A beam of light is split and introduced into different ends of a light path whose rotation is to be sensed. At least one frequency shifter is placed in the light path to affect the frequency difference of the two beams so as to introduce or adjust a nonreciprocal phase shift. The beams are then mixed back together and the resultant beam is detected and analyzed by suitable circuitry to provide an output indicative of rotation of the light path.

Phase nulling optical gyro

The frequency of an optical signal output from an optical source is controlled by dividing a signal output from the source into two signal portions each of which is guided along its own optical path. The signal portions are combined to form two optical beams each including components of the two signal portions and having intensities dependent on an adjusted frequency of the two beams.

Apparatus and method for optical signal source stabilization

A gyroscope system includes a coherent light source that supplies counter propagating waves to a sensing loop through a pair of directional couplers. The polarizations of the waves are controlled so that they traverse identical optical paths before recombining in one of the couplers to form an interference pattern. Rotation of the sensing loop, a phase modulator and a frequency shifter cause phase changes in the counter propagating waves. A detector monitors the interference pattern of the combined waves and provides a signal to a coherent demodulator that controls the phase modulator. The output of the coherent demodulator is input to a servo-loop circuit that drives a voltage controlled oscillator. The output of the voltage controlled oscillator is an oscillatory signal having a frequency equal to the shift in frequency that the counter propagating waves experience in traversing the frequency shifter. The feedback circuitry adjusts the frequency shift to null the phase difference between the counter propagating waves. The frequency shift is linearly related to the frequency of the signal output from the voltage controlled oscillator. Each cycle of the output of the voltage controlled oscillator coresponds to a fixed angular increment of displacement of the sensing loop. The rotation rate of the sensing loop is a function of the frequency shift and the transit time of the waves through the sensing loop. The gyroscope system determines rotation rates and angular displacements over a wide dynamic range by measuring the frequency and zero crossings of the oscillatory output of the voltage controlled oscillator.

Phase nulling optical gyroscope

A fiber gyroscope provides improved bias stability and repeatability and has a greatly reduced polarizer extinction ratio requirement compared previous devices. This fabrication technique is compatible with both an all fiber gyroscope configuration and an integrated optics or bulk optics device. The present invention comprises a substrate that is preferably formed of fused silica. A pair of optical fibers, or two lengths of one fiber, are mounted to the substrate, and first planar surfaces are formed in the cladding. Optical couplers, polarizers and other components used in forming the rotation sensor are formed on the planar cladding surfaces of the fibers. Polarizers formed on the fibers have a transmission axis aligned with an axis of birefringence of the fiber to remove undesired linear polarization components from optical signals guided by the fibers while permitting a desired linear polarization component to propagate unattenuated. A sensing coil of optical fiber is arranged to guide light between the first and second optical fibers, the first and second optical fibers and the optical coupler cooperating to introduce counterpropagating light waves in the sensing coil.

Fiber optic gyroscope with improved bias stability and repeatability and method

A fiber optic gyroscope includes a sensing coil formed of ordinary single mode fiber and a module including polarization maintaining optical fibers. A clockwise beam guided by a polarization maintaining fiber passes through a polarizer before being input to the sensing coil. The polarization module includes means for providing an an unpolarized counterclockwise beam to the sensing coil and means for phase modulating a predetermined polarization component. The module also depolarizes the clockwise beam after it has traversed the sensing coil. The clockwise and counterclockwise waves are both unpolarized when they combine in an optical coupler before impinging upon a detector that produces an electrical signal indicative of changes in the interference pattern to indicate rotation of the coil.

Dual fiber optic gyroscope

Means are disclosed for frequency modulating opposing modes in a ring laser assembly whereby locking is minimized or eliminated. The use of three types of modulators comprising an acoustic generator, a light shutter and an electro-optic crystal are described. In each case, the modulators are driven in accordance with a time-varying signal provided by a signal generator.

Marvin Chodorow

Papers

Means for avoiding locking in ring lasers

Gyromagnetic resonance apparatus