Investigation of a D-Shaped Plastic Optical Fiber Assisted by a Long Period Grating for Refractive Index Sensing

A D-shaped plastic optical fiber (POF) assisted by a long period grating (LPG) is proposed as a refractive index (RI) sensor. The LPG is fabricated on the D-shaped region by a simple mechanical die press print method. The RI sensing performances of the D-shaped POFs with LPGs imprinted on POFs with different diameters (of 0.25, 0.50, and 1.00mm) are studied, and the results show that the D-shaped POF with an LPG achieve higher RI sensitivity than that of the one without an LPG. When the D-shaped POF with an LPG fabricated on POF with a thin diameter of 0.25mm, the extremely high sensitivities of 2676%/RIU and 9786%/RIU are obtained in the RI ranges of 1.33-1.40 and 1.40-1.45, respectively. Additionally, the temperature dependence of the sensor is also investigated. The experimentally confirmed high sensitivity of our proposed sensor, combined with its simple structure, easy fabrication and low cost, makes it a promising candidate for RI sensing applications.