A cobalt carbonate hydroxide hydrate-based optics fiber sensor for humidity and temperature detection

•A highly sensitive sensor based on MZI interferometer principle was fabricated.•CCOH nanosheet arrays were firstly used to improve sensitivity of MZI interferometer.•The sensor could measure temperature and humidity simultaneously by cascading a FBG.•The sensor has many merits of simple structure, good repeatability and stability. A highly sensitive sensor based on a Mach-Zehnder interferometer (MZI) with “SMF-MMF-TCF-MMF-SMF” structure is proposed to measure temperature and humidity. To improve the sensitivity of this sensor, cobalt carbonate hydroxide hydrate nanosheet arrays were grown on the surface of TCF with a facile hydrothermal method. The sensor exhibits high sensitivity measurement of multiple parameters including 1.29 nm/°C in the temperature range of 24 °C–60 °C and 0.56 nm/%RH in the humidity range of 65 %–89 %. Through systematic experiments, results show that the fabricated MZI structure can measure one quantity only if other one is known. Based on this, a fiber Bragg grating could be used to eliminate the cross-sensitivity between temperature and humidity by a wavelength conversion method. In addition, this sensor also exhibits many other merits such as simple structure, compact volume, robust structure, good repeatability and stability. This all-fiber sensor is anticipated to be applied in various devices which could measure temperature and humidity in agriculture, chemical industry, semiconductor manufacturing, electricity and other fields.