DYNAMIC PRESSURE SENSING WITH A FIBEROPTIC POLARIMETRIC PRESSURE TRANSDUCER WITH 2-WAVELENGTH PASSIVE QUADRATURE READOUT

We describe the combination of a polarimetric pressure sensor with a t wo-wavelength passive quadrature demodulation system allowing for dyna mic pressure sensing in the 10-MPa range with unambiguous fringe count ing. Furthermore, continuous phase measurement with the arctan method applied to the quadrature interference signals after automatic offset subtraction is demonstrated for the first time, to our knowledge. A si ngle low-coherent superluminescent diode is used as a light source, an d a polarizing beam splitter in combination with two adjustable interf erence filters of slightly different central wavelengths serves for th e creation of the quadrature signals. Results of initial experiments w ith 60-ms pressure relaxation-time constants with the fringe-counting technique demonstrate the performance that was predicted theoretically . The measured pressure sensitivity exhibits excellent agreement with the previous research of Beck and Urbanczyk [IEEE Trans. Instrum. Meas . 44, 694-697 (1995)] using a polarimetric readout. The fringe-contras t variation and the measurement range obtained experimentally show the fiber dispersion to influence dephasing (deviation from quadrature) a nd visibility decrease significantly with increasing pressure. (C) 199 8 Optical Society of America.