The pressure sensitivity of the phase of light propagating in a single-mode fiber coated with a thin nickel jacket is determined both analytically and experimentally. The measured acoustic response of the fiber is found to be 1 order of magnitude lower than that of the bare fiber, in agreement with analytical predictions. The technique thus appears to be a promising way for desensitizing optical-fiber leads for use with fiber-optic sensors.

A system has been developed to accurately detect phase signals produced in optical interferometric sensors. The system employs optical heterodyning and synchronously detects optical phase by feeding back an error signal to a phase modulator in the reference leg of the interferometer. This system is seen to have properties similar to a phase-locked loop. The system is mathematically analyzed and a simple second-order model developed which accurately predicts the system response.

(Continue on reveree tide If neceeeary and Identify by block number)A system has been developed to accurately detect phase produced in optical interf erometric sensors. The system employs optical heterodyning, and it synchronously detects optical phase by feeding an error signal back to a phase modulator in the reference leg of the interferometer. This system is seen to have properties similar to a phase-locked loop used for the demodulation of FM signals. The system model is second order and nonlinear, but a linear approximation serves to accurately describe the system in synchronous operation and (over)

No abstract

A system has been developed to accurately demodulate the acoustically induced, phase-modulated signal produced by an interferometric fiber-optic sensor. The system utilizes phase-lock techniques to produce a feedback signal to the fiber interferometer that serves the dual purpose of maintaining phase lock and producing an estimate of the acoustic signal. The system is very unique in terms of simplicity of design, versatility, and accuracy of measurement. Its main features are insensitivity to laser intensity fluctuations, the ability to operate in adverse thermal environments, insensitivity to acute polarization rotation, and component minimization. The system was designed and set up at NRL-USRD, Orlando. It demonstrated impressive signal-to-noise levels indicative of the potential to sense very small signals. The theoretical model generated for the system confirms experimental results that demonstrate an accuracy of measurement to less than 1% error.