Sensitivity and stability of an air-core fibre-optic gyroscope

We report a detailed experimental and theoretical analysis of a novel type of fibre- optic gyroscope ( FOG) that utilizes an air- core photonic- bandgap fibre ( PBF) in its sensing coil. The anticipated benefits of using an air- core fibre include dramatically reduced phase bias drift due to temperature ( Shupe effect), magnetic field ( Faraday effect) and optical nonlinearity ( Kerr effect), all of which result from the fact that the fibre mode now propagates in air instead of silica. The reduced Kerr sensitivity, combined with the low theoretical limit of backscattering in air- core fibre, offers the unprecedented potential of ultimately driving this type of FOG with a laser instead of a broadband source, which would yield lower noise and a greater scale- factor stability. We demonstrate some of these anticipated benefits in a PBF FOG with a 235 m coil of air- core fibre interrogated by a broadband Er- doped fibre source. We show that it exhibits a noise limited by the excess noise of the broadband source, as is a conventional gyroscope of the same length ( random walk of similar to 0.015 degrees h(-1/2)), but a greatly reduced sensitivity to the Kerr effect (> 170), temperature transients (similar to 6.5), and Faraday effect (> 20), compared to a conventional FOG, in quantitative agreement with theory.