1.38, with a SRI resolution up to 2.6 × 10(-5) RIU, which has been increased for almost two orders of magnitude compared with the traditional fundamental mode monitoring technique (~3.6 × 10(-3) RIU). Due to the high Q value (about 27), the whole process of DNA hybridization can be in situ monitored. The proposed MPF-based bio-sensing system provides a new interrogation method over the frequency domain with improved sensing resolution and rapid interrogation rate for biochemical and environmental measurement.

An integrated high-performance ratio-metric wavelength measurement device on glass

The measurable wavelength range and the resolution of the ratio-metric wavelength monitor are limited by each other in a conventional structure. To solve this problem we designed and fabricated a high-performance integrated double ratio-metric wavelength measurement device on glass by the method of ion-exchange. It consists of four unbalanced Mach–Zehnder interferometers (MZIs) to form a rough wavelength measurement with a wide range and a fine wavelength measurement with high resolution. The highest measured resolution can reach 10 pm in a 1.6 nm-wide wavelength range for the fine wavelength measurement together with a 45 nm-wide wavelength range for the rough measurement. By heating the unbalanced MZI, the performance of the fine wavelength monitor can be improved.

Simultaneous monitoring the real and imaginary parts of the analyte refractive index using liquid-core photonic bandgap Bragg fibers.

We demonstrate simultaneous monitoring of the real and imaginary parts of the liquid analyte refractive index by using a hollow-core Bragg fiber. We apply this two-channel fiber sensor to monitor concentrations of various commercial cooling oils. The sensor operates using spectral monitoring of the fiber bandgap center wavelength, as well as monitoring of the fiber transmission amplitude at mid-bandgap position. The sensitivity of the fiber sensor to changes in the real part of the core refractive index is found to be 1460nm/Refractive index unit (RIU). By using spectral modality and effective medium theory, we determine the concentrations of the two commercial fluids from the measured refractive indices with an accuracy of ~0.57% for both low- and high-loss oils. Moreover, using an amplitude-based detection modality allows determination of the oil concentration with accuracy of ~1.64% for low-loss oils and ~2.81% for the high-loss oils.

Study on content determination of alkaloids and HPLC fingerprint of “Jianlian” Nelumbinis Plumula

This study is to determine the content of three alkaloids and establish the HPLC fingerprint of "Jianlian" Nelumbinis Plumula. The HPLC method of content determination was as follows: Thermo C18 (4. 6 mm x 250 mm, 5 μm) was conducted with acetonitrile-sodium dodecyl sulfonate solution-acetic acid (56: 43: 1) at a flow rate of 1.0 mL x min(-1). The monitoring wavelength was set at 282 nm and the column temperature was 35 degrees C. The method of HPLC fingerprint was as follows: Agilent ZORBAX SB-Aq C18 (4.6 mm x 250 mm, 5 μm) was conducted with gradient elution of methanol and water at a flow rate of 0.8 mL x min(-1), the monitoring wavelength was set at 282 nm and the column temperature was 35 degrees C. Similarities evaluation and hierarchical clustering analysis were applied to demonstrate the variability of 12 batches of "Jianlian" Nelumbinis Plumula samples. The results demonstrated that 11 batches showed good similarity on chemical constituents. The method could well display the chemical information of "Jianlian" Nelumbinis Plumula. It was simple, reliable and could be used for the chemical quality control of "Jianlian" Nelumbinis Plumula.

Method Development and Validation for the Determination of Potential Impurities Present in Olmesartan Medoxomil and Hydrochlorothiazide in Fixed Dose Combination Drug Product by Using Reverse Phase – Ultra-Performance Liquid Chromatography Coupled with Diode-Array Detector

A simple, sensitive, and reproducible ultra-performance liquid chromatography (UPLC) method for the determination of nine known potential impurities present in Olmesartan medoxomil and Hydrochlorothiazide tablets in fixed dose combination drug product was developed. Chromatographic separation was achieved between impurities at satisfactory level using Acquity UPLC HSS T3, 100 mm length × 2.1 mm id with 1.8 µm particle size column. Gradient elution mode was kept using mobile phase A as 0.1% orthophosphoric acid buffer adjusted the pH 2.5 and acetonitrile as mobile phase B. Flow rate was kept at 0.5 mL min−1 with a monitoring wavelength of 225 nm. The method is fast and uses less consumption of solvents with shorter run time of 9 min. This can enable the separation of all known potential impurities of two active compounds in a rapid, precise, sensitive, cost, and time effective manner. The performance of the method was validated according to the present ICH guidelines for specificity, limit of detection, limit of quantification, linearity, accuracy, precision, solution stability, and robustness. The method is fast and is suitable for high-throughput analysis of the drug facilitating the processing of large-number batch samples.

