Fiber optic measuring device, rate gyro, navigation and stabilization system, and current sensor

A fiber optic measuring device in which variation in a measured parameter engenders a phase difference between two waves, the device comprising:

• a) a quasi-monochromatic light source;
• b) a preferably monomode SAGNAC ring interferometer in which two counter-propagating waves propagate, the propagation time of the waves between their splitting and their recombining being .tau.;
• c) a detector;
• d) a phase modulator;
• and
• e) electronic means comprising a processing system furnishing a signal which is a function of the measured parameter, the electronic means controlling the phase modulator, wherein:
• the control signal for the modulator is the superposition of (a) a first, periodic gating, bias signal .PHI..sub.b (t) with period 2.tau. and amplitude .PHI..sub.bm, and (b) a second, staircase, negative-feedback signal .PHI..sub.m (t) synchronized with .PHI..sub.b (t), each step of which has a duration equal to .tau. or to one of its sub-multiples, and an amplitude .PHI..sub.s, which is a function of the value of the measured parameter and which falls back to zero when its amplitude exceeds a predetermined value .PHI..sub.mm ;
• .PHI..sub.bm and .PHI..sub.mm are slaved to 2.PHI..sub.bm +.PHI..sub.mm =2n.tau. (where n is an integer);
• the response to the singular phase shift introduced during the fall-back of the negative-feedback signal is for this slaving and hence used to keep the gain of the modulation chain constant;
• and
• the electronic means negative-feedback controls the phase modulator as a function of the signal received from the detector so that (a) the variation in the demodulated error signal as a function of the phase difference in the neighborhood of zero is approximately linear, and (b) this phase difference is kept null and furnishing, by exploiting the modulating signal, a signal which is a function of the variation in the measured parameter;
• said electronic means further comprising:
• a clock synchronizing all the components of the electronic means;
• an analog-digital converter for digitizing the signal emitted by the detector, the analog-digital converter being specified so that the analog value of its least significant bit has a value less than or equal to the standard deviation of the noise in the signal coming from the detector;
• a servo-loop digital filter, fed by the signal leaving a digital processing system, furnishing a signal representing the measured parameter;
• a register receiving the signal leaving the servo-loop digital filter and furnishing a signal which is a function of the measured parameter for any desired external use;
• an accumulator fed by the signal leaving the register, generating a negative-feedback signal from the measured parameter, .PHI..sub.m (t);
• a modulation generator producing a modulating signal .PHI..sub.b (t);
• an adder comprising two inputs and one input, its first input being fed by the signal which is a function of the measured parameter produced by the register and the accumulator, its second input being fed by the modulating signal;
• a digital-analog converter fed by the output signal from the adder and controlling the phase modulator via a gain amplifier;
• a processing system which produces the difference between the signal sampled by the converter before the fall-back and that sampled after;
• a second servo-loop integrating filter receiving the signal issuing from the processing system;
• and
• a second analog-digital converter which controls the gain of the amplifier;
• wherein .PHI..sub.b (t) and .PHI..sub.m (t) are in phase, .PHI..sub.bm =.pi./2 and .PHI..sub.mm =.pi..

A fiber optic rate gyro in which the variation in a speed of rotation engenders a phase difference between two waves, the fiber optic rate gyro comprising:

