Brillouin grating in optical fibers is of considerable interest due to its applications in optical fiber communication and distributed sensing. However, the intrinsic Brillouin grating spectrum is still unknown and several kinds of spectra were reported. In this paper, we experimentally investigate the characteristics of the Brillouin grating spectra in a polarization-maintaining fiber, and the results show that it agrees with the theory of fiber Bragg grating but not determined by the natural Brillouin gain bandwidth as thought previously, and in the case of weak grating, the bandwidth is only length-limited, i.e., inversely proportional to the length of the Brillouin grating. In addition, the apodization of the Brillouin grating induced by the acoustic wave decay, a unique feature that is different from the Bragg grating, is observed for the first time to the best of our knowledge.
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