Generation And Characteristic Analysis Of Random Brillouin Dynamic Grating

Brillouin dynamic grating(Brillouin dynamic grating,BDG)has wide applications in distributed fiber sensing,high-precision spectral analysis,and all-optical signal processing due to its characteristics of dynamic generation,controllable parameters,and read-write separation.At present,Brillouin dynamic gratings mainly include two types.One type is based on different fiber media,there are single-mode fiber BDG,polarization-maintaining fiber BDG,few-mode fiber BDG,and photonic crystal fiber BDG.In the other category,the corresponding Brillouin dynamic grating is generated by changing the characteristics of light source,such as introducing chirp to generate chirped BDG;phase modulating the light source to generate phase-shifted BDG;or using chaotic light source to generate chaotic BDG.On this basis,a new type of random Brillouin dynamic grating is proposed in this paper.The random BDG is similar to the random fiber Bragg grating to provide random feedback.It has important application prospects in random fiber lasers,random multi-parameter sensors,and ultrasonic sensors.In this paper,the numerical simulation model is built by the five-wave coupling equation.Random Brillouin dynamic grating is generated using two sources of random pulse light and chaotic light,respectively.The specific research work is carried out as follows:(1)The random pulse light is used to generate random Brillouin dynamic grating,and its related characteristics are analyzed.The 8 m polarization-maintaining fiber is used in the numerical simulation,and the average maintenance time of the grating is 40 ns.Through its research,it is found that: the random pulse light width is inversely proportional to the random BDG reflection spectrum width and the grating length,and has no effect on the grating intensity.The random pulse light power has no effect on the random BDG reflection spectrum width.The fiber length only affects the location of random BDG,But its random state remains unchanged.(2)Random Brillouin dynamic grating is generated using chaotic light,and its related characteristics are analyzed.The 2 m polarization-maintaining fiber is used in the numerical simulation,and the average maintenance time of the generated grating is 60 ns.Through its research,it is found that: the random BDG acoustic wave field generated by chaotic light lasts longer,and the grating strength and length increase.As the length and duration of chaotic optical coherence increase,the length of the grating increases and the intensity increases.The power of chaotic light increases,the intensity of the grating increases nonlinearly and the length remains unchanged.The fiber length only affects the location of random BDG,but has no effect on its random state.In addition,the application advantages of the random Brillouin dynamic grating in the random fiber laser and the proposed experimental scheme are briefly analyzed.