Fiber Optic Probe Research Articles

Direct laser micro-drilling of high-quality photonic nanojet achieved by optical fiber probe with microcone-shaped tip

Photonic nanojet can serve as a powerful tool for direct laser micro-machining based on a non-resonance focusing phenomenon. In this study, we propose a photonic nanojet-based direct micro-drilling technique for polymer material with low-cost and low-power continuous-wave laser. The high-quality photonic nanojet is produced using the microcone-shaped probe tip, which is fabricated by the dynamic chemical etching method. By utilizing laser photonic nanojet triggered thermoplasmonics, the high-aspect-ratio microcavity is fabricated with the low threshold value of laser power. The influences of the photonic nanojet peak intensities and distributions on the drilled microcavities are systematically investigated by the experiments and the finite-difference time-domain simulations. With the continuous-wave solid-state laser at a wavelength of 671 nm, the simulations show that the photonic nanojet with a quality factor of 103 is generated at a distance of ~ 20 μm from the surface of the microcone-shaped tip with a beam waist of 252 nm in the x direction, which could overcome the diffraction limit. The experimental results show that the length and peak intensity of the photonic nanojet have increased considerably in the propagation direction by the microcone-shaped probe tip, which leads to form a deep microcavity in the polymer substrate with an aspect ratio of 5.73. The presented microcone-shaped probe tip has potential applications in processing sub-diffraction features with a high aspect ratio.

Real-time monitoring of multiparameter in 1,3-propanediol production process with near-infrared spectroscopy

1,3-propanediol (1,3-PDO) is a significant product of fermentation, with glycerol serving as the primary substrate in most cases. Bioprocess control based on real-time information of feedstock and main products is crucial for reducing the cost of production. However, rapid quantification of 1,3-PDO and glycerol remains challenging due to their highly similar molecular structures. In this study, the feasibility of near-infrared (NIR) spectroscopy to monitor 1,3-PDO, glycerol, acetate, and butyrate concentrations in the fermentation process using strain Clostridium pasteurianum was evaluated. NIR spectra were acquired through at-line measurement involving sampling and ex-situ analysis or on-line measurement with a fiber optic probe immersed in fermentation broth, integrated with Partial Least Squares (PLS) regression to establish calibration models on a laboratory-scale and pilot-scale. The best PLS regressions of 1,3-PDO, glycerol, acetate, and butyrate with two measurement approaches provided excellent performance, with the root-mean-squared errors of prediction (RMSEP) of 1.656g/L, 1.502g/L, 0.746g/L, and 0.557g/L in at-line measurement and 1.113g/L, 1.581g/L, 0.415g/L, and 0.526g/L in on-line measurement. The cross-scale application performance of at-line measurement was evaluated by an external fermentation trial and an acceptable result was achieved. At-line measurement technique represents a superior choice for the optimization of fermentation process since the robustness across varying fermentation scales and its applicability in multiple bioreactors. Thus, a calibration model developed for one bioreactor is likely to be used in other bioreactors, which enables the reduction of modeling costs. On-line measurement technique, owing to its automated operation and frequent data acquisition, enables real-time monitoring and precise control of the fermentation process, thereby reducing cost and improving production efficiency.

In-situ synthesis and integration of gold nanoparticles into 3D printed optical fiber probes

This work uses the polymeric reduction method to explore the in-situ synthesis of gold nanoparticles (AuNPs) within 3D-printed optical fiber probes (OFPs). Digital light processing (DLP) 3D printing is employed to fabricate the OFPs using a resin consisting of hydroxyethyl methacrylate (HEMA) and polyethylene glycol diacrylate (PEGDA). After printing, OFPs were immersed in a boiling gold precursor solution to facilitate the synthesis of AuNPs inside the polymer matrix. We produced single material (HEMA/PEGDA) and multimaterial (HEMA/PEGDA + Dentaclear) OFPs loaded with AuNPs at different concentrations. Scanning electron microscopy analysis confirmed the effective distribution and dispersion of AuNPs within the polymer matrix. The optical properties, including reflection and transmission spectra, are comprehensively measured using customized setups. The localized surface plasmon resonance of the embedded AuNPs created a distinct dip in the 500–600 nm wavelength range. Higher AuNP concentrations and longer dipping times enhanced light absorption, reducing reflection and transmission intensities. Multimaterial OFPs also exhibited tunable wavelength filtering capabilities based on the AuNP concentration. The AuNP-loaded OFPs demonstrated stable optical performance across varying temperatures and pH environments, highlighting their potential for diverse applications.

