Hollow microsphere probes formed by hollow core optical fiber discharging for monitoring gas pressure and temperature

A hollow core fiber (HCF) is spliced with a single-mode fiber, and then, the end face of the HCF is etched to form a microsphere interferometer for measuring gas pressure and environmental temperature. The total length of each microsphere is less than 200 μm. We fabricated two such structures and used femtosecond laser pulses to drill micro-holes on the HCF walls of both structures. One of the structures is directly used to measure air pressure, achieving a sensitivity of up to 2.857 nm/MPa while being almost insensitive to temperature. This structure is capable of assessing pressure down to 3.4 kPa within the range of 0–0.5 MPa. Another structure is filled with thermally sensitive material dimethyl silicone oil through a micro-hole, and then, it is sealed with AB adhesive to form a harmonic Vernier effect temperature sensor, with a sensitivity of up to −5.16 nm/°C. This structure is capable of assessing temperature down to 0.38 °C within the range of 30–60 °C. Additionally, the sensors have good repeatability and stability and compact structure and simple manufacturing and can be used as a sensing probe for monitoring gas pressure and temperature under extreme environments.