Litton Systems, Inc.

James R Steele

Eric Lee Goldner

Amado Cordova

Ronald James Michal

John G Mark

Mark E Jones

Ralph A Patterson

John E Higbee

Daniel Eugene Auerbach

Ka Kha Wong

Bernard C Fidric

Craig C Hansen

A fiber optic rotation sensor system having improved scale factor stability includes an optically pumped gain fiber arranged to provide optical signals to an integrated optics chip connected to a fiber optic sensing coil. An optical coupler receives optical signals from the gain fiber and provides the optical signals to an optical fiber. The optical fiber is arranged to guide optical signals from the optical coupler along an optical path toward the integrated optics chip such that optical signals from the gain fiber are input to the fiber optic sensing coil to form counter-propagating waves therein. The counter-propagating waves traverse the sensing coil and then combine in the integrated optics chip to form a gyro output signal. A depolarizer is placed in the optical path between the first optical coupler and the integrated optics chip to prevent random changes in the state of polarization of optical signals propagating between the gain fiber and the integrated optic chip.

Apparatus and method for scale factor stabilization in interferometric

An interferometric rotation rate sensor is arranged to overcome effects of the unavoidable generation of intensity spikes in the modulated optical output. An electrooptical device is located within the optical path of the sensor for receiving the optical output signal from the sensor coil and transforming it prior to application to the photodetector. The electrooptical device is driven by a periodic electrical signal with a period equal to the loop transit time of light traveling through the sensor coil. By synchronizing the periods of attenuation with the predictable presence of spikes in the optical output, valid optical signal information is preserved while gyro electronics are sheltered from the results of optical intensity spiking.

Fiber optic gyro with optical intensity spike suppression

A power boosted source of broadband optical power comprising a broadband light source, optical fiber amplifier and a relative intensity noise reduction system. The optical fiber amplifier amplifies the power level of the optical input signal to provide a power boosted source of broadband optical power out of an output port. A coupler samples a portion of the broadband optical power out of the output port as a sample portion signal. A detector and transimpedance amplifier detect the optical signal and provide a buffered signal having an instantaneous amplitude that faithfully characterizes the intensity of the sample portion signal. A bandpass amplifier amplifies the buffered signal and provides an output control signal to a light source responsive to a composite bias and control current for providing an output optical signal. The output optical signal is coupled to the input of the optical fiber amplifier to be the optical input signal to the optical fiber amplifier. The output optical signal from the ELED has a substantially constant output intensity level and smooth and bell shaped broad band spectrum with a center optical wavelength within the gain bandwidth of the optical fiber amplifier.

Optical fiber amplifier eled light source with a relative intensity

Apparatus and methods for detecting when the birefringent axes of two polarization preserving fibers have their ends oriented into a position to locate the respective axes at 45 degrees. A fusion splicer and a heating controller for the fiber sensing coil are added to a reciprocal interferometer to produce a predetermined pattern of percent light intensity versus time in the returned light, when the axes are properly aligned for fusing. A computer may control the automatic making of depolarizers by this invention.

Fiber depolarizer using heated fiber coil and fusion splicer and two

A phase modulator for use in a circuit for measuring the output of a fiber optic gyroscope. The phase modulator is adapted to receive the digital word generated by such a circuit that comprises phase shift information. The digital word includes both the feedback Serrodyne ramp and the phase modulation conventionally generated for shifting the operating point of the gyroscope to enhance the sensitivity of output beam intensity to phase difference. The modulator employs a plurality of electrode elements with the lengths of adjacent segments having a power-of-two relationship. As a result, the digital word may be directly received by the phase modulator without prior conversion to an analog signal.

Digital phase modulator for fiber optic sagnac interferometer

Setting the driving signal of a phase modulator in the sensing loop of a fiber optic gyroscope to zero for a period of time .tau. equal to the transit time of the light waves through the gyro causes the gyro to assume a known zero reference state. In this zero reference state the counterpropagating light waves are in phase except for the phase shift caused by rotation of the sensing loop. During this zero reference state, a biase signal for demodulation purposes and a signal that will cause a phase shift equal and opposite to the rotation-induced phase shift are applied to the phase modulator. These signals null the rotation-induced phase shift as seen by a photodetector for a period equal to the transit time.

Rotation rate nulling servo and method for fiber optic rotation sensor

A phase locked loop is disclosed which subtracts an estimated signal from an input signal and operates upon the residual signal. The residual signal is demodulated and applied to a controlled oscillator which produces feedback signals approximately the sine and cosine of the input signal. The cosine feedback signal is multiplied by the residual signal whose resultant signal is a frequency correction signal. The sine feedback signal is multiplied by the residual signal for multiplication again by the sine feedback signal to produce the estimated signal which is amplitude and frequency controlled. This signal is then subtracted from the input signal to reduce the residual signal to near zero.

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Northridge, CA, United States of America

James R Steele