Showing papers on "Fiber optic sensor published in 1986"

Polymer Modification of Fiber Optic Chemical Sensors as a Method of Enhancing Fluorescence Signal for pH Measurement

Abstract: The authors have prepared a pH fiber optic sensor based on fluorescence intensity. Fluoresceinamine is incorporated into an acrylamide-methylenebis(acrylamide) copolymer that is attached covalently to a surface-modified glass fiber via thermal or photopolymerization. The sensor gives instantaneous responses and reversible measurements over the pH range of 4.0-8.0 with signal-to-noise ratios of typically 275/1. The results indicate that specific fiber optic chemical sensors can be miniaturized and still retain sufficient signal intensity and stability.

Side-hole fiber for fiber-optic pressure sensing.

Abstract: An optical fiber whose structure is similar to that of the PANDA fiber, but with two open channels in the place of the stress members, is investigated. Variations of the internal or external gas pressure permit tuning of the fiber birefringence (10−4 rad m−1 Pa−1) over a wide range, including sign reversal, and application as a pressure sensor.

Optical fiber laser

Abstract: To provide a low-cost, high reliability and high-powered operation enabled optical fiber laser, in the optical fiber laser for oscillating a laser light by introducing an excitation light for exciting the rare earth elements into the optical fiber doped partially by the rare earth elements, the optical fiber is wrapped around the base member, and one part of the outer circumferential area of the wrapped optical fiber is processed in order to form a flat surface, and one face of the prism is made contacted to the flat surface, and the excitation light is introduced to another surface of the prism

Fluid flow sensing apparatus for in vivo and industrial applications employing novel optical fiber pressure sensors

Abstract: A fiber optical fiber fluid flow measuring device is provided for in vivo determination of blood flow in arteries. The device includes a fiber optical fluid differential pressure measuring device having at least one optical fiber sensor which optical fiber sensor is positioned in the blood flow passage in a restricted flow area. The fiber optical differential pressure fluid sensor is connected to a divided interferometer associated with an opto-electronic demodulator which has an output signal representing the differential pressure in the sensed area. The device also has utility in industrial applications.

Distributed sensor and method using coherence multiplexing of fiber-optic interferometric sensors

Abstract: A distributed sensor system including an optical source having a short coherence length for optionally continuously monitoring each sensor in the system. In one preferred embodiment, an array of fiber-optic sensors are organized in a ladder configuration, with the sensors positioned in spaced relation and defining the rungs of the ladder. Light transmitted through the sensors is multiplexed onto a return arm of the ladder, with sensor spacing being such that interference between light from different sensors is prevented. The multiplexed signals are received by an optical fiber receiver which couples the multiplexed light with an interfering optical reference signal to produce a phase difference signal representing conditions influencing selected sensors. Embodiments are disclosed for use of either pulsed or continuous wave light sources. In another preferred embodiment, the sensors comprise a plurality of interferometers connected in series configuration by a common optical fiber, which provides multiplexed output signals from the sensors to another plurality of interferometers comprising receivers. Functional equivalents of the series configuration provide sensors and receivers comprising birefringent or two-mode fiber. The optical path length differences between each pair of sensor arms are selected to prevent interference between the multiplexed sensor output signals from the various sensors. The optical path lengths through the sensors and receivers are structured so that each receiver produces a phase difference signal relating to conditions affecting light transmission through a specific sensor. A phase and amplitude modulation technique is disclosed for providing heterodyned output signals from the distributed sensor system.

Bit-Error-Rate Degradation in a Multimode Fiber Optic Transmission Link Due to Modal Noise

Abstract: A review is given of the statistics of modal noise and of the expressions for the signal-to-noise ratio for the cases of a monochromatic and a nonmonochromatic light source including the effects of source frequency fluctuations. Using the results, a quantitative analysis is made of how modal noise degrades the bit-error-rate performance of a digital transmission link with multimode fiber. Plots of the bit-error rate versus the received optical power show the characteristic asymptotic behavior (BER floor); expressions are derived for the asymptotic BER. The power penalty due to modal noise can be considerably reduced by suitable system modifications, e.g., by optimization of the decision threshold setting or by application of a low coherent light source such as an LED or a laser diode operating with several spectral emission lines of low coherence and low partition noise.

