Interferometric Feedback
Electro-optic phase modulators apply counteracting optical phase shifts within fiber optic gyro sensing coils to maintain optical destructive interference at the detector. In closed-loop optical rotation sensors, IFOG phase rebalance nulls Sagnac-induced phase shifts by applying a digital staircase voltage waveform to an integrated optics chip. This closed-loop operation transforms non-linear cosine intensity interference patterns into a linear digital output directly proportional to rotation rate.
The control regime governs the operating dynamic range of interferometric fiber optic gyroscopes and breaks down when phase modulator drive voltages hit maximum digital-to-analog converter rail limits.
Serrodyne Modulation
Optical phase accumulation in the counter-propagating light beams is continuously reset using 2-pi phase jumps. When rotation induces a Sagnac phase difference, IFOG phase rebalance circuits adjust the slope of the voltage ramp delivered to the electro-optic crystal to generate an equal and opposite optical phase shift. Reset timing errors and finite voltage flyback times introduce scale factor non-linearities that require active compensation.
Optical Bias
Proper square-wave bias modulation shifts the optical operating point to the highest sensitivity slope of the interference fringe. Deviations in drive voltage amplitude cause bias instability and increase angle random walk metrics.
Scale Linearity
Calibration procedures evaluate scale factor stability across wide rate ranges using precision rate tables referenced to optical angle encoders. Metrology protocols verify phase reset gain matching across broad temperature spans to prevent step-transition transients. Wavelength stability of the broadband superluminescent diode light source sets the ultimate boundary for scale factor accuracy in field environments.
