Fiber Evanescent Wave Spectroscopy Research Articles

4D Optical fibers based on shape-memory polymers

Adaptative objects based on shape-memory materials are expected to significantly impact numerous technological sectors including optics and photonics. In this work, we demonstrate the manufacturing of shape-memory optical fibers from the thermal stretching of additively manufactured preforms. First, we show how standard commercially-available thermoplastics can be used to produce long continuously-structured microfilaments with shape-memory abilities. Shape recovery as well as programmability performances of such elongated objects are assessed. Next, we open the way for light-guiding multicomponent fiber architectures that are able to switch from temporary configurations back to user-defined programmed shapes. In particular, we show that distinct designs of fabricated optical fibers can maintain efficient light transmission upon completion of multiple temperature-triggered bending/straightening cycles. Such fibers are also programmed into more complex shapes including coils or near 180 ° curvatures for delivering laser light around obstacles. Finally, a shape-memory exposed-core fiber is employed in fiber evanescent wave spectroscopy experiments to optimize the performance of the sensing scheme. We strongly expect that such actuatable fibers with light-guiding abilities will trigger exciting progress of unprecedented smart devices in the areas of photonics, electronics, or robotics.

Spotting Interface Structuring during Na‐Insertion into the NaSICON Na3V2(PO4)3 by EQCM and Operando Fiber Optic Infrared Spectroscopy

AbstractReliable operation of Na‐ion batteries requires a mastering of the interfacial processes governing intercalation kinetics. Ion desolvation, amongst others, is a crucial phenomenon as far as power applications are envisioned. Studying the intricacies of interfacial processes faces experimental challenges. Here the complementary use of electrochemical quartz crystal microbalance (EQCM) and operando infrared fiber evanescent wave spectroscopy (IR‐FEWS) combined with molecular dynamics (MD) simulations is reported to investigate the electrode/electrolyte interface of polyanionic Na‐insertion compounds Na3V2(PO4)3 (NVP) and Na3V2(PO4)2F3 (NVPF). Through screening of various electrolytes that differ in their solvation energy and viscosity, the existence of an unusual mass uptake/depletion signal is demonstrated at the NVP interfaces only, indicative of a dissimilarity in migration kinetics of solvent molecules between NVP and NVPF interfaces as supported by IR‐FEWS. This finding is rationalized by positing that sodium depletion is caused by the unusually rapid ion diffusion within NVP mediated by an intermediate metastable phase, which leads to opposite Na+ concentration and free solvent molecule gradients at the interface that causes the unusual and anomalous feature observed on EQCM frequency profiles. This feature does not appear with NVPF showing lower ionic diffusion. Altogether, this fundamental study provides valuable fundamental insights into the interface structuring of insertion compounds depending upon their Na+ mobility.

Mid-Infrared Spectroscopy as a New Tool for Ruling Out Spontaneous Bacterial Peritonitis: A Proof-of-Concept Study.

A highly sensitive and specific point-of-care method for diagnosing spontaneous bacterial peritonitis (SBP) is currently lacking. The objective of the present study is to evaluate the diagnostic value of a rapid, easy-to-use, mid-infrared fiber evanescent wave spectroscopy (MIR-FEWS) method for ruling out SBP. Cirrhotic patients (n = 256) at five centers in France were included for suspected SBP or for the scheduled evacuation of ascites fluid. The mid-infrared spectrum of 7 µL of an ascites fluid sample was recorded using a MIR-FEWS system. To define a model for the diagnosis of SBP, the patients were divided into a calibration group (n = 170) and a validation group (n = 86). Most of the patients were male (71%). The mean age was 60.25 years. Alcohol-related liver disease was the most common cause of cirrhosis. SBP was observed in 18% of the patients. For the diagnosis of SBP in the calibration and validation groups, respectively, the model gave areas under the receiver operating characteristic curves of 0.87 and 0.89, sensitivities of 90% and 87%, specificities of 78% and 80%, positive predictive values of 48% and 50%, negative predictive values of 97% and 96%, positive likelihood ratio of 4.09 and 4.35, negative likelihood ratio of 0.13 and 0.16, Youden index of 0.68 and 0.67, and correct classification rates of 80% and 81%. The results of this proof-of-concept study show that MIR-FEWS is a highly sensitive diagnostic method for ruling out SBP. The method warrants further investigation.

