Fiber optic gyroscope modulation error reduction

A rotation sensor capable of sensing rotation about an axis of a coiled optical fiber, said sensing based on electromagnetic waves propagating in opposite directions in said coiled optical fiber to impinge on a photodetector with a phase relationship which has an effective maximum offset error associated with a specified maximum rotation rate offset error, said rotation sensor comprising:

• a bias optical phase modulator means having an input and being positioned in an optical path portions selected from among those optical path portions taken by electromagnetic waves to reach or leave said coiled optical fiber en route on an optical path to said photodetector, said bias optical phase modulator means for phase modulating any such electromagnetic waves passing therethrough and propagating along said optical path so as to provide a varying phase difference between such electromagnetic waves propagating through said coiled optical fiber in opposing directions in response to a corresponding electrical signal on said input thereof which, if substantially periodic at a selected fundamental frequency, causes said varying phase at a frequency twice that of said fundamental frequency to have an amplitude that is a first fraction of that amplitude that said varying phase has at said fundamental frequency;
• a phase modulation generator means having an output electrically connected to said bias optical phase modulator means input, said phase modulation generator means for providing a substantially periodic electrical output signal at said output thereof having a fundamental component at said selected fundamental frequency and a selected amplitude, and having a harmonic component at a frequency twice that of said fundamental frequency with an amplitude that is a second fraction of said fundamental component amplitude;
• and
• a signal component selection means having a detection input, electrically connected to said photodetector to receive an output therefrom representative of any phase differences occurring between pairs of electromagnetic waves impinging thereon, and having an output, said signal component selection means for causing signals to appear at said output thereof representing amplitudes of components of signals occurring at said detection input thereof based on said fundamental frequency, said bias optical phase modulator means providing a varying phase difference at said fundamental frequency between electromagnetic waves propagating through said coiled optical fiber in opposing directions of a fundamental phase difference amplitude in response to said phase modulation generator means providing said phase modulation generator means output signal at said output thereof, said bias optical phase modulator means and said phase modulation generator means having means for establishing parameter values therein so as to provide a weighting factor multiplying at least one of said first fraction and said second fraction to form a product therewith such that the remaining one of said first and second fractions and said product are both of values less than an output ratio of said effective maximum offset error to said fundamental phase difference amplitude with that one of said first and second fractions used in forming said product being greater than said output ratio.

A bias optical phase modulator for positioning in an optical path and capable of phase modulating electromagnetic waves passing therethrough propagating along said optical path, said bias optical phase modulator comprising:

• a piezoelectric material structure having an input and having a surface of revolution with a perimeter which can vary in extent in response to an electrical signal provided to said input;
• a length of optical fiber insertable in said optical path and forming a coil wrapped about sad surface of revolution;
• a pair of interface layers which are compressible but with nonlinear stiffness in resisting compression such that resistance to compression increases substantially with sufficient increases in compression;
• and
• clamping means for mounting said piezoelectric material structure between said pair of interface layers.