Litton Systems, Inc.

Other

Northrop Grumman Systems Corporation

L-3 Communications Corporation

Northrop Grumman Guidance and Electronics Company, Inc.

Donald A Frederick

Craig W Hodgson

David Barnett Hall

Samuel N Fersht

Daniel A Tazartes

John G Mark

Agop Hygasov Cherbettchian

Edward Kanegsberg

Akbar Arab-Sadeghabadi

Tae W Hahn

Steven J Maas

Kurt R Carlson

William Christopher Knaack

James S Bunn, Jr

Karlheinz vonBieren

James Brett Bunn

Robert P Goldman

Laurence G Cote

John F Cappi

Joseph Scott Salinas

John A Roscigno

David C Winslow

Michael J Carter

John E Mansell

Steven G Bell

James S Bunn Jr

James B Bunn

A re-enterable end-to-end hydrophone assembly which is at least partially transparent, so that the routing of the hydrophone fibers is visible during all phases of assembly and operation. The inventive hydrophone assembly includes a cylindrical sensing mandrel with at least one optical fiber wrapped around its outer wall, and an at least partially transparent oil-filled reference housing attached to the sensing mandrel. The reference housing contains an internal support for holding at least one end of the optical fiber, as well as other hydrophone components such as input couplers, output couplers, and the like. The inventive hydrophone assemblies can be easily disassembled, repaired, and reassembled, facilitating recovery and reuse of expensive optical components.

Repairable fiber optic hydrophone assembly

Sensor arrays utilizing standard 1&#xd7;2 couplers reduce the differences in the returned optical power levels by appropriate selection of the coupling ratios. Preferred embodiments are described that comprise 6 distribution fiber lines and 16 return fiber lines. One embodiment includes 16 sensor groups in which each sensor group has a dedicated return line. In another embodiment, 8 sensor groups are configured so that no two adjacent sensors have either a common distribution fiber line or a common return fiber line.

Architecture for large optical fiber array using standard 1&#xd7;2 couplers

Sensor arrays utilizing standard 1&times;2 couplers reduce the differences in the returned optical power levels by appropriate selection of the coupling ratios. Preferred embodiments are described that comprise 6 distribution fiber lines and 16 return fiber lines. One embodiment includes 16 sensor groups in which each sensor group has a dedicated return line. In another embodiment, 8 sensor groups are configured so that no two adjacent sensors have either a common distribution fiber line or a common return fiber line.

Architecture for large optical fiber array using standard 1&times;2 couplers

An improved pressure vessel comprises a tubular casing having an internal cavity and a first and second opening at each end. The internal cavity is divided into a first and second cylindrical plug region extending inward from the first and second opening and a hollow interior region. An optical component in the hollow interior has at least a plurality of optical fiber pigtails extending therefrom. A first and second cylindrical plug is force fit into the plug regions. At least one plug has a through-hole for receiving optical fiber pigtails. At least one plug has a ceramic adhesive plug formed by inserting adhesive into the through-hole and preferably filing the void space therein. The adhesive encapsulates the optical fibers passing through the through-hole. The plug has a channel machined into its outer circumference to receive an O-ring. A cap covers over and beyond the outer surface of the plug.

Pressure vessel

A system for sensing subterranean acoustic waves emitted from an acoustic source includes a plurality of laser sources, a plurality of subterranean optical sensors, at least one optical detector, and electronics. The laser sources each emit light at a different frequency. The subterranean optical sensors receive the light and alter the light in response to the acoustic waves. The optical detector receives the altered light and outputs an electrical signal. The electronics receives the electrical signal and converts it into seismic data format. The hydrophone for sensing the acoustic signals is able to operate at pressures of at least 5,000 psi and temperatures of at least 130 degrees Celsius. A hydrophone may be housed in a cable having a diameter of less than about 1.5 inches. The hydrophone's sensor preferably includes a reference mandrel, two sensing mandrels, and a telemetry can, all of which are aligned in a coaxial, end-to-end configuration to reduce the profile of the hydrophone. Flexible interlinks having grooves therein for receiving optical fiber join the mandrels together. The reference mandrel and sensing mandrels advantageously have hemispherically-shaped endcaps, permitting them to operate at high pressure.

