Optical fiber–Ta2O5 waveguide coupler covered with hydrophobic zeolite film for vapor sensing

•Fiber optic coupler covered with highly hydrophobic MFI-type zeolite film was investigated.•The optical response of coupler was predicted by theoretical modeling and confirmed experimentally.•The application of coupler for vapor sensing was demonstrated.•The advantages of both fiber optic sensors and spin-on zeolite films as selective medium were combined.