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Results for “Optical Fibers”

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At least 91 records · Page 5Linked to original sources
PubMed1988

Fiber optic surface fluorometry/reflectometry and 31-p-NMR for monitoring the intracellular energy state in vivo.

Various members of the respiratory chain exhibit different optical properties in the reduced and oxidized forms, thus enabling the non-invasive monitoring of various organs in vitro as well as in vivo. Since the pioneering work of Chance, Cohen, Jobsis and Schoener in 1962, many groups of investigators adopted their approach in monitoring NADH oxidation reduction states in vivo for the brain as well as for other body organs. In 1972, we introduced flexible, optical fibers into the surface fluorometry replacing the usual "rigid" optical system used by other groups. During the last decade, this technique has been developed, improved and applied to many experimental setups in brain research and very recently was combined with 31P NMR spectroscopy for the puppy and the adult dog brain in vivo. In our system, the effects of movement artifacts and changes in blood oxygenation are negligible while the effects of tissue absorption or blood volume changes are considerable and could be minimized by subtraction of the reflectance signal from that of the fluorescence (1:1 ratio) providing the corrected fluorescence signal.

Anaerobiosis↗
PubMed2004

Optical fiber relative-humidity sensor with polyvinyl alcohol film.

We describe a fiber-optic relative-humidity (RH) sensor comprising a moisture-sensitive overlay on a single-mode side-polished fiber. The hygroscopic polymeric material deposited was polyvinyl alcohol (PVA), which proved to have good adherence and stability. The film reached a fast equilibrium with atmospheric moisture (in less than 1 min), inducing changes in the output optical power of approximately 10 dB for the 70%-90% RH range. To yield a low-cost device, single-mode standard communication fibers were used; therefore all the components of the sensor can be commercial, mass-produced telecommunication devices. The experimental results obtained are consistent with the expected behavior of the system; the output power decreases because of losses in the polished region of the fiber as the refractive index of its external medium approaches the fiber core value. Because the external medium is PVA film, its refractive index changes in response to its water content.

Journal Article↗
PubMed2005

Optical-fiber source of polarization-entangled photons in the 1550 nm telecom band.

We present a fiber-based source of polarization-entangled photons that is well suited for quantum communication applications in the 1550 nm band of standard fiber-optic telecommunications. Polarization entanglement is created by pumping a nonlinear-fiber Sagnac interferometer with two time-delayed orthogonally polarized pump pulses and subsequently removing the time distinguishability by passing the parametrically scattered signal and idler photon pairs through a piece of birefringent fiber. Coincidence detection of the signal and idler photons yields biphoton interference with visibility greater than 90%, while no interference is observed in direct detection of either signal or idler photons. All four Bell states can be prepared with our setup and we demonstrate violations of the Clauser-Horne-Shimony-Holt form of Bell's inequality by up to 10 standard deviations of measurement uncertainty.

Journal Article↗
PubMed2002

Dual temperature and strain measurement with the combined fluorescence lifetime and Bragg wavelength shift approach in doped optical fiber.

We have constructed fiber-optic sensors to measure temperature and strain by combining the properties of fiber Bragg gratings with the fluorescent lifetimes of various doped fibers. Sensors have been made with the fiber Bragg grating written directly into the doped fiber to ensure the collocation of the strain and temperature measurement points. Results are compared with those obtained previously from a Bragg grating written into standard photosensitive fiber spliced to doped fiber. Standard deviation errors of 7 microepsilon and 0.8 degrees C have been obtained for strain and temperature ranges of up to 1860 microepsilon and 120 degrees C, respectively.

Journal Article↗
PubMed2006

Picoliter droplet formation on thin optical fiber tips.

In this paper, we present experimental results on how minute droplets are formed on fiber optic end faces. Results show that reproducible picoliter volumes can be generated when fibers are retracted from an aqueous phase contained under an inert fluorinated immiscible liquid, with a coefficient of variation (CV) of 0.7-2.3%. The droplet formation was analyzed as a function of the fiber diameter, retraction speed, and wettability. Experiments reveal a volume-determining critical equilibrium contact angle between 60 degrees and 75 degrees , defining the onset of fiber end-face dewetting. The dynamics of the droplet snap-off progression was characterized using high-speed imaging in order to explain the observed wettability-volume dependency.

