公开(公告)号：NO983281A

公开(公告)日：1999-02-01

申请号：NO983281

申请日：1998-07-16

Applicant: LITTON SYSTEMS INC

Inventor： FREDERICK DONALD A ,  BELL STEVEN G

IPC: G01B9/00 ,  G01H9/00 ,  H01S3/06 ,  H01S3/07 ,  G01D5/353

CPC classification number: G01H9/004

公开(公告)号：CA2240572A1

公开(公告)日：1999-01-31

申请号：CA2240572

申请日：1998-07-07

Applicant: LITTON SYSTEMS INC

Inventor： FREDERICK DONALD A ,  BELL STEVEN G

IPC: G01B9/00 ,  G01H9/00 ,  H01S3/06 ,  H01S3/07 ,  G01J9/02 ,  H04B10/08 ,  H01S3/102

Abstract: 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 opt ical 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 f ed through a phase modulator connected to the optical fiber for applying a phase ge nerated carrier on the lasing mode signals. The output from the phase modulator is suppl ied to a receiving interferometer having a predetermined path imbalance for interferometr ically analyzing the frequency shifts of each of the lasing mode signals, wherein the predetermined path imbalance is matched with the longitudinal mode spacing betwe en 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 receiv ing interferometer to determine the frequency shift incurred by the lasing mode sign als, wherein the demodulated frequency shift is proportional to the strain acting on the acoustic sensor. In an alternative embodiment,. a plurality of active fiber sens ors 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 sig nals.

公开(公告)号：NO983281D0

公开(公告)日：1998-07-16

申请号：NO983281

申请日：1998-07-16

Applicant: LITTON SYSTEMS INC

Inventor： FREDERICK DONALD A ,  BELL STEVEN G

IPC: G01B9/00 ,  G01H9/00 ,  H01S3/06 ,  H01S3/07 ,  G01L ,  G01H

Abstract: A system (10) for performing high resolution measurement of frequency variations in multimode fiber laser acoustic sensors having an end-pumped active fiber sensor (16) 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 (14) is connected to the active fiber sensor (16) for transmitting the lasing modes. The optical fiber transmits the multiple lasing modes to an optical amplifier fiber (22) where the lasing mode signals are amplified. The amplified lasing modes signals are then fed through a phase modulator (34) connected to the optical fiber for applying a phase generated carrier on the lasing mode signals. The output from the phase modulator (34) is supplied to a receiving interferometer (36) 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 (46) is connected to the receiving interferometer (36) 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.

公开(公告)号：AU693402B2

公开(公告)日：1998-06-25

申请号：AU2487797

申请日：1997-06-13

Applicant: LITTON SYSTEMS INC

Inventor： FREDERICK DONALD A ,  GOLDMAN ROBERT P ,  MAAS STEVEN J ,  MANSELL JOHN E

IPC: G01H9/00 ,  H04B10/18

Abstract: A fiber optic hydrophone (30) is formed as a single interferometer having widely separated interferometer segments (32-35) formed in each of a pair of optical fibers (56-70). The interferometer segments (32-35) are designed to allow averaging of the effects of local noise sources over a broad area in order to increase the acoustic signal-to-noise ratio. The interferometer segments (32-35) also allow deployment of the hydrophone around sharp bends. A first optical fiber (56) is formed into a plurality of spatially separated outer coils (58,90,94). A second optical fiber (70) is formed into a plurality of inner coils (72,92,96) corresponding to the outer coils. The inner (50) and outer coils (72) are preferably arranged in concentric pairs to form a plurality of sensor segments (32-35). A plurality of spacers (40-42) is arranged such that a spacer is between successive sensor segments. The spacers (40-42) are formed to guide the outer (56) and inner (70) optical fibers between successive sensor segments (32-35) such that changes in the physical parameter between the sensor segments (32-35) produce no phase difference between optical signals guided by the outer (56) and inner (70) fibers. The outer (58) and inner coils (70) are preferably arranged for exposure to the parameter such that changes in the parameter at each sensor segment produce opposite phase changes between the optical signals in the outer coils and the corresponding outer coil.

