利用一块相位掩模和两块棱镜改