Response Characteristic of Twisting Second-Azimuthal-Order Few-Mode Long-Period Fiber Grating
(2.Department of Electronics and Information, Huzhou University Qiuzhen College, Huzhou, Zhejiang Province, China 313000)
【Abstract】This study experimentally and theoretically examines the response characteristic of twisting the second-azimuthal-order few-mode long-period fiber grating (FM-LPFG). The theoretical analysis shows that the twisting responsivity of the coupled resonant wavelength of the high-order FM-LPFG is closely related to the azimuthal order of the grating, namely the twisting responsivity of the resonant wavelength of the second-azimuthal-order FM-LPFG is almost two times larger than that of the first-azimuthal-order FM-LPFG. The twisting-induced phase mismatching leads to the almost linear decay of the intensity of the resonant peak in the transmission spectrum of the grating with the increase in the grating twisting rate in a relatively small twisting-rate domain. This decay rate is inversely related to the value of the phase mismatch. Further, the experimental results show that the twisting responsivity of the resonant wavelength of the second-azimuthal-order FM-LPFG is approximately 1.5 times larger than that of the first-azimuthal-order FM-LPFG, which reaches 0.72 nm· (rad·m−1)−1 and 0.82 nm· (rad·m−1)−1 in the cases of clockwise and counter-clockwise twisting, respectively. The intensity of the resonant peak varies linearly with the increase in the twisting-rate in the small twisting-rate domain, and the linear sensitivities are 0.81 dB· (rad·m−1)−1 and 0.72 dB· (rad·m−1)−1 in the cases of clockwise and counter-clockwise twisting, respectively. However, the corresponding intensity of the resonant peak has the characteristics of small variation amplitude and fluctuation in the large twisting-rate domain, indicating that experimental results are generally in agreement with the theoretical analysis. These twisting response characteristics of the wavelength and intensity of the resonant peak of the second-azimuthal-order FM-LPFG have potential applications in high-precision sensing of twisting mechanical parameters (such as twisting capacity, twisting speed, and acceleration) and simultaneous measurement of multiple parameters in the same monitoring twisting-rate domain.
【Keywords】 optical communications; second-azimuthal-order few-mode long-period fiber grating; twisting; response characteristic; resonant peak ;
(Translated by WEI JM)
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