A fiber-optic extrinsic Fabry-Perot interferometer strain sensor (EFPI-S) of ls = 2.5 cm sensor length using three-wavelength digital phase demodulation is demonstrated to exhibit <50 pm displacement resolution (<2nm/m strain resolution) when measuring the cross expansion of a PZT-ceramic plate. The sensing (single-mode downlead-) and reflecting fibers are fused into a 150/360 microm capillary fiber where the fusion points define the sensor length. Readout is performed using an improved version of the previously described three-wavelength digital phase demodulation method employing an arctan-phase stepping algorithm. In the resent experiments the strain sensitivity was varied via the mapping of the arctan - lookup table to the 16-Bit DA-converter range from 188.25 k /V (6 Volt range 1130 k ) to 11.7 k /Volt (range 70 k ).

No abstract

A new active homodyne sawtooth fringe counting technique is described for eliminating the direcflonal ambiguity in incremental readout of interferometric strain gauges. Results of quantitative strain measurements using unbalanced Michelson and capillary based intrinsic Fabry-Perot sensors agree reasonably well with the readout of a resistive strain gauge as well as with the theoretically predicted sensitivity.

No abstract

No abstract