Acoustic sensing system for downhole seismic applications utilizing an array of fiber optic sensors

An optical sensor architecture receives an input optical signal from a signal source and outputs a perturbed optical signal from at least one sensor to a receiver. An optical amplifier is positioned along a return fiber at an optical distance at least 10 kilometers from the receiver, with the optical amplifier amplifying the perturbed optical signal propagating to the receiver. If only one optical amplifier is used, the optical distance between the amplifier and the receiver may be between about 10 km and about 80 km, and an optical distance of between about 10 km and about 150 km may separate the sensor and the receiver. If additional optical amplifiers and dedicated pump distribution fibers are used, the optical distances may be correspondingly greater. Alternatively, increasing the number of sensors necessitates a reduction in the optical distance separating the sensors from shore.

Long distance, all-optical telemetry for fiber optic sensor using remote optically pumped EDFAs

A fiber-optic acoustical sensor system includes a light source, an elongate optical cable conducting light from the light source to an optical acoustical transducer located at a distance from the light source along this cable, and a polarizer at the acoustical transducer. The sensor system includes a polarizer providing orthogonally-polarized light along the optical cable to the polarizer located adjacent to the transducer. Because of the polarizer adjacent to the transducer, disturbances of the optical cable and resulting polarization perturbations of the light transmitted along this cable do not affect the optical acoustical transducer. The acoustic transducer is responsive to sound energy to provide an optical return signal indicative of this sound energy. An in-line fiber-optic polarizer suitable for use in this acoustical transducer includes a pair of confronting optical fiber portions aligned along an optical axis and which each define end surfaces disposed at a Brewster polarizer angle with respect to light transmitted along this optical axis. The end surface of one of these optical fibers carries plural alternating sub-layers of high-index and low-index dielectric material, which are effective to p-polarize the transmitted light and substantially eliminate s-polarized light transmission to the optical acoustical transducer.

In-line fiber-optic polarizer

A system for sensing subterranean acoustic waves emitted from an acoustic source includes a plurality of laser sources, a plurality of subterranean optical sensors, at least one optical detector, and electronics. The laser sources each emit light at a different frequency. The subterranean optical sensors receive the light and alter the light in response to the acoustic waves. The optical detector receives the altered light and outputs an electrical signal. The electronics receives the electrical signal and converts it into seismic data format. Preferably, the light emitted from the optical sources is modulated at a plurality of modulation frequencies. The electronics can be used to demodulate the signal. The electronics may demodulate the electrical signal by mixing the signal with periodic waveforms having frequencies corresponding to the modulation frequencies and twice the modulation frequencies. The modulation frequencies are selected such that at least one of the second harmonic frequencies associated with the modulation frequencies is interleaved in a non-interfering manner within the corresponding set of first harmonic frequencies. Preferably, the modulation frequencies are selected such that at least one of the first harmonic frequencies is interleaved in a non-interfering manner within the corresponding set of modulation frequencies. The hydrophone for sensing the acoustic signals is able to operate at pressures of at least 5,000 psi and temperatures of at least 130 degrees Celsius. The hydrophone may be housed in a cable having a diameter of less than about 1.5 inches. The hydrophone's sensor preferably includes a reference mandrel, two sensing mandrels, and a telemetry can, all of which are aligned in a coaxial, end-to-end configuration to reduce the profile of the hydrophone. Flexible interlinks having grooves therein for receiving optical fiber join the mandrels together. The reference mandrel and sensing mandrels advantageously have hemispherically-shaped endcaps, permitting them to operate at high pressure.

A system for sensing subterranean acoustic waves emitted from an acoustic source includes a plurality of laser sources, each emitting light at different frequencies; a plurality of subterranean optical sensors, receiving and altering the light in response to acoustic waves; at least one optical detector, receiving the altered light and outputting an electrical signal; and electronics, receiving the electrical signal and converting it into seismic data format. Light from the optical sources is modulated at a plurality of modulation frequencies. The electronics can demodulate the signal by mixing the signal with periodic waveforms having frequencies corresponding to one and two times the modulation frequencies. The modulation frequencies are selected such that at least one of the second harmonic frequencies associated with the modulation frequencies is interleaved in a non-interfering manner within the corresponding set of first harmonic frequencies, and preferably such that at least one of the first harmonic frequencies is interleaved in a non-interfering manner within the corresponding set of modulation frequencies. The hydrophone for sensing the acoustic signals is able to operate at pressures and temperatures of at least 5,000 psi and 130&deg; C., respectively. The hydrophone may be housed in a cable having a diameter less than about 1.5 inches. The hydrophone's sensor preferably includes a reference mandrel, two sensing mandrels, and a telemetry cam, which are aligned in a coaxial, end-to-end configuration to reduce the profile of the hydrophone. The mandrels have hemispherically-shaped endcaps and are joined by flexible interlinks having grooves for receiving optical fiber.

