Quadrupolar Fiber Gyroscope Bias Drift Mitigation under Transient Thermal Gradients
Quadrupolar winding cancels symmetric thermal gradients, leaving elasto-optic drift manageable via compliant potting and multi-point sensor compensation.
Serrodyne Modulation
Frequency Shifting
Optical frequency translation techniques generate a controlled frequency shift by applying a linear phase ramp that resets periodically. The execution of serrodyne modulation employs a sawtooth waveform to continuously sweep the phase of an optical carrier by exactly 2pi radians before resetting. This phase sweep acts as a constant frequency shift, shifting the optical carrier to a new frequency.
Modulator Execution
Integrated optical phase modulators process the electrical sawtooth signal to shift the light wave frequency. In these devices, serrodyne modulation requires a highly linear ramp and an extremely fast fall time to minimize unwanted sidebands in the optical spectrum. An ideal modulator shifts the optical frequency by an amount equal to the repetition frequency of the sawtooth wave.
Spectral Purity
Deviation from the ideal sawtooth profile degrades the performance of the frequency shifter. Imperfect flyback times, amplitude errors, and non-linearities in the ramp generate spurious sidebands that interfere with the primary shifted frequency. These unwanted frequency components introduce measurement errors in interferometric sensors, so designers use specialized electronic circuits to optimize the drive waveform and suppress the unwanted sidebands.
Instrument Integration
Fiber-optic sensor systems use this technique to implement heterodyne detection without requiring bulky bulk-optic components. Laser vibrometers and gyroscopes integrate these modulators directly into their optical paths to achieve high sensitivity and stable scale factors.
Fundamentals of Sagnac Phase Shift and Thermal Shupe Effect Cancellation
Quadrupolar winding cancels thermal Shupe non-reciprocity by spatially pairing symmetric fiber segments equidistant from the coil center.