Showing papers on "Fiber optic sensor published in 1988"

Fiber loop reflectors

Abstract: The theory and application of fiber loop reflectors, fabricated by forming a fiber loop between the output ports of a directional coupler, is described. The reflectivity of the loop is shown to depend upon the coupling characteristics of the coupler and on the degree of birefringence in the fiber loop. Measured loop reflectivities, in terms of wavelength response, coupling ratio, and loop birefringence are shown to agree very well with theory. Two applications of the fiber reflector are briefly discussed; an all fiber laser and a duplex optical communications link using a single light source. >

Optical fiber sensors

Abstract: Optical Fiber-Chemical Sensing Using Direct Spectroscopy Chemical Sensing Using Indicator Dyes Dynamic Light Scattering Applied and Its Application in Concentrated Suspensions In Vivo Medical Sensors Fiber-Optic Gyros Fiber-Optic Sensors for Condition Monitoring and Engineering Diagnostics Sensors in Industrial Systems Distributed Sensors -- Recent Developments Multiplexing Techniques for Fiber-Optic Sensors Fiber Optics and Smart Structures Fiber-Optic Sensors -- Commercial Presence

Fiber-optic fluorosensor for oxygen and carbon dioxide

Abstract: The capability of fiber-optic light guides to transmit a variety of optical signals simultaneously has been exploited to construct an optical fiber sensor for measurement of both oxygen and carbon dioxide. The oxygen-sensitive material (a Kieselgel-adsorbed fluorescent metal-organic complex) and the CO/sub 2/-sensitive material (an immobilized pH indicator in a buffer solution) are entrapped in a gas-permeable polymer matrix that is attached to the distal end of the fiber. Both indicators have the same excitation wavelength (in order to avoid energy transfer) but quite different emission maxima. The two emission bands can easily be separated with the help of interference filters and give independent signals. Oxygen can continuously be determined in the 0-200 Torr (0-26.6 kPa) range with +/- 1 Torr accuracy and CO/sub 2/ in the 0-150 Torr (0-20 kPa) range with +/- 1 Torr. The accuracy is higher at low partial pressure, so that the detection limits are at approx. 0.5 Torr in both cases.

Low-loss highly overcoupled fused couplers: fabrication and sensitivity to external pressure

Abstract: A flame brush technique for fabrication of optical directional couplers that maintain low loss over many coupling cycles is discussed. Couplers with excess losses less than 3% and with 2500 power transfer cycles in the coupling are reported. Such couplers, which have a narrow wavelength band transmission (0.12 nm), can be tuned by applying an external hydrostatic pressure. The long fused couplers can also have application as optical fiber sensors. >

Optimization and stabilization of visibility in interferometric fiber-optic sensors using input-polarization control

Abstract: The effects of input polarization on the output fringe visibility of two-beam interferometric fiber-optic sensors are investigated, and an analysis which predicts the existence of input states of polarization of eigenmodes of the interferometer for which optimum output visibility is obtained is presented. Experimental results obtained using both a bulk-optic and a fiber Mach-Zehnder interferometer are reported that verify this analysis. Active feedback stabilization of the output fringe visibility of an interferometric sensor using automatic input-polarization control is demonstrated. >

Performance of a fiber-optic temperature sensor from −200 to 1050°C

Abstract: A reflectively monitored Fabry-Perot temperature sensor is characterized over a 1250 degrees C temperature range. Dielectric mirrors for the interferometer are incorporated into a continuous length of single-mode fiber by a fusionsplicing technique. The change in optical phase per unit temperature is nearly constant above room temperature but decreases at lower temperatures. Phase-shift data for the germania-doped silica fiber used in these experiments are compared with calculations based on previously reported information on the temperature dependence of refractive index and length in bulk fused silica.

A Novel Distributed Optical Fibre Sensing System Enabling Location Of Disturbances In A Sagnac Loop Interferometer.

Abstract: The paper describes a novel, distributed fibre optic sensor capable of detecting and locating a disturbance on a continuous length of fibre. The sensor is based on a Sagnac loop interferometer. Any disturbance that causes a phase shift in the light propagating within the fibre loop, such as a change in the mechanical strain or temperature of the fibre, can be located. The basic principle of operation is described and preliminary results, obtained from a feasibility experiment, are given.

Mode couplings due to external forces distributed along a polarization-maintaining fiber: an evaluation

Abstract: A new interferometric scheme for measuring mode conversion distributed locally along a polarization-maintaining fiber is presented. Using this technique the power coupling coefficient, varying with magnitude and angle of external pressure transversely applied to a fiber, was evaluated both theoretically and experimentally. The coupling point location is determined with ±1.5-cm accuracy and resolution of better than 10 cm for a 220-m long fiber having modal birefringence of 4.4 × 10−4. The coupling coefficient was proportional to the external force in the range from 5 × 10−3 to 0.1 kg/mm. The relationships determined experimentally reflected those predicted by theory.

Radiation sensitive optical fiber and detector

Abstract: An optical fiber sensitive to nuclear radiation includes a thin filament core formed of a plastic scintillator material which scintillates in the presence of nuclear radiation. An optical cladding material is provided around the optical fiber. A second fiber is connected to the optical fiber for efficiently transmitting the scintillating light from the optical fiber to a radiation detector.

