Abstract
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.
Highlights
In the past two to three decades, fiber gratings have been intensively studied for applications in optical communications and sensing [1,2,3]
To simulate the process of propagation of acoustic shock front through the long-period fiber gratings (LPFGs), we assume that the amplitude of the front profile is described by the following function, which changes the strain from one level to another with controllable smoothness defined by the parameter η: s0 z − z0 s(z) =
We have studied the spectral behavior of LPFGs deformed by propagating acoustic shock front
Summary
In the past two to three decades, fiber gratings have been intensively studied for applications in optical communications and sensing [1,2,3]. The scientific community focused their attention on the development of sensors able to detect deformations caused by shock waves working at frequencies from hundred kHz up to several GHz; examples of such acoustic shock waves are explosive detonation waves In this context, fiber Bragg gratings have already proved their potential and several papers have been published in literature [7,8,9,10,11], while the interaction of a shock wave front with a fiber Bragg grating was studied [12]. 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 homogeneous long-period fiber gratings, π-shift, and reflective gratings with propagating acoustic shock front producing non-uniform deformation along the optical fiber. We consider the influence of smoothness of the acoustic front and the magnitude of the phase shift on the spectra of various types of LPFG structures
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