Showing papers on "Fiber optic sensor published in 1983"

Fiber optic amplifier

Abstract: An amplifier for use with fiber optic systems comprises a neodymium YAG crystal placed in series with a signal-carrying optical fiber. The ND:YAG crystal is supplied by the optical fiber with both the signal to be amplified, and pumping illumination. The pumping illumination is coupled onto the optical fiber by a multiplexing coupler which is used to combine the signal to be amplified and illumination from a pumping illumination source onto a single optical fiber. The pumping illumination inverts the neodymium ions within the ND:YAG crystal. The signal to be amplified propagates through this crystal to stimulate emission of coherent light from the neodymium ions, resulting in amplification of the signal. Because this arrangement permits the ND:YAG crystal to be end-pumped with pumping illumination, and because the length of the ND:YAG crystal may be substantially greater that the absorption length for the crystal at the wavelength of the pumping illumination, virtually all of the pumping illumination may be absorbed within the ND:YAG crystal and used for amplification of the signal carried by the optical fiber.

High‐temperature optical fiber thermometer

Abstract: A high‐temperature optical fiber thermometer made from single crystal sapphire has been developed for use from 600 to approximately 2000 °C. The device consists of a small blackbody cavity which is sputtered on the end of a thin (0.25–1.25‐mm diameter, 0.05–0.30‐m length) sapphire fiber, a connecting low‐temperature glass fiber, and a conventional optical detector. The radiance from the cavity is used to measure its temperature. The present instrument is calibrated at a single temperature and uses the fundamental radiation laws to extrapolate to other temperatures. It is accurate and has a high sensitivity and rapid temporal response. There appear to be a number of applications of the device both in science and industry.

A distributed temperature sensor based on liquid-core optical fibers

Abstract: The principles of operation, the design, and performance of a fiber-optic temperature-distribution sensor are discussed. The sensor uses optical time-domain reflectometry (OTDR) to detect temperature-induced changes of backscatter power at many separate locations in the fiber. In liquid-core fibers, a sensitivity of 2.3 \times 10^{-2} dB/°C (0.54 percent° C-1) was observed. A measurement accuracy of 1°C with a spatial resoltuion of 1 m is attainable over a fiber length of 100 m.

Fiber-optic gyroscopes with broad-band sources

Abstract: The use of broad-band sources, polarized and unpolarized, in fiber gyroscopes with linearly birefringent fibers, is studied theoretically. Polarization-mode coupling in the fiber is modeled using one-mode coupling center. Gyroscope output equations are obtained which are useful in interpreting an origin of fiber noise in the limiting cases of low and high fiber birefringence. Interference effects in the output are shown to be related to mode coupling at particular locations in the fiber. The extent of these locations is governed by a depolarization length for which numerical estimates are given.

Optical fiber delay line signal processing

Abstract: Single-mode optical fiber is an attractive delay medium for processing microwave frequency signals due to its extremely low loss (<0.1 dB/µs) and large available time-bandwidth product (in excess of 10/sup 5/). Recent progress in the efficient tapping of light from single-mode fibers has made it possible to construct recirculating and nonrecirculating (tapped) delay-line structures that can perform a variety of important signal processing functions. These functions include coded sequence generation, convolution, correlation, matrix-vector multiplication, and frequency filtering. This paper presents the fundamental properties of single-mode fiber delay lines and reviews recent experimental results that demonstrate the feasibility of fiber delay-line devices for broad-band signal-processing applications.

Semiconductor Laser Amplifier for Single Mode Optical Fiber Communications

Abstract: The recent advent of very low loss single mode optical fibers (< 0.2 dB/km at the 1.55μπι wavelength) opens the possibility for very long distance, high information bandwidth (^1 Gbit/s) communication systems, as transoceanic cable links or trunk networks. With such fibers, especially when chromatic dispersion is negligible, the range is only limited by attenuation, so there would be no need for complete signal regeneration (pulse shaping, timing, etc...). In these conditions, direct light amplifiers would be very attractive as \"on-line\" amplifiers as an alternative to sophisticated optoelectronic repeaters; they could also be used in a receiver as low noise preamplifiers, in combination with a pinphotodiode, especially at the 1.3 ... 1.55 μη wavelength, where avalanche photodiodes (APD) are more \"noisy\" than silicon APDs. It is our purpose to discuss the possibility for semiconductor laser amplifiers to be used in a single mode fiber communication system. We shall first derive the power budget improvement due to the insertion of a laser amplifier in a digital optical communication system. A review of semiconductor laser amplifiers (SCLA) characteristics of the traveling-wave type (TW), Fabry-Perot type (FP) and injection locked laser type (ILL) will then be presented, with emphasis on recent experimental results. Finally, possible applications of these devices in single mode fiber communication systems will be discussed. 2 Noise characteristics of a laser amplifier in an optical communication system

Wavelength multiplexing in single-mode fiber couplers.

