Optical fiber humidity sensor based on vernier effect of Fabry-Perot interferometers with microsphere

•The proposed sensor uses a microsphere and PVA film to form the cascaded F-P cavities to create vernier effect.•The sensor has a high humidity sensitivity of 0.316 nm/%RH.•The humidity response of the sensor with and without vernier effect is compared.•The proposed sensor has high sensitivity, compact size and good stability.