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We experimentally report fiber Bragg gratings (FBGs) in a single mode step-index polymer optical fiber (POF) with a core made of TOPAS and cladding made of ZEONEX using 520 nm femtosecond pulses and a point-by-point (PbP) inscription method. With different pulse energies between 69.8 nJ and 80.4 nJ, 12 FBGs are distributed along the cores of two pieces of POFs with negative averaged effective index change up to ~6 × 10−4 in the TOPAS. For POF 1 with FBGs 1–6, the highest reflectivity 45.1% is obtained with a pulse energy of 76.1 nJ. After inscription, good grating stability is reported. Thanks to the post-annealing at 125 °C for 24 h, after cooling the grating reflectivity increases by ~10%. For POF 2 with FBGs 7–12, similar FBG data are obtained showing good reproducibility. Then, the FBGs are annealed at 125 °C for 78 h, and the average reflectivity of the FBGs during the annealing process increases by ~50% compared to that before the annealing, which could be potentially applied to humidity insensitive high temperature measurement. [ABSTRACT FROM AUTHOR]

FBG Inscription Using 520 nm Femtosecond Pulses, Paragraph 1 i b ": "In this work, 2-mm-long FBGs were fabricated in two pieces of POFs using the femtosecond laser PbP inscription method. FBG Inscription Using 520 nm Femtosecond Pulses, Paragraph 3 i b ": "For FBGs 2-6, the insertion losses induced by laser pulses are depicted in Figure 3. A correction has been made to " B I Abstract i b ": " B Abstract: b We experimentally report fiber Bragg gratings (FBGs) in a single mode step-index polymer optical fiber (POF) with a core made of TOPAS and cladding made of ZEONEX using 520 nm femtosecond pulses and a point-by-point (PbP) inscription method. [Extracted from the article]