Abstract: Theoretical and experimental studies of wavelength-division multiplexing in a single-mode fiber optic coupler fabricated by mechanical polishing are reported. The variable spacing geometry of the device allows fine tuning of the center wavelength of operation. Wavelength selectivities ranging from 200 to 35 nm have been experimentally demonstrated, with cross talk ranging from 50 to 10 dB. Selectivity control is simply achieved by proper choice of the interaction length of the coupler. The dependence of the multiplexer behavior on all relevant parameters is investigated and found to satisfy predicted results.

Fiber optic sensor for detecting very small displacements of a surface

Abstract: A light source (10) coupled to a first fiber optic waveguide (14) which is coupled by a first directional coupler (22) and a second directional coupler (24) to a second waveguide (20). The first waveguide (14) has a phase modulator (60), a delay loop (62) and a polarization controller (68) therein to cause a differential delay time T on counterpropagating coherent light waves phase modulated at a frequency 1 M . The first directional coupler (22) has one part connected to a photodector (28) and the second directional coupler (24) has a probe (20D) coupled to the first fiber (14) and the second fiber (20). The probe directs light toward a surface (18) whereupon the counterpropagating waves are shifted in phase by an amount proportional to the amplitude of displacement of the surface 18.

Brillouin ring laser

Abstract: A Brillouin ring laser comprises a fiber optic resonator formed from a loop (14) of fiber optic material (10) and a fiber optic directional coupler (20) for optically closing the loop (14).

Optical fiber gyro

Abstract: An optical fiber gyro system provides a pair of separated optical paths containing partial common portions. A phase difference Δθ is detected using a plurality of detectors which yield sin and cos functions in Δθ. Functions are formed as linear couplings of these functions, and the phase difference Δθ is obtained using the function of best sensitivity for the given range of Δθ.

Fiber-optic gyroscope with polarization-holding fiber

Abstract: A fiber gyroscope is reported that uses polarization-holding fiber in the coil, the phase modulator, and the coupler The random-drift coefficient, calculated from rms noise levels, was 810−4deg/h, within a factor of 2 of an experimentally determined quantum and thermal limit White-noise behavior was observed for integration time constants from 1 to 40 sec Device characteristics and performance are presented

Cross-talk fiber-optic temperature sensor

Abstract: The temperature sensitivity of cross talk between closely spaced cores in a common cladding is calculated and compared with measurements. A periodic variation in core contrast is observed when one core is illuminated and the temperature is changed. The variation in light distribution, which is ascribable to a change in coupling between the cores, agrees with theoretical predictions. It is shown that cross talk can be made to be a sensitive, predictable function of temperature or by proper selection of materials, wavelength, and fiber geometry essentially temperature independent.

Fiber-Optic Acoustic Sensor Based On The Sagnac Interferometer

Abstract: A series of fiber-optic acoustic sensors based on the Sagnac interferometer are described. Features of these sensors include filtering of low-frequency signal components, use of a laser light source as an amplifier, and selection of the mechanism whereby the acoustic signature is impressed upon the light beams propagating in the fiber coil.

Process of tuning a grated optical fiber and the tuned optical fiber

Abstract: A tuned optical fiber grating and a tuning process is disclosed. The gratings on the optical fiber ar tuned so that the reflectance of the grating can occur at a specific wavelength. The process involves encasing that portion of the fiber containing the grating while shining light of the wavelength of desired reflectance through the fiber and stretching the grating until reflectance occurs. Thereafter, the tuned grating is sealed within a tube formed around the tuned grating.

A fiber-optic DC magnetometer

Abstract: An interferometric fiber-optic magnetometer capable of measuring dc magnetic fields is demonstrated. Sensitivity on the order of 10-6Oe per meter of sensor fiber at 1-Hz bandwidth has been achieved.

