A flat-shaped plastic optical fiber assisted by a long period grating for refractive index sensing

A flat-shaped plastic optical fiber (POF) assisted by a corrugated surface long period grating (LPG) is fabricated by a simple heat pressing and mechanical die press print method. By changing the structural parameters of the flat-shaped POF with LPG, the refractive index (RI) sensing performance of the obtained sensor are evaluated. It shows that the structure parameters of sensor affect the RI sensing performance, and the sensor with a thinner flat thickness and a deeper groove depth of the corrugated surface LPG exhibits better RI sensing performance. Moreover, the sensitivity of the sensor after removing the cladding is better than that of the sensor without removing the cladding. When the POF diameter D is 1mm, the LPG period is 300μm, the thickness d of flat-shaped POF without cladding is 600μm, and the LPG groove depth h is 200μm, we obtained the highest sensitivity of 591.3%/RIU with a resolution of 2.872×10-4RIU in the RI range of 1.3330-1.4230. The proposed sensor is a low-cost solution for RI measurement and with the features of easy fabrication, high sensitivity and intensity modulation at visible wavelengths.