We report an optical fiber sensor capable of bend-insensitive simultaneous measurements of strain and temperature by using cascaded long-period fiber gratings (LPFGs) inscribed on a polarizationmaintaining photonic crystal fiber (PMPCF). The cascaded LPFGs written on the PMPCF have two different interference spectra for orthogonal input polarization states exciting the principal axes of the PMPCF. Each fringe spectrum is created by the interference between the uncoupled core mode and the cladding mode recoupled to the core mode at the second LPFG. Due to the birefringence of the PMPCF, the order of this cladding mode can be different depending on the input polarization. The lowest dip in each interference spectrum is designated as a sensor indicator dip (SID) A or B. These SIDs originating from cladding modes with dissimilar orders can have different strain or temperature sensitivities. The strain and the temperature responses of these SIDs were investigated in an applied strain range of 0 −2244 με and an ambient temperature range of 25 −95 °C, respectively. The strain sensitivities of the SIDs A and B were measured as approximately −0.93 and −1.41 pm/με (R 2 values: ~0.9984 and ~0.9949), and their temperature sensitivities as ~11.48 and ~15.14 pm/°C (R 2 values: ~0.9974 and ~0.9905), respectively. In particular, their bending responses were also explored over a wide curvature range of 0 − 7.984 m −1 . Themaximum bend-induced wavelength shift was ~0.06 nm. Owing to their linear and independent responses to strain and temperature and their insensitivity to bending, our LPFG device can be a strong candidate for a practical sensor head for simultaneous measurements of strain and temperature.

中文翻译：

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基于刻在保偏光子晶体光纤上的级联长周期光纤光栅对应变和温度不敏感的同时测量

我们报告了一种光纤传感器，通过使用刻在保偏光子晶体光纤 (PMPCF) 上的级联长周期光纤光栅 (LPFG)，能够对应变和温度进行弯曲不敏感的同时测量。写在 PMPCF 上的级联 LPFG 具有两个不同的干涉光谱，用于激发 PMPCF 主轴的正交输入偏振态。每个条纹光谱是由未耦合的纤芯模式和在第二个 LPFG 处重新耦合到纤芯模式的包层模式之间的干扰产生的。由于 PMPCF 的双折射，这种包层模式的顺序可能会因输入偏振而不同。每个干扰频谱中的最低倾角被指定为传感器指示倾角 (SID) A 或 B。这些源自具有不同阶次的包层模式的 SID 可能具有不同的应变或温度敏感性。分别在 0 -2244 με 的应用应变范围和 25 -95 °C 的环境温度范围内研究了这些 SID 的应变和温度响应。SID A 和 B 的应变敏感性测量为大约 -0.93 和 -1.41 pm/με（R 2 值：~0.9984 和 ~0.9949），它们的温度敏感性为~11.48 和 ~15.14 pm/°C（R 2值：分别为 ~0.9974 和 ~0.9905)。特别是，还在 0 - 7.984 m -1 的宽曲率范围内探索了它们的弯曲响应。最大弯曲引起的波长偏移为~0.06 nm。由于它们对应变和温度的线性和独立响应以及它们对弯曲不敏感，