  We present a groundbreaking navigation-grade interferometric air-core fibre
optic gyroscope (IFOG) using a quadrupolar-wound coil of four-tube truncated
double nested antiresonant nodeless fibre (tDNANF). This state-of-the-art
tDNANF simultaneously achieves low loss, low bend loss, single-spatial-mode
operation, and exceptional linear polarization purity over a broad wavelength
range. Our 469 m tDNANF coil demonstrated a polarization extinction ratio (PER)
of ~20 dB when illuminated by an amplified spontaneous emission (ASE) source
spanning 1525-1565 nm. Under these conditions, the gyro archives an angular
random walk (ARW) of 0.0038 deg h-1/2 and a bias-stability (BS) drift over 8500
s of 0.0014 deg h-1, marking the first instance of navigation-grade performance
in air-core FOGs. Additionally, we validated the low thermal sensitivity of
air-core FOGs, with reductions of 9.24/10.68/6.82 compared to that of
conventional polarization-maintaining solid-core FOGs of the same size across
various temperature ranges. These results represent a significant step towards
long-standing promise of high-precision inertial navigation applications with
superior environmental adaptability.
