A polarisation maintaining fiber optimized for high temperature gyroscopes and applications

Fiber Optic Gyroscopes (FOGs) are being used in increasing severe environments and hence the upper maximum temperature may be in excess of the normal operating range used on optical fiber. These environments where high temperature FOGs could be used are in exploration of oil and gas fields, and subsequent fuel extraction from such deep wells. Also many military operating environments have higher temperatures; hence specifications such as the DoD's MIL-PRF-49291 recent revisions of fiber exist, which calls for operation from -55°C to +165°C. Therefore coatings which can operate to 180°C are being assessed. This paper will describe the relative merits of two high temperature acrylate coatings for an optical fiber designed for a FOG in such an operating environment. When assessing performance in gyroscopes, it was seen that both coating types give very good polarisation extinction ratio (PER) performance at high temperature up to 180°C. The fiber is a bow-tie design giving a shorter beat-length and thus a superior polarisation extinction ratio. The long term thermal exposure effects have been investigated and experimental results presented for reliability assurance. After damp heat and dry heat treatments, the tensile strengths of the fibers were found to be well within the Telcordia limits. We have also tested the PER performance over temperature both before and after an extended period of high temperature endurance. This has demonstrated the relative merits of different styles of coatings. From the PER performance the h-parameter of the fiber can be calculated and hence the preferred coating type selected and recommended for the customer operating environment.