Fiber optic sensor arrangement having reflective gratings responsive to particular wavelengths

Abstract: An arrangement for sensing changes in a monitored parameter includes an optical fiber which has at least one sensing fiber length including a sensing portion situated at a monitoring location of a body. Two periodic gratings of the same periodicity are situated in the fiber each at a different end of the sensing fiber length. Such gratings are reflective to a predominant portion of any light that propagates in the fiber and has a wavelength in a stopband range around twice the periodicity. When broadband coherent light including sensing light with wavelengths within the stopband range is launched into a first end of the optical fiber for propagation longitudinally of the fiber toward a first of the gratings, the predominant portion of the sensing light is reflected from the first grating and the remainder of the sensing light passes into the sensing fiber length, where resonant buildup of light at certain wavelengths that are located within the stopband range and depend on the length of the sensing portion as influenced by changes in the monitored parameter takes place, and the gratings are rendered substantially transparent to the sensing light at the plurality of wavelengths following the buildup. The effect of the gratings and of the sensing length on the wavelengths of the light emerging from one of the end portions of the optical fiber is then detected.

Fiber-optic immunochemical sensor for continuous, reversible measurement of phenytoin

Abstract: This fiber optic sensor, based on a homogeneous fluorescence energy-transfer immunoassay, operates in a continuous, reversible manner to quantify the anticonvulsant drug phenytoin. B-Phycoerythrin-phenytoin and Texas Red-labeled antibody to phenytoin were sealed inside a short length of cellulose dialysis tubing, which was cemented to the distal end of an optical fiber. When the sensor was alternately placed into solutions with various concentrations of free phenytoin, the drug crossed the dialysis membrane and displaced a fraction of the B-phycoerythrin-phenytoin from the antibody. The resulting change in fluorescence signal was measured with a fiber optic fluorometer. A typical competitive-binding calibration curve was seen between 5 and 500 mumol of phenytoin per liter. Equilibrium response time ranged from 5 to 30 min for different sensors. Replicate equilibrium measurements with one sensor, alternated eight times between two solutions of phenytoin, gave a CV of 2.1% (n = 16) at 0 mumol/L and 2.4% (n = 13) at 100 mumol/L. A reversible immunochemical sensor can be made that has a response time suitable for continuous concentration measurements.

Fiber Fox–Smith resonators: application to single-longitudinal-mode operation of fiber lasers

Abstract: An optical-fiber Fox–Smith resonator was demonstrated for the first time to our knowledge. It was applied to obtain single-longitudinal-mode operation from an erbium-doped fiber laser. Both the passive performance and the active performance of the device are studied in detail. Good agreement is found between theoretical and experimental results.

Observation of input-polarization-induced phase noise in interferometric fiber-optic sensors

Abstract: It is shown that polarization fluctuations in the input fiber to an interferometric sensor can result in the generation of excess phase noise in the output. Experimental observations of this phenomenon are compared with theoretical models, and the impact of this noise source in interferometric sensors is briefly discussed.

Multiple axis, fiber optic interferometric seismic sensor

Abstract: A mechanical vibration transducer includes a seismic mass is supported by a plurality of cylindrical silicone rubber mandrels. Each mandrel is wound with a length of optical fiber which has a reflective end and a transmissive end. A case surrounds the assemblage and is connected to the supports. When the case is displaced, the supports change diameter in response to the relative motion between the seismic mass and the case. This change in diameter is translated to a change in length of the optical fiber. By using the fibers as arms of a michelson interferometer, a sensitive instrument responsive to displacing vibrations is obtained. This instrument is energized entirely by light transmitted through optical fiber waveguides and whose information is transmitted to the observor using only light . waves in optical fibers.

Optical fiber sensors for chemical detection

Abstract: Distributed region optical sensors for chemical detection are provided by utilizing optical fiber technology. A core is provided with a surrounding region that is permeable to the chemical to be detected. A composition whose optical characteristics are altered upon interaction with the chemical to be detected is provided within the permeable material. This change in optical characteristics allows chemical detection through detection of light guided by the fiber.

Multiplexed fiber optic sensor

Abstract: An all fiber optic hydrophone or sensor array has significant size, cost, reliability, and operational advantages over other hydrophone arrays. The array comprises a distributed network of appropriately coiled optical fiber encased in commercially available marine cable. The terminal end of the sensor array preferably contains a modulated miniature solid-state laser diode and photodetector matrix which mate to power and multiplexing electronics. The distributed sensor assembly itself is entirely passive. The hydrophone array comprises an optical signal source and at least one transmitting optical fiber for guiding signals output from the optical signal source. The array further includes a plurality of sensing interferometers coupled to the transmit optical fiber and means for measuring differential changes in the optical path of each sensing interfereometer. The hydrophone array comprises means for superimposing signals output from each sensing interferometer, and a detector for converting optical signals in the receive fiber into electrical signals. The signal processing system in the array includes a compensating interferometer having optical phase modulating means formed in one arm thereof.