Unlocking cell chemistry evolution with operando fibre optic infrared spectroscopy in commercial Na(Li)-ion batteries

Improvements to battery performance, reliability and lifetime are essential to meet the expansive demands for energy storage. As part of this, continuous monitoring of the dynamic chemistry inside cells offers an exciting path to minimizing parasitic reactions and maximizing sustainability. Building upon recent fibre-optic/battery innovations, we report the use of operando infrared fibre evanescent wave spectroscopy to monitor electrolyte evolution in 18650 Na-ion and Li-ion cells under real working conditions. This approach enables identification of chemical species and reveals electrolyte and additive decomposition mechanisms during cycling, thereby providing important insights into the growth and nature of the solid–electrolyte interphase, the dynamics of solvation and their complex interrelations. Moreover, by directly embedding fibres within the electrode material, we demonstrate simultaneous observations of both the material structural evolution and the Na(Li) inventory changes upon cycling. This illuminating sensing method has the power to reveal the otherwise opaque chemical phenomena occurring within each key battery component.

A fluoride fiber optics in-line sensor for mid-IR spectroscopy based on a side-polished structure

We report a side-polished sensor structure for mid-infrared (IR) fiber evanescent wave spectroscopy, produced by means of a mechanical polishing process. By integrating a mid-IR light source into this sensor system, spectroscopic analyses could be performed over the range from 2515 to 3735 nm. Two types of sensor structures were fabricated to examine their characteristics and performance. Spectroscopic analyses of liquid and gas samples were successfully performed using one of the fiber sensors without any further decoration/customization of the sensing portion. Qualitative/quantitative measurements were demonstrated for glycerin and diethylene glycol as liquid samples. The measurement results for CH4 gas samples with concentrations of 1% and 5% allowed the lowest detectable concentration to be estimated at 0.52%.

Ruling out septic arthritis risk in a few minutes using mid-infrared spectroscopy in synovial fluids.

The aim of this study was to show the usefulness of a mid-infrared fibre evanescent wave spectroscopy point of care device in the identification of septic arthritis patients in a multicentre cohort, and to apply this technology to clinical practice among physicians. SF samples from 402 patients enrolled in a multicentre cohort were frozen for analysis by mid-infrared fibre evanescent wave spectroscopy. The calibration cohort was divided into two groups of patients (septic arthritis and non-septic arthritis) and relevant spectral variables were used for logistic regression model. Model performances were tested on an independent set of 86 freshly obtained SF samples from patients enrolled in a single-centre acute arthritis cohort and spectroscopic analyses performed at the patient's bedside. The model set-up, using frozen-thawed SFs, provided good performances, with area under the curve 0.95, sensitivity 0.90, specificity 0.90, positive predictive value 0.41 and negative predictive value 0.99. Performances obtained in the validation cohort were area under the curve 0.90, sensitivity 0.92, specificity 0.81, positive predictive value 0.46 and negative predictive value 0.98. The septic arthritis probability has been translated into a risk score from 0 to 4 according to septic risk. For a risk score of 0, the probability of identifying a septic patient is very low (negative predictive value of 1), whereas a risk score of 4 indicates very high risk of septic arthritis (positive predictive value of 1). Mid-infrared fibre evanescent wave spectroscopy could distinguish septic from non-septic synovial arthritis fluids with good performances, and showed particular usefulness in ruling out septic arthritis. Our data supports the possibility of technology transfer. ClinicalTrials.gov, http://clinicaltrials.gov, NCT02860871.

The mid-infrared spectroscopy: A novel non-invasive diagnostic tool for NASH diagnosis in severe obesity.

Background & AimsThere is an urgent medical need to develop non-invasive tests for non-alcoholic steatohepatitis (NASH). This study evaluates the diagnostic performance of an innovative model based on mid-infrared (MIR) spectroscopy for the diagnosis of NASH.MethodsSeverely obese patients who underwent a bariatric procedure at the University Hospital of Nice, France (n = 395) were prospectively recruited. The clinico-biological characteristics were measured prior to surgery. Liver biopsies were collected during the surgical procedure and assessed by a pathologist. A training group (316 patients, NASH: 16.8%) and a validation group (79 patients, NASH: 16.5%) were randomly defined. MIR spectra were acquired by fiber evanescent wave spectroscopy, using chalcogenide glass fiber optic sensors and a spectrometer. This absorption spectroscopic technique delivers a spectrum that identifies the molecular composition of a sample, defining a patient's metabolic fingerprint.ResultsThe areas under the receiver operating curve (AUROC) for the diagnosis of NASH were 0.82 and 0.77 in the training and validation groups, respectively. The best threshold was 0.15, which was associated with a sensitivity of 0.75 and 0.69, and a specificity of 0.72 and 0.76. Negative predictive values of 0.94 and 0.93 and positive predictive values of 0.35 and 0.36, as well as correctly classified patient rates of 72% and 75% were obtained in the training and validation groups, respectively. A composite model using aspartate aminotransferase level, triglyceride level and waist circumference alongside the MIR spectra led to an increase in AUROC (0.88 and 0.84 for the training and validations groups, respectively).ConclusionsMIR spectroscopy provides good sensitivity and negative predictive values for NASH screening in patients with severe obesity.Lay summaryThere is an urgent need for tools to non-invasively diagnose and monitor non-alcoholic steatohepatitis (NASH). This study evaluates the performance of a new tool for fast NASH diagnosis based on mid-infrared (MIR) spectroscopy. Using serum samples from severely obese patients who underwent a bariatric procedure, which enabled a concomitant liver biopsy to be performed, the MIR spectroscopy model performed well in screening patients for NASH compared to a traditional, histological diagnosis.

