发现高频CO2激光脉冲写入的长周期光纤光栅(LPFG)具有独特的扭曲特性:1) 扭曲特性具有明显的扭曲方向相关性——顺时针扭曲时谐振波长发生“红”移,逆时针扭曲时谐振波长发生“蓝”移,无论顺时针还是逆时针扭曲损耗峰幅值都近似线性减小;2) 若被扭曲的光纤比被扭曲的长周期光纤光栅长得多,则扭曲时长周期光纤光栅谐振波长和幅值的变化出现周期性的起伏。利用扭曲光栅引起椭圆双折射进而导致偏振态变化的相关理论合理解释了这些独特的扭曲特性。

It is demonstrated that the torsion characteristics of the novel long period fiber gratings (LPFGs) written by high-frequency CO2 laser pulses depend strongly on twist direction. That is, the resonant wavelength shifts linearly toward the longer wavelength as the LPFG is twisted clockwise, whereas it shifts linearly toward the shorter wavelength as the LPFG is twisted anticlockwise, and the amplitude decreases with the twist rate applied. If the twisted fiber is much longer than the LPFG, the resonant wavelength shifts periodically toward the longer (or shorter) wavelength as the LPFG is twisted clockwise (or anticlockwise), and the amplitude decreases periodically with the twist rate applied. The unique torsion characteristics of the novel LPFG are analyzed theoretically by taking into consideration of the twist-induced elliptic birefringence.