Reflective humidity and temperature sensor based on lateral-integration fiber with the rod-in-tube configuration

A reflective, laterally integrated dual-channel surface plasmon resonance (SPR) sensor based on a hollow-core fiber (HCF) with an embedded thin coreless fiber (TCLF), forming a rod-in-tube configuration, is proposed for simultaneous humidity and temperature measurement. Two distinguishable SPR-influenced spectral features are generated within the 4-mm sensing length. For the selected 5-cycle device, Channel 1 is tracked by the dip minimum, whereas Channel 2 is tracked by the center wavelength of an inter-dip peak formed by the overlap of the neighboring spectral features. Graphene oxide/magnetic graphene oxide (GO/MGO) multilayers are used to measure humidity response, while polydimethylsiloxane (PDMS) offers stable thermo-optical properties for temperature measurement. The humidity sensitivity of Channel 1 is 0.15 nm/%RH (28–88%RH), showing a pronounced enhancement above ∼90%RH. In contrast, Channel 2 exhibits a strong temperature sensitivity of −1.67 nm/°C with only a weak humidity dependence (0.048 nm/%RH). Within the experimentally validated linear calibration range (28–88%RH), humidity and temperature are decoupled using a sensitivity-matrix method with errors of [−1.77%RH, + 0.94 °C] (50%RH@20 °C) and [−3.59%RH, −0.74 °C] (60%RH@30 °C). This miniaturized dual-channel strategy offers a practical route to temperature-compensated humidity sensing and to compact dual-parameter laterally integrated fiber sensors.