Abstract
Long period fiber gratings (LPFGs) were fabricated in a standard single mode fiber (SMF-28e) through femtosecond (fs) laser direct writing. LPFGs with longer and shorter periods were fabricated, which allows coupling from the fundamental core mode to lower and higher order asymmetric cladding modes (LP1,6 and LP1,12, respectively). For the grating periods of 182.7 and 192.5 µm, it was verified that the LP1,12 mode exhibits a TAP at approximately 1380 and 1448 nm in air and water, respectively. Characterization of the LPFGs subjected to high-temperature thermal treatment was accomplished. Fine-tuning of the resonance band’s position and thermal stability up to 600 °C was shown. The temperature sensitivity was characterized for the gratings with different periods and for different temperature ranges. A maximum sensitivity of −180.73, and 179.29 pm/°C was obtained for the two resonances of the 182.7 µm TAP LPFG, in the range between 250 and 600 °C.
Highlights
Long period fiber gratings (LPFGs) are applied to couple light between the core mode and the co-propagating cladding modes in different types of fibers [1], such as photonic crystal fibers [2], standard single mode optical fibers [3], polarization-maintaining fibers [4], and photosensitive fibers [5,6]
Following the procedures described in the fabrication section, two LPFGs were first fabricated with different refractive index (RI) modulation periods (372.5 and 390 μm), 30.0 and 28.5 mm long, respectively
The non-linear nature of the absorption process of the fs laser pulses, combined with the high precision and flexibility of the developed direct writing system allowed the fabrication of LPFGs with different cladding order modes (e.g., LP1,6 and LP1,12 ) by just selecting a particular period
Summary
Long period fiber gratings (LPFGs) are applied to couple light between the core mode and the co-propagating cladding modes in different types of fibers [1], such as photonic crystal fibers [2], standard single mode optical fibers [3], polarization-maintaining fibers [4], and photosensitive fibers [5,6] They are intrinsically sensitive to external perturbations, enabling the measurement of several parameters [7]. The entire fabrication and characterization process of the LPFGs in SMF-28e fibers inscribed by fs-laser direct writing with periods to couple to low and high order cladding modes is described. The LPFGs thermal annealing was realized to improve temperature stability
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