Two-Parameter Optical Fiber Sensor Using Photopolymer Microtips

We propose and develop a two-parameter optical fiber sensor based on photopolymer microtips, which may measure both refractive index (RI) and temperature simultaneously. We fabricate the sensor by growing two microtips on the end face of a twin-core fiber (TCF) and launch two beams of supercontinuous laser source with a wide spectral range into two cores independently. One microtips works as an RI sensing unit. The laser entering into the microtip will produce multimode interference (MMI), and the interference spectrum will shift along with the environmental RI. The other microtip works as a temperature-sensing unit. To improve the temperature sensitivity, we coat a layer of polydimethylsiloxane (PDMS) on the surface of the microtip. We receive the reflective spectrum with two overlapped MMIs, separate the spectrum by using the fast Fourier transform (FFT) method, and finally, realize the independent detection of the two parameters. Experimental results show that the RI sensitivity is −274 nm/RIU with the range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.33\sim 1.413$ </tex-math></inline-formula> RIU, while the temperature sensitivity is 1.188 nm/°C with the range of 10 °C–90 °C. In practical application, we construct a matrix equation with the testing sensitivity to solve the crosstalk between two parameters. The proposed two-parameter optical fiber sensor, featuring the benefits of low cost, easy manufacturing, and simplicity of structure, can find potential application prospects in various areas such as industry, environment, and medicine.