Showing papers on "Fiber optic sensor published in 1981"

Optical frequency domain reflectometry in single‐mode fiber

Abstract: The backscattered light amplitude is measured from one end of a fiber as a function of optical frequency by tuning a HeNe laser over its linewidth. Fourier transform by a low‐frequency electronic spectrum analyzer then reveals the spatial distribution of scattering and of the fiber losses.

Polarization-optical time domain reflectometry: a technique for the measurement of field distributions.

Abstract: Consideration is given to a new optical fiber technique for the measurement of the spatial distribution of physical fields (e.g., magnetic field, electric field, temperature, mechanical stress): polarization—optical time domain reflectometry (POTDR). The technique relies upon the time resolution of light backscattered from a pulse propagating in a monomode optical fiber to measure the spatial distribution of the fiber’s polarization properties. These properties are modified by the field under investigation. The technique appears feasible and could form the basis for a new measurement technology.

Sagnac effect in fiber gyroscopes

Abstract: We review the kinematic explanation of the Sagnac effect in fiber gyroscopes and recall that the index of the dielectric medium does not have any influence. Furthermore, we present a novel electrodynamic approach that confirms in more detail that the Sagnac phase shift of a ring-waveguide interferometer is the same as for the original Sagnac experiment with plane waves in a vacuum.

Interferometric method for chromatic dispersion measurement in a single-mode optical fiber

Abstract: Chromatic dispersion of a single-mode optical fiber only 1 m long is measured by a newly proposed interferometric method. Interference fringes are produced by two laser beams, one transmitting through the fiber and the other through air. Path length shifts in an interferometer for attaining the visibility maximum are measured by varying optical source wavelengths between 818 and 904 nm. Group delay time differences around 1 ps are measured. The measured results are in good agreement with those measured by the conventional pulse method for the identical 1.3 km long fiber.

All-single-mode fiber-optic gyroscope with long-term stability

Abstract: A new all-fiber gyroscope is described. All components are constructed directly on a single continuous optical fiber, removing localized sources of reflection. A laser-diode source is used to reduce coherent scattering effects. Proper choice of modulation frequency is shown to reduce instabilities further. Long-term stability at rest of better than 0.2 masculine/h is observed with 30-sec integration time.

Frequency domain optical reflectometer.

Abstract: A correlation reflectometer operating in the frequency domain is described. It is shown that such an instrument is well adapted to detecting weak discrete reflections. The detection of end reflections in a 2.2-km length of fiber whose end is index matched is demonstrated. A round-trip range of over 70 dB is obtained with a 1-mW optical source power. The method shows promise for characterizing the reflective properties of optical fiber elements, such as tapers, microbends, and splices, and may be useful in fault location.

All-single-mode fiber-optic gyroscope.

Abstract: We present an optical fiber gyroscope that, for the first time, is composed completely of single-mode fiber-optic components. This system has increased simplicity and stability over previous bulk-optic designs and has the potential for very high rotation sensitivity.

Temperature sensing by mode-mode interference in birefringent optical fibers.

Abstract: Fiber-optic sensors are described that utilize the mode–mode interference of the two orthogonal linear polarizations of the HE11 mode in strongly birefringent single-mode fibers. The sensitivities of various versions of these one-fiber interferometers are calculated. When fibers with high internal stress are used, the temperature sensitivity is reduced by only a factor of 50 compared with that of two-fiber interferometers while the pressure sensitivity is reduced by 7.3 × 103. Thus the cross sensitivity is reduced by a factor of 150.

Closed-loop, low-noise fiber-optic rotation sensor.

Abstract: A closed-loop, multiturn fiber-optic rotation sensor has been developed that exhibits low noise of the order of 0.1°/h for an averaging time of 30 sec. This performance is consistent with the photon-noise limit for our setup. The length of the fiber is 200 m, and the coil diameter is 19 cm. Nonreciprocal phase modulation is accomplished with an electro-optic crystal driven at 470 kHz, and closed-loop operation is achieved by means of acousto-optic frequency shifters.

Optical time domain reflectometry in a single-mode fiber

Abstract: This paper describes the theoretical and experimental study of an optical time domain reflectometry (OTDR) in a single-mode fiber. The maximum measurable distance by the OTDR is theoretically studied. In the experiment, the cylindrical lens attached to the laser diode, the low-loss and low-crosstalk directional coupler, and the digital averaging technique combined enabled us to measure a break in a single-mode fiber up to 17 km in length. This paper also describes the application of the OTDR to loss measurement of a single-mode fiber.

Fiber resonator gyroscope: sensitivity and thermal nonreciprocity.

