In the mechanically induced long‐period fiber grating (MLPFG) fabricated by applying the periodical pressure on an optical fiber, the small bending occurs due to the periodical pressure, which influences the losses of the core and cladding modes. We propose the theoretical model of the MLPFG for estimating its transmittance based on the transfer matrix method and investigate the effect of the losses of the core and cladding modes in the MLPFG on the transmittance, theoretically and experimentally. We numerically clarify that the transmitted light spectrum of MLPFG shows only the main attenuation lobe, no side lobe, and the attenuation bandwidth is broadened as the cladding mode loss increases. We also clarify that the coupling coefficient, and the losses of the core and cladding modes in the fabricated MLPFG can be estimated from the measured transmitted spectrum based on our model. Moreover, we measure the transmittance of two types of MLPFGs that fabricated with a screw, weights, and metallic plates, and that fabricated with a screw and a heat‐shrinkable tube. The measured spectra show good agreements with the calculated ones using our model. Our model will be useful for designing MLPFGs applied to the sensors.

中文翻译：

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包层模损对机械诱导长周期光纤光栅传输特性的影响

在通过对光纤施加周期性压力而制成的机械感应长周期光纤光栅（MLPFG）中，由于周期性压力而产生了较小的弯曲，这会影响纤芯和包层模式的损耗。我们基于传递矩阵法提出了MLPFG透过率的理论模型，并在理论上和实验上研究了MLPFG的纤芯和包层损耗对透过率的影响。我们从数值上阐明了MLPFG的透射光谱仅显示了主衰减波瓣，而没有旁波瓣，并且随着包层模式损耗的增加，衰减带宽变宽。我们还澄清了耦合系数，根据我们的模型，可以从测得的传输频谱中估算出制造的MLPFG中纤芯和包层模的损耗。此外，我们测量了两种类型的MLPFG的透射率，这两种类型的MLPFG是用螺钉，砝码和金属板制造的，以及用螺钉和热缩管制造的。使用我们的模型测得的光谱与计算的光谱显示出良好的一致性。我们的模型对于设计应用于传感器的MLPFG很有用。