Signals indicative of the Sagnac phase shift between counterpropagating waves in a sensing loop are combined to produce an error signal. A phase modulator is arranged to modulate the phase of optical signals that pass through the sensing loop. A phase modulator driver apparatus responsive to the error signal produces a ramp signal to drive the phase modulator to null the error signal. A reset apparatus is arranged for resetting the ramp signal to when the phase reaches a predetermined limit. The reset apparatus preferably includes a reset integrator circuit arranged to produce an output that is a ramp signal whose slope is proportional to the rotation rate of the sensing loop. A pair of comparators is arranged to determine when the reset integrator reaches one of two rollover limits. Rollover logic circuitry is connected to the pair of comparators and arranged such that when the reset integrator reaches one of the rollover limits, the integrator is forced to the other integration limit. Gating apparatus zeros the phase modulator driver during rollover transients. Rollover logic creates pulses that increment or decrement an up/down counter to provide a digital rollover count that is processed to determine the rotation rate. Scale factor circuitry corrects the rollover limits of the reset integrator if the output of the fiber optic rotation sensor is non-zero immediately following rollover.
A rotational rate comparator for a fiber optic gyroscope has a 3.times.3 coupler and an evaluating computer to calculate the rotational rate from photodiode signals generated by the fiber optic gyroscope. An electrical circuit is provided that is independent of the evaluating computer, and embodies an algorithm for producing at least one signal that depends on the rotational rate as a function of the photodiode signals. When the rotational rate dependent signal exceeds at least one presettable limiting value the comparator supplies an output signal.
A digital feedback system for an optical gyroscope include a fiber optic sensing coil, an optical phase modulator, a photo detector and a processor. The sensing coil induces a phase differential between light waves traveling though the coil. The optical phase modulator causes a second phase differential between the light waves. The photo detector receive the light waves and outputs an intensity signal representing a phase difference between the light waves. The processor determines a rate of rotation of the fiber optic sensing coil based on the phase difference. for the system operates by generating a closed loop feedback signal, demodulating the signal to determine the phase difference, determining a rate of rotation, periodically incrementing a feedback ramp signal once every .tau. second period based on the rate of rotation, and resetting the feedback ramp signal when the ramp is incremented a predetermined number of times since a previous reset.
A fiber optic acoustic sensor array is based upon a Sagnac interferometer rather than being based upon Mach-Zehnder interferometers as in known acoustic sensor arrays. The fiber optic acoustic sensor array is used to detect acoustic waves in water. By basing the sensor array on the Sagnac interferometer rather than on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, has a larger dynamic range, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of acoustic sensors can be multiplexed into the architecture of the Sagnac interferometer.
A folded Sagnac fiber optic acoustic sensor array operates in a manner similar to a Sagnac interferometer but uses a common delay path to reduce distributed pickup in downlead fibers. The fiber optic acoustic sensor array is used to detect acoustic waves in water. By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer rather than basing the array on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of acoustic sensors can be multiplexed into the architecture of the folded Sagnac fiber optic acoustic array.
A folded Sagnac fiber optic acoustic sensor array operates in a manner similar to a Sagnac interferometer but uses a common delay path to reduce distributed pickup in downlead fibers. The fiber optic acoustic sensor array is used to detect acoustic waves in water. By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer rather than basing the array on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of acoustic sensors can be multiplexed into the architecture of the folded Sagnac fiber optic acoustic array.
