Long period gratings imprinted on the commercial plastic optical fibers for refractive index sensing

It is well known that the sensitivity could be enhanced by modifying the structure of plastic optical fibers (POFs) in some ways, such as side-polishing, tapering, bending, and so on. Therefore, in this work we tried to a new approach to modify the structure of POFs for RI sensing purpose. The corrugated surface long period gratings (LPGs) were fabricated on the commercial POFs by a simple mechanical die press print method using a periodic V-grooved metal plate as the mould. The LPGs were fabricated on two kinds of commercial POFs with the diameters of 0.5 and 1.0mm, respectively. The results indicate that the LPGs on the POF with the thinner diameter exhibits better performance in term of RI sensitivity and SNR. By altering the LPG structural parameters, the RI sensing performances were studied. When the LPG with the tilted angle of 20 degrees, the period of 100 mu m and the groove depth of 45 mu m, the highest sensitivity of 1058%/RIU with a resolution of 4.88x10(-4)RIU in the RI range of 1.333-1.430 was obtained in our experiments. The RI sensor is a low cost solution, which has the features of simple structure, easy fabrication, compact size and intensity modulation at visible wavelengths.