Method Development and Validation for the Determination of Four Potential Impurities Present in Darunavir Tablets by Reverse Phase–Ultra-Performance Liquid Chromatography Coupled with Diode-Array Detector

The present paper describes strategic development and validation of stability-indicating method for the determination of impurities present in Darunavir tablets. Separation of impurities at satisfactory level is achieved in 100 mm length × 2.1 mm ID, octadecyl column with 1.8 µm particle size. Mobile phase buffer consists of 0.1% orthophosphoric acid in water adjusted the pH 3.0 with triethylamine and acetonitrile using gradient elution mode. Finalized flow rate was 0.2 mL min−1 with a monitoring wavelength of 265 nm. Developed method was successfully validated for specificity, linearity, precision, accuracy, determination of limit of detection, limit of quantification, and robustness as per International Conference on Harmonization general guidelines requirement. The proposed validated reverse phase–ultra-performance liquid chromatography (RP-UPLC) method was shorter in run time and successfully used for quantification of all process and degradation impurities present in Darunavir tablets.

Influence of rapid laser heating on the optical properties of in-flame soot

To understand the effect of rapid heating on the optical properties of in-flame soot and its potential influence on the laser-induced incandescence (LII) signal, the time-resolved extinction coefficient of soot is measured in diffusion and premixed flames during laser heating. Heating is performed using a 1064-nm pulsed laser with fluences ranging from 0.2 to 6.2 mJ/mm2. Extinction measurements are carried out using continuous-wave lasers at four different wavelengths. A rapid enhancement of extinction, by up to 10 % in the diffusion flame and 18 % in the premixed flame, occurs during laser heating most likely as a result of temperature-dependent optical properties and laser-induced thermal annealing of soot. The thermal expansion of flame gases causes a gradual decline of soot concentration for about 2 μs after the laser pulse. Significant loss of soot material by sublimation is observed at fluences as low as 1.03 and 2.06 mJ/mm2 for the diffusion and premixed flames, respectively. A secondary rise in extinction coefficient is observed from about 50 to 800 ns after the laser pulse at low monitoring wavelengths, attributed to the formation of light-absorbing gaseous species from the sublimated soot material. These effects may impact the LII signal and should be accounted for in LII analysis.

Ultrahigh-Resolution Ratio-Metric Wavelength Monitors Based on Tunable Microrings on Silicon

An ultrahigh-resolution ratio-metric wavelength monitor based on microring resonators (MRRs) is demonstrated on silicon. The theoretical wavelength resolution is related to the functional wavelength range and the quality ( $Q$ )-factor of the microring. We analyze the relationship and experimentally demonstrate that the functional range and the resolution can be adjusted by thermally tuning the resonance spacing of the MRRs. The resolution is also limited by the noise introduced in the measurements. An ultrahigh experimental resolution of 1.5 pm is obtained within a 0.72 nm functional range and an ultrahigh theoretical extreme resolution of $\sim 0.4$ pm can be expected considering of the intrinsic systems noise only. The causes of the difference between the experimental and theoretical resolution and the measures to reduce the difference are also discussed.

Automated construction of monochromatic monitoring strategies.

We focus our efforts on development of an advanced monochromatic monitoring strategy to assist the optical coating engineer in finding a single wavelength or a sequence of monitoring wavelengths that meet simultaneously several practical demands, namely, specified input and output swing values, specified amplitude of a monitoring signal variation, and the distance between trigger point and the last signal extremum. Additionally, the most important demand is that the number of different monitoring wavelengths must be as small as possible. Manual construction of such a monitoring strategy is almost impossible because of a large number of conditions to be satisfied. We propose an algorithm that automatically generates a monitoring spreadsheet so that all demands can be satisfied as closely as possible. We consider six typical design problems and obtain a series of solutions for each of them. Then, we provide computational simulations of deposition processes assuming that they are controlled by monochromatic monitoring with the monitoring strategy generated by our algorithm, and we demonstrate how an optical coating engineer can select design solutions that exhibit the highest production yields.

Method Development and Validation for the Determination of Potential Impurities Present in Azilsartan medoxomil Tablets by Reverse Phase-Ultra Performance Liquid Chromatography

The present paper describes about precise, sensitive, rapid method for the determination of five potential impurities present in Azilsartan medoxomil Tablets. Separation of impurities at satisfactory level is achieved in Acquity UPLC BEH C18, 100 mm length x 2.1 mm id with 1.7 µm particle size column. Mobile phase A consists of 0.1% ortho phosphoric acid in water adjusted the pH to 3.0 with dilute sodium hydroxide and acetonitrile as Mobile phase B using gradient elution mode. Flow rate was kept at 0.5 mL.min-1 with a monitoring wavelength of 215 nm. Developed method was successfully validated as per method validation parameters recommended by International Conference on Harmonisation (ICH) for specificity, linearity, precision, accuracy, determination of LOD, LOQ, solution stability and robustness. The validated Reverse phase-Ultra Performance Liquid Chromatography (RP-UPLC) method was successfully used for quantitative determination of potential known and unknown impurities of Azilsartan medoxomil in Azilsartan medoxomil tablet dosage form, helping to identify the therapeutic efficacy at shorter run time.