Controlled Fabrication of Polymer End-Capped Fiber Optic Sensors

We demonstrate a simple method for fabricating polymer end-capped fiber optic sensors with highly reproducible features. The polymer used for the devices is polydimethylsiloxane (PDMS) deposited on the cleaved end of a standard single-mode fiber forming a fiber-optic Fabry-Perot interferometer (FFPI). Deposition is done by immersing the fiber tip into pre-cured PDMS at a prescribed velocity set by the viscosity and surface tension of the polymer. This speed-controlled dip-coating process, along with the pre-curing conditions for the PDMS, yield fiber devices with similar dimensions and spectral features. We demonstrate this upon evaluating the spectral response of the FFPIs throughout the different stages of the fabrication process; the variations in the resulting cavity lengths are estimated to be within 30 nm. The performance of the FFPI sensors for measuring the refractive index of different liquids is evaluated showing that consistent measurements are effectively achievable. Finally, we demonstrate that the spectral features of the FFPIs provide a means to account for temperature effects on refractive index measurements.