Spectroscopy analysis of mixed organic liquid detection with Ge20Se60Te20 glass-tapered fiber

In this study, the high-purity Ge20Se60Te20 glass was prepared by melt-quenching method and drawn into a bare glass fiber with a diameter of 450 μm. The minimum transmission loss of this fiber is approximately 3.4 dB/m at 5.9 μm. Then, the fibers were tapered into different waist diameters of 30, 50, 70, and 90 μm. Those tapered fibers were used as sensor for detection of mixed liquid containing different ratios of methanol (CH3OH) and dichloromethane (CH2Cl2) by fiber evanescent wave spectroscopy in situ. Finally, the sensing characteristics of the tapered fibers to the mixed liquid were simulated based on finite-element method. The simulation results were in good agreement with the experimental results.

Fiber sensor on the basis of Ge26As17Se25Te32 glass for FEWS analysis

The high-purity Ge26As17Se25Te32 glass sample was prepared by chemical distillation purification method. This glass is characterized by high value of glass transition temperature (263°С), high optical transparency in the spectral range of 2–10 μm, and low content of residual impurities. The Ge26As17Se25Te32 glass rods were drawn into single-index fibers using the ”rod” method and the single crucible technique. The optical losses in the 400 μm diameter fiber, fabricated by the ”rod” method, were within 0.3–1 dB/m in the spectral range 5.2–9.3 μm. The minimum optical losses in the 320 μm diameter fiber, fabricated by the ”crucible” technique, were 1.6–1.7 dB/m in the spectral range 6–8.5 μm. Using these Ge26As17Se25Te32 glass fibers as a sensor, the aqueous solutions of acetone (0–20 mol.%) and ethanol (0–90 mol.%) were analyzed by fiber evanescent wave spectroscopy. Peculiarities in the change of the integrated intensity and spectral position of absorption bands of these organic substances in dependence on the analyte composition and the length of the sensitive zone were established.

Mid-infrared spectroscopy of serum, a promising non-invasive method to assess prognosis in patients with ascites and cirrhosis.

Background & aimsPrognostic tests are critical in the management of patients with cirrhosis and ascites. Biological tests or scores perform poorly in that situation. Mid-infrared fibre evanescent wave spectroscopy (MIR-FEWS) which allows for global serum metabolic profiling may provide more relevant information by measuring a wider range of metabolic parameters in serum. Here we present the accuracy of a MIR-FEWS based predictive model for the prognosis of 6 months survival in patients with ascites and cirrhosis.MethodsPatients with ascites were prospectively included and followed up for 6 months. MIR-FEWS spectra were measured in serum samples. The most informative spectral variables obtained by MIR-FEWS were selected by FADA algorithm and then used to build the MIR model. Accuracy of this model was assessed by ROC curves and 90%/10% Monte Carlo cross-validation. MIR model accuracy for 6 months survival was compared to that of the Child-Pugh and MELD scores.Results119 patients were included. The mean age was 57.36±13.70, the MELD score was 16.32±6.26, and the Child-Pugh score was 9.5±1.83. During follow-up, 23 patients died (20%). The MIR model had an AUROC for 6 months mortality of 0.90 (CI95: 0.88–0.91), the MELD 0.77 (CI95: 0.66–0.89) and Child-Pugh 0.76 (CI95: 0.66–0.88). MELD and Child-Pugh AUROCs were significantly lower than that of the MIR model (p = 0.02 and p = 0.02 respectively). Multivariate logistic regression analysis showed that MELD (p<0.05, OR:0.86;CI95:0.76–0.97), Beta blockers (p = 0.036;OR:0.20;CI95:0.04–0.90), and the MIR model (p<0.001; OR:0.50; CI95:0.37–0.66), were significantly associated with 6 months mortality.ConclusionsIn this pilot study MIR-FEWS more accurately assess the 6-month prognosis of patients with ascites and cirrhosis than the MELD or Child-Pugh scores. These promising results, if confirmed by a larger study, suggest that mid infrared spectroscopy could be helpful in the management of these patients.

