Simultaneous hydrostatic pressure and temperature measurement employing an LP01-LP11 fiber-optic polarization-sensitive intermodal interferometer

A fiber-optic LP₀₁-LP₁₁ polarization-sensitive intermodal interferometer is proposed to simultaneously measure hydrostatic pressure and temperature using the same sensing element. In analogy to the case of strain sensing it was found that the experimental parameters T_P and T_T describing the 2π phase shifts in the interferogram are significantly different for the X- and Y-polarizations of two polarization modes. This represents a fundamental phenomenon which can be put to use for simultaneous two-parameter sensing. The results obtained are found to be in agreement with a recently developed Muller-Stokes formalism describing polarization effects in the case of two-mode interference by means of spatial Stokes parameters. Initial calibration of the two-parameter simultaneous pressure-and-temperature sensor has been performed up to 100 MPa using a primary pressure standard (deadweight tester Harwood DWT-35)