Fiber optic gyroscope coils: performance characterization

The need for precision guidance of systems in tactical theaters is becoming increasingly more important. This need has renewed interest in Interferometric Fiber Optic Gyroscopes (IFOG) that are capable of delivering navigation grade performance. The challenges however, include satisfactory performance over a large and severe operating temperature range (-60°C to +90°C), low unit cost and relatively small footprint. Performance of the IFOG depends critically on the quality of the sensing element, optical fiber coil, and many of the performance limiting issues of the IFOG can be traced back to coil quality. Although significant progress has been made in the fabrication of temperature insensitive coils with high optical reciprocity, more needs to be done. In this paper, data is presented on the performance of similar size (inside diameter, outside diameter, height) freestanding coils that were wound in quadrupole winding pattern at low tension using different polarization maintaining fibers. Performance characteristics of the coils were measured under variables including (i) fiber geometry, (ii) fiber coating, (iii) winding epoxy, and (iv) epoxy curing profile. Although each coil had the same footprint, they contained different lengths of fiber based on the fiber coating size. Coils were characterized as a function of temperature with respect to: (i) optical loss, (ii) polarization extinction ratio (PER), and (iii) coherence. The data suggests that high performance navigation grade coils can be realized over a large and severe temperature range with careful choice of fiber, winding epoxy and cure cycle.