Investigation of a Macro-Bending Tapered Plastic Optical Fiber for Refractive Index Sensing

A plastic optical fiber (POF) probe with a macro-bending tapered structure was proposed and optimized for the refractive index (RI) sensing. The principle of operation is based on the macro-bending loss and evanescent wave, which are introduced by the macro-bending tapered structure on the fiber, and modulated by the environmental RI. A heating and drawing method and thermal setting process were used to fabricate a tapered POF and form a stable macro-bending structure for the probe. The probes with cladding and without cladding were fabricated. By changing the taper waist and curvature radius, the sensing performance of the probe was optimized. The highest sensitivity of the probe with cladding reached 937%/RIU in the RI range of 1.33-1.41. By removing the cladding, the RI sensing range was expanded to 1.33-1.45, and the sensitivity was about 800%/RIU, lower than the ones with cladding. In addition, the temperature dependence of the sensor was investigated. The POF probe is a low cost solution for RI sensing applications, which has the features of simple structure, compact, and intensity modulation at visible wavelength.