Method and apparatus for phase modulating a fiber-optic rotation sensor

An optical apparatus for measuring rotation employing a SAGNAC interferometer, comprising:

• a first coil of optical fiber for use as a sensing coil;
• means for providing counter-propagating coherent light beams along a fiber-optic light path at least part of which path consists of the first coil of optical fiber;
• means for recombining the counter-propagating beams to produce an interferometric output signal the intensity of which varies with rotation rate according to the SAGNAC effect;
• a second separate coil of optical fiber for use as a modulator coil, the second coil being located in the optical path of the counter-propagating beams near one end of the first coil, the second coil being free to rotate independently of the first coil;
• means for oscillating the second coil, comprising a rigid support hub having spokes extending radially outward therefrom for bending in mechanical synchronism in response to a piezoelectrically induced motive force, the second coil being wrapped as a rim around the outside of the spokes and attached thereto for being vibrated in an oscillatory manner about a hub axis for introducing a time varying phase shift between the counter-propagating beams for causing the intensity of the output signal containing the rotation rate information to be modulated at the frequency of the oscillation;
• detection means, responsive to the interferometric output signal for providing an electrical output signal indicative thereof;
• and
• electronic means, responsive to the electrical output signal for demodulating the electrical output signal for recovering a signal from which the rotation rate may be inferred.

An optical fiber vibrator, comprising:

• a rigid support hub having an axis;
• spokes, extending radially outward from the hub axis for bending in mechanical synchronism in response to a piezoelectrically induced motive force;
• and
• an optical fiber, being part of a SAGNAC interferometer light path, wrapped like a rim around the outside of the spokes and attached thereto for being vibrated in an oscillatory manner rotationally about the hub axis in order to effect a phase difference modulation.