Noninvasive detection of bladder cancer using mid-infrared spectra classification

In this paper, we focus on the detection of Bladder Cancer (BC) via mid infrared spectroscopy. Two main contributions, material and methods, are presented. In terms of material, a new minimally invasive technology, combining fiber evanescent wave spectroscopy and newly patented biosensors, is used for the first time to acquire mid-infrared spectra from voided urine/bladder wash. This new machine promises practicality, cheapness and high-quality of spectrum acquisition. As for classical systems, the data acquired using the new system was highly correlated, resulting in a poor classification performance using classical methods. Therefore, the second contribution consists in developing statistical methods that alleviate the problem. Three new statistical methods based on Partial Least Square Discriminant Analysis algorithm (PLSDA) are proposed. PLSDA is a supervised classifier well-known for its ability to process correlated data. The key point is the choice of the most discriminant latent variables in the training step. In this work, we propose three new decision rules in order to select the most relevant latent variables. These decision rules give rise to three algorithms, namely bayesian, joint and best model PLSDA. A comparative study between the proposed methods and standard ones, namely SVM, K-MEANS and classical PLSDA, confirms clearly the efficiency of the former. The best performance in terms of accuracy is achieved by joint and best model PLSDA (82.35%). Besides, by embedding the proposed statistical methods in the new machine, we are able to provide a new medical device that is very promising in terms of automatic bladder cancer detection.

Early diagnosis of NAFLD-NASH transition using mid infrared spectroscopy.

Non-alcoholic fatty liver disease (NAFLD) is defined as an excessive accumulation of fat in the liver in the absence of excessive drinking of alcohol. Initially considered as benign and self-limited, NAFLD may progress to the malignant stage of non-alcoholic steatohepatitis (NASH) characterized by degenerate hepatocellular ballooning and lobular inflammation. NASH can lead to hepatic fibrosis and ultimately to cirrhosis and hepatocellular carcinoma. Unfortunately, the transition from NAFLD to NASH is difficult to detect so far. In this paper, we propose to evaluate the characterization of NASH using mid infrared fiber evanescent wave spectroscopy on blood serum. We used an heuristic variable selection method and a generalized linear model to classify NAFLD and NASH spectra. The obtained results proved that this technique is a promising non-invasive and simple diagnosis tool for NASH.

Fast and Non-Invasive Medical Diagnostic Using Mid Infrared Sensor: The AMNIFIR Project

AimAmnifir project, part of the ANR TECSAN program, intended to assess the capabilities of a new Mid InfraRed spectroscopy (MIR) device. It used a simple fiber optic sampling method: Fiber Evanescent Wave Spectroscopy (FEWS), which makes Point of Care applications possible and delivers a result within a few minutes. Material and methodTo investigate the technology application range, different biological media (tissues, fluids) as well as pathologies (chronic, cancerous) were considered during the project. We present work on one cancer diagnostic, measuring tissues (colorectal polyp examination), and one chronic disease diagnostic, using a fluid sample (Non-Alcoholic SteatoHepatitis (NASH) markers in serum).We used specific FEWS sensors for both cases, made of chalcogenide infrared glass fiber, as well as proper signal analysis algorithm that first selected spectra area of interest by genetic algorithm, then discriminated the healthy population from the sick one by linear discriminant analysis. ResultsMeasurements using liquid samples provide very encouraging results for NASH identification. On other hand, fiber sensor proved more difficult to use on tissues, as the fiber mechanical resistance appeared too low to sustain a contact with the hardest polyps. ConclusionsAMNIFIR project demonstrated capabilities of MIR FEWS for medical diagnostic using biological fluids, leading to recruitments of further cohorts of NASH and other hepatic disorders patients. Mechanical resistance of fiber needs to be improved for tissues diagnostics.