An improved method to process the data of optical Fiber signals for identifying the instantaneous flow structure in a gas-solid fluidized bed

The instantaneous signals recorded with the optical fiber probe (OFP) directly reflect the hydrodynamic behaviors in fluidized beds. A new data-processing method is put forward to calculate the threshold voltage that is used to discern the bubble phase and emulsion phase. It is found that the threshold voltage is not only related to the flow pattern but also to the color of the used particles. Then the data-processing programs including the Fast Fourier filter have been developed for determining the flow characteristics such as the bubble/particle velocity, bubble/agglomerations chord length, etc. By comparing them with other different methods, the suitability of the proposed method for quantifying the hydrodynamic behaviors in bubble/turbulent fluidized beds is verified. Finally, this method is employed to analyze the characteristics of bubbles, agglomerations and particles in a gas-solid fluidized bed. It is found that the hydrodynamic behaviors of bubbling beds and turbulent beds have significant differences.

AuNPs enhanced electrochemical and optical dual-mode fiber optic sensor for trace Hg2+ detection

Efficient and low-concentration detection of heavy metal ions is crucial for healthcare and environmental monitoring. Traditional fiber optic surface plasmon resonance (SPR) sensors face challenges in detecting trace heavy metal ions due to limited sensitivity and the need for complex specific modifications. To overcome these challenges, an innovative electrochemical and optical dual-mode fiber optic sensor for in situ, real-time detection of trace mercury ions is proposed in this paper. The sensor utilizes a reflection-type fiber optic probe coated with thin gold (Au)/indium tin oxide (ITO) film and gold nanoparticles (AuNPs), enabling simultaneous electrochemical and optical interrogation. The coupling effect between the SPR of thin film and the localized surface plasmon resonance (LSPR) of AuNPs significantly improves optical sensitivity, with AuNPs also offering additional active sites for the redox reaction of Hg2+. The ITO film not only facilitates the stripping of Hg2+, leading to sharper stripping peaks but also enhances the ability of the sensor to rapidly respond to anomalous potential changes. Experimental results show that the sensor has a wide dynamic detection range from 10−10 M to 10−5 M, with a limit of detection reaching the pM level. The dual-mode functionality allows the simultaneous collection of voltage, current, and optical information, enabling cross-validation of the detection results and improving the accuracy and reliability of detection.

Optical manipulation of magnetic microspheres Enables high-sensitivity Fiber-optic magnetic field sensors

This study uses single-fiber optical tweezers to capture non-uniform magnetic particles, producing a novel type of magnetic field sensor for implementing the measurement of external magnetic field changes. A tapered fiber optic probe is used to capture magnetic particles as a sensing probe, constituting an Fabry–Pérot (F-P) interferometric structure. When an external magnetic field is applied, the magnetic particles at the tip of the optical fiber are deflected, affecting the length change of the interference cavity. By reconstructing the axial displacement of the particles, the accurate measurement of the magnetic field within the range of 1–10 mT is successfully realized with a sensitivity of 258 nm/mT. The minimum detectable intensity is 1.44 nT/Hz. This method offers a feasible and effective solution for the realization of magnetic field measurements by using the capture of non-uniform magnetic particles, which can play an important role in the fields of medicine and biology.

Design of a new fiber-optical transmission-based fast ion loss probe on Experimental Advanced Superconducting Tokamak

For the first time, a new probe for fast ion loss has been developed for use in the Experimental Advanced Superconducting Tokamak (EAST) and utilizes optical fiber transmission, the aim of the probe is to study fast ion losses triggered by the ion cyclotron range of frequencies (ICRF) heating and neutral beam injection (NBI) synergy. This probe is used to determine the pitch angle and gyroradii of the ion losses based on the particle positions striking the two-dimensional scintillator. In this paper, the calculation and design of the probe scintillator by using the NLSDETSIM code is discussed. The emitted light from the scintillator is captured by a high-speed camera via an optical lens and high-temperature-resistant fibers and then processed by a signal processing system to determine the real-time energy and angle of the fast ion. Due to the flexible nature of the fiber, the probe is capable of measuring the fast ion losses at various locations within the EAST. Furthermore, the probe can be easily installed by using one of the numerous vacuum feeds on the EAST instead of occupying the entire window. This feature enhances the flexibility of the diagnostic technique.

