All-fiber pressure sensor up to 100 MPa

A novel structure incorporating an all-fiber configuration for a fiber-optic sensor of high pressure up to at least 100 MPa is discussed. This configuration is based on the hydrostatic pressure-induced polarization coupling occurring in highly birefringent optical fibers, which the authors reported earlier. The application of two light launching systems--one based on a semiconductor laser diode pigtailed to a single-mode fiber, the other on a similar laser diode pigtailed to a highly birefringent fiber--is reviewed and analyzed. The paper discusses the principles on which the design is based; the construction, instrumentation, and operation of this sensor; and its performance under various conditions, including pressure and temperature coefficients of the output signal. Temperature desensitization procedure is briefly described, and the advantages of the sensor over a sensor utilizing bulk optical polarization controlling elements and a HeNe laser are analyzed.