公开(公告)号：NO971036D0

公开(公告)日：1997-03-06

申请号：NO971036

申请日：1997-03-06

Applicant: LITTON SYSTEMS INC

Inventor： FREDERICK DONALD A ,  CAPPI JOHN F

IPC: G01H9/00 ,  G01V1/18 ,  G01B9/02 ,  G02B6/36 ,  H04B13/00 ,  H04R1/44 ,  H04R23/00

Abstract: A hydrophone has a fibre optic interferometer with a reference arm (26) formed by a length of optical fibre wound around a rigid mandrel (30) and with constant optical path length, elastic material (42) over the arm, and a concentric sensing arm (24) with a length of optical fibre wound over the material in a coil so that optical path length changes when the hydrophone is exposed to an acoustic field. Optical output signals are passed to a processor to measure acoustic pressure. Preferably, the elastic material is preferably polyurethane, and the sensing arm is encased in further elastic material (44) and spaced from the reference arm. The mandrel is e.g. a solid rod of metal or other rigid material with end flanges, and the reference arm is potted.

公开(公告)号：NO323869B1

公开(公告)日：2007-07-16

申请号：NO983282

申请日：1998-07-16

Applicant: LITTON SYSTEMS INC

Inventor： HALL DAVID B ,  FREDERICK DONALD A

IPC: G01L11/02 ,  H04B10/00 ,  G08C15/00

Abstract: A pressure measuring device which utilizes an array of optical, non-acoustic pressure sensors (22) with a laser light source (12) which generates a pulsed light signal into a light transmitting cable (16), wherein the pulsed light signal propagates along the light transmitting cable through the array of optical pressure sensors. A plurality of optical couplers (18) are attached to the light transmitting cable (16) 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 (22) and a pressure insensitive reflector (26), wherein the branched off portion of the pulsed light signal is transmitted into both the optical pressure sensor (22) and the reflector (26). Each optical pressure sensor (22) reflects a pressure indicating signal back into the optical coupler (18), while the pressure insensitive reflector (26) reflects a reference signal back into the optical coupler. The pressure indicating signal and the reference signal are reflected through the optical coupler (18) 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 (32) . The retrieved pressure indicating signal is compared with the retrieved reference signal to determine the pressure acting upon the optical pressure sensor.

公开(公告)号：CA2240727C

公开(公告)日：2005-11-08

申请号：CA2240727

申请日：1997-11-14

Applicant: LITTON SYSTEMS INC

Inventor： FERSHT SAMUEL N ,  FREDERICK DONALD A

IPC: G01L1/24 ,  G01B9/02 ,  G01D5/353 ,  G01J9/02 ,  G01K11/12

Abstract: The invention is a method and apparatus for determining the phase difference of light waves (31) after propagating through each of one or more two-path pairs, a two-path pair being two optical transmission paths connecting a common entry point (25) to a common exit point (29). Coherent light pulses (27) of predetermined duration are fe d into the entry point (25) of each two-path pair in a group of two-path pairs at predetermined time intervals, the pulse duration being subdivided into a plurality of predetermined time segments. The phase difference for each two-path pair is determined from amplitude values of the electrical signal.

公开(公告)号：NO20015515D0

公开(公告)日：2001-11-12

申请号：NO20015515

申请日：2001-11-12

Applicant: LITTON SYSTEMS INC

Inventor： HODGSON CRAIG W ,  FREDERICK DONALD A

IPC: G01D5/26 ,  G01D5/353 ,  G08B13/186 ,  H04B10/17 ,  H04B

公开(公告)号：NO20005442A

公开(公告)日：2001-04-30

申请号：NO20005442

申请日：2000-10-27

Applicant: LITTON SYSTEMS INC

Inventor： FREDERICK DONALD A ,  CARTER MICHAEL J ,  FERSHT SAMUEL N ,  WINSLOW DAVID C

IPC: G01H9/00 ,  G01V1/18 ,  G01V1/40 ,  G01V1/52 ,  G01V8/00

CPC classification number: G01V1/186 ,  G01H9/004 ,  G01V1/40 ,  Y10S367/912

公开(公告)号：CA2315438A1

公开(公告)日：2001-04-29

申请号：CA2315438

申请日：2000-07-27

Applicant: LITTON SYSTEMS INC

Inventor： HODGSON CRAIG W ,  FREDERICK DONALD A

IPC: G01V20060101 ,  G01V1/16 ,  G01V1/32 ,  G01V8/24

Abstract: A system for sensing subterranean acoustic waves emitted from an acoust ic 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 lig ht 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 electroni cs can be used to demodulate the signal. The electronics may demodulate the electrical signal by mixing the signal with periodic waveforms having frequencies corresponding t o 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-interferi ng 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 mannerwithin 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 sensi ng 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.