Evaluation of Diffuse Reflectance Spectroscopy Vegetal Phantoms for Human Pigmented Skin Lesions.

Pigmented skin lesions have increased considerably worldwide in the last years, with melanoma being responsible for 75% of deaths and low survival rates. The development and refining of more efficient non-invasive optical techniques such as diffuse reflectance spectroscopy (DRS) is crucial for the diagnosis of melanoma skin cancer. The development of novel diagnostic approaches requires a sufficient number of test samples. Hence, the similarities between banana brown spots (BBSs) and human skin pigmented lesions (HSPLs) could be exploited by employing the former as an optical phantom for validating these techniques. This work analyses the potential similarity of BBSs to HSPLs of volunteers with different skin phototypes by means of several characteristics, such as symmetry, color RGB tonality, and principal component analysis (PCA) of spectra. The findings demonstrate a notable resemblance between the attributes concerning spectrum, area, and color of HSPLs and BBSs at specific ripening stages. Furthermore, the spectral similarity is increased when a fiber-optic probe with a shorter distance (240 µm) between the source fiber and the detector fiber is utilized, in comparison to a probe with a greater distance (2500 µm) for this parameter. A Monte Carlo simulation of sampling volume was used to clarify spectral similarities.

Quantitative estimation of optical properties in bilayer media within the subdiffusive regime using tilted fiber-optic probe diffuse reflectance spectroscopy, part 2: probe design, realization, and experimental validation.

Tissues like skin have a layered structure where each layer's optical properties vary significantly. However, traditional diffuse reflectance spectroscopy assumes a homogeneous medium, often leading to estimations that reflects the properties of neither layer. There's a clear need for probes that can precisely measure the optical properties of layered tissues. This paper aims to design a diffuse reflectance probe capable of accurately estimating the optical properties of bilayer tissues in the subdiffusive regime. Using Monte Carlo simulations, we evaluated key geometric factors-fiber placement, tilt angle, diameter, and numerical aperture-on optical property estimation, following the methodology in Part I. A robust design is proposed that balances accurate intrinsic optical property (IOP) calculations with practical experimental constraints. The designed probe, featuring eight illumination and eight detection fibers with varying spacings and tilt angles. The estimation error of the IOP calculation for bilayer phantoms is less than 20% for top layers with thicknesses between 0.2 and 1.0mm. Building on the approach from Part I and using a precise calibration, the probe effectively quantified and distinguished the IOPs of bilayer samples, particularly those relevant to early skin pathology detection and characterization.

Quantitative estimation of optical properties in bilayer media within the subdiffusive regime using a tilted fiber-optic probe in diffuse reflectance spectroscopy, part 1: a theoretical framework for designing probe geometry.

As biological tissues are highly heterogeneous, there is a great interest in developing non-invasive optical approaches capable of characterizing them in a very localized manner. Obtaining accurate absolute values of the local optical properties from the measured reflectance requires finding a probe geometry, which allows us to solve this inverse problem robustly and reliably despite neglecting the higher-order moments of the scattering phase function. Our goal is to develop a theoretical framework for designing tilted-fiber diffuse reflectance probes that allow quantitative estimation of the optical properties corresponding to limited tissue volume (typically a few cubic millimeters). Relationships among probe geometry, sampled tissue volume, and robustness of the inverse solver to calculate optical properties from reflectance are studied using Monte Carlo simulations. The analysis of the number of scattering events of the collected photons leads to the establishment of relationships among the probe geometry, the sampled tissue volume, and the validity of a subdiffusive regime for the reflectance. A methodology is proposed for the design of new compact probes with tilted fiber geometry that can quantitatively estimate the values of the optical coefficients in a localized manner within living biological tissues by recording diffuse reflectance spectra.