The length of optical cable affected when splicing in sensors is reduced by cutting and splicing two distribution fiber lines and two return fiber lines to each sensor. The cable includes a spare distribution fiber line and a spare return fiber line. The optical cable is first stripped back to expose the optical fibers therein. For both the distribution and return lines, one fiber is cut at the proximal end of the stripped back portion of the cable, and another fiber is cut at the distal end of the stripped back portion. These fibers are then fused to respective ports on the sensor. Thus, each of the optical channels is formed from more than one optical fiber. The resulting cable is less stiff and more flexible.

System for splicing sensors into a multiple fiber optical cable

Method of operating a fiber-optic acoustical sensor, apparatus for

A pressure measuring device which utilizes an array of optical, non-acoustic pressure sensors with a laser light source which generates a pulsed light signal into a light transmitting cable, wherein the pulsed light signal propagates along the light transmitting cable through the array of optical pressure sensors. A plurality of optical couplers are attached to the light transmitting cable at multiple locations spaced apart from one another in order to branch off at least a portion of the pulsed light each location. Each of the plurality of optical couplers includes a respective optical pressure sensor and a pressure insensitive reflector, wherein the branched off portion of the pulsed light signal is transmitted into to both the optical pressure sensor and the reflector. Each optical pressure sensor reflects a pressure indicating signal back into the optical coupler, while the pressure insensitive reflector reflects a reference signal back into the optical coupler. The pressure indicating signal and the reference signal are reflected through the optical coupler into the light transmitting cable as a pair of non-overlapping pulsed signals, which are then retrieved from the light transmitting cable by a signal detector. The retrieved pressure indicating signal is compared with the retrieved reference signal to determine the pressure acting upon the optical pressure sensor.

TDM array of optical non-acoustic pressure sensors

The invention is a method for obtaining a measure of the light propagation time difference for two light-propagating-media paths. The first step consists of generating two substantially-identical frequency-modulated light waves whereby the frequency of the light waves is offset from a reference frequency by a different frequency increment for each basic time interval in each of a plurality of groups of three or more basic time intervals. Each frequency increment is the sum of a specified increment and a frequency-modulation-error increment. The frequency-modulation-error increments associated with the specified increments are independent of each other and unknown. The second step consists of feeding the two light waves into the entry points of two light-propagating-media paths having a light propagation time difference and obtaining a combination light wave by summing the light waves emerging from the exit points of the two light-propagating-media paths. The third step consists of calculating an estimated corrected or estimated uncorrected phase measure of the light propagation time difference for the two paths for a plurality of groups using only measured properties of the combination light wave.

Method for determining the phase difference of light waves propagated

A system for performing high resolution measurement of frequency variations in multimode fiber laser acoustic sensors having an end-pumped active fiber sensor emitting a plurality of lasing modes, wherein precise frequencies of the lasing modes emitted are dependent upon a strain acting on said acoustic sensor. An optical fiber is connected to the active fiber sensor for transmitting the lasing modes. The optical fiber transmits the multiple lasing modes to an optical amplifier fiber where the lasing mode signals are amplified. The amplified lasing modes signals are then fed through a phase modulator connected to the optical fiber for applying a phase generated carrier on the lasing mode signals. The output from the phase modulator is supplied to a receiving interferometer having a predetermined path imbalance for interferometrically analyzing the frequency shifts of each of the lasing mode signals, wherein the predetermined path imbalance is matched with the longitudinal mode spacing between the lasing modes of the active fiber sensor. A demodulation unit is connected to the receiving interferometer for receiving and demodulating the output of the receiving interferometer to determine the frequency shift incurred by the lasing mode signals, wherein the demodulated frequency shift is proportional to the strain acting on the acoustic sensor. In an alternative embodiment, a plurality of active fiber sensors may be pumped by a single laser light source with their outputs multiplexed together and fed through the receiving interferometer for interferometric analysis of all the signals.

Growing community of inventors

Woodland Hills, CA, United States of America

Donald A Frederick