Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Optical Fibers”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed2004

Germania-glass-core silica-glass-cladding modified chemical-vapor deposition optical fibers: optical losses, photorefractivity, and Raman amplification.

Germania-glass-core silica-glass-cladding single-mode fibers (deltan as great as 0.143) with a minimum loss of 20 dB/km at 1.85 microm were fabricated by modified chemical-vapor deposition. The fibers exhibit strong photorefractivity, with type IIa index modulation of 2 x 10(-3). A Raman gain of 300 dB/(kmW) was determined at 1.12 microm. Only 3 m of such fibers is sufficient for constructing the 10-W Raman laser at 1.12 microm with a 13-W pump at 1.07 microm.

Journal Article↗
PubMed1986

Mid-infrared fiber optics.

Fiber optics for carbon dioxide laser surgery have been in developmental research for the past ten years. An up-to-date presentation of infrared fiber optics as they pertain to laser surgery is presented. Optical properties such as intrinsic and extrinsic electronic absorption, multiphonon absorption, and scatter mechanisms are discussed. Real-world considerations for materials selection and fabrication techniques for both crystalline and glassy fiber optics give the reader a perspective regarding the stage of development of these devices. Data are presented indicating transmission ranges and absorption coefficients for both bulk materials and fabricated fiber optics. The conclusions are drawn based on the needs of the clinician as they relate to the degree of existing technology.

Carbon Dioxide↗
PubMed2003

Propagating modes in gain-guided optical fibers.

Optical fibers in which gain-guiding effects are significant or even dominant compared with conventional index guiding may become of practical interest for future high-power single-mode fiber lasers. I derive the propagation characteristics of symmetrical slab waveguides and cylindrical optical fibers having arbitrary amounts of mixed gain and index guiding, assuming a single uniform transverse profile for both the gain and the refractive-index steps. Optical fibers of this type are best characterized by using a complex-valued v-squared parameter in place of the real-valued v parameter commonly used to describe conventional index-guided optical fibers.

Journal Article↗
PubMed2001

A readout scheme providing high spatial resolution for distributed fluorescent sensors on optical fibers.

Optical fiber sensors using fluorescent probes distributed along the fiber cladding are of great interest for monitoring physical and chemical properties in their environment. The location of an emitting fluorophore along a fiber can be determined by measuring the time delay between a short, exciting laser pulse propagating in the fiber core and the returning fluorescence pulse. However, fluorescence lifetimes limit the spatial resolution, since a minimum separation of the fluorophores is required to resolve returning light pulses. For many applications, a closer spacing of sensor regions is desirable. We present a new method for the readout of closely packed fluorescent chemosensors located in the cladding of an optical fiber. By using a second fiber as an optical delay line, the minimum spacing between adjacent sensor regions can be well below the fluorescence lifetime limit. Since the coupling between the two fibers is evanescent, the attenuation of the excitation pulse is low, making long arrays of sensor regions feasible. This is particularly important since the one-dimensional combinatorial chemistry method developed by us allows for efficient preparation of diverse linear arrays. Detection sensitivities of 10(-7) mol/L are demonstrated, with the potential for significant improvement.

Journal Article↗
PubMed1994

Two-point electrical-fluorescence recording from heart with optical fibers.

Optical recordings from frog myocardium, stained with a voltage-sensitive dye, have been made through a fiber optic system that uses fiber couplers to provide two excitation/detection paths and to separate excitation light from the fluorescence signal. The excitation light, from a green He-Ne laser (543 nm), is focused into a 100 microns-core fiber then is split 1:1 to two other fibers. Each of these two fibers transmits part of the excitation light through a fiber coupler (1:15 transmittance ratio) to the heart preparation which is stained with the voltage-sensitive dye RH237. The returning red fluorescence is split at the same fiber coupler (15:1 transmittance ratio) and is directed to a photomultiplier tube through a longpass filter. With this two-point mapping method, differences in action potential shape and timing have been observed.

Action Potentials↗
PubMed2005

Long optically controlled delays in optical fibers.

Optically controlled delay lines in optical fibers are demonstrated by use of the group-velocity control of signal pulses based on stimulated Brillouin scattering. We achieve continuous time delay within the range of 150 ns, much larger than the width of the 40 ns signal pulse, using cascaded fiber segments joined by unidirectional optical attenuators. In the meantime, we also observe a large amount of pulse broadening, which agrees well with a theoretical prediction based on linear theory.

Journal Article↗
PubMed2004

Dark variants of luminous bacteria whole cell bioluminescent optical fiber sensor to genotoxicants.

