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发现高频聚焦CO2激光脉冲三束对称写入法制备的长周期光纤光栅(LPFG)具有新奇的扭曲特性:首先,当被扭曲光纤和长周期光纤光栅长度接近时,扭曲特性有明显的方向相关性,顺时针扭曲时,谐振波长和峰值损耗随扭曲率的增大而减小;逆时针扭曲时,谐振波长和峰值损耗随扭曲率的增大而增大,并与之成良好的线性关系,其平均灵敏度分别为0.133 nm/(rad.m-1)和0.061 dBm/(rad.m-1);其次,当被扭曲光纤远长于长周期光纤光栅时,扭曲特性随扭曲率变化周期性起伏,而且起伏次数(10次)超过光纤被扭曲周数(6周),但整体特性基本保持不变。利用扭转光栅导致椭圆双折射理论对扭曲特性进行了解释,并发现光栅内部固有线性双折射对扭曲特性有着重要的作用。
It is found that long-period fiber grating (LPFG) fabricated by three-beam symmetric write method with high-frequency focused CO2 laser pulses has novel twist characteristics. First, when the length of twisted fiber and long-period fiber grating is close, the twist characteristics have obvious directional correlation In the case of clockwise and clockwise twist, the resonance wavelength and the peak loss decrease with the increase of the twist rate. When the counterclockwise twist is made, the resonance wavelength and the peak loss increase with the increase of the twist rate, and have a good linear relationship , The average sensitivities are 0.133 nm / (rad.m-1) and 0.061 dBm / (rad.m-1), respectively. Secondly, when the distorted fiber is much longer than the long-period fiber gratings, the twist characteristics change with the periodicity Ups and downs, and the number of undulations (10 times) exceeded the number of warped weeks (6 weeks) of the optical fiber, but the overall characteristics remained basically unchanged. The torsion properties were explained by the theory of elliptical birefringence caused by the twisted grating, and the intrinsic linear birefringence inside the grating was found to play an important role in the torsional characteristics.