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 (LP_1,6 and LP_1,12, respectively). For the grating periods of 182.7 and 192.5 µm, it was verified that the LP_1,12 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.

中文翻译：

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飞秒激光直接写入制造的长周期光纤光栅的温度稳定性和光谱调谐。

通过飞秒（fs）激光直接写入，在标准单模光纤（SMF-28e）中制造了长周期光纤光栅（LPFG）。制作了具有更长和更短周期的LPFG，这允许从基本核心模式耦合到较低和较高阶的非对称包层模式（分别为LP _1,6和LP _1,12）。对于182.7和192.5 µm的光栅周期，已验证LP _1,12模式在空气和水中分别显示出大约1380和1448 nm的TAP。对经过高温热处理的LPFG进行了表征。显示了对共振带的位置和高达600°C的热稳定性的微调。对具有不同周期和不同温度范围的光栅的温度敏感性进行了表征。对于182.7 µm TAP LPFG的两个共振，在250至600°C的范围内，可获得的最大灵敏度为-180.73和179.29 pm /°C。