A stable dark variant separated from photobacterium phosphoreum (A2) was fixed in agar-gel membrane and immobilized onto an exposed end of a fiber-optic linked with bioluminometer. The variant could emit a luminescent signal in the presence of genotoxic agents, such as Mitomycin C (MC). The performance of this whole-cell optical fiber sensor system was examined as a function of several parameters, including gel probe thickness, bacterial cell density, and diameter of the fiber-optic core and working temperature. An optimal response to a model genotoxicant, Mitomycin C, was achieved with agar-bacterial gel membrane: the thickness of gel membrane was about 5 mm; the cell density of bacteria in gel membrane was about 2.0 x 10(7)/ml; the diameter of fiber-optic core was 5.0 mm; the working temperature was 25 degrees C. Under these optimized conditions, the response time was less than 10 h to Mitomycin C, with a lower detection threshold of 0.1 mg/L.

Biosensing Techniques↗
PubMed2001

Quasi-distributed fiber-optic strain sensor: principle and experiment.

Sensors capable of making distributed measurements allow for monitoring of the entire structure. Optical fiber sensors are especially attractive for this purpose, since they are geometrically versatile and can be readily integrated within various types of structure and material. Development and characteristics of a quasi-distributed intrinsic fiber-optic strain sensor based on white-light interferometry are described. The research presented here describes the development of a new optical fiber sensor system for measurement of structural strains based on double white-light interferometry. Individual segments of single-mode optical fibers forming a common-path interferometer are linked in series, and a scanning white-light interferometer provides for distributed sensing of strain signals from various locations in the structure. The system is configured for automatic compensation of drift due to environmental effects, i.e., temperature and vibration. Strain gauges were employed for comparison and verification of strain signals as measured by the new system. The experimental results demonstrate the linearity of the system and the capability for distributed sensing of strains.

Journal Article↗
PubMed1996

Analytical properties and sensor size effects of a micrometer-sized optical fiber glucose biosensor.

A micrometer-sized fiber-optic fluorescence biosensor for glucose has been fabricated. The sensor is 100 times smaller than existing glucose optodes. It is based on the enzymatic reaction of glucose oxidase that catalyzes the oxidation of glucose to gluconic acid and hydrogen peroxide while consuming oxygen. Tris(1,10-phenanthroline)ruthenium chloride, an oxygen indicator, is used as a transducer. The ruthenium complex and glucose oxidase are incorporated into acrylamide polymer that is attached covalently to a silanized optical fiber tip surface by photocontrolled polymerization. A study of the dependence of the fluorescence intensity on sensor size shows that, under normal operating conditions, the signal decreases with the sensor diameter rather than its volume. Also, the response of micrometer-sized sensors is improved by about 20% compared to that of larger fiber-optic glucose sensors. Due to its small size and the lack of membrane support, the response time of the sensor is only 2 s. An absolute detection limit of around 1 x 10(-15) mol is achieved. The new glucose sensor is at least 25 times faster and its absolute sensitivity 5-6 orders of magnitude higher than that of current glucose optodes.

Biosensing Techniques↗
PubMed2002

Non-contact detection of laser-generated surface acoustic waves using fiber optic Sagnac interferometer.

A high powered Q-switched Nd:YAG laser was used to excite the surface waves, and an optical fiber sensor was used to detect the out-of-plane displacements due to the propagating waves. This sensor is based on the fiber optic Sagnac interferometer, which has the path-matched configuration and does not require active stabilization. Quadrature phase bias between two interfering laser beams in the Sagnac loop is applied by controlling the birefringence in an optical path using a fiber polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output according to the change of phase bias. Additional signal processing is not needed for the detection of ultrasonic waves using the Sagnac interferometer. The performance of the fiber optic Sagnac interferometer was investigated, and laser-generated surface wave signals were detected using this fiber optic sensor. The developed fiber optic sensor configured in this study is very simple and is effective for non-contact detection of ultrasonic waves.

Journal Article↗
PubMed1993

Developing a fiber-optic probe to combine subcutaneous fat depth and meat quality measurements.

This feasibility study demonstrates that the boundary between porcine subcutaneous fat and longissimus muscle can be detected with a probe using optical fibers to illuminate and detect anatomical boundaries. A relatively large optical window (approximately 3 mm2) seemed to give the best resolution of fat to muscle boundaries, whereas a smaller window gave a better resolution of marbling. Scattered, obliquely sectioned optical fibers gave reflectance spectra of fat and muscle that were relatively flat and parallel (fat > muscle). Thus, white light may be used with optical fibers to detect fat to muscle boundaries, although the greatest monochromatic separation was at 820 nm. In comparing measurements made as the probe penetrated the meat with those made as the probe was withdrawn, structures appeared to be deeper on the way in than on the way out, because of compression of the meat. Multichannel operation allowed tissue transmittance to be measured as well as reflectance and channels to be averaged to improve performance. These observations will be useful in developing new apparatus to measure fat depth and meat quality in one operation using optical fibers.

