Optical Fiber Tip Research Articles

On the possible ultrasonic inspection of micro-bubbles generated by the optical fiber tip

We demonstrate the possibility of detection and monitoring of bubbles emerging near the tip of an optical fiber by means of ultrasonic method. The excitation of bubbles at their resonant frequencies is performed using short ultrasonic pulses having a wide frequency range simultaneously with their modulation by means of a long pulse of a monochromatic frequency. This method allows detection of bubbles of various sizes. Used signal processing method, which allows increased bubble detection accuracy, is proposed for research in environments of biological-like medium which show continuous variations in structure and properties when exposed to optical emission. The method has been demonstrated on model objects: in a liquid and in a biological tissue phantom using various methods of bubble generation (hydrolysis and optical emission). We studied bubble formation by the tip of a fiber of the surgical laser LSP-007/10 “IRE Polus” with a wavelength of 0.97[Formula: see text][Formula: see text]m coated with a highly absorbing graphite layer.

Quality Detection of Alcoholic Beverages Using Optical Fiber Tips

This paper presents the direct detection of the quality of alcoholic beverages by simultaneously measuring the refractive index and evaporation rate using an optical fiber tip. The fiber tip acts as a submicrometer axicon lens. The optical path difference between the glass tip and outside medium results in a focused spot with its intensity modulated by the refractive index (RI) of the medium. The intensity sensitivity is as high as 5000%/RI unit for 32° tapered angle. When the fiber tip is immersed in a drop (300 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{L}$ </tex-math></inline-formula> ) of alcohol, the measured optical intensity is gradually decreased due to the evaporation of solvent. The evaporation rate and the refractive index are intrinsic properties for various alcoholic beverages. Both parameters can be used together to identify the quality with high sensitivity and specificity. We used the sensitive fiber to detect different wines, wine frauds with methanol and water. Clear differences for different ratios of the fake wines were observed from the initial RI and evaporation rate.

Analysis of a plasmonic based optical fiber optrode with phase interrogation

Abstract Optical fiber optrodes are attractive sensing devices due to their ability to perform point measurement in remote locations. Mostly, they are oriented to biochemical sensing, quite often supported by fluorescent and spectroscopic techniques, but with the refractometric approach considered as well when the objective is of high measurement performance, particularly when the focus is on enhancing the measurand resolution. In this work, we address this subject, proposing and analyzing the characteristics of a fiber optic optrode relying on plasmonic interaction. A linearly tapered optical fiber tip is covered by a double overlay: the inner one–a silver thin film and over it–a dielectric layer, with this combination allowing to achieve, at a specific wavelength range, surface plasmonic resonance (SPR) interaction sensitive to the refractive index of the surrounding medium. Typically, the interrogation of the SPR sensing structures is performed, considering spectroscopic techniques, but in principle, a far better performance can be obtained, considering the reading of the phase of the light at a specific wavelength located within the spectral plasmonic resonance. This is the approach which is studied here in the context of the proposed optical fiber optrode configuration. The analysis performed shows the combination of a silver inner layer with a dielectric titanium oxide layer with tuned thicknesses enables sensitive phase reading and allows the operation of the fiber optic optrode sensor in the third telecommunication wavelength window.

PH-Dependent response of a hydrogen peroxide sensing probe

The response of a fiber-optic hydrogen peroxide (H2O2) sensing probe is investigated under a range of pH conditions. The H2O2 optrode is prepared by depositing a thin layer of Prussian blue (PB) onto the tip of a multimode optical fiber, and its detection mechanism is based on the PB/Prussian white (PW) redox reaction. PW is oxidized to PB by H2O2 leading to changes in the absorption of visible light. The sensor can be restored after usage by reducing the PB to PW with ascorbic acid. This optrode was previously shown to have good repeatability and sensitivity to H2O2 concentrations at room temperature and a pH of 4. For practical applications, the sensor must be capable of detecting H2O2 in environments spanning a range of pH conditions, including biological and industrial environments which together span pH values from 7 to less than 3. We present experiments using multiple PB optrodes, at pH values ranging from 7 to 2, and for different concentrations of H2O2. The work demonstrates that the optrode remains functional and provides stable and reproducible measurements of H2O2 under a range of pH conditions that correspond, in particular, to those in an operating PEM fuel cell.

Fabrication of a phase photon sieve on an optical fiber tip by focused ion beam nanomachining for improved fiber to silicon photonics waveguide light coupling.

