公开(公告)号：CA2315438C

公开(公告)日：2009-11-17

申请号：CA2315438

申请日：2000-07-27

Applicant: LITTON SYSTEMS INC

Inventor： FREDERICK DONALD A ,  HODGSON CRAIG W

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

Abstract: 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 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 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.

公开(公告)号：DE60032709D1

公开(公告)日：2007-02-15

申请号：DE60032709

申请日：2000-09-01

Applicant: LITTON SYSTEMS INC

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

IPC: G01V1/50 ,  G01H9/00 ,  G01V1/18 ,  G01V1/40 ,  G01V1/52

Abstract: A system for sensing subterranean acoustic waves emitted from an acoustic source includes a plurality of laser sources (LS1-LS6), a plurality of subterranean optical sensors (1000), at least one optical detector (D1-D16), and electronics (601). The laser sources each emit light at a different frequency. The subterranean optical sensors are hydrophones (1000) that receive the light and alter the light in response to the acoustic waves. The optical detector (D1-D16) receives the altered light and outputs an electrical signal. The electronics (601) receives the electrical signal and converts it into seismic data format. The hydrophones (1000) are able to operate at pressures of at least 5,000 psi and temperatures of at least 130 degrees Celsius. The hydrophone (1000) may be housed in a cable (1002) having a diameter of less than about 1.5 inches. The hydrophone's sensor preferably includes a reference mandrel (1110), two sensing mandrels (1120), and a telemetry can (1104), all of which are aligned in a coaxial, end-to-end configuration to reduce the profile of the hydrophone (1000). Flexible interlinks (1296) having grooves therein for receiving optical fiber join the mandrels (1110, 1120) together. The reference mandrel (1110) and sensing mandrels (1120) advantageously have hemispherically-shaped endcaps (1264), permitting them to operate at high pressure.

公开(公告)号：CA2320449C

公开(公告)日：2004-11-30

申请号：CA2320449

申请日：2000-09-21

Applicant: LITTON SYSTEMS INC

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

IPC: G01H9/00 ,  G01V1/18 ,  G01V1/40 ,  H04R1/44

Abstract: A system for sensing subterranean acoustic waves emitted from an acoustic source includes a plurality of laser sources (LS1-LS6), a plurality of subterranean optical sensors (1000), at least one optical detector (D1-D16), and electronics (601). The laser sources each emit light at a different frequency. The subterranean optical sensors are hydrophones (1000) that receive the light and alter the light in response to the acoustic waves. The optical detector (DI-D16) receives the altered light and outputs an electrical signal. The electronics (601) receives the electrical signal and converts it into seismic data format. The hydrophones (1000) are able to operate at pressures of at least 5,000 psi and temperatures of at least 130 degrees Celsius. The hydrophone (1000) may be housed in a cable (1002) having a diameter of less than about 1.5 inches. The hydrophone's sensor preferably includes a reference mandrel (1110), two sensing mandrels (1120), and a telemetry can (1104), all of which are aligned in a coaxial, end-to-end configuration to reduce the profile of the hydrophone (1000). Flexible interlinks (1296) havi ng grooves therein for receiving optical fiber join the mandrels (1110, 1120) together. The reference mandrel (1110) and sensing mandrels (1120) advantageously ha ve hemispherically-shaped endcaps (1264), permitting them to operate at high pressure.

公开(公告)号：NO20015515L

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

公开(公告)号：CA2240572C

公开(公告)日：2001-09-11

申请号：CA2240572

申请日：1998-07-07

Applicant: LITTON SYSTEMS INC

Inventor： BELL STEVEN G ,  FREDERICK DONALD A

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 ac tive 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 mo des. The optical fiber transmits the multiple lasing modes to an optical amplifier fi ber where the lasing mode signals are amplified. The amplified lasing modes signals are th en fed through a phase modulator connected to the optical fiber for applying a phas e generated carrier on the lasing mode signals. The output from the phase modulator is s upplied to a receiving interferometer having a predetermined path imbalance for interfero metrically analyzing the frequency shifts of each of the lasing mode signals, wherein t he predetermined path imbalance is matched with the longitudinal mode spacing b etween the lasing modes of the active fiber sensor. A demodulation unit is connecte d to the receiving interferometer for receiving and demodulating the output of the re ceiving 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 toge ther and fed through the receiving interferometer for interferometric analysis of all the signals.

公开(公告)号：AU735031B2

公开(公告)日：2001-06-28

申请号：AU9408198

申请日：1998-11-23

Applicant: LITTON SYSTEMS INC

Inventor： HALL DAVID B ,  FREDERICK DONALD A ,  BUNN JAMES B ,  BUNN JAMES S JR

IPC: G01J9/00 ,  G01J9/02 ,  G01B9/02

Abstract: 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.

公开(公告)号：AU732668B2

公开(公告)日：2001-04-26

申请号：AU7511698

申请日：1998-07-09

Applicant: LITTON SYSTEMS INC

Inventor： FREDERICK DONALD A ,  HALL DAVID B

IPC: H04B10/00 ,  G01L11/02 ,  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：NO20005444D0

公开(公告)日：2000-10-27

申请号：NO20005444

申请日：2000-10-27

Applicant: LITTON SYSTEMS INC

Inventor： ROSCIGNO JOHN A ,  HODGSON CRAIG W ,  FREDERICK DONALD A ,  KNAACK WILLIAM C

IPC: G01H9/00 ,  G01V1/52 ,  G01V

公开(公告)号：NO20005441D0

公开(公告)日：2000-10-27

申请号：NO20005441

申请日：2000-10-27

Applicant: LITTON SYSTEMS INC

Inventor： HODGSON CRAIG W ,  FREDERICK DONALD A

IPC: G01V20060101 ,  G01V1/16 ,  G01V1/32 ,  G01V8/24 ,  G01V

公开(公告)号：BR9802829A

公开(公告)日：1999-11-23

申请号：BR9802829

申请日：1998-07-31

Applicant: LITTON SYSTEMS INC

Inventor： FREDERICK DONALD A ,  BELL STEVEN G

IPC: G01B9/00 ,  G01H9/00 ,  H01S3/06 ,  H01S3/07 ,  G01B9/02

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.