Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1984-02-17
1987-11-17
Willis, Davis L.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
G01C 1964
Patent
active
047071362
ABSTRACT:
A fiber optic rotation sensor, employing the Sagnac effect comprising all fiber optic components positioned along a continuous, uninterrupted strand of fiber optic material. The rotation sensor includes a detection system utilizing a modulator or modulators for phase modulating at first and second frequencies light waves which counter-propagate through a loop formed in the fiber optic strand. The second phase modulation is at a frequency much lower than the first frequency and comprises a phase ramp signal which is applied to the counter-propagating light waves. The phase difference modulation which results from application of the phase ramp defines a substantially DC value which may be adjusted to bias the counter-propagating light wave phase difference to substantially null the phase shift produced in the phase difference by the rotation rate. Because the phase ramp modulation signal is simulated from a periodic waveform, an output signal from the sensor is gated synchronously with respect to the phase modulation at the second frequency so that the detected optical output signal is provided only during those intervals when it is influenced by the ramped portion of the phase modulation signal.
A phase sensitive detector generates a feedback error signal proportional to the magnitude of the optical output signal at the first phase modulation frequency. The feedback error signal controls a modulator which controls the amplitude of the second frequency driving signal for the phase modulator such that the signal at the first phase modulation frequency in the output signal from the rotation sensor is substantially cancelled by the phase difference modulation produced at the second modulation frequency during the interval when the optical output signal is present.
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Stanford University
Turner S. A.
Willis Davis L.
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