Optical device for strain detection, method for the measurement of strain by means of the said device and their application to scales

Abstract: An optical device and method for strain detection. The device is provided with at least one optical fiber arranged so as to form a network. A light emitting device is arranged at one end of the fiber and a receiver is arranged at the other end, enabling the generation of information relative to the light intensity transmitted by the fiber or fibers in the presence of strain, and a measurement corresponding to the strain.

Coherent distributed sensor and method using short coherence length sources

Abstract: A distributed sensor system including an optical source (100) having a short coherence length for optionally continuously monitoring each sensor in the system. In one preferred embodiment, an array of fiber-optic sensors (110) are organized in a ladder configuration, with the sensors positioned in spaced relation and defining the rungs of the ladder. Light transmitted through the sensors is multiplexed onto a return arm (114) of the ladder, with sensor spacing being such that interference between light from different sensors is prevented. The multiplexed signals are received by an optical fiber receiver (118, 120) which couples the multiplexed light with an interfering optical reference signal to produce a phase difference signal representing conditions influencing selected sensors. Embodiments are disclosed for use of either pulsed or continuous wave light sources In another preferred embodiment, the sensors comprise a plurality of Mach-Zehnder interferometers (404,406) connected in series configuration by a common optical fiber (402), which provides multiplexed output signals from the sensors to a plurality of Mach-Zehnder interferometers (418, 420) comprising receivers. The optical path length differences between the arms (409, 410, 411 and 412) of each of the sensors (404, 406) are selected to prevent interference between the multiplexed sensor output signals from various sensors. The optical path lengths through the sensors (404, 406) and receivers (418, 420) are structured so that each receiver (418, 420) produces a phase difference signal relating to conditions affecting light transmission through a specific sensor (404,406). A phase and amplitude modulation technique is disclosed for providing heterodyned output signals from the dristributed sensor system.

On the application of optical-fiber image scramblers to astronomical spectroscopy

Abstract: Single, step-index optical fibers, when properly employed, can function as optically efficient image scramblers. Their use as optical feeds for astronomical slit spectrographs can reduce zonal error levels in those instruments by orders of magnitude. As a consequence, the application of optical-fiber couplers to new and existing spectrographs may greatly increase the wavelength metric quality of conventional astronomical spectroscopy. The optical efficiencies of fiber couplers of a few tens of meters in length can be comparable to those of typical coude mirror trains in the visible portions of the spectrum. Elements of the design of fiber couplers are illustrated by discussion of a currently operational instrument.

Fiber optic interferometric thermometer with serially positioned fiber optic sensors

Abstract: A single fiber optical fiber temperature measuring device is provided for in vivo determination of temperature at a plurality of spaced points The device includes a fiber optical temperature sensing device having at least first and second optical fiber sensors which optical fiber sensors are positioned at the measurement sites and at least two fiber optical sensors are connected to a divided interferometer associated with an opto-electronic demodulator which has an output signal representing the temperature at the sensed sites The device also has utility in industrial or chemical temperature sensing applications

Dispersion compensated fiber Raman oscillator

Abstract: A dispersion compensation delay line is added to a synchronously pumped fiber Raman ring oscillator to generate subpicosecond pulses. A pair of spaced gratings form the delay line. An interference filter is used as a bandwidth limiting tuning element to provide a good quality short pulse. An integrated design eliminates the discrete optical elements by using only an optical fiber and an optical fiber coupler.

A Conceptional Design on Optical Frequency-Division-Multiplexing Distribution Systems with Optical Tunable Filters

Abstract: Optical frequency-division-multiplexing distribution systems providing more than ten frequency multiplexed optical signals separated by on the order of gigahertz, distribute signals to plural receivers, where one of the signals is selected by a frequency selection switch (FS-SW). This paper describes the design of an optical frequency-divisionmultiplexing distribution system. Investigation is made of periodic filters for frequency division multiplexers and FS-SW, and the optical source, as well as single-mode fiber polarization mode dispersion. Preliminary transmission experiments using a bit rate of 450 Mbits/s, fiber length of 13 km, and frequency spacing of 11 GHz are also demonstrated at a 1.5 μm wavelength to show the design's suitability.

