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We have studied the history of vibration and demonstrate a laser-based noncontact interferometric vibration sensor. The sensor promises the measurement of microdisplacement by using a Fabry-Perot cavity formed between a partially coated gradient-index lens and a movable reflector. Displacement is determined by the detection of interference fringes caused by phase modulation within the cavity. The sensor was tested in conjunction with both multimode and single-mode fiber transmission. Calibration with multimode fiber produced a fringe-contrast function that decreased monotonically with displacement. This calibration allowed at least 30 fringes to be discriminated, giving a displacement resolution of 0.034 microm across a range of 10.2 microm. Dynamic tests demonstrated a working range of at least 3.74 microm at frequencies as high as 2 kHz. Similar tests in which single-mode fiber was used indicated a dynamic working range of at least 4.29 microm.

An alternative approach for measuring large currents at high potentials is presented. The output signal from a conventional current transformer is measured by transducing the voltage developed across the transformer secondary into a shift in the reflected wavelength from an in-fibre Bragg grating using a piezoelectric element. A pseudo-heterodyne detection scheme was used to determine this shift. We demonstrate the scheme's performance over a current range of 700 A. The current resolution was about over a frequency range of about 50 to .

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