A fiber-optic strain sensor that can show strain via color change and which can be viewed using human eyes has demand in the civil engineering field for alerting purposes. A previous sensor was fabricated using PMMA (Poly(methyl methacrylate)), which had the exceeding hardness to exhibit satisfactory sensor performance. In this research, an elastomer-based fiber-optic structure was fabricated to enhance the elastic response of such sensors and to enlarge the waveguide cross section. Various organic fluorophores were added to the core and cladding regions of the elastic waveguide to induce energy flow from the core to the cladding when stress is applied to the waveguide. Elastomer pairs suitable for the core and cladding were selected from among several candidate materials having high transparency. A method of dispersing fluorophores to each host elastomer and constructing an excellent core–cladding interface using the selected materials was proposed. To investigate the time-dependent changes in the fluorescence of the doped elastomer waveguide, the absorption and emission spectra were monitored after the host elastomers were cured.

A fiber-optic strain sensor using a fluorophore-doped polymer optical fiber (POF) was fabricated at various waveguiding conditions. The effects attributed to each structural feature of the sensor were characterized by observing the sensor's response. Two fluorophores, Coumarin 540A and Rhodamine 6G, were used to dope the core and the cladding of a poly(methyl methacrylate)-based POF, respectively. Using doped POFs with different numerical apertures (NAs), the changes in the fluorophore peaks upon the application of stress were analyzed by applying macrobending(s) to the fiber. Although the sensor response did not show linearity with respect to the NA, it was found that the shape of the Coumarin 540A-attributed peak was a factor that represented the sensor's sensitivity. As a result, the double-cladding structure demonstrated its effectiveness in improving the stress sensitivity.