connected to an optical fiber obtaining a FOS with a working wavelength of 1.5 lm. On the other hand, the sensing element is widely tailorable, in the sense that one could explore other DBR parameters and metal nanoparticles in order to control the selectivity of the sensing element in different wavelength domains. The underlying physical phenomenon, i.e., the diffusion of solvent molecules in a metal nanoparticle/ polymer composite layer, is indeed poorly understood and depends on several factors, such as the physical and chemical properties of the polymer and the metal nanoparticles. In conclusion, the DBR based on Teflon-like and Au nano-particle/Teflon-like polymers is a promising sensing element, the attraction of which is essentially threefold: first, the Teflon-like polymer is characterized by important properties such as a remarkable chemical resistance, a high thermal stability, a good flame resistance, and an excellent toughness, which are added to the typical polymer advantages such as low-cost fabrication and immense tailorability; second, the DBR can be easily integrated with an optical fiber, with the possibility of tuning the operation wavelength in the optical telecommunica-tion range; third, the sensor can operate at room temperature. All these properties make this sensor particularly suitable for commercial devices, as well as for use in hostile conditions. Experimental DBR Deposition: The DBR was fabricated by an ion-beam sputtering technique at room temperature. This consisted of four pairs of Teflon-like (315 nm) and Au nanoparticle/Teflon-like composite (244 nm) on a Si substrate. The Tef-lon-like layers were deposited by sputtering a target of Teflon with an argon ion beam (Ar +) with an energy of 850 eV and a current of 50 mA. The Au nanopar-ticle/Teflon-like composite layers were obtained by co-sputtering a target of Teflon and a target of Au using Ar + ion beams. The ion-beam sputtering the Teflon target was characterized by an energy and a current fixed at 850 eV and 50 mA, respectively. The energy and the current of the ion-beam sputtering the Au target were 500 eV and 40 mA, respectively. The Au content in the Teflon-like composite layers was controlled by the deposition rates of the Au and Tef-lon species and checked by X-ray photoelectron spectroscopy (XPS) on reference samples. More details on the ion-beam sputtering deposition, and the structural and chemical properties of the Au nanoparticle/Teflon-like composite are reported elsewhere [16]. Vapor-Sensing Properties: The effects of the surrounding vapor on our sensing DBR …