Detection of vaccinia virus proteins in wastewater environment using biofunctionalized optical fiber semi-distributed FBG-assisted interferometric probes

In this work, we present the detection of proteins expressed by poxvirus with fiber-optic probes based on a semi-distributed interferometer (SDI) assisted by a fiber Bragg grating (FBG), performing the measurement directly into a wastewater sample. Modern biosafety applications benefit from real-time, dynamic-sensing technologies that can perform diagnostic tasks into a wide set of analytes, with a particular emphasis on wastewater, which appears to collect a significant number of viral titers in urban and indoor environments. The SDI/FBG probe can perform substantial progress in this field, as it embeds a dual sensitivity mechanism to refractive index changes (sensitivity up to 266.1 dB/RIU (refractive index units)) that can be exploited in biosensing, while simultaneously having the capability to measure the temperature (sensitivity 9.888 pm/°C), thus providing an intrinsic cross-sensitivity compensation. In addition, a standard FBG analyzer can be used as an interrogator, improving affordability and real-time detection over previous works. The probes have been functionalized with antibodies specific for L1, A27 and A33 vaccinia virus proteins, performing detection of a protein concentration in a scenario compatible with online viral threat detection. Direct detection of wastewater samples shows that the L1-functionalized sensor has a higher response, 9.1–11.3 times higher than A33 and A27, respectively, with a maximum response of up to 1.99 dB and excellent specificity. Dynamic detection in wastewater shows that the sensors have a response over multiple detection cycles, with a sensitivity of 0.024–0.153 dB for each 10-fold increase of concentration.

Use of a Single-Fiber Optical Probe for the Detection of Tumor Fluorescence in High-Grade Glioma.

High-grade glioma (HGG) is the most common primary brain tumor in adults. The overall median survival is between 14 and 16 months. Fluorescence-guided surgery by detection of protoporphyrin IX (PpIX) fluorescence has been shown to improve the extent of resection, translating to improved progression-free survival. Microscope-based fluorescence detection techniques are associated with several pain points, some of which may be addressed by using contact-based spectroscopy. We aimed to investigate the accuracy of an optical fiber at detecting PpIX fluorescence by performing real-time spectroscopy in patients with HGG. Adult patients undergoing fluorescence-guided surgery for suspected HGG were recruited prospectively. Intraoperatively, samples from cortex, white matter, and tumor were taken. These samples were interrogated using standard white and blue light microscope techniques and the optical fiber. These specimens were then assessed by neuropathology to determine whether the tumor tissue was present within them. We collected 89 samples from 28 patients. There was an equal ratio of men to women, with a median age of 66.5 years. The accuracy of the probe for detecting PpIX fluorescence was 75.9%, compared with 56.6% for the operating microscope, with a significant improvement in sensitivity (χ2 = 11.84, P < .001). The optical fiber probe was more accurate than the operating microscope for detecting PpIX fluorescence. This technology has potential value in improving the accuracy of fluorescence-guided surgery and has potential practical benefits relating to surgical workflow.

Simple and Efficient Laser-Induced Evaporation Assembly Method to Fabricate SERS Optical Fiber Probe for Detection of PAHs

Simple and Efficient Laser-Induced Evaporation Assembly Method to Fabricate SERS Optical Fiber Probe for Detection of PAHs

Upconverting thermal history paint for investigations of short thermal events

The main goal of the work was to develop phosphorescent coating for investigations of surface temperature distribution resulted from short duration and high energy thermal events such as small rocket engine testing. For that purpose, we developed thermal history paint with upconverting Gd2O3: Er3+, Yb3+, Mg2+ nanopowder. The developed paint was heated by Joule effect with precise control over temperature and heating time. Photoluminescence signal of cooled samples was excited with 980 nm laser and collected in automatic manner with use of an optical fibre probe connected to photospectrometer. The results show that irreversible changes of paint emission are temperature and heating time specific for calcination temperatures from 700 °C to 1150 °C. Calibration curves were prepared for heating times of 10, 60 and 180 seconds. Finally, 2D surface temperature samples were determined with use of upconverting thermal history paint and compared to IR camera and pyrometric measurements. The results indicate that uncertainty of temperature measurement below 10 °C was achieved for temperatures above 1000 °C. It has been demonstrated that developed thermal history paint allows for measurements of 2D surface temperature distribution with high spatial resolution and good agreement to standard measurements techniques like thermal camera and pyrometer.