Current sensing utilizing heterodyne detection of the Faraday effect in single-mode optical fiber

Abstract: A fiber-optic current sensor based on the Faraday effect is described which utilizes laser-diode frequency modulation in order to synthesize a heterodyne-type sensor output. The relative phase of the output carrier is directly modulated by the magnetically induced circular polarization mode-phase delay. Current sensing over three orders of magnitude is demonstrated, and a Verdet constant of 2.57 \times 10^{-6} rad/A (at 0.83μm) is reported for the fiber used.

Fiber Optic Sensor Overview

Abstract: An overview of fiber optic sensors and their practical applications are discussed. Various optical schemes being used for interferometric and non-interferometric sensors are addressed. Transduction coatings along with various applications to sensing elements are also presented. Finally, state-of-the-art sensitivities are given for several sensors, and sensor and component needs are discussed.

Fiber-optic interferometric sensor arrays with freedom from source phase-induced noise.

Abstract: We propose arrays of all-passive remote sensors with freedom from both source phase-induced intensity noise and cross talk between sensors. These arrays employ high-duty-cycle time-domain addressing, utilize laser diodes, and have downlead insensitivity. A synthetic heterodyne demodulation technique is used to prevent environmentally induced signal fading. An experimental all-fiber implementation of a single remote sensor yielded a measured sensitivity of below 40 microrad/ radicalHz at signal frequencies above 600 Hz.

Crossed fiber optic tactile sensor

Abstract: A fiber optic sensor array includes a row of transmitting optical fibers, with a column of detecting optical fibers overlapping the transmitting fibers. A planar compliant spacer separates the transmitting fibers from the detecting fibers, so that a sensor element is defined at each location where a detecting fiber overlaps a transmitting fiber. The surfaces of each transmitting fiber and each receiving fiber are modified at the location of each sensor element to increase the optical coupling between the transmitting fiber and the receiving fiber at that element. The spacer in the array includes an opening between the transmitting fiber and the detecting fiber at the location of each sensor element. A support surface is affixed to the detecting fibers opposite the compliant spacer and a protective cover layer is affixed to the transmitting fibers opposite the compliant spacer. An array of light emitting elements, with each element in the emitting array being adapted to transmit light into one of the transmitting fibers, and an array of light detecting elements, each element in the detecting array being adapted to detect light emanating from one of the detecting fibers are provided. A clock times the emission of light from each emitting element and times the detection of light at each detecting element. The clock is connected to cause each detecting element to detect light in sequence after each emitting element has emitted light.

Fiber optic rotary switching device

Abstract: A fiber optic rotary switching device having a single optical fiber rotatable between a plurality of optical fibers. The arrangement for rotating the single optical fiber is designed such that the single optical fiber flexes but does not twist with respect to an end thereof which is fixed to a light source (or, in the alternative to a light detector). As a result, the switching device switches light passing through the single optical fiber to a preselected one of the plurality of optical fibers while simultaneously preventing extraneous light from reaching the other optical fibers.

Fiber optic sensor

Abstract: There is provided a fiber optic sensor for sensing environmental effects on counterpropagating light beams in an optical loop by comparing the modulation of the light beams in an optical coil exposed to the environmental effects and comparison with a reference fiber shielded from the environmental effects. The counterpropagating light paths contain optical phase modulators for creating nonreciprocal phase shifts and may comprise elongated sections forming a long line array.

Phase error bounds of fiber gyro with polarization-holding fiber

Abstract: Phase error bounds for a fiber gyro with an imperfect polarizer are calculated assuming a broad-band source and high-birefringence fiber. The phase error and resulting zero-point drift is related to the polarization-holding parameter h of the fiber. Comparison of the theory with recent experimentally observed bias drift is made.

High-resolution photoelastic pressure sensor using low-birefringence fiber

Abstract: The effect of birefringence induced in a single-mode fiber by a lateral force has been applied to measure the absolute value of force or pressure with high resolution. A sensor configuration with an extended detecting surface has been investigated by means of calibrated weights. The sensor is sensitive to an incremental force of 2 × 10−3 N, independently of the length of the fiber. The maximum force applied was 10 N/m of fiber length.

