用两个周期为600 μm,齿宽为200 μm的周期性刻槽板彼此错开从上下两面对单模光纤施压,在光纤中形成了微弯式长周期光纤光栅。由于齿宽小于二分之一周期,可产生更深的光纤微弯调制,获得更大的交流交叉耦合系数。通过测量两个光栅长度分别为6 cm和12 cm的微弯式长周期光纤光栅在不同压力下的透射谱,研究了峰值损耗、附加损耗、损耗谱半峰全宽与压力和光栅长度的关系。对于长12 cm的微弯式长周期光纤光栅,在第一饱和压力点峰值损耗达到19.2 dB,损耗谱半峰全宽(FWHM)为20 nm,附加损耗只有0.26 dB;经过三次过耦合得到34 dB的峰值损耗。然后用理论结合实验数据分析发现当光纤所受压力小于饱和压力时,光纤光栅交流交叉耦合系数与压力成正比。

Micro-bend long period fiber gratings (MBLPFG) are presented by pressing a single mode fiber from double sides with two identical grooved plates whose pitch is 600 μm and teeth width is 200 μm. Because the teeth width is smaller than half pitch of the grooved plate,deeper micro-bend modulation in fiber can be made,and so a bigger “AC” cross-coupling coefficient can be achieved. By measuring the transmission spectra of two micro-bend long period fiber gratings with lengths of 6 cm and 12 cm,respectively,the relations between peak loss,out of band loss,full width at half maximum (FWHM) of loss ratio spectra with applied pressure for different grating length are investigated. For the micro-bend long period fiber grating of 12 cm length,near the first saturation pressure,the peak loss reaches 19.2 dB,the FWHM is 20 nm,out of band loss is only 0.26 dB. After over coupling out and back three times,a peak loss of 34 dB is achieved. Then,through analysis from theory and experimental data,it is found that the “AC” cross-coupling coefficient grows linearly with applied pressure,when the pressure on the fiber is less than saturation pressure.