Assessment of bending waves in Torsion Hopkinson Bar experiments using Photon Doppler Velocimetry

A Photon Doppler Velocimetry system that measures the propagation of elastic shear waves in a Torsion Hopkinson Bar (THB) system is presented. The method uses multiple fibre optic probes located symmetrically on opposing sides of the apparatus bars, and provides data with high spatial (a laser irradiated spot size of 35μm) and temporal resolution that is ultimately limited by the data acquisition system and used electronic components. A series of validation experiments simulating the movement of the bar subjected to bending and misalignments demonstrated that this approach is effective in detecting and accounting for the bending waves. The THB experiment under non-ideal conditions, where a combination of shear and bending waves propagates in the system, conclusively confirmed that the disturbance in the acquired signals can be properly addressed with the proposed arrangement of the PDV probes. It was reflected in similar measurements of the component of tangential velocity to the strain gauges. This approach shown to be complementary to the conventional strain gauge technique, but can provide better precision and be more robust under loading and/or temperature conditions that may affect the reliability of strain gauge measurements.

Detection of picometer scale vibration based on the microsphere near-field probe

We introduce an innovative vibration detection method utilizing a microsphere near-field probe, affixed to an optical fiber probe. Notably, when the microsphere probe is positioned at a distance of approximately 100 nm from the vibrating objects, it exhibits a substantial increase in detection sensitivity, enabling the detection vibration as small as 5 pm. This enhancement arises from the strong near-field interaction between the sample and probe, where the evanescent wave dominates. This effect is confirmed for the first-time through both theoretical analysis and experimental validation. This innovative probe has great potential for applications in cellular acoustics, vibrational detection of biomolecules and their complexes, in situ measurements, and imaging of microstructures and nanostructures.

Spatially Resolved Fibre-Optic Probe for Cervical Precancer Detection Using Fluorescence Spectroscopy and PCA-ANN-Based Classification Algorithm: An In Vitro Study.

Cervical cancer can be detected at an early stage through the changes occurring in biochemical and morphological properties of epithelium layer. Fluorescence spectroscopy has the ability to identify these subtle changes non-invasively and in real time with good accuracy in comparison with conventional techniques. In this paper, we report the usage of a custom designed spatially resolved fibre-optic probe (SRFOP), which consists of 77 fibres in two concentric rings, for the detection of cervical cancer using fluorescence spectroscopy technique. The aim of this study is to classify different grades of cervical precancer on the basis of their fluorescence spectra followed by a robust classification algorithm. Fluorescence spectra of 28 cervical tissue samples of different categories have been recorded using six detector fibres of FOP at different spatial locations with the source fibre (SF). A 405 nm laser diode source has been utilised to excite the samples and a USB 4000 Ocean Optics spectrometer to collect the output spectra in the wavelength range 400-700 nm. Principal component analysis (PCA) was applied to the collected spectra to reduce the dimensionality of the data while preserving the most significant features for classification. The first 10 principal components, which captured the majority of the variance in the spectra, were selected as input features for the classification model. Classification was then performed using an artificial neural network (ANN) with a specific architecture, including an input layer, hidden layers, and a softmax activation function in the output layer. Experimental and classification results both demonstrate that proximal fibres (PFs) perform better than distal fibres (DFs) in capturing the discriminatory features present in the epithelium layer of cervical tissue samples as PF collect most of the signal from the epithelium layer. The combined approach of spatially resolved fluorescence spectroscopy and PCA-ANN classification techniques is able to discriminate different grades of cervical precancer and normal with an average sensitivity, specificity and accuracy of 93.33%, 96.67% and 95.57%, respectively.

Expedient measurement of total protein in human serum and plasma via the biuret method using fiber optic probe for patient samples and certified reference materials.