Journal Article↗
PubMed2003

Erbium-doped optical fiber fluorescence temperature sensor with enhanced sensitivity, a high signal-to-noise ratio, and a power ratio in the 520-530- and 550-560-nm bands.

We analyze and predict the performance of a fiber-optic temperature sensor from the measured fluorescence spectrum to optimize its design. We apply this analysis to an erbium-doped silica fiber by employing the power-ratio technique. We develop expressions for the signal-to-noise ratio in a band to optimize sensor performance in each spectral channel. We improve the signal-to-noise ratio by a factor of 5 for each channel, compared with earlier results. We evaluate the analytical expression for the sensor sensitivity and predict it to be approximately 0.02 degrees C(-1) for the temperature interval from room temperature to above 200 degrees C, increasing from 0.01 degrees C(-1) at the edges of the interval to 0.03 degrees C(-1) at the center, at 100-130 degrees C. The sensitivity again increases at temperatures higher than 300 degrees C, delineating its useful temperature intervals.

Journal Article↗
PubMed1997

Photostimulation with caged neurotransmitters using fiber optic lightguides.

'Caged' neurotransmitters are molecules that are transformed to a neuroactive state by exposure to light of an appropriate wavelength and intensity. Use of these substances has centered on in vitro bath application and subsequent activation using light from lasers or flashlamps that is delivered into the preparation through microscope optics. We have tested a new and simpler method, using finely tapered fiberoptic lightguides, that promises to expand the use of caged compounds for in vitro and in vivo experimentation. We demonstrated the feasibility and flexibility of this method for caged neurotransmitter delivery using a range of ex vitro, in vitro and in vivo approaches. The degree and timing of uncaging could be controlled by manipulating the wavelength, intensity and timing of the light projected into the optical fiber. Because of the small size of the light guide and the ability to control light exposure at the source, this new method promises greater control over the spatial and temporal delivery of neuroactive substances than simple bath or iontophoretic application, and enables delivery of conventional neurotransmitters with a spatial and temporal resolution closer to that of the natural neuronal circuitry. In addition, this new method allows the application of normally labile substances, such as the free radical gas nitric oxide, by the photoconversion of photosensitive precursors.

Animals↗
PubMed2003

Axial resolution limit of a fiber-optic fluorescence probe.

We examine the limit of spatial resolution achievable when a sine optical fiber is used for excitation and collection of fluorescence from a bulk specimen. We calculate the probability of detecting a fluorescent particle as a function of its position relative to the fiber face, using excitation wavelength lambda, radius a, numerical aperture N.A., and the particle's fluorescence and absorbance spectra. Treating Rhodamine B as a model fluorescent analyte and using appropriate fiber parameters, we show that the maximum axial resolution (defined as the axial distance in a homogenous solution within which 50% of the detected signal originates) achievable is approximately 10 microm. We experimentally measured the axial resolution for a 500-microM aqueous solution of Rhodamine B with lambda = 543 nm, a = 1.31 microm, and a N.A. of 0.16 and found good qualitative agreement with the calculation.

Journal Article↗
PubMed2006

High-bandwidth laser frequency stabilization to a fiber-optic delay line.

Stabilization of laser frequency to interferometers with a large time delay in one arm is of significant interest to space-based gravitational wave detectors such as the Laser Interferometer Space Antenna. A recently proposed technique allows a control bandwidth larger than the inverse delay time to be achieved. We present experimental results demonstrating laser frequency stabilization to an optical fiber delay line. A control bandwidth approximately 50 times the inverse delay time is demonstrated.

Journal Article↗
PubMed2006

Electro-optic fiber sensor for amplitude and phase detection of radio frequency electromagnetic fields.

