HIGH-PRESSURE POLARIMETRIC SENSOR USING BIREFRINGENT OPTICAL FIBERS

A new fiber-optic high-pressure sensor has been developed for a pressure range up to 200 MPa and for a standard range of temperatures. The sensor is based on the effect of polarization coupling between two orthogonally polarized eigenmodes of the highly birefringent, polarization preserving optical fiber used as a sensing element. When linearly polarized light is launched into such fiber at 45° to each of its principal axes of polarization, the output signal (monitored in the direction perpendicular to the direction of the major axis of the polarization state of the light exiting from the fiber) is directly dependent on external pressure. The sensing element was configured inside a high-pressure chamber using a specially designed fiber-optic lead-through system. This configuration, however, is very flexible and can be easily altered to fit the specific type of application. Preliminary tests of this new sensor show that its sensitivity is far superior to currently used solid-state sensors for high pressure. It can also be adjusted readily to a specified pressure range through an appropriate choice of wavelengths and sensor dimensions. This paper discusses principles, construction, and operation of the sensor and its performance under various conditions, including pressure and temperature coefficients of the output signal. Being immune to electromagnetic interference and safe in explosive environments, this new device will likely find numerous industrial applications. © 1990 IEEE