• a) a quasi-monochromatic light source;
• b) a preferably monomode SAGNAC ring interferometer in which two counter-propagating waves propagate, the propagation time of the waves between their splitting and their recombining being .tau.;
• c) a detector;
• d) a phase modulator;
• and
• e) electronic means comprising a processing system furnishing a signal which is a function of the measured parameter, the electronic means controlling the phase modulator, wherein:
• the control signal for the modulator is the superposition of (a) a first, periodic gating, bias signal .PHI..sub.b (t) with period 2.tau. and amplitude .PHI..sub.bm, and (b) a second, staircase, negative-feedback signal .PHI..sub.m (t) synchronized with .PHI..sub.b (t), each step of which has a duration equal to .tau. or to one of its sub-multiples, and an amplitude .PHI..sub.s, which is a function of the value of the measured parameter and which falls back to zero when its amplitude exceeds a predetermined value .PHI..sub.mm ;
• .PHI..sub.bm and .PHI..sub.mm are slaved to 2.PHI..sub.bm +.PHI..sub.mm =2n.tau. (where n is an integer);
• the response to the singular phase shift introduced during the fall-back of the negative-feedback signal is for this slaving and hence used to keep the gain of the modulation chain constant;
• and
• the electronic means negative-feedback controls the phase modulator as a function of the signal received from the detector so that (a) the variation in the demodulated error signal as a function of the phase difference in the neighborhood of zero is approximately linear, and (b) this phase difference is kept null and furnishing, by exploiting the modulating signal, a signal which is a function of the variation in the measured parameter;
• said electronic means further comprising:
• a clock synchronizing all the components of the electronic means;
• an analog-digital converter for digitizing the signal emitted by the detector, the analog-digital converter being specified so that the analog value of its least significant bit has a value less than or equal to the standard deviation of the noise in the signal coming from the detector;
• a servo-loop digital filter, fed by the signal leaving a digital processing system, furnishing a signal representing the measured parameter;
• a register receiving the signal leaving the servo-loop digital filter and furnishing a signal which is a function of the measured parameter for any desired external use;
• an accumulator fed by the signal leaving the register, generating a negative-feedback signal from the measured parameter, .PHI..sub.m (t);
• a modulation generator producing a modulating signal .PHI..sub.b (t);
• an adder comprising two inputs and one input, its first input being fed by the signal which is a function of the measured parameter produced by the register and the accumulator, its second input being fed by the modulating signal;
• a digital-analog converter fed by the output signal from the adder and controlling the phase modulator via a gain amplifier;
• a processing system which produces the difference between the signal sampled by the converter before the fall-back and that sampled after;
• a second servo-loop integrating filter receiving the signal issuing from the processing system;
• and
• a second analog-digital converter which controls the gain of the amplifier.

A fiber optic rate gyro in which the variation in a rotation measured engenders a phase difference between two waves, the fiber optic rate gyro comprising:

• a) a quasi-monochromatic light source;
• b) a preferably monomode SAGNAC ring interferometer in which two counter-propagating waves propagate, the propagation time of the waves between their splitting and their recombining being .tau.;
• c) a detector;
• d) a phase modulator;
• and
• e) electronic means comprising a processing system furnishing a signal which is a function of the measured parameter, the electronic means controlling the phase modulator, wherein:
• the control signal for the modulator is the superposition of (a) a first, periodic gating, bias signal .PHI..sub.b (t) with period 2.tau. and amplitude .PHI..sub.bm, and (b) a second, staircase, negative-feedback signal .PHI..sub.m (t) synchronized with .PHI..sub.b (t), each step of which has a duration equal to .tau. or to one of its sub-multiples, and an amplitude .PHI..sub.s, which is a function of the value of the measured parameter and which falls back to zero when its amplitude exceeds a predetermined value .PHI..sub.mm ;
• .PHI..sub.bm and .PHI..sub.mm are slaved to 2.PHI..sub.bm +.PHI..sub.mm =2n.tau. (where n is an integer);
• the response to the singular phase shift introduced during the fall-back of the negative-feedback signal is for this slaving and hence used to keep the gain of the modulation chain constant;
• and
• the electronic means negative-feedback controls the phase modulator as a function of the signal received from the detector so that (a) the variation in the demodulated error signal as a function of the phase difference in the neighborhood of zero is approximately linear, and (b) this phase difference is kept null and furnishing, by exploiting the modulating signal, a signal which is a function of the variation in the measured parameter;
• said electronic means further comprising:
• a clock synchronizing all the components of the electronic means;
• an analog-digital converter for digitizing the signal emitted by the detector, the analog-digital converter being specified so that the analog value of its least significant bit has a value less than or equal to the standard deviation of the noise in the signal coming from the detector;
• a servo-loop digital filter, fed by the signal leaving a digital processing system, furnishing a signal representing the measured parameter;
• a register receiving the signal leaving the servo-loop digital filter and furnishing a signal which is a function of the measured parameter for any desired external use;
• an accumulator fed by the signal leaving the register, generating a negative-feedback signal from the measured parameter, .PHI..sub.m (t);
• a modulation generator producing a modulating signal .PHI..sub.b (t);
• an adder comprising two inputs and one output, its first input being fed by the signal which is a function of the measured parameter produced by the register and the accumulator, its second input being fed by the modulating signal;
• a digital-analog converter fed by the output signal from the adder and controlling the phase modulator via a gain amplifier;
• a processing system which produces the difference between the signal sampled by the converter before the fall-back and that sampled after;
• a second servo-loop integrating filter receiving the signal issuing from the processing system;
• and
• a second analog-digital converter which controls the gain of the amplifier;
• wherein .PHI..sub.b (t) and .PHI..sub.m (t) are in phase, .PHI..sub.bm =.pi./2 and .PHI..sub.mm =.pi..

