Because in an air-core photonic-bandgap fiber the fundamental mode travels mostly in air, as opposed to silica in a conventional fiber, the phase of this mode is expected to have a much lower dependence on temperature than in a conventional fiber. We confirm with interferometric measurements in air-core fibers from two manufacturers that their thermal phase sensitivity is indeed ~3 to ~6 times smaller than in an SMF28 fiber, in agreement with an advanced theoretical model. With straightforward fiber design changes (thinner jacket and thicker outer cladding), this sensitivity could be further reduced down to ~11 times that of a standard fiber. This feature is anticipated to have important benefits in fiber optic systems and sensors, especially in the fiber optic gyroscope where it translates into a lower Shupe effect and thus a greater long-term stability.

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 ∼0.015° h−1/2), but a greatly reduced sensitivity to the Kerr effect (>170), temperature transients (∼6.5), and Faraday effect (>20), compared to a conventional FOG, in quantitative agreement with theory.

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