We present a miniature fiber-optic electromagnetic field (EMF) sensor that is capable of simultaneously detecting the amplitude and phase of an EMF in the range of 0.1-6 GHz. We focus on magnetic field measurements, since the H-field is more significant in our target applications due its direct relation to the current. The sensor is based on an open optical platform to which various antennas can be attached and contains a radio-frequency amplifier for signal conditioning and a vertical-cavity surface-emitting laser as an electro-optic converter. The millimeter size and the full electrical isolation of the sensor allow EMF detection with minimal disturbance. We have characterized the sensor in the near field of a lambda/2 dipole, a rectangular waveguide, and a microstrip line, and we explain the experimental results with a simple theoretical model confirming the mapped near-field distribution of the investigated field source.

Journal Article↗
PubMed2005

A MULTICHANNEL FIBER-OPTIC MAPPING SYSTEM FOR INTRAMURAL RECORDING OF CARDIAC ACTION POTENTIALS.

Measuring cardiac action potentials at many sites within the ventricular wall is important for understanding cardiac arrhythmias; however, recording in the depth of the heart wall presents many difficulties. We have developed a multichannel optical mapping system for recording cardiac action potentials transmurally. Each channel uses a single small-diameter optical fiber to transmit and collect light from the cardiac tissue. Excitation light is supplied by low-power green lasers. Wavelength separation is performed with a dichroic mirror, and fluorescence is detected with a photodiode. We have recorded action potentials with an unfiltered signal-to-noise ratio (SNR) as high as 60:1 and a temporally filtered SNR as high as 200:1. The collection of fluorescence is optimized so that low excitation light intensity can be used, which increases the available recording time. Channels are modular and compact, and the system can be easily expanded to include additional channels, ratiometry or dual-dye mapping. In addition, the system is highly flexible and can be used for virtually any experiment from single cell recording to surface and transmural mapping of the whole heart.

Journal Article↗
PubMed2006

Application of micro-attenuated total reflectance infrared spectroscopy to quantitative analysis of optical fiber coatings: effects of optical contact.

Micro-attenuated total reflectance (ATR) infrared spectroscopy is one of the few methods applicable for an in situ analysis of polymer coatings. In this method, the information is collected using an internal reflection element (IRE), which is brought into contact with the coated substrate. Perfect optical contact is hardly achievable for non-flat substrates and/or for those samples that cannot be well aligned with respect to the IRE. Consequently, the infrared peak intensities, their ratios, and all quantities calculated from the spectra become dependent upon the optical contact quality. In this work, we suggest a model that describes the peak intensities in terms of the optical contact. As an illustration, we apply this model to polymer-coated optical fibers. Relatively small diameters of tested fibers and their cylindrical shape result in imperfect optical contact between the sample and the IRE. Spectroscopic approaches of determining the degree of cure of polymer coatings are analyzed in view of the obtained results. Ways of minimizing the error induced by imperfect optical contact are suggested.

Absorption↗
PubMed2004

Mechanical and optical characteristics of a new fiber optical system used for cardiac contraction measurement.

In order to obtain a better physiological performance and a closer restoration of the regular rhythm of failing hearts, a new fiber optical sensor system for the measurement of cardiac contraction has been developed. It consists of an opto-electrical unit and a sensing fiber which has to be positioned in the heart. The objective of this new fiber optic sensor system is to use the inotropic information to adjust a stimulation algorithm in single or multichamber pacing or to detect arrhythmia in insufficient heart function. In this study, the mechanical and optical characteristics of different fibers are investigated. The relationship between the attenuation (with an achieved numerical maximum of 0.3 dB), the bending diameter and the angle of bending is determined in a range of 20-160 mm. The most suitable fiber for the application in cardiological problems is determined (WT8 fiber), for which the sensitivity is analyzed. Additionally, power spectra are calculated from WT8 fiber signals obtained from pig hearts, working under physiological conditions. The maximal frequency response was 23 Hz. It is concluded that the fiber optical measurement of cardiac contraction is not only feasible and reproducible, but the WT8 fiber also shows optimal behavior in the range of parameters occurring in the heart chambers. Nevertheless, in order to restrict the measured signal reliably to bending processes within the chambers only, it is concluded that a special combined fiber has to be constructed with a high sensitivity only at its terminal section within the heart.

Algorithms↗
PubMed2000

Intracellular measurements in mammary carcinoma cells using fiber-optic nanosensors.