An inertial stabilization or navigation system comprising at least one rate optic fiber gyro in which variation in rotation engenders a phase difference between two waves, the system comprising:

• a) a quasi-monochromatic light source;
• b) a preferably monomode SAGNAC ring interferometer in which two counter-propagating waves propagate, the propagation time of the waves between their splitting and their recombining being .tau.;
• c) a detector;
• d) a phase modulator;
• and
• e) electronic means comprising a processing system furnishing a signal which is a function of the measured parameter, the electronic means controlling the phase modulator, wherein:
• the control signal for the modulator is the superposition of (a) a first, periodic gating, bias signal .PHI..sub.b (t) with period 2.tau. and amplitude .PHI..sub.bm, and (b) a second, staircase, negative-feedback signal .PHI..sub.m (t) synchronized with .PHI..sub.b (t), each step of which has a duration equal to .tau. or to one of its sub-multiples, and an amplitude .PHI..sub.s, which is a function of the value of the measured parameter and which falls back to zero when its amplitude exceeds a predetermined value .PHI..sub.mm ;
• .PHI..sub.bm and .PHI..sub.mm are slaved to 2.PHI..sub.bm +.PHI..sub.mm =2n.pi. (where n is an integer);
• the response to the singular phase shift introduced during the fall-back of the negative-feedback signal is for this slaving and hence used to keep the gain of the modulation chain constant.

A fiber optic magnetic field and current sensor in which variation of a magnetic field and current engenders a phase difference between two waves, the sensor comprising:

• a) a quasi-monochromatic light source;
• b) a preferably monomode SAGNAC ring interferometer in which two counter-propagating waves propagate, the propagation time of the waves between their splitting and their recombining being .tau.;
• c) a detector;
• d) a phase modulator;
• and
• e) electronic means comprising a processing system furnishing a signal which is a function of the measured parameter, the electronic means controlling the phase modulator, wherein:
• the control signal for the modulator is the superposition of (a) a first, periodic gating, bias signal .PHI..sub.b (t) with period 2.tau. and amplitude .PHI..sub.bm,and (b) a second, staircase, negative-feedback signal .PHI..sub.m (t) synchronized with .PHI..sub.b (t), each step of which has a duration equal to .tau. or to one of its sub-multiples, and an amplitude .PHI..sub.s, which is a function of the value of the measured parameter and which falls back to zero when its amplitude exceeds a predetermined value .PHI..sub.mm ;
• .PHI..sub.bm and .PHI..sub.mm are slaved to 2.PHI..sub.bm +.PHI..sub.mm =2n.pi. (where n is an integer);
• the response to the singular phase shift introduced during the fall-back of the negative-feedback signal is for this slaving and hence used to keep the gain of the modulation chain constant.