Abstract: The rotational sensitivity of the fiber resonator gyro is derived and shown to be approximately equal to that of the fiber interferometer gyro for typical fiber and source parameters. The fiber resonator, like the fiber interferometer, is susceptible to errors due to thermally induced nonreciprocity; however, by reducing splice and coupler losses, it should be possible to reduce these errors well below those in the fiber interferometer.

Magnetic-field sensing with a single-mode fiber.

Abstract: A fiber-optic magnetic-field sensor is constructed by bonding a single-mode fiber to a nickel cylinder The magnetic field, by means of the magnetostrictive effect, alters the state of polarization of light in the fiber A sensitivity of 176 × 10−2 rad/m Oe is demonstrated, permitting detection of fields as small as 44 × 10−6 Oe/m of fiber

Fiber optic sensor with enhanced immunity to random environmental perturbations

Abstract: A sensor is provided for sensing or detecting the presence of an environmental field condition such as acceleration, temperature change, magnetic or acoustic fields. The field is sensed by interference between two mutually orthogonal polarized eigenmodes in a single monomode optical fiber which may be disposed either linearly or wound on a mandrel made of compliant material for sensing an acoustic field, or made of magnetostrictive material for sensing a magnetic field. Polarized light propagated through the optical fiber is detected at its outlet independent of environmentally induced low frequency variations whereby the sensor may be maintained at quadrature and maximum sensitivity.

Heterodyne-type optical fiber communications

Abstract: Standard optical fiber communication systems employ intensity-modulation/direct-detection schemes. This is noise-carrier communication and in a sense is more primitive than the radio engineering in Marconi’s age. However, it has the practical advantage of system simplicity and low cost. On the other hand, some applications of optical fiber communication exist in which a long repeater separation is the primary concern; an example is submarine optical cable communication between islands, in this case, the improvement of the bit-error rate (BER) by a coherent modulation/demodulation scheme such as PCM-PSK or PCM-FSK may be advantageous even at the sacrifice of simplicity and low cost.

Determination of optical-fiber diameter from resonances in the elastic scattering spectrum.

Abstract: Highly accurate determination of the outer diameter of unclad glass fibers has been achieved by analyzing, at fixed scattering angle, the wavelength dependence of elastically scattered radiation. The positions of resonance peaks in the scattering spectrum are strongly dependent on fiber diameter. The linewidths of the peaks are sensitive to the circularity of the fiber cross section and to optical loss within or on the fiber surface. This new technique may be useful for the characterization of optical-communication fibers.

Fiber optic temperature-measuring apparatus

Abstract: The invention relates to a fiber optic temperature-measuring apparatus, based on the photo-luminescence of a solid material which is subjected to the temperature to be measured. The apparatus is characterized in that several sensors made of such a temperature-sensitive luminescent material are located in various places, each one being connected to a light-emitting diode via at least one optical fiber. Luminescent light emitted from each sensor is arranged to be supplied, via at least one separate optical fiber, possibly partially via the above-mentioned fiber and a fiber branch, to a receiver unit, common to all the sensors, the excitation light signal from each light-emitting diode being time-division multiplexed.

Optical deformation sensor

Abstract: This invention relates to a lightweight and compact optical sensor that provides an indication of a deformation (e.g. fatigue, vibration, flex, torsion, bending, slippage) occurring at a monitored area. The sensor includes at least one light transmitting optical fiber and an optical detector that is responsive to the optical characteristics (e.g. amplitude, phase, polarization angle) of a supply of light signals being transmitted through the fiber. In the event that deformation occurs at the monitored region, the optical fiber undergoes a displacement which thereby causes a corresponding change in the optical characteristics of the light signals supplied to the detector. The optical characteristics of the light signals supplied to the detector relative to those of the light signals supplied to the optical fiber provide an accurate indication of the physical parameter.

Fiber Faraday circulator or isolator

Abstract: We demonstrate a Faraday circulator or isolator that uses a silica-core, single-mode, birefringent fiber as the active medium and small permanent magnets for the magnetic field. Circulators were constructed for wavelengths of 632.8 and 830 nm using about 2 m of fiber. This is the first description to our knowledge of such potentially useful working devices made in birefringent fiber. Bandwidth and temperature dependence were also investigated.

Sensing device having a multicore optical fiber as a sensing element

Abstract: A sensing device which includes a sensing element in the form of an optical fiber, a device for coupling light into the fiber and a device for measuring changes in the specific physical parameters of the light passing through the fiber to determine special physical influences applied to the fiber characterized by the fiber being a multicore fiber having at least two adjacently extending cores surrounded by a common cladding and the means for measuring the changes in the parameter of the light measuring the alterations in the light passing through each of the cores. To make the device sensitive to bending and deformation in all directions, the fiber may have two cores and be twisted through 90° or the fiber may have three or more cores which are not disposed in the same plane. The measuring of the amount of change may be by measuring the interference pattern from superimposed beams of the output from the two cores or by measuring the intensity of each of the output beams separately.