Submicrometer fiber-optic biosensors have been developed and used to measure toxic chemicals within single cells. Optical fibers that have been pulled to a distal-end diameter of less than 1 micrometer are coated with antibodies to selectively bind the species of interest. This paper describes the use of these fibers to selectively measure the concentration of benzo[a]pyrene tetrol (BPT), a metabolite of benzo[a]pyrene, within individual cells of two different cell lines, human mammary carcinoma cells and rat liver epithelial cells. The results from these measurements have been used to determine the sensitivity, reproducibility, and usefulness of these nanosensors. The detection limit of these biosensors has been determined to be 0.64 +/- 0.17 x 10(-11) M for BPT.

Animals↗
PubMed1994

An evanescent wave biosensor--Part I: Fluorescent signal acquisition from step-etched fiber optic probes.

A fiber-optic biosensor capable of remote continuous monitoring has recently been designed. To permit sensing at locations separate from the optoelectronic instrumentation, long optical fibers are utilized. An evanescent wave immuno-probe is prepared by removing the cladding near the distal end of the fiber and covalently attaching antibodies to the core. Probes with a radius unaltered from that of the original core inefficiently returned the signal produced upon binding the fluorescent-labelled antigen. To elucidate the limiting factors in signal acquisition, a series of fibers with increasingly reduced probe core radius was examined. The results were consistent with the V-number mismatch, the difference in mode carrying capacity between the clad and unclad fiber, being a critical factor in limiting signal coupling from the fiber probe. However, it was also delineated that conditions which conserve excitation power, such that power in the evanescent wave is optimized, must also be met to obtain a maximal signal. The threshold sensitivity for the optimal step-etched fiber probe was improved by over 20-fold in an immunoassay, although, it was demonstrated that signal acquisition decreased along the probe length, suggesting that a sensor region of uniform radius is not ideal.

Biosensing Techniques↗
PubMed2005

Characterization of coated optical fibers by Fourier-domain optical coherence tomography.

Fourier-domain optical coherence tomography is used to image the cross sections of coated optical fibers. A standard single-mode fiber with a dual coating and a hard-clad silica fiber with a single thin low-index coating are studied. The individual coating dimensions, coated and uncoated fiber diameters, and the fiber coating's concentricity are retrieved from a single measurement.

Algorithms↗
PubMed1997

Fiber-optic-based biomonitoring of benzene derivatives by recombinant E. coli bearing luciferase gene-fused TOL-plasmid immobilized on the fiber-optic end.

TOL plasmid in Pseudomonas putida mt-2 has a series of genes for the degradation of xylene, toluene, and their derivatives to pyruvate and acetaldehyde (or propionaldehyde). Two operons, i.e., upper operon and meta operon, play indispensable roles for the digestion of xylene derivatives: When XyIR protein recognizes xylene derivatives, another controlling gene, xyIS, is activated, which results in the activation of meta operon. Therefore, we have constructed a fusion gene between TOL plasmid and the firefly luciferase gene under the control of XyIR and the promoter of xyIS gene; i.e., by using fusions of the meta operon with promotorless luciferase expression vector from firefly, we have constructed and tested biomonitors for benzene derivatives. Bioluminescence specified by Escherichia coli (pTSN316), carrying xyIR and xyIS promoters, Ampr and luc, was measured in either a benzene derivative-saturated or o-methylbenzyl alcohol-dissolved medium both in the case of cell suspension and in the case of immobilized cell form. The utility of the biosensing system for monitoring in chemical plant drainage was demonstrated with samples supplemented with benzene derivatives. The xyIR-xyIS promoter-lux fusion carried by pTSN316 responded to a benzene-related chemical in sample solutions. Immobilization of the transformed E. coli, at one end of fiber optic, bearing firefly luciferase gene fused to TOL plasmid, has been demonstrated to fabricate a luminescent remote biomonitoring device for the protection of environmental deterioration. Due to the luminescent detection, the detection limits for benzene-related aromatics that are recognized by a binding protein (XyIR) were parts-per-million. We had already submitted a preliminary report concerning the possibility of environmental monitoring based on the above idea by using the transformed E. coli in a cell-suspended solution. This paper describes mainly a fiber-optic-based biomonitoring device for the protection of environmental deterioration.

Bacterial Proteins↗