All-optical graphene-oxide humidity sensor based on a side-polished symmetrical twin-core fiber Michelson interferometer

•It provides a new fiber structure to realize humidity measurement with a high sensitivity.•The twin cores act independently as two arms of the interferometer to avoid the simultaneous change of transmission modes in single core fiber, therefore the proposed sensor not only possesses the high sensitivity with good linearity, but also has a good mechanical strength.•The proposed humidity sensor can work in intensity and racing-wavelength modes. The response time of the sensor is only about 3.6 s. A high-sensitive graphene-oxide (GO) humidity sensor based on a side-polished twin-core fiber (SPTCF) Michelson interferometer (MI) has been demonstrated. The MI was fabricated by splicing a section of TCF to a standard single mode fiber (SMF) and tapering the splicing point. The exposed polished core has a stronger evanescent field and enhances the interaction between light and external environment. The GO-SPTCFMI can operate in the wavelength- and intensity- modulated sensor. The super-high humidity sensitivities of ˜2.72 nm/RH% in the RH range of 40–75% and ˜3.76 dB/RH% in the RH range of 60–62.1% are obtained experimentally. The high-performance GO-SPTCFMI is a promising candidate for potential applications, such as gas sensing and biochemical detection.