Fiber evanescent wave spectroscopy based on IR fluorescent chalcogenide fibers

Chalcogenide glasses, owing to their transparency in the infrared window and the appropriate solubility of rare earth, allows the generation of middle infrared (mid-IR) radiation from a near infrared or visible pumping source. These emitted mid-IR broad bands can probe the vibrational modes of several molecules, e.g. CH, CO or CCl. Relying on this principle, a mid-IR optical sensor using the mid-IR fluorescence of Pr3+: Ga-Ge-Sb-S fibers has been developed. The detection principle is based on Fiber Evanescent Wave Spectroscopy (FEWS). The spectroscopic characterization of praseodymium ions (Pr3+) was performed in the near and mid-IR and is discussed on the basis of comparison with Judd–Ofelt calculations. The broad emission spectrum of the Pr3+: Ga-Ge-Sb-S fiber from 4 to 5μm could enable the monitoring of multiple pollutants. In this study, chloroform detection is carried out via a novel technique derived from FEWS. In this way, an infrared sensor was developed, composed of a pumping source in near-IR, a mid-IR detector and a tapered Pr3+: chalcogenide fiber to enhance the detection sensitivity. These results demonstrate for the first time the feasibility of detecting molecules by FEWS using the mid-IR fluorescence emitted by rare earth ions doping chalcogenide fibers. This method is an effective alternative to the classical FEWS system, as RE doped chalcogenide fibers have the advantage of being a compact mid-IR source.

Mid-infrared fibre evanescent wave spectroscopy of serum allows fingerprinting of the hepatic metabolic status in mice.

Non-alcoholic fatty liver disease is associated with obesity, diabetes, and metabolic syndrome. The detection of systemic metabolic changes associated with alterations in the liver status during non-alcoholic fatty liver disease could improve patient follow-up. The aim of the present study was to evaluate the potential of mid-infrared fibre evanescent wave spectroscopy as a minimum-invasive method for evaluating the liver status during non-alcoholic fatty liver disease. Seventy-five mice were subjected to a control, high-fat or high-fat-high carbohydrate diets. We analysed the serum biochemical parameters and mRNA levels of hepatic genes by quantitative RT-PCR. Steatosis was quantified by image analysis. The mid-infrared spectra were acquired from serum, and then analysed to develop a predictive model of the steatosis level. Animals subjected to enriched diets were obese. Hepatic steatosis was found in all animals. The relationship between the spectroscopy-predicted and observed levels of steatosis, expressed as percentages of the liver biopsy area, was not linear. A transition around 10% steatosis was observed, leading us to consider two distinct predictive models (<10% and >10%) based on two different sets of discriminative spectral variables. The model performance was evaluated using random cross-validation (10%). The hypothesis that additional metabolic changes occur beyond this transition was supported by the fact that it was associated with increased serum ALT levels, and Col1α1 chain mRNA levels. Our data suggest that mid-infrared spectroscopy combined with statistical analysis allows identifying serum mid-infrared signatures that reflect the liver status during non-alcoholic fatty liver disease.

Chalcogenide glass fibers: Optical window tailoring and suitability for bio-chemical sensing

Glassy materials based on chalcogen elements are becoming increasingly prominent in the development of advanced infrared sensors. In particular, infrared fibers constitute a desirable sensing platform due to their high sensitivity and versatile remote collection capabilities for in-situ detection. Tailoring the transparency window of an optical material to the vibrational signature of a target molecule is important for the design of infrared sensor, and particularly for fiber evanescent wave spectroscopy. Here we review the basic principles and recent developments in the fabrication of chalcogenide glass infrared fibers for application as bio-chemical sensors. We emphasize the challenges in designing materials that combine good rheological properties with chemical stability and sufficiently wide optical windows for bio-chemical sensing. The limitation in optical transparency due to higher order overtones of the amorphous network vibrations is established for this family of glasses. It is shown that glasses with wide optical window suffer from higher order overtone absorptions. Compositional engineering with heavy elements such as iodine is shown to widen the optical window but at the cost of lower chemical stability. The optical attenuations of various families of chalcogenide glass fibers are presented and weighed for their applications as chemical sensors. It is then shown that long-wave infrared fibers can be designed to optimize the collection of selective signal from bio-molecules such as cells and tissues. Issues of toxicity and mechanical resistance in the context of bio-sensing are also discussed.