Fiber optic interferometer using two wavelengths or variable wavelength

Abstract: A fiber optic interferometric physical sensor. A fiber optical Mach-Zehnder interferometer includes a sensor arm and a reference arm having different optical path lengths. A transducer coupled to the sensor arm modulates the phase of light signals passing therethrough in response to a physical quantity. The interferometer is supplied with an input optical signal which includes light components at two different wavelengths. The detected intensity of the output of the interferometer includes two components, each of which vary in relation to the physical quantity. Each output component is related to one of the two optical input wavelengths. The two output components differ in phase by an amount proportional to the path length difference between the sensor and reference arms and proportional to the wavelength difference between the light components of the input optical signal. The phase difference is adjusted such that the sensitivities of the two output components to the physical quantity are never simultaneously at a minimum. In an alternative embodiment, a single laser having a continuously variable wavelength is used with the interferometer having differing sensor and reference path lengths to achieve maximum sensitivity.

Temperature-sensitive optrode

Abstract: Method and apparatus are provided for measuring temperature and for generating optical signals related to temperature. Light from a fiber optic is directed to a material whose fluorescent response varies with ambient temperature. The same fiber optic delivering the excitation beam also collects a portion of the fluorescent emission for analysis. Signal collection efficiency of the fiber optic is enhanced by requiring that the fluorescent probe material be in the shape of an oblong parabolically tapered solid. Reproducibility is enhanced by using Raman backscatter to monitor excitation beam fluctuations, and by using measurements of fluorescence lifetime.

Safety device for detecting trouble in optical transmission fibers

Abstract: A safety device for detecting troubles in an optical transmission fiber of a medical laser application to prevent accidents characterized by using either a laser light reflector from the exit end surface of the fiber or a secondary light. When trouble is detected, the safety device operates a mechanism for interrupting the coupling of a beam of laser light into the transmission fiber. The safety device includes an electrical circuit which allows appropriate use of the apparatus with the tip of the fiber in water or a physiological salt solution for treatment of a tumor in a urinary bladder. The electrical circuits will include amplifiers, comparators and logic circuits.

Stabilized fiber optic sensor

Abstract: A fiber optic sensor comprises a length of optical fiber, forming a loop, and a fiber optic directional coupler for optically closing the loop. The loop and coupler form a resonant cavity for light circulating therethrough. A PZT cylinder, about which the fiber loop is wrapped, is utilized to control the total round trip phase delay of the circulating light, and thus, control the intensity of the optical output signal. The phase delay is adjusted to a point where the optical output signal is at maximum sensitivity to changes in phase. When the fiber loop is exposed to, e.g., acoustic waves, the loop length changes correspondingly, thereby causing the phase delay, and thus, the optical output signal to vary. By detecting variations in output signal intensity, the frequency and intensity of the acoustic waves may be determined. The sensor also includes a feedback system for stabilizing the fiber loop against low frequency thermal drift.

Demodulation of interferometric sensors using a fiber-optic passive quadrature demodulator

Abstract: The passive quadrature demodulator (PQD) eliminates the phase stretcher and feedback electronics frequently used in fiber interferometric sensors by passively extracting the desired signal using two distinct interferometers which differ in phase by \pi/2 . A fusion technique is described to fabricate a fiber PQD which is sufficiently stable with respect to temperature, polarization, and wavelength to maintain the sensitivity of interferometric sensors constant to 0.25 dB.

An all single-mode fiber Michelson interferometer sensor

Abstract: A Michelson interferometer made from a single-mode fiber directional coupler with silver mirrors deposited on fiber ends is presented. This interferometer is simple to fabricate and has a theoretical visibility of unity, irrespective of the splitting ratio of the coupler. A theoretical analysis of its performance is described. Locking to quadrature was achieved by tuning the frequency of the laser source at 1.52μm. Results are presented for the interferometer operating over one kilometer of single-mode fiber, in a passive remote sensing configuration.

Broad-band ultrasonic sensor based on induced optical phase shifts in single-mode fibers

Abstract: A broad-band ultrasonic sensor based on induced optical phase shifts in single-mode fibers is demonstrated over a frequency regime of 0.5-50 MHz. In addition, a recently developed theory used to predict the magnitudes of acoustically induced strains in optical fibers is verified.

A composite optical fiber and imaging catheter and method for producing the same

Abstract: A composite optical fiber for use with a sensor includes an imaging optical fiber which receives information-carrying light that is reflected from a target, and a transparent material that includes the imaging optical fiber in its interior and which transmits an illuminating light from a light source to the target. The light-receiving optical fiber is an integral part of the transparent material, and it has an increased cross-sectional area for transmitting the illuminating light with respect to its overall outside diameter. The optical fiber can be produced by the extrusion technique without arranging a multiplicity of light-transmitting fibers and encasing them within a heat-shrinkable tube.

