Litton Systems, Inc.

Leland Stanford Junior University

James S Bunn, Jr

David Barnett Hall

Donald A Frederick

Byoung Y Kim

Michael R Layton

Kenneth A Fesler

James Brett Bunn

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

Leakage optical signals injected into a time division multiplexed sensor system are modulated during off periods in the duty cycle in the sensor interrogation signal. The leakage light is modulated such that its unwanted contributions to the sensor output signals are displaced in frequency from the base band frequency. This frequency displacement greatly reduces unwanted noise power in the received signals.

Noise suppression apparatus and method for time division multiplexed

An interferometer used as a rotation sensor is constructed using a strand of optical fiber, a portion of which is formed into a sensing loop. A pair of light waves are caused to counterpropagate in the sensing loop and are combined to form an optical output signal that has an intensity that varies in accordance with the difference in the phases of the two counterpropagating light waves. A phase modulator is positioned on the optical fiber in the sensing loop at a location such that the two counterpropagating light waves are modulated approximately 180 degrees out of phase. The time-varying phase modulation causes a time-varying phase difference that is combined with a rotationally-induced Sagnac effect phase to provide a total phase difference that is detected by a photodetector. The photodetector provides an electrical output signal that is processed to determine the Sagnac phase difference. The rotation rate is then calculated from the Sagnac phase difference. The processing occurs in a feedback loop in which a reference signal is multiplied by the electrical output signal to provide a feedback signal. The reference signal is adjusted so that the feedback signal is maintained at a predetermined value. The magnitude of the adjustment of the reference signal is measured and the Sagnac phase difference is determined from the measured magnitude.

Optical fiber sensor having digital integrating detection system

A phase modulation control apparatus is taught in combination with an interferometer excited by a coherent light source providing a light beam to the interferometer having first and second optical paths. The interferometer senses a physical quantity such as pressure. The interferometer is coupled to provide an optical signal containing information providing a measure of the physical quantity via first and second interfering beams to a detector. The detector provides a composite output signal. The invention phase modulation control apparatus has a modulation means responsive to a modulating frequency signal and a phase modulation control signal to provide a frequency modulating factor signal for frequency modulating at least a portion of the light beam to provide a phase modulation between the first and second interfering beams at a carrier frequency. The composite output signal has at least four harmonic signals referenced to the carrier frequency. A synchronous detection means responsive to the carrier frequency signal and to the composite output signal provides a pair of even harmonic filtered signals and a pair of odd harmonic filtered signals. A reference channel means and quadrature channel means each respond to the even and odd harmonic pairs of filtered signals and respectively provide first and second integrator input error signals which have null values in response to their respective harmonic pairs having a predetermined ratio. An integration means combines and integrates the first and second integrator input error signals to provide the phase modulation control signal to the modulation means.

Interferometer phase modulation controller apparatus using ratios of two

A switch-selectable calibration signal is applied to an interferometric sensor channel of fiber optic sensor array for monitoring its operation. A calibration signal is applied at a single physical location to determine the channel scale factors and proper operability of multiple sensors at remote locations in the array. An optical signal input to each interferometric sensor channel in the array, and a compensating interferometer receives optical signals output from the fiber optic sensor array. A signal is applied to the compensating interferometer to form an output signal that simulates signals output from each interferometric sensor in the array. These signals are processed to determine the scale factor of each interferometer in the fiber optic sensor array.

Growing community of inventors

Malibu, CA, United States of America

James S Bunn, Jr