Fiber optical magnetic field sensor using magnetostrictive material

Abstract: A sensing element of magnetostrictive material associated with an optical fiber of an interferometer arm defining apparatus for detecting magnetic fields. The magnetostrictive material is adhered in close co-extensive adjacency with the optical fiber and in the presence of a magnetic field undergoes responsive longitudinal dimension changes which strains the optical fiber and induces a strain related phase shift in an optically propagating beam in the fiber detectable by interferometry.

Laser Doppler velocimeter with a novel optical fiber probe

Abstract: A practical laser Doppler velocimeter with optical fibers in the whole system was developed. The novel optical probe designed for this LDV is constructed of a graded-index rod lens attached to the end of an optical fiber. Since the laser beam from the probe is well collimated, the velocity accuracy and sensitivity are significantly improved. Mechanical vibration measurements were also carried out with this LDV; vibration amplitude down to 1.0 μm p-p can be measured at a frequency of 120 Hz with high accuracy.

Optical fiber profiles using the refracted near-field technique: a comparison with other methods.

Abstract: Multimode fiber profiles by the refracted near-field method (RNF) agree to within +/-0.5% with profiles obtained by the highly accurate interferometric slab technique in regions of adequate resolution of the latter. Nineteen multimode fiber profiles by the RNF and transverse interferometric methods differ in Delta and alpha on the average by 4% and 3%, respectively. The precision of a refractive-index determination by the RNF technique is 4 x 10(-5). A rapid method of calibrating the profiles by measuring the liquid temperature is presented, and the effect of foreign matter on the fiber face is discussed.

Opto-acoustic transducer and telephone receiver

Abstract: An optical fiber element of low density, low heat capacity, a large coefficient of thermal expansion, and a large Young's modulus varies in light transmissivity gradually between its ends from high transmissivity to opacity, whereby power modulated light transmitted through the fiber element is absorbed to cause a change in temperature of the fiber element and a resultant thermal expansion and contraction thereof. As a transducer in a telephone receiver, a light absorbing fiber element or group of such elements is coupled between the optical fiber waveguide in the receiver and a resiliently mounted acoustical diaphragm which is caused to respond over the audible range.

Apparatus for producing ultrasonic waves in a workpiece

Abstract: Laser light for producing acoustic waves in a specimen to be examined is carried to the specimen from a single laser by a plurality of fiber optic cables. The fiber optic cables have different path lengths to cause a specific time delay between adjacent fiber optic cables to focus and steer the sonic waves in a desired direction.

Optical fiber gyroscope with (3×3) directional coupler

Abstract: A Sagnac rotation sensing interferometer disposed on a rotating platform for use as a gyrsocope comprising a closed optical light path and a beam splitter for splitting an input light beam into two beams directed to transverse the closed optical path in opposite directions wherein the beam splitter is composed of a directional coupler with three input ports and three output ports. The first of the three input ports receives optical input and the second and third of the input ports are disposed symmetrically with respect to the first input port. Optical output from two output ports corresponding to the second and third input ports are directed to both ends of the closed optical fiber light path. A gyroscope according to this arrangement provides light output from the beam splitter which operates automatically near quadrature without a nonreciprocal π/2 phase bias applied in the fiber loop as required in conventional optical fiber gyroscopes.

Fiber optics transducers for sensing parameter magnitude

Abstract: A transducer for sensing the magnitude of a parameter, such as mechanical displacement/motion, pressure, temperature, electrical voltage, current and the like, uses a multimode optical waveguide fiber. At least one portion of the fiber is subjected to bending in an amount changing with a change in the sensed parameter magnitude. The resulting microbending losses in the fiber vary the attenuation of light energy between an optical source and an optical detector, response to variations in the sensed parameter magnitude. The variations of the detector output may be monotonically continuous, or may be processed to assume one of a pair of levels for "on-off" switching purposes.

Outer diameter measurement of low birefringence optical fibers by a new resonant backscatter technique.

Abstract: A new, highly precise, optical fiber outer diameter measuring technique based on near-field resonant backscattered light is described. Relative accuracies of ±10−2μm were achieved in diameter measurements using Fabry-Perot resonances and ±10−3μm in average diameter measurements using dielectric surface-wave resonances for ∼100-μm fibers. The shape of a new type of low birefringence spun fiber, made by rapidly spinning a near circular preform in the pulling oven, was measured. We observed a small ellipticity which rotated helically along the fiber. The possibility of making absolute and real-time outer diameter measurements is discussed.