PSS) as an alternative, more advantageous method to the metallization prior to FIB milling. The near field scans of the intensity profile along the optical axis under fiber illumination of a laser at λ = 1.55 μm are presented. We have analyzed the focusing properties and demonstrated the validity of our structure for light coupling into silicon photonics waveguides with improved efficiency and alignment tolerance.

Optical fibers as beam shapers: from Gaussian beams to optical vortices.

This Letter reports a new method for the generation of optical vortices using a micropatterned optical fiber tip. Here, a spiral phase plate (2π phase shift) is micromachined on the tip of an optical fiber using a focused ion beam. This is a high resolution method that allows milling the fibers with nanoscale resolution. The plate acts as a beam tailoring system, transforming the fundamental guided mode, specifically a Gaussian mode, into the Laguerre-Gaussian mode (LG01), which carries orbital angular momentum. The experimental results are supported by computational simulations based on the finite-difference time-domain method.

Optical fiber tip-based quartz-enhanced photoacoustic sensor for trace gas detection

We reported the development of an evanescent-wave quartz-enhanced photoacoustic sensor (EW-QEPAS) using a single-mode optical fiber tip for sensitive gas detection in the extended near-infrared region. It is a spectroscopic technique based on the combination of quartz-enhanced photoacoustic spectroscopy with fiber-optic evanescent-wave absorption to achieve low optical noise, easy optical alignment, and high compactness. Carbon monoxide (CO) detection at 2.3 μm using a fiber-coupled, continuous-wave, distributed-feedback laser was selected for the sensor demonstration. By tapering the optical fiber down to 2.5 μm diameter using the flame-brushing technique, an evanescent field of ~0.6 mW around the fiber tip was absorbed by CO molecules. Besides an excellent linear response (R 2 = 0.9996) to CO concentrations, the EW-QEPAS sensor achieved a normalized noise-equivalent absorption (NNEA) coefficient of 8.6 × 10−8 cm−1W/√Hz for an incident optical power of 1.8 mW and integration time of 1 s. The sensor detection sensitivity can be further improved by enhancing the evanescent-wave power on the fiber tip.

Control of Bubble Formation at the Optical Fiber Tip by Analyzing Ultrasound Acoustic Waves

The problems of controlling the processes of generation of acoustic waves and microbubbles at the optical fiber tip of moderate-power surgical lasers with wavelengths of 1.9 µm and 0.97 µm using active and passive acoustic methods are considered. It is shown that microbubbles of various sizes can be detected with an ultrasound method, in which the interaction area is recorded simultaneously at two frequencies. By measuring noise with a receiving transducer of an ultrasonic locator, we determine the frequency range of the acoustic signals occurring when large diameter bubbles, including gas-vapor bubbles, collapse. Model experiments are conducted to detect noise and bubbles in water and in a water-saturated 1.5% agarose phantom at various laser powers with an optical fiber tip having a strongly absorbing coating.

Multipoint Hydrogen Sensing of Hetero-Core Fiber SPR Tip Sensors With Pseudorandom Noise Code Correlation Reflectometry

In this paper, we describe multipoint hydrogen sensing in real time using surface plasmon resonance (SPR) fiber optic hydrogen tip sensors with Au/Ta2O5/Pd multilayers film combined with a time-domain interrogating system based on pseudorandom noise code correlation reflectometry. This method uses the correlation between a launched pseudorandom noise code signal and its reflection enabling simultaneous measurement at many points along the optical fiber in real time with a high signal-to-noise ratio. In a light intensity-based experiment with an 850-nm LED, the tested three hetero-core optical fiber hydrogen tip sensors proved to be reproducible responses with and without hydrogen absorption, with showing the similar time response and sensitivity compared with those of our previously reported sensor. Multipoint hydrogen detection was demonstrated using four SPR hydrogen tip sensors. Our experimental results showed that four sensors using the 25 nm Au/60 nm Ta2O5/5 nm Pd multilayer film exhibited a response time of $\sim 25$ s for a 4% hydrogen concentration. In addition, it was found that all sensors can detect the hydrogen concentration with sufficient sensitivities in real time.

Photothermal lesions in soft tissue induced by optical fiber microheaters.

Photothermal therapy has shown to be a promising technique for local treatment of tumors. However, the main challenge for this technique is the availability of localized heat sources to minimize thermal damage in the surrounding healthy tissue. In this work, we demonstrate the use of optical fiber microheaters for inducing thermal lesions in soft tissue. The proposed devices incorporate carbon nanotubes or gold nanolayers on the tips of optical fibers for enhanced photothermal effects and heating of ex vivo biological tissues. We report preliminary results of small size photothermal lesions induced on mice liver tissues. The morphology of the resulting lesions shows that optical fiber microheaters may render useful for delivering highly localized heat for photothermal therapy.

