Optical gyroscope

Claim 2

A fiber optic gyro comprising: a source of light; amplitude modulating and source driving means for driving the source; an optic fiber coil rotatable about an axis of sensitivity; means for optically coupling light from the source to the coil to create counterpropagating beams therethrough; means connected intermediate the coupling means and the coil for optically phase modulating the beams propagating (a) in a first direction prior to introduction into the coil, (b) in a second counterpropagating direction after passage through the coil; photodetecting means receiving the optically phase modulated counterpropagated light beams, for producing a signal at its output responsive to the coil rotation rate; control means having its input connected to the photodetecting means output for translating the output signal from the photodetecting means to a variable frequency signal responsive to coil rotation rate; feedback means connecting an output of the control means to the amplitude modulating and source driving means for generating a phase-modulated source driving signal.

Claim 3

The structure set forth in claim 1 wherein the control means comprises: a phase sensitive detector having a first input connected to the photodetecting means output and a second input connected to a fixed reference frequency.

Claim 4

The structure of claim 2 wherein the control means further comprises single sideband modulating means having a first input thereof connected to the output of the phase sensitive detector, a second input of the single sideband modulating means being connected to the error signal for generating at its output a modulated signal which is a measure of the rotating rate.

Claim 5

The structure set forth in claim 3 wherein the control means further comprises a voltage controlled oscillator, and integrating means connected between the single sideband modulating means and an input of the voltage controlled oscillator for producing a variable frequency signal at the output of the voltage controlled oscillator which is the error signal.

Claim 6

The structure set forth in claim 4 wherein the control means further comprises means having a first input thereof connected to a second output of the voltage controlled oscillator and a second input connected to a fixed frequency for phase modulating a variable frequency signal from the voltage controlled oscillator and producing a control means output for connection to the amplitude modulating and source driving means.

Claim 9

The method of claim 6 wherein translating the photodetected signal to a corresponding variable frequency signal includes the step of phase detecting the photo detected signal with a fixed frequency.

Claim 10

The method of claim 7 wherein the photodetected signal translation includes the step of single sideband modulating the detected signal with the variable frequency signal.

Claim 11

The method of claim 8 wherein the single sideband modulated signal generates oscillations modulated with a fixed frequency for the feeding back of a signal which controls the amplitude modulating of the light source.

Claim 12

An optical interferometer comprising: a source of light; amplitude modulating means for driving the source of light; signal generating means for driving the amplitude modulating means comprising a source of a variable frequency sinusoid phase modulated at a fixed phase modulation frequency; an optical fiber coil producing a non-reciprocal phase shift responsive to a phenomenon to be measured; means for optically coupling light from the source of light to the optical fiber coil to create counterpropagating beams therethrough; means located assymmetrically in the coil path for optically phase modulating the counterpropagating beams at the said fixed modulation frequency; photodetecting means receiving the counterpropagating light beams for producing a signal responsive to both the said non-reciprocal phase shift and a second non-reciprocal phase shift created by the said variable frequency; means setting the frequency and phase modulation amplitudes of said phase modulations such that unwanted signal components vanish at the frequency of a selected harmonic of the said phase modulations frequency; signal processing means for changing the signal from the photodetecting means to a signal which is a function only of the algebraic sum of the two said non-reciprocal phase shifts when that sum is small; and adjustment means whereby said signal responsive to the algebraic sum of the two said non-reciprocal phase shifts is made to vanish by adjusting said variable frequency; whereby the said variable frequency is output as a measure of the phenomenon to be measured.

Claim 13

An optical interferometer comprising: a source of light; amplitude modulating means for driving the source of light; signal generating means for driving the amplitude modulating means comprising a source of a variable frequency sinusoid phase modulated at a fixed phase modulation frequency; an optical fiber coil producing a non-reciprocal phase shift responsive to a phenomenon to be measured; means for optically coupling light from the source of light to the optical fiber coil to create counterpropagating beams therethrough; means located assymmetrically in the coil path for optically phase modulating the counterpropagating beams at the said fixed modulation frequency; photodetecting means receiving the counterpropagating light beams for producing a signal responsive to both the said non-reciprocal phase shift and a second non-reciprocal phase shift created by the said variable frequency; means setting the frequency and phase modulation amplitudes of said phase modulations such that unwanted signal components vanish at the frequency of a selected harmonic of the said phase modulations frequency; signal processing means for changing the signal from the photodetecting means to a signal which is a function only of the algebraic sum of the two said non-reciprocal phase shifts when that sum is small; and adjustment means whereby said signal responsive to the algebraic sum of the two said non-reciprocal phase shifts is made to vanish by adjusting said variable frequency; whereby the said variable frequency is output as a measure of the phenomenon to be measured.