Adipose Tissue↗
PubMed2003

Colloidal gold-modified optical fiber for chemical and biochemical sensing.

A novel class of fiber-optic evanescent-wave sensor was constructed on the basis of modification of the unclad portion of an optical fiber with self-assembled gold colloids. The optical properties and, hence, the attenuated total reflection spectrum of self-assembled gold colloids on the optical fiber changes with different refractive index of the environment near the colloidal gold surface. With sucrose solutions of increasing refractive index, the sensor response decreases linearly. The colloidal gold surface was also functionalized with glycine, succinic acid, or biotin to enhance the selectivity of the sensor. Results show that the sensor response decreases linearly with increasing concentration of each analyte. When the colloidal gold surface was functionalized with biotin, the detection limit of the sensor for streptavidin was 9.8 x 10(-11) M. Using this approach, we demonstrate proof-of-concept of a class of refractive index sensor that is sensitive to the refractive index of the environment near the colloidal gold surface and, hence, is suitable for label-free detection of molecular or biomolecular binding at the surface of gold colloids.

Biosensing Techniques↗
PubMed2005

Fiber-optic fluorescence imaging.

Optical fibers guide light between separate locations and enable new types of fluorescence imaging. Fiber-optic fluorescence imaging systems include portable handheld microscopes, flexible endoscopes well suited for imaging within hollow tissue cavities and microendoscopes that allow minimally invasive high-resolution imaging deep within tissue. A challenge in the creation of such devices is the design and integration of miniaturized optical and mechanical components. Until recently, fiber-based fluorescence imaging was mainly limited to epifluorescence and scanning confocal modalities. Two new classes of photonic crystal fiber facilitate ultrashort pulse delivery for fiber-optic two-photon fluorescence imaging. An upcoming generation of fluorescence imaging devices will be based on microfabricated device components.

Animals↗
PubMed2002

A simple, low-cost, remote fiber-optic micro volume fluorescence flowcell for capillary flow-injection analysis.

A small volume flowcell for fluorescence detection in capillary flow injection (CFI) analysis has been created by using a low cost, commercially available fluidic device. Fluorescence detection is achieved using an optical fiber to deliver excitation light to the sample flowing through the device and another optical fiber to collect fluorescence emission. The flowcell is a standard fluidic cross with a swept volume of 721 nL. Optical fibers were oriented at right angles using standard sleeves and ferrules to set their position near the cross intersection. Multiple excitation sources were used including a low power UV laser and blue and UV light emitting diodes (LED). The full emission spectrum detection limits, using the laser, for fluorescein and bovine serum albumin (BSA) were 0.30 ppb and 2.1 x 10(-4)% (w/w), respectively. Two fluidic crosses were used in series for multi-wavelength fluorescence excitation using fiber-optically coupled LED.

Journal Article↗
PubMed2002

Coupling fiber optics to a permeation liquid membrane for heavy metal sensor development.

We present the first sensing system for metal ions based on the combination of separation/preconcentration by a permeation liquid membrane (PLM) and fluorescence detection with an optical fiber. As a model, a system for the detection of Cu(II) ions was developed. The wall of a polypropylene hollow fiber serves as support for the permeable liquid membrane. The lumen of the fiber contains the strip solution in which Cu(II) is accumulated. Calcein, a fluorochromic dye, acts as stripping agent and at the same time as metal indicator. The quenching of the calcein fluorescence upon metal accumulation in the strip phase is detected with a multimode optical fiber, which is incorporated into the lumen. Fluorescence is excited with a blue LED and detected with a photon counter. Taking advantage of the high selectivity and sensitivity of PLM preconcentration, a detection limit for Cu(II) of approximately 50 nM was achieved. Among five tested heavy metal ions, Pb(II) was the only major interfering species. The incorporation of small silica optical fibers into the polypropylene capillary allows for real-time monitoring of the Cu(II) accumulation process.

Biosensing Techniques↗
PubMed2000

Selective photothermolysis in skin by using subcutaneous optical fibers.