IR Fiber Optics-An Introduction

During the past many years of the development of IR fibers there has been a great deal of fundamental research designed to produce a fiber with optical and mechanical properties close to that of silica. We can see that today we are still far from that Holy Grail but some viable IR fibers have emerged which as a class can be used to address some of the needs for a fiber which can transmit greater than 2 μm. Yet we are still limited with the current IR fiber technology by high loss and low strength. Nevertheless, more applications are being found for IR fibers as users become aware of their limitations and, more importantly, how to design around their properties. There are two near-term applications of IR fibers; laser power delivery and sensors. An important future application for these fibers, however, may be more in active fiber systems like the Er and Pr doped fluoride fibers and emerging doped chalcogenide fibers. As power delivery fibers, the best choice seems to be hollow waveguides for CO2 lasers and either SC sapphire, germanate glass, or HGWs for Er: YAG laser delivery. Chemical, temperature, and imaging bundles make use mostly of solid -core fibers. Evanescent wave spectroscopy (EWS) using chalcogenide and fluoride fibers are quite successful. A distinct advantage of an IR fiber EWS sensor is that the signature of the analyte is often very strong in the infrared or fingerprint region of the spectrum. Temperature sensing generally involves the transmission of blackbody radiation. IR fibers can be very advantageous at low temperatures especially near room temperature where the peak in the blackbody radiation is near 10 □m. Finally, there is an emerging interest in IR imaging using coherent bundles of IR fibers. Several thousand chalcogenide fibers have been bundled by Amorphous Materials (Garland, TX) to make an image bundle for the 3 to 10 □m region.

Shaping of looped miniaturized chalcogenide fiber sensing heads for mid-infrared sensing.

Chalcogenide glass fibers are promising photonic tools to develop Fiber Evanescent Wave Spectroscopy (FEWS) optical sensors working in the mid-infrared region. Numerous pioneering works have already been carried out showing their efficiency, especially for bio-medical applications. Nevertheless, this technology remains confined to academic studies at the laboratory scale because chalcogenide glass fibers are difficult to shape to produce reliable, sensitive and compact sensors. In this paper, a new method for designing and fabricating a compact and robust sensing head with a selenide glass fiber is described. Compact looped sensing heads with diameter equal to 2 mm were thus shaped. This represents an outstanding achievement considering the brittleness of such uncoated fibers. FEWS experiments were implemented using alcoholic solutions as target samples showing that the sensitivity is higher than with the routinely used classical fiber. It is also shown that the best compromise in term of sensitivity is to fabricate a sensing head including two full loops. From a mechanical point of view, the breaking loads of the loop shaped head are also much higher than with classical fiber. Finally, this achievement paves the way for the use of mid-infrared technology during in situ and even in vivo medical operations. Indeed, is is now possible to slide a chalcogenide glass fiber in the operating channel of a standard 2.8 mm diameter catheter.

Te-based glass fiber for far-infrared biochemical sensing up to 16 μm.

Chalcogenide glass fibers are very suitable to carry out mid-infrared spectroscopy by Fiber Evanescent Wave Spectroscopy (FEWS). Nowadays, selenide glasses are used for FEWS, but the reachable domain is limited in the infrared to typically 12 µm. Te-rich glasses, due to their heavy atomic weight, are better for far-infrared sensing but they crystallize easily and until now that was difficult to prepare operational optical fibers from such glasses. In this work, Te-Ge-AgI highly purified glasses have been prepared and successfully drawn into optical fiber. The minimum of attenuation is 3 dB/m around 10 μm, which is up to now the lowest value ever measured for Te-based fiber. Overall, such fibers open the sensing window up to 16 μm against 12 µm so far. Then, for the first time, tapered telluride fibers with different diameters at the sensing zone were obtained during the fiber drawing process. Chloroform and butter were used to test the fiber infrared sensing ability, and the sensitivity has been greatly enhanced as the sensing zone fiber diameter decreases. Finally, the new protocol of telluride glass preparation allows shaping them into efficient functional fibers, opening further in the mid-infrared which is essential for chemical spectroscopy.

Chalcogenide optical fibers for mid-infrared sensing

Chalcogenide glasses are a matchless material as far as mid-infrared (IR) applications are concerned. They transmit light typically from 2 to 12 μm and even as far as 20 μm depending on their composition, and numerous glass compositions can be designed for optical fibers. One of the most promising applications of these fibers consists in implementing fiber evanescent wave spectroscopy, which enables detection of the mid-IR signature of most biomolecules. The principles of fiber evanescent wave spectroscopy are recalled together with the benefit of using selenide glass to carry out this spectroscopy. Then, two large-scale studies in recent years in medicine and food safety are exposed. To conclude, the future strategy is presented. It focuses on the development of rare earth-doped fibers used as mid-IR sources on one hand and tellurium-based glasses to shift the limit of detection toward longer wavelength on the other hand.