Fiber optic gyroscope for continuous measurement of low and high rates of rotation

A method of determining a rate of rotation of an optical fiber coil about an axis of the coil, comprising:

• providing a light source;
• providing a phase modulator for shifting the phases of light signals directed into and out of the coil, in response to a modulation waveform;
• arranging an optical network for receiving light of a certain intensity from the light source and for dividing the light into a pair of first light signals;
• directing the first light signals to counter-propagate through the coil thus defining a corresponding pair of second light signals the phases of which have been shifted by the phase modulator;
• interfering the phase-shifted second light signals with one another to produce a recombined light signal having an intensity (I) that is a known function of a total phase difference between the second light signals, and the phase difference includes a Sagnac shift (R) produced when the coil rotates about said axis;
• defining the modulation waveform to obtain a determined sequence of at least five phase shifts between the pair of second light signals, including shifts of substantially zero degrees, +90 degrees, −90 degrees, +180 degrees and −180 degrees;
• producing measurement signals corresponding to the intensity of the recombined light signal for each overall phase shift in said sequence;
• and
• determining a rotation rate of the optical fiber coil about said axis according to the measurement signals and said known function.