Embedded structure fiber-optic radiation dosimeter for radiotherapy applications

An investigation into a novel in-vivo PMMA (polymethyl methacrylate) plastic fiber-optic dosimeter for monitoring low doses of ionizing radiotherapy radiation in real time and for integrating measurements is presented. The fabricated optical fiber tip possessed an embedded structure. A scintillation material, terbium-doped gadolinium oxysulfide (Gd2O2S:Tb), capable of emitting visible light at around 545 nm which is ideal for transmission through the PMMA when exposed to ionizing radiation was embedded in the PMMA plastic fiber. The dose rate of incident ionizing radiation is measured by analyzing the signal intensity emitted from the scintillation material which propagates through the fiber to a distal MPPC (multi-pixel photon counter). The dosimeter exhibits good repeatability with an excellent linear relationship between the fiber-optic dosimeter output and the absorbed radiation dose with an outstanding isotropic response in its radial angular dependence.

Sensitive Detection of Small Particles in Fluids Using Optical Fiber Tip with Dielectrophoresis.

This work presents using a tapered fiber tip coated with thin metallic film to detect small particles in water with high sensitivity. When an AC voltage applied to the Ti/Al coated fiber tip and indium tin oxide (ITO) substrate, a gradient electric field at the fiber tip induced attractive/repulsive force to suspended small particles due to the frequency-dependent dielectrophoresis (DEP) effect. Such DEP force greatly enhanced the concentration of the small particles near the tip. The increase of the local concentration also increased the scattering of surface plasmon wave near the fiber tip. Combined both DEP effect and scattering optical near-field, we show the detection limit of the concentration for 1.36 μm polystyrene beads can be down to 1 particle/mL. The detection limit of the Escherichia coli (E. coli) bacteria was 20 CFU/mL. The fiber tip sensor takes advantages of ultrasmall volume, label-free and simple detection system.

Method for producing angled optical fiber tips in the laboratory

A simple laboratory method is presented for producing optical fibers with tips polished at various angles. Angled optical fiber tips are used in applications such as optical sensing and remote laser surgery, where they can be used to control the angle of light leaving the fiber or direct it to the side. This allows for greater control and allows areas to be reached that otherwise could not. Optical fibers were produced with tip angles of 45 deg using a Perspex mounting block with an aluminum base plate. The dispersion of light leaving the tip was tested using a blue (470 nm) LED. The angle imposed an angular shift on the light diffracting out of the tip of approximately 30 deg. Additionally, some light reflected from the tip surface to diffract at 90 deg through the side of the fiber. These observations are consistent with theory and those seen by other studies, validating the method. The method was simple to perform and does not require advanced manufacturing tools. The method is suitable for producing small quantities of angle-tipped optical fibers for research applications.

Preliminary scanning fluorescence detection of a minute particle running along a waveguide implemented microfluidic channel using a light switching mechanism

It has long been thought that an optical sensor, such as a light waveguide implemented total analysis system (TAS), is one of the functional components that will be needed to realize a "ubiquitous human healthcare system" in the near future. We have already proposed the fundamental structure for a light waveguide capable of illuminating a living cell or particle running along a microfluidic channel, as well as of detecting fluorescence even from the extremely weak power of such a minute particle. In order to develop novel functions to detect the internal structure of living cells quickly, an angular scanning method that sequentially changes the direction of illumination of the minute cell or particle may be crucial. In this paper, we investigate fluorescence detection from moving particles by switching the laser power delivery path of plural light waveguides as a preliminary experiment toward this novel method. To construct an experimental system able to incorporate a switching light source mechanism cost effectively, we utilized a conventional TAS chip with plural waveguide pairs arranged in parallel, and a forced vibration mechanism on an optical fiber tip by a piezoelectric actuator. With this system, we performed an experiment to detect extremely weak fluorescence using micro particles with a fluorescent substance attached and an optical TAS chip that incorporated a microfluidic channel and three pairs of laser-power-delivering light waveguide cores. We successfully obtained clear, quasi-triangular-shaped pulses in fluorescent signals from resin particles running across the intersection under three different conditions: (1) a particle with approximately the same velocity as that of a forced-vibrated optical fiber tip of approximately 700 mm/s, (2) a particle with velocity 1 digit smaller than that of an optical fiber tip, and (3) a particle with velocity approximately 1/20 that of an optical fiber tip.

