Optical fiber humidity sensor

The utility model discloses an optical fiber humidity sensor and a preparation method thereof. The optical fiber humidity sensor comprises a micro-nano optical fiber and a porous film, wherein at least one bending part is formed on the micro-nano optical fiber; the porous film is coated on the surface of the bent part; a plurality of holes are formed in the surface of the porous film, and the porous film is configured to be capable of swelling through water absorption, so that the duty ratio of the holes is reduced. According to the invention, humidity sensing is realized by coupling an evanescent field of the U-shaped micro-nano optical fiber with the porous film. In different relative humidity environments, the sizes of pores of the porous film on the surface of the U-shaped micro-nano optical fiber are different, so that the sizes of energy scattered by the porous film are different, and the changes of optical power of the output end of the optical fiber are different, thereby realizing humidity sensing. T