Gated fiber optic rotation sensor with extended dynamic range

A method of determining a rotation rate of a Sagnac fiber optic rotation sensor having counter-propagating waves which have phase modulation at a first frequency and which are combined to form an optical output signal, wherein the method comprises the steps of:

• phase modulating the counter-propagating waves at a second frequency which is lower than the first frequency;
• providing the optical output signal during only a portion of each period of the second frequency phase modulation;
• adjusting the amplitude of the second frequency phase modulation so that during the time the optical output signal is provided, the time average value of the second frequency phase modulation substantially cancels the component of said optical output signal at the first frequency caused by the rotation rate;
• and
• monitoring the amplitude of the second frequency phase modulation so as to identify the rotation rate of the rotation sensor.

A method of detecting the rotation rate of an optical loop having counter-propagating light waves therein which are phase modulated at a first frequency, comprising the steps of:

• combining the counter-propagating waves to produce an optical output signal;
• gating the optical output signal so as to provide said signal only during a portion of each period of a second frequency which is lower than the first frequency;
• detecting the amplitude of a component of the optical output signal which is caused by the rotation rate;
• converting the amplitude of the component to a feedback error signal;
• applying a driving signal at the second frequency to a phase modulator in the loop;
• amplitude modulating the driving signal with the feedback error signal as the modulating signal so that during the time the optical signal is provided, a time average amplitude of the second frequency phase modulation substantially cancels the component of the optical output signal which is caused by the rotation rate;
• and
• monitoring the amplitude of the second frequency phase modulation so as to identify the rotation rate of the optical loop.

An apparatus for determining the rotation rate of an optical loop having counter-propagating light waves which are phase modulated at a first frequency and which are combined to form an output signal, the apparatus comprising:

• means for blanking at least a component of the output signal at selected times to provide a gated signal;
• means for biasing the phase of the counter-propagating light waves at a second, substantially fixed frequency, to substantially null a component in the gated signal which is produced by the rotation rate;
• and
• means for measuring the amount of bias to determine the rotation rate.

An apparatus for determining the rotation rate of an optical loop wherein light waves are counter-propagated, said light waves being phase modulated at a first frequency and being combined to form an output signal, the apparatus comprising:

• a gating circuit for blanking at least a component of the output signal at selected times to provide a gated signal;
• a biasing circuit for biasing the phase of the counter-propagating light waves at a second, substantially fixed frequency, to substantially null a component in the gated signal which is produced by loop rotation;
• and
• an output circuit for measuring the amount of bias to determine the rotation rate.

An apparatus for sensing phase shifts resulting from rotation of a fiber optic gyro having counter-propagating waves which have phase modulation at a first frequency and which are combined to form an optical output signal, the apparatus comprising:

• means for phase modulating the counter-propagating waves at a second frequency which is lower than the first frequency;
• means for providing the optical output signal during only a portion of each period of the second frequency phase modulation;
• means for adjusting the amplitude of the second frequency phase modulation so that during the time the optical output signal is provided, the time average value of the second frequency phase modulation substantially cancels the component of said optical output signal at the first frequency caused by the rotation rate;
• means for monitoring the amplitude of the second frequency phase modulation so as to identify the rotation rate of the rotation sensor.

An apparatus for sensing phase shifts resulting from rotation of a fiber optic gyro having counter-propagating waves which have phase modulation at a first frequency and which are combined to form an optical output signal, the apparatus comprising:

• an electronic circuit for phase modulating the counter-propagating waves at a second frequency which is lower than the first frequency;
• a gating device, responsive to the electronic circuit, for providing the optical output signal during only a portion of each period of the second frequency phase modulation;
• a feedback circuit, responsive to the optical output signal, for adjusting the amplitude of the second frequency phase modulation so that during the time the optical output signal is provided, the time average value of the second frequency phase modulation substantially cancels the component of said optical output signal caused by the rotation rate;
• and
• an output circuit electrically connected to the phase modulating circuit for monitoring the amplitude of the second frequency phase modulation so as to identify the rotation rate of the fiber optic gyro.

A method of determining the rotation rate of an optical loop having counter-propagating light waves which are phase modulated at a first frequency and which are combined to form an output signal, wherein the method comprises:

• phase modulating the counter-propagating light waves at a second, substantially fixed frequency;
• blanking at least a component of the output signal at selected times to provide a gated signal;
• adjusting the amplitude of the second frequency phase modulation to substantially null a component in the gated signal which is produced by the rotation rate;
• and
• measuring the amplitude of the second frequency phase modulation to determine the rotation rate.

An apparatus for determining the rotation rate of an optical loop wherein light waves are counter-propagated, said light waves having a phase difference which is shifted by the rotation rate of the optical loop, comprising:

• first frequency phase modulating means for biasing the counter-propagating light wave phase difference, said first frequency being independent of the rotation rate;
• means for combining the counter-propagating light waves to form an output signal;
• means for blanking at least a component of the output signal at selected times to provide a gated signal;
• second frequency phase modulating means for biasing the phase of the counter-propagating light waves, said second frequency being independent of the rotation rate;
• and
• means for driving the second frequency phase modulator means at said second frequency to substantially null a component in the gated signal which is produced by the rotation rate, said driving means providing a signal representative of said rotation rate.

An apparatus for determining the rotation rate of an optical loop wherein optical signals are counter-propagated and combined to form a periodically varying output signal comprised of plural periods, comprising:

• means for providing a continuous wave optical signal to the optical loop to form two continuous waves which traverse the loop in opposite directions and are combined to form the output signal;
• means for blanking corresponding portions of each of said plural periods of the output signal to provide a gated signal, said blanked portion comprising a signal which has traversed the entire loop in opposite directions;
• and
• means for biasing the phase of the two continuous waves traversing the loop to substantially null a component in the gated signal which is produced by loop rotation, wherein the amount of bias represents the loop rotation rate.

A method of determining the rotation rate of an optical loop wherein optical signals are counter-propagated and combined to form an output signal, comprising the steps of:

• providing a continuous wave optical signal to the optical loop to form two continuous waves which traverse the loop in opposite directions and are combined to form the output signal;
• blanking a portion of the output signal to provide a gated signal in response to measurement of a single portion of the output signal at any given time, said blanked portion comprising a signal which has traversed the entire loop in opposite directions;
• and
• biasing the phase of the two continuous waves traversing the loop to substantially null a component in the gated signal which is produced by loop rotation, wherein the amount of bias represents the loop rotation rate.