  We report on high-temperature sensing measurements using a tubular-lattice
hollow-core photonic crystal fiber displaying a microstructure formed of eight
2.4 um-thick cladding tubes. The larger thickness of our fiber's cladding tubes
compared to other hollow fibers operating in the visible and infrared ranges
entails multiple narrow transmission bands in its transmission spectrum (6
bands in the spectral range between 400 nm and 950 nm) and benefits the
realization of the temperature sensing measurements. The principle of operation
of our device is based on the thermo-optic effect and thermal expansion-induced
spectral shifts of the fiber transmission bands due to temperature variations.
To study the sensor operation, we monitored the fiber transmission bands'
spectral positions from room temperature to 1085 oC in both ramp-up and
ramp-down scenarios. Additionally, we investigated the optimization
opportunities by assessing an analytical model describing the fiber
transmission characteristics and discussed the alternatives for enhancing the
sensor performance. Moreover, our fiber characterization experiments revealed a
consistent confinement loss trend aligned with the scaling laws in
tubular-lattice hollow-core fibers. We thus understand that the results
presented in this manuscript highlight a relevant path for the development of
temperature sensors based on microstructured hollow-core optical fibers endowed
with thick cladding tubes.
