Polymer-coated symmetrical metal-cladding waveguide for chemical vapor detection with high sensitivity

An optical platform for sensitive detection of chemical vapor based on a polymer-coated symmetrical metal-cladding waveguide is proposed. The diffusion of chemical vapor usually leads to a combinational effect in the polymer layer, i.e., swelling and refractive index change. Owing to the high sensitivity of ultrahigh-order modes, the vapor-induced effect will give rise to a dramatic variation of the reflected light intensity. For proof-of-concept, a good linearity and a low detection limit of toluene and benzene are experimentally demonstrated with an amorphous Teflon AF polymer layer.