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.

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

A communication system can include a transmitter which transmits a signal, and at least one sensing device which receives the signal, the sensing device including a line contained in an enclosure, and the signal being detected by the line through a material of the enclosure. A sensing system can include at least one sensor which senses a parameter, at least one sensing device which receives an indication of the parameter, the sensing device including a line contained in an enclosure, and a transmitter which transmits the indication of the parameter to the line through a material of the enclosure. Another sensing system can include an object which displaces in a subterranean well. At least one sensing device can receive a signal from the object. The sensing device can include a line contained in an enclosure, and the signal can be detected by the line through a material of the enclosure.

Communication through an enclosure of a line

A method and apparatus for the non-invasive sensing of the pressure within a pipe (or other vessel) is disclosed. An optical source produces a first light beam. This first light beam is split between a first (reference) and a second (measurement) optical fiber. The second optical fiber is associated with the pipe such that circumferential displacements in the pipe, due to changes in internal pressure, result in corresponding displacements in the length of the second optical fiber. Length changes in the optical fibers result in variations in the phase of the light emerging therefrom. The phase difference between the light beams emitted from the first and second optical fibers is then determined and related to changes in the internal pressure of the pipe.

Method and apparatus for the non-invasive measurement of pressure inside pipes using a fiber optic interferometer sensor

An optical pulse source for producing short optical pulses comprises first and second optical loops coupled together by a beam splitter so as to define a figure eight optical path in which a light beam propagating toward the beam splitter in one of the first and second loops is split by the beam splitter to form two light beams propagating in opposite directions around the other of the first and second loops. The first loop includes a direction dependent loss element for reducing the intensity of light propagating in a predetermined direction around the first loop, and the second loop includes an element having an intensity dependent nonlinear optical transmission characteristic. One of the first and second loops includes an optical gain medium. Coupling apparatus is also provided for coupling pump light into the loop including the gain medium and for coupling optical pulses out of the source.

Figure eight shaped coherent optical pulse source

A current is measured by making use of a rotation of polarization plane in a magnetic field, that is, a Faraday effect. A conductor under measurement is transversely inserted into a center opening of a Faraday effect glass which has at least two total reflection areas on a periphery thereof so that a light directed into the Faraday effect glass is circulated around the conductor and emitted externally. The light emitted from the Faraday effect glass is split into at least two light beams, which are converted to electric signals by photoelectric elements, and A.C. components contained in the electric signals are extracted and compared. The electric signals are corrected based on the comparison result. The present measuring apparatus and method attain high precision current measurement in a stable manner over an extended period.

Method and apparatus for optically measuring a current

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.

Fiber optic sensor with enhanced immunity to random environmental perturbations

A fiber optic sensor for detecting and/or measuring a physical quantity varying at any frequency from a maximum desired frequency down to zero frequency with minimum disturbance from environmentally induced perturbations. A first highly birefringent optical fiber is positioned longitudinally adjacent to a second equally birefringent fiber. Each fiber has orthogonally disposed fast and slow axes. The fibers are oriented such that their fast axes are perpendicular to each other. When subjected to stress caused by a physical quantity acting on the fibers through a transducer, the birefringence of each of the two fibers is asymmetrical altered thereby rotating the states of polarization of coherent light signals passing through the two fibers in a common direction. Environmental perturbations symmetrically alter the birefringence of each of the fibers thereby rotating the states of polarization of the light signals in opposite directions. The states of polarization of the light signals emanating from the two fibers are detected and combined such that the changes due to the physical quantity enhance each other while the changes due to environmental perturbations are cancelled.

Fiber optic sensors operating at DC

A fiber-optic gyroscope designed to operate at maximum sensitivity by suping two equal-intensity input beams with a specific phase difference to the gyroscope optical coupler. When the coupler outputs into the gyroscope optical fiber coil are of equal intensity, reciprocity requires the gyroscope to operate at quadrature. This device is realized by splitting a laser beam into two paths with a phase shifter in one of the paths to control the phase shift and thereby the intensity of the beams, and coupling the light from these paths into a fiber optic coil via a four-port 3dB coupler.

Dual input gyroscope

A Sagnac rotation sensing interferometer that uses a Mach-Zehnder interferometer to provide incident light beams that counter-propagate through an optical-fiber loop. The Sagnac interferometer operates at maximum sensitivity for zero rotation rates when the Mach-Zehnder is adjusted so that the intensities of the incident light beams are equal. By peiodically varying the position of a mirror in the Mach-Zehnder the interferometer is switched into and out of quadrature so that the amplitude of the interferometer output signal is modulated at frequency f o . Phase sensitive detection at 2f o or multiples thereof reduces the background noise level several orders of magnitude below the level for dc operation.

Scott C. Rashleigh

Papers

Fiber optic sensor with enhanced immunity to random environmental perturbations

Fiber optic sensors operating at DC

Dual input gyroscope

Fiber optic gyroscope with alternating output signal