Fiber optic bidirectional data bus tap

Abstract: A fiber optic data bus tap includes a tap coupler for coupling signals traveling in either direction in a data bus fiber into one of two lengths of a tap fiber. The signals are then guided to a receiver. The tap fiber may include a fiber optic coupler formed between the two lengths thereof for splitting the signal coupled from the data bus between the two lengths of the tap fiber so that they both carry the same information. The receiver is couple to one of the two lengths of the tap fiber. One of the lengths of the tap fiber may terminate in a mirror so that signals are reflected back to the tap coupler where a portion of the reflected signal is transmitted to the receiver. A transmitter may be coupled to the power splitter for supplying signals to the tap fiber for input to the data bus. The system may employ a light emitting diode as a transceiver instead of having a separate receiver and transmitter.

Multiplexing fiber-optic sensors by frequency modulation: cross-term considerations.

Abstract: The cross-term problem in a multiplexed fiber-optic sensor system using a frequency-modulated laser source is described, and two proposed solutions are presented. One is to eliminate cross terms by locating them at different frequencies from the signal frequencies. The other is to separate the sensors by several source coherence lengths so that their outputs do not interfere. The latter technique is demonstrated experimentally, resulting in only two peaks corresponding to the two fiber interferometers at frequencies of 200 Hz and 1 kHz.

Measurement and analysis of light transmission through a modified cladding optical fiber with applications to sensors

Abstract: The effect of a modified cladding on the transmission of light through a step-index optical fiber is investigated using 3-D geometrical optics. Measurements of the light transmission of the optical fiber as a function of the modified cladding refractive index and length are presented for the case of focused illumination and compared with 3-D ray theory. The effect of defocus on the transmission of the modified fiber is also studied. Applications to intensity sensors are discussed.

Optical sensor for sensing displacement speed or displacement of a moveable element in musical instrument

Abstract: In an optical sensor for displacement speed/displacement of a movable element in a musical instrument, light emitted from a light-emitting element is guided to a sensor head through a transmission optical fiber and is further guided to a light-receiving element through a reception optical fiber. The sensor head is located at a position corresponding to a shutter movable in accordance with the movable element in the musical instrument. The shutter controls photocoupling and nonphotocoupling between the transmission and reception optical fibers. The sensor is of transmission or reflection type.

Fiber optic sensor with an optical modulator having a permanent magnet for the detection of the movement or position of a magnetic component

Abstract: A fiber optic sensor for the detection of the position or movement of a component, for example the speed of rotation of a shaft, is described, which is particularly suitable for use in a coarse environment. The optical modulator of the sensor comprises a permanent magnet and a modulator part, the permanent magnet and/or the modulator part being mounted so as to be movable relative to a transmitting and receiving light guide. A change caused by a movement generator, for example the shaft, causes a change in the course of the field lines emanating from the permanent magnet which causes a corresponding movement of the modulator part, whereby a greater or lesser proportion of the light radiated out by the transmitting optical fiber is modulated by the modulator part and is transmitted into the receiving optical fiber. The corresponding modulation of the light according to the intensity, color or polarization is then utilized as a measure of the movement or position of the component, and appropriately analyzed.

Thermochromic transducer optical fiber thermometer

Abstract: A new dielectric thermometer based on multimode optical fibers for light transmission and on a thermochromic solution transducer for temperature sensing is presented. The working principle of the transducer, technical data of the optoelectronic system, and experimental results are described and discussed.

Fiber-optic heterodyne phase-shift measurement of plasma current

Abstract: By combining twisted optical sensing fiber and heterodyne phase detection of circular birefringence we have (a) overcome the distortion problem caused by residual linear birefringence in the Faraday rotation method of measuring enclosed current and (b) used only a single output detector without requiring intensity normalization. Resolution of 400 ampere-turns has been obtained in the hostile electromagnetic environment of a working thermonuclear fusion research device. The fiber was simply wound around the existing machine. The measured values are in excellent agreement with those of the electrical Rogowski coil installed when the machine was built.

Fiber optic modal coupler, interferometer and method of coupling spatial modes using same

Abstract: A modal coupler, for coupling between first and second order modes of an optical fiber, comprises a single continuous strand of optical fiber, and a device for applying stress to the optical fiber at spaced intervals along the fiber. The stress deforms the fiber and abruptly changes the fiber geometry at the beginning and end of each stressed region. The change in fiber geometry causes coupling of light from the fundamental mode to the second order mode. The coupler, under certain conditions, exhibits polarization dependence, and thus, it may be utilized as a fiber optic polarizer. In addition, the device couples coherently, and may be used in interferometric systems.