Ivanov Oleg V, Caldas Paulo, Rego Gaspar
Ulyanovsk Branch of Kotel'nikov Institute of Radio Engineering and Electronics of Russian Academy of Sciences, Ulitsa Goncharova 48, 432071 Ulyanovsk, Russia.
Ulyanovsk State University, S.P. Kapitsa Research Institute of Technology, Ulitsa L. Tolstogo 42, 432017 Ulyanovsk, Russia.
Sensors (Basel). 2021 Oct 29;21(21):7212. doi: 10.3390/s21217212.
In this paper, we investigate modification of transmission spectra of long-period fiber grating structures with an acoustic shock front propagating along the fiber. We simulate transmission through inhomogeneous long-period fiber gratings, π-shift and reflective π-shift gratings deformed by an acoustic shock front. Coupled mode equations describing interaction of co-propagating modes in a long-period fiber grating structures with inhomogeneous deformation are used for the simulation. Two types of apodization are considered for the grating modulation amplitude, such as uniform and raised-cosine. We demonstrate how the transmission spectrum is produced by interference between the core and cladding modes coupled at several parts of the gratings having different periods. For the π-shift long-period fiber grating having split spectral notch, the gap between the two dips becomes several times wider in the grating with the acoustic wave front than the gap in the unstrained grating. The behavior of reflective long-period fiber gratings depends on the magnitude of the phase shift near the reflective surface: an additional dip is formed in the 0-shift grating and the short-wavelength dip disappears in the π-shift grating.
在本文中，我们研究了沿光纤传播的声激波前沿对长周期光纤光栅结构透射谱的调制。我们模拟了通过非均匀长周期光纤光栅、由声激波前沿变形的π移位和反射式π移位光栅的透射。描述长周期光纤光栅结构中具有非均匀变形的同向传播模式相互作用的耦合模方程用于模拟。对于光栅调制幅度考虑了两种类型的变迹，如均匀变迹和升余弦变迹。我们展示了透射谱是如何由在具有不同周期的光栅的几个部分处耦合的纤芯模和包层模之间的干涉产生的。对于具有分裂光谱陷波的π移位长周期光纤光栅，与未受应变的光栅中的间隙相比，在有声波前沿的光栅中两个凹陷之间的间隙变宽了几倍。反射式长周期光纤光栅的行为取决于反射表面附近的相移大小：在0移位光栅中形成一个额外的凹陷，而在π移位光栅中短波长凹陷消失。