Fiber optic magnetic field sensor

Abstract: A fiber optic magnetic field sensor employing Faraday effect. The sensor has two pieces of birefringent substance interposed between the ends of optical fibers and a rod lens for effecting polarization separation. In addition, the sensor employs a reflex optical system in which light reciprocates through a Faraday material. Thereby, a magnetic field sensor has been realized which is more compact and lightweight and lower in cost as well as more accurate.

Measurement of polarization mode coupling along a polarization-maintaining optical fiber using a backscattering technique

Abstract: A new technique for measuring the polarization mode coupling of a polarization-maintaining optical fiber has been proposed that uses a modified optical time-domain reflectometry in which two kinds of backscattered signals coming through each principal axis of the fiber are utilized. This technique shows how the mode coupling occurs along the fiber. The extinction ratio evaluated by the present technique is in good agreement with that obtained by a conventional technique (within ±0.5 dB).

Single mode fiber optic single sideband modulator and method of frequency

Abstract: A fiber optic frequency shifter comprising two waveguides having different indices of refraction. In some embodiments the waveguides are two modes of propagation in one fiber. Plural distributed coupling ridges, or electrodes mounted adjacent piezoelectric materials, are independently driven to apply sinusoidally varying forces to the fiber. In some embodiments, the phase relationship of the driving signals for the electrodes or ridges is such that a travelling acoustic wave is launched in the fiber. In other embodiments, regions of stress in the fiber are created by an acoustic wave coupled into the fiber from a transducer coupled to an acoustic medium surrounding the fiber. The input carrier light is shifted in frequency by the frequency of the acoustic wave.

Polarization-maintaining fiber system and method of manufacturing the same

Abstract: In an optical fiber system comprising first and second polarization-maintaining fibers, a first orthogonal coordinate system of the first polarization-maintaining fiber is azimuthally rotated relative to a second orthogonal coordinate system of the second polarization-maintaining fiber by the use of an optical coupler by a preselected angle between 0° and 90°, both exclusive. Preferably, the optical coupler is shorter than a beat length of each fiber and the preselected angle is equal to 45°. The optical fiber system is applicable to an optical sensor for sensing a variable physical parameter. In the sensor, a light beam is incident onto one end of the first polarization-maintaining fiber so that a plane of polarization of the light beam is matched to one of those planes of the first polarization-maintaining fiber which are determined by the first orthogonal coordinate system. A third polarization-maintaining fiber is coupled through an additional optical coupler to the second polarization-maintaining fiber. The optical fiber system can be manufactured either by twisting and locally fusing a single polarization-maintaining fiber or by splicing together two polariation-maintaining fibers.

Fiber-optic diaphragm-curvature pressure transducer.

Abstract: A novel fiber-optic sensor that determines pressure from diaphragm curvature is discussed. This sensing technique exhibits a high degree of sensitivity and linearity and is less susceptible to environmental perturbations than previous intensity-modulating techniques. Experimental results are presented for a miniature pressure transducer suitable for in vivo medical applications.

Review of Fundamentals of Optical Fiber Systems

Abstract: This paper is a brief review of the principles of optical fiber systems to serve as an introduction to the specific application and technology papers in this issue. Fibers, transmitters, receivers, point-to-point transmission systems, multipoint buses, and sensor systems are discussed. Subsystems are reviewed in terms of thier input/ output characteristics.

Thermal characteristics of optical pulse transit time delay and fiber strain in a single-mode optical fiber cable.

Abstract: Thermal characteristics of optical pulse transit time delay and fiber strain in a single-mode optical fiber cable are investigated theoretically and experimentally Measurements of the transit time delay shift are made by a spatial interference technique using a 15-in long fiber, six-fiber unit, and cable Experimental results for a jacketed fiber whose fiber axis is well centered in nylon coating are in good agreement with those predicted from the theory A jacketed fiber whose fiber axis is positioned eccentrically from the jacket center exhibits a small change in fiber strain at low temperature due to fiber buckling compared with that for the well-centered jacketed fiber The loss increase for the off-centered jacketed fiber is explained by the buckling model Furthermore, thermal characteristics of the unit-type cable examined here are found to coincide with those for the constituent six-fiber unit