Donald R Frederick

US Patent:

6434283, Aug 13, 2002

Filed:

Feb 28, 2000

Appl. No.:

09/514922

Inventors:

Donald Adam Frederick - Woodland Hills CA
David Barnett Hall - La Crescenta CA

Assignee:

Litton Systems, Inc. - Woodland Hills CA

International Classification:

G02B 600

US Classification:

385 11, 385 70, 385 72, 385 73

Abstract:

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.

US Patent:

6768829, Jul 27, 2004

Filed:

Apr 2, 2001

Appl. No.:

09/824119

Inventors:

Craig W. Hodgson - Thousnd Oaks CA
Donald A. Frederick - Woodland Hills CA

Assignee:

Litton Systems, Inc. - Woodland Hills CA

International Classification:

G02B 626

US Classification:

385 15, 385 17, 385 31

Abstract:

Sensor arrays utilizing standard 1Ã2 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.

US Patent:

6072921, Jun 6, 2000

Filed:

Jul 18, 1997

Appl. No.:

8/896433

Inventors:

Donald Adam Frederick - Woodland Hills CA
David Barnett Hall - La Crescenta CA

Assignee:

Litton Systems, Inc. - Woodland Hills CA

International Classification:

H04R 304

US Classification:

385 12

Abstract:

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.

US Patent:

59952075, Nov 30, 1999

Filed:

Nov 26, 1997

Appl. No.:

8/979162

Inventors:

David B. Hall - La Crescenta CA
Donald A. Frederick - Woodland Hills CA
James B. Bunn - Austin TX
James S. Bunn - Malibu CA

Assignee:

Litton Systems, Inc. - Woodland Hills CA

International Classification:

G01C 308
G01B 902

US Classification:

356 509

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.

US Patent:

56968574, Dec 9, 1997

Filed:

Jul 25, 1996

Appl. No.:

8/686988

Inventors:

Donald A. Frederick - Woodland Hills CA

Assignee:

Litton Systems, Inc. - Woodland Hills CA

International Classification:

G02B 604

US Classification:

385 12

Abstract:

A fiber optic sensor comprises a first optical signal source that produces an optical signal of wavelength. lambda. sub. 1 and a second optical signal source that produces an optical signal of wavelength. lambda. sub. 2. A first WDM coupler is connected to the first and second optical signal sources to combine signals output therefrom. An optical fiber is connected to the WDM coupler to guide the combined optical signals therefrom. A second WDM coupler is connected to the optical fiber to separate the optical signals of wavelength. lambda. sub. 1 and. lambda. sub. 2. A fiber optic sensor array containing a plurality of fiber optic sensors is connected to the second WDM coupler and arranged such that optical signals of the wavelengths. lambda. sub. 1 and. lambda. sub. 2 are directed to different fiber optic sensors in the fiber optic sensor array. A third WDM coupler is arranged for combining signals of wavelength. lambda. sub. 1 and. lambda. sub.

US Patent:

58672583, Feb 2, 1999

Filed:

Oct 27, 1997

Appl. No.:

8/958365

Inventors:

Donald A. Frederick - Canoga Park CA
Steven G. Bell - Woodland Hills CA

Assignee:

Litton Systems, Inc. - Woodland Hills CA

International Classification:

G01B 902

US Classification:

356 355

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 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.

US Patent:

60389265, Mar 21, 2000

Filed:

Sep 4, 1997

Appl. No.:

8/923707

Inventors:

Donald A. Frederick - Woodland Hills CA
David B. Hall - La Crescenta CA

International Classification:

G01L 900
G01J 156
G01J 546

US Classification:

73705

Abstract:

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.

US Patent:

57514259, May 12, 1998

Filed:

Dec 30, 1996

Appl. No.:

8/777498

Inventors:

Donald A. Frederick - Woodland Hills CA
John G. Mark - Pasadena CA
Daniel A. Tazartes - West Hills CA
David B. Hall - La Crescenta CA
Tae W. Hahn - Chatsworth CA

Assignee:

Litton Systems, Inc. - Woodland Hills CA

International Classification:

G01C 1964

US Classification:

356350

Abstract:

A ring laser gyroscope having an alternating Faraday bias includes mode combining apparatus arranged to cause interference between the modes that propagate within the cavity. Signal separating apparatus separates a signal indicative of rotation of the frame from other components of the combined intensity signal. The signal separating apparatus produces two signals indicative of the light intensity in the interference pattern of the combined modes. These two signals have a 180. degree. phase difference in corresponding components that are dependent upon the geometric bias caused by the non-planar optical path to produce a rotation signal that is independent of the spatially uniform interference fringes caused by the geometric bias.