Sensing characteristics of a compact gourd-type MZ interferometer based on hollow-core fiber.

• The sensor is simply fabricated by a section of HCF with low cost. • A gourd-shaped structure is formed by using a fusion splicer. • The sensor structure behaves high refractive index sensitivity and low cross-sensitivity to temperature. • Encapsulation of this structure with glycerol can realize high sensitivity to temperature. A gourd-type hollow-core fiber (HCF) based Mach–Zehnder interferometer (MZI) is proposed, and its sensing properties are investigated and extended. The MZI splices both ends of a section of HCF with single-mode fibers and uses a fusion splicer to cone between the HCF-SMF fusion point and the HCF to form a gourd-shaped structure. The conical part and the collapsed region inside the HCF form the light splitting/combining part of the MZI. Studies have shown that the MZI has high refractive index (RI) sensitivity (up to 2705.7 nm/RIU) and low cross-sensitivity to temperature (1.21×10-5 °C/RIU), which is very suitable for biochemical sensing. Encapsulation of this structure using capillary glass tubes and glycerol can convert its high sensitivity to RI into a high sensitivity to temperature, increasing the temperature sensitivity (527.88 pm/ °C) by a factor of about 16. The temperature sensitivity and range of the sensor are adjustable. The MZI has the characteristics of easy preparation, low price, compact structure, and superior detecting performance, and has excellent application prospects in biochemical sensing and physical sensing such as RI and temperature. [ABSTRACT FROM AUTHOR]