Dielectric-Grating-Coupled Surface Plasmon Resonance From the Back Side of the Metal Film for Ultrasensitive Sensing

We propose a dielectric grating that can launch surface plasmon resonance (SPR) modes efficiently on the other side of flat metal films, which is similar to the conventional prism coupling mechanism. Importantly, this structure can excite SPR under the normal incident light, which is particularly suitable for the integration with optical fiber tips. By launching the SPR mode near the wavelength of 1.55 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu\text{m}$</tex-math></inline-formula> with a very narrow resonance line width (∼4 nm), this structure is promising for the development of high-performance portable, flexible, and real-time refractometric sensing applications.

Metallic Nanoislands on Graphene as Highly Sensitive Transducers of Mechanical, Biological, and Optical Signals.

This article describes an effect based on the wetting transparency of graphene; the morphology of a metallic film (≤20 nm) when deposited on graphene by evaporation depends strongly on the identity of the substrate supporting the graphene. This control permits the formation of a range of geometries, such as tightly packed nanospheres, nanocrystals, and island-like formations with controllable gaps down to 3 nm. These graphene-supported structures can be transferred to any surface and function as ultrasensitive mechanical signal transducers with high sensitivity and range (at least 4 orders of magnitude of strain) for applications in structural health monitoring, electronic skin, measurement of the contractions of cardiomyocytes, and substrates for surface-enhanced Raman scattering (SERS, including on the tips of optical fibers). These composite films can thus be treated as a platform technology for multimodal sensing. Moreover, they are low profile, mechanically robust, semitransparent and have the potential for reproducible manufacturing over large areas.

Photoacoustic shock wave emission and cavitation from structured optical fiber tips

Photoacoustic waves generated at the tip of an optical fiber consist of a compressive shock wave followed by tensile diffraction waves. These tensile waves overlap along the fiber axis and form a cloud of cavitation bubbles. We demonstrate that shaping the fiber tip through micromachining alters the number and direction of the emitted waves and cavitation clouds. Shock wave emission and cavitation patterns from five distinctively shaped fiber tips have been studied experimentally and compared to a linear wave propagation model. In particular, multiple shock wave emission and generation of strong tension away from the fiber axis have been realized using modified fiber tips. These altered waveforms may be applied for novel microsurgery protocols, such as fiber-based histotripsy, by utilizing bubble-shock wave interaction.

Polymer Optical Fiber Compound Parabolic Concentrator fiber tip based glucose sensor: in-Vitro Testing

We present in vitro sensing of glucose using a newly developed efficient optical fiber glucose sensor based on a compound parabolic concentrator (CPC)-tipped polymer optical fiber (POF). A batch of nine CPC-tipped POF sensors with a 35-mm fiber length is shown to have an enhanced fluorescence pickup efficiency with an average increment factor of 1.7 as compared with standard POF sensors with a plane cut fiber tip. in vitro measurements for two glucose concentrations (40 and 400 mg/dL) confirm that the CPC-tipped sensors can efficiently detect both glucose concentrations.

A Dual Sensor for pH and Hydrogen Peroxide Using Polymer-Coated Optical Fibre Tips.

This paper demonstrates the first single optical fibre tip probe for concurrent detection of both hydrogen peroxide (H2O2) concentration and pH of a solution. The sensor is constructed by embedding two fluorophores: carboxyperoxyfluor-1 (CPF1) and seminaphtharhodafluor-2 (SNARF2) within a polymer matrix located on the tip of the optical fibre. The functionalised fibre probe reproducibly measures pH, and is able to accurately detect H2O2 over a biologically relevant concentration range. This sensor offers potential for non-invasive detection of pH and H2O2 in biological environments using a single optical fibre.

Fabrication of Tapered Tip Fibers With a Controllable Cone Angle Using Dynamical Etching

Recently, optical fiber tips have been used in many scientific applications requiring a special tip with a predetermined cone angle. In this study, we have developed a new type of dynamic chemical etching for fabricating fiber tips which enables us to fabricate tips with predetermined cone angles. The fiber tips are fabricated by injecting or withdrawing hydrofluoric acid to the container in which the fiber is vertically inserted. By changing the flow rate of the acid injection or withdrawal, the height of the fiber in contact with the acid can be controlled. This method produces cone angles from 3° to 33°. Additionally, a model is proposed for this procedure which covers all the special cases and is in good agreement with the experimental results.