Linear birefringence effects on fiber-optic current sensors.

Abstract: The occurrence of linear birefringence is inevitable when dealing with fiber optics. Intrinsic birefringence can be minimized, but deploying the fiber on an experiment will introduce stress birefringence due to bending and pressure. We have studied the effects of this extraneous linear birefringence on the measurement of current-induced circular birefringence in a fiber which also has a strong twist circular birefringence bias. Orienting the analyzing polarizer by a proscribed procedure gives minimum error. Quantitative error limits on the current for given fiber coil radii and winding tensile stress are calculated. Additional restrictions on the fiber lead-in and lead-out sections are discussed.

Fiber optic polymer cure sensor

Abstract: An in situ method is presented for monitoring the curing of polymeric compositions, including epoxy- and polymide-based composites. The sensor measures the difference between the refractive index of the cured and uncured composition, with the index increasing as polymerization proceeds. The method differs from all existing methods in that it relies on a self-referential differential measurement rather than on an absolute measurement, the sensor is totally independent of curing conditions and is sensitive to the extent of cure even at the latest stages. It can be used within the body of large composite structures undergoing curing in an autoclave, and it can indicate the end of cure without calibration of any kind. >

Acousto-optic modulators for optical fibers using Hertzian contact with a grooved transducer substrate

Abstract: The authors describe acousto-optic modulators for optical fibers, fabricated by the deposition of thin zinc-oxide transducers onto specially lapped glass capillary tubes. By exposing the inner surface of the capillary and contacting it to an optical fiber of the same diameter, a good Hertzian contact can be easily attained, providing efficient throughput of acoustic energy at frequencies in excess of 1 GHz. A phase modulator for a single-mode fiber has been fabricated in such a manner, achieving a maximum phase retardation of 1.0 rad/W input electrical power at 416 MHz. Its frequency, power, and polarization characteristics are discussed. Also presented are data from a frequency shifter/modal coupler for a two-mode optical fiber. This device achieved 6% power coupling from the fundamental optical mode to the second-order mode with 500 mW input power at 1.03 GHz. Single sideband modulation was observed with >19-dB suppression of the unwanted sideband. The authors also describe the design of an optical tap using the same technology. >

Porous optical fibers for high-sensitivity ammonia-vapor sensors.

Abstract: A new porous glass optical fiber has been developed for use as a sensor for the detection of ammonia vapors at low concentrations. The porous structure that remains after selective heat treatment, phase separation, and chemical leaching of a borosilicate glass imparts a high surface area to the fiber core. Ammonia vapors permeating into the porous zone, which is pretreated with a reversible pH dye indicator, produce a spectral change in transmission. The resulting pH change is measured by in-line optical absorbance and is proportional to the ambient-ammonia concentration. Ammonia-vapor concentrations as low as 0.7 part in 106 have been detected.

Dependence of visibility on input polarization in interferometric fiber-optic sensors.

Abstract: We present an analysis of the effects of input polarization on the output fringe visibility of two-beam interferometric fiber-optic sensors, which predicts the existence of interferometer input-polarization eigenmodes for which optimum visibility is obtained. Experimental results that verify this are also presented.

Optical Kerr switch using elliptical-core two-mode fiber.

Abstract: A new optical–optical switching technique is proposed and demonstrated with a probe–pump scheme, utilizing nonlinear differential phase shift between two spatial modes in a highly elliptical-core fiber. The probe beam is switched from one intensity-lobe position of the fiber output radiation pattern to the other in a 33-m-long fiber at a pump power of 1.6 W.

Fiber optic polarizer

Abstract: In the present invention, a multilayer stack of alternating layers of a metal and a dielectric is deposited directly onto the surface of an optical fiber that has been processed to remove the cladding from one side of the fiber. The multilayer metal-dielectric structure is constructed to give high birefringence and large differential attenuation for two orthogonal polarizations.

Fiber-optic sensing of electric field components

Abstract: Symmetry properties of the converse piezoelectric effect are investigated for their use in fiber-optic sensing of individual electric field components. Three basic sensor designs are analyzed in detail. Suitable sensor materials are identified and relevant material properties are discussed. The sensitivity of the sensor to a specified field component is experimentally verified. A dynamic range of approximately 5 orders of magnitude is found for frequencies in the kilohertz range. The sensor concept is compared to electrooptic sensors.

System for detecting chemical changes in materials by embedding in materials an unclad fiber optic sensor section

Abstract: A system for detecting chemical characteristics within a material includes an optical fiber having a relatively short unclad sensor section for embedding in a material, a source of infrared radiation to direct infrared radiation into the fiber, and an optical decoder connected to the fiber to detect the spectrum of infrared radiation absorbed by the material in which the sensor section is embedded.

Design And Characterization Of Fiber-Optic Accelerometers

Abstract: Six self-contained fiber-optic accelerometers have been built based on the microbend fiber-optic sensor. The accelerometer systems feature a simple loss-compensation technique that removes the DC offsets that are developed as a result of spurious signals that arise due to cable bending and vibration. The sensor optical and mechanical systems are described and the results of the sensor system calibrations are reported.