The biuret method is currently recognized as a reference measurement procedure for serum/plasma total protein by the Joint Committee for Traceability in Laboratory Medicine (JCTLM). However, as the reaction involved in this method is highly time-dependent, to ensure identical measurement conditions for calibrator and samples for high accuracy, a fast and simple measurement procedure is critical to ensure the precision and trueness of this method. We measured serum/plasma total protein using a Cary 60 spectrophotometer coupled with a fiber optic probe, which was faster and simpler than the conventional cuvette method. The biuret method utilizing alkaline solutions of copper sulfate and potassium sodium tartrate was added to the sample and calibrator (NIST SRM 927e) incubated for 1h before measurement. A panel of samples consisting of pooled human serum, single donor serum, and certified reference materials (CRMs) from three sources were measured for method validation. Sixteen native patient samples were measured using the newly developed biuret method and compared against clinical analyzers. Additionally, the results of three cycles of a local External Quality Assessment (EQA) Programme submitted by participating clinical laboratories were compared against the biuret method. Our biuret method using fiber optic probe demonstrated good precision with within-day relative standard deviation (RSD) of 0.04 to 0.23% and between-day RSD of 0.58%. The deviations between the obtained values and the certified values for all three CRMs ranged from -0.38 to 1.60%, indicating good method trueness. The routine methods using clinical analyzers were also found to agree well with the developed biuret method using fiber optic probe for EQA samples and native patient samples. The biuret method using a fiber optic probe represented a convenient and reliable way of measuring serum total protein. It also demonstrated excellent precision and trueness using CRMs and patient samples, which made the method a simpler candidate reference method for serum protein measurement.

Cerebral Microcirculation: Progress and Outlook of Laser Doppler Flowmetry in Neurosurgery and Neurointensive Care.

Laser Doppler flowmetry (LDF) is a well-established technique for the investigation of tissue microcirculation. Compared to skin, the use in the human brain is sparse. The measurement of cerebral microcirculation in neurointensive care and during neurosurgery is challenging and requires adaptation to the respective clinical setting. The aim of the review is to present state of the art and progress in neurosurgery and neurointensive care where LDF has proven useful and can find clinical importance in the investigation of cerebral microcirculation. The literature in the field is summarized and recent technical improvements regarding LDF systems and fiber optical probe designs for neurosurgical and neurocritical care described. By combining two signals from the LDF unit, the measurement of the microcirculation (Perfusion) and gray whiteness (TLI) of the brain tissue, the full potential of the device is achieved. For example, a forward-looking LDF-probe detects high-risk hemorrhage areas and gray-white matter boundaries along intraoperative trajectories during stereotactic neurosurgery. Proof of principles are given for LDF as a guidance tool in deep brain stimulation implantation, brain tumor needle biopsies, and as long-term monitoring device in neurocritical care. With well-designed fiber optical probes, surgical fixation, and signal processing for movement reduction, LDF monitoring of the cerebral microcirculation is successful up to 10 days. The use of LDF can be combined with other physiological measurement techniques, for example, fluorescence spectroscopy for identification of glioblastoma during tumor surgery. Fiber optics can also be used during magnetic resonance imaging (MRI). Despite the many advantages, fiber optical LDF has not yet reached its full potential in clinical neuro-applications. Multicenter studies are required to further evaluate LDF in neurosurgery and neurointensive care. In conclusion, the present status of LDF in neurosurgery and neurointensive care has been reviewed. By combining Perfusion and TLI with tailored probe designs the full potential of LDF can be achived in measuring cerebral microcirculation. This includes guidance during DBS implantation and needle biopsies, and long-term monitoring in neurocritical care.

Controlling spatial optical illuminations in optogenetics using an angled optical fiber tip

The advent of optogenetic tools has revolutionized neuroscience research through its spatiotemporally precise activation of specific neurons by illuminating light on opsin-expressing neurons. A long-standing challenge of in vivo optogenetics remains in delivering light to multiple brain sites simultaneously and maintaining high spatial resolution. Optical fiber-based technologies have been proposed to address these challenges. This work presents the fabrication and characterization of an innovative angled optical fiber probe based on a double-sided angled tip (DSAT) structure. A custom griding setup was used for the reproducible fabrication of a smooth DSAT probe. The designed probe enables precise spatial control of light propagation in brain tissue in which DSAT at angled tip 55° achieving a maximum lateral illumination position of ± 420 μm away from the optical axis and a peak irradiance of 478.5 mW/mm2, using a 5 mW of 473 nm laser light. Also, the designed DAST probe was simulated based on ray tracing method and obtained the practical tip angle to evaluate the propagation of light rays emitted from the DSAT at various input optical angles ranging from 0° to 12.5° to predict their irradiance and positions in the modelled tissue. The results indicate the probe generates two elliptical rings each containing two spots with higher optical concentration. Consequently, this device provides four optical spots with irradiance peaks that enable simultaneous illumination of four different locations in the brain tissue. Obtained experiment results are in good agreement with simulation results which can be used for multipoint illumination of brain tissue in optogenetics applications.