Ultrasensitive fiber-optic temperature sensor based on cascaded Sagnac interferometers with a nematic liquid crystal film

•An ultrahigh-sensitive fiber-optic temperature sensor based on cascaded Sagnac interferometers with a nematic liquid crystal film was proposed and experimentally demonstrated.•The molecules of NLC film changed from isotropic to isotropic just by rotating the two single-mode patch cables without any orientation agent, electric, or magnetic devices.•Experimental results revealed that the temperature sensor based on the cascaded configuration showed an ultrahigh sensitivity of 43.13 nm/°C, which was amplified about 5 times contrast to a single Sagnac interferometer.