BACKGROUND AND OBJECTIVE: Vascular selective photothermolysis has been shown to be effective in treating hypertrophic scars. Performing selective photothermolysis on the vasculature deep within thick scars requires new methods for delivering laser energy. It is the objective of this study to model the use of subcutaneous fiber optics to perform selective photothermolysis in skin as a possible aid in the treatment of thick scars. STUDY DESIGN/MATERIALS AND METHODS: A Monte Carlo simulation was performed to study the expected region of vascular necrosis in a two layer skin model when 585-nm radiation is delivered into the dermis by means of subcutaneous optical fibers. RESULTS: The extent of vascular necrosis is independent of fiber diameter for a fixed total energy. A fiber penetrating barely below the epidermis decreases the maximum epidermal fluence by more than an order of magnitude relative to a superficial beam. Using four fibers simultaneously can significantly increase the depth of vascular necrosis. CONCLUSIONS: Small diameter fibers are optimum if the maximum fluence tolerable in the dermis is not a limiting factor. Shallowly inserted fibers can significantly decrease epidermal damage to dark-skinned patients undergoing laser therapy.

Algorithms↗
PubMed1998

Near-ultraviolet evanescent-wave absorption sensor based on a multimode optical fiber.

Fiber-optic near-ultraviolet evanescent-wave sensors have been constructed, and their feasibility for practical applications has been demonstrated. The sensors, used for the detection of ozone near the 254-nm peak of the Hartley absorption band, were fabricated from coiled segments of low-cost multimode plastic-clad silica optical fibers. The sensing sections were produced alternatively by stripping only the protective jacket from the fiber to expose the gas-permeable silicone cladding or by stripping the jacket and the cladding to expose the bare-silica fiber core. Response characteristics are given, including sensitivity to ozone, reversibility, and aging effects. The useful lifetime was unacceptably short for the sensor that employed the bare-silica core, whereas the exposed-cladding sensor demonstrated good stability over the entire two-month period of investigation. The latter, more useful sensor demonstrated a linear response to ozone over the range 0.02-0.35 vol% and a reversible response with a time constant on the order of 1 min. Differences in ozone absorption spectra obtained in the transmission and evanescent-wave modes are discussed. Projected applications of the new exposed-cladding sensor include ozone determination in water-treatment processes and ozone production plants.

Absorption↗
PubMed2001

Application of a fiber-optic NIR-EFA sensor system for in situ monitoring of aromatic hydrocarbons in contaminated groundwater.

Interaction of analyte molecules with the evanescent wave of light guided in optical fibers is among the most promising novel sensing schemes that can be applied for environmental monitoring and on-line process analysis. By combining this measuring principle with the solid-phase extraction of analyte molecules into the polymer cladding of a fiber, it is possible to perform direct absorption measurements in the cladding, if the fiber is adapted to a conventional spectrometer/photometer. A big advantage of this arrangement is that the measurement is scarcely disturbed by matrix effects (background absorption of water in IR measurements, stray light due to turbidity in the sample). By using near-infrared (NIR) evanescent field absorption (EFA) measurements in quartz glass fibers coated with a hydrophobic silicone membrane it is possible to design and construct sensors for monitoring apolar hydrocarbons (HCs) in aqueous matrices.The paper presents a fiber-optic sensor system for the determination of aromatic HCs in groundwater or industrial wastewater. Generally, this instrument is suitable for quantitative in situ monitoring of pollutants such as aromatic solvents, fuels, mineral oils or chlorinated HCs with relatively low water saturation solubility (typically between 0.01 and 10 g l(-1)). The sensor probe is connected via all-silica fibers to a filter photometer developed at the IFIA, thus, allowing even remote analysis in a monitoring well. This portable instrument provides a total concentration signal of the organic compounds extracted into the fiber cladding by measuring the integral absorption at the 1st C--H overtone bands in the NIR spectral range. In situ measurements with the sensor system were performed in a groundwater circulation well at the VEGAS research facility of the University of Stuttgart (Germany). The NIR-EFA sensor system was tested within the frame of an experiment that was carried through in a tank containing sandy gravel with a groundwater-saturated aquifer, where soil and groundwater were contaminated with technical grade xylene. The goal of this experiment was to model and optimize the groundwater circulation well used for the remediation of the aquifer and soil surrounding the well. The sensor proved to trace reliably the total hydrocarbon concentration in the process water pumped from the well to a stripper column. Measurements were performed continuously over 4 months with C8 HC sum concentrations in the process water between 80 mg l(-1) down to the limit of detection, which is around 200 microg l(-1). It could be demonstrated that the fiber-optic sensor system is a valuable tool for near-real-time control of a remedial action technique and verification and documentation of its success.

Environmental Monitoring↗