Digital integrating fiber-optic gyroscope with electronic phase tracking.

A novel demodulation scheme for interferometers with optical phase modulation is described. The optical phase shift is measured by mixing a train of square digital pulses with a photodetector current and adjusting the pulse spacing by using an electronic closed loop. The optical phase shift is tracked with deviation less than 0.007 rad, which can be easily corrected by using a look-up table. An experimental optically open-loop fiber-optic gyroscope that uses this demodulation shows a linear scale factor in good agreement with theory.

Stable fiber-source gyroscopes.

We describe two new configurations of fiber gyroscopes that use superfluorescent fiber laser sources. In the first configuration we introduce a backward-pumping technique that achieves an order-of-magnitude increase in the power that can be launched into the gyroscope without instabilities. In the second configuration we employ the optical gain of the superfluorescent fiber laser source to amplify the signal returned from the gyroscope, obtaining an additional three-orders-of-magnitude increase in the optical power incident upon the detector, with an implication for simplification of the electronics. In both configurations, source beat-noise-limited rotation sensitivity is achieved.

Selective interferometric sensing by the use of coherence synthesis.

A technique is discussed and demonstrated whereby the sensitivity of an imbalanced fiber-optic interferometric sensor is changed by as much as 70 dB by modifying the power spectrum and thus the coherence function of the input optical source. This phenomenon is then extended and used to monitor selectively single sensors in a small fiber-optic ladder array by synthesizing coherence functions that result in a high sensitivity for the sensor to be observed but a low sensitivity for all the others. Limitations of the demonstrated implementation are discussed and possible future designs presented.

Fiber-optic interferometric sensor arrays with freedom from source phase-induced noise.

We propose arrays of all-passive remote sensors with freedom from both source phase-induced intensity noise and cross talk between sensors. These arrays employ high-duty-cycle time-domain addressing, utilize laser diodes, and have downlead insensitivity. A synthetic heterodyne demodulation technique is used to prevent environmentally induced signal fading. An experimental all-fiber implementation of a single remote sensor yielded a measured sensitivity of below 40 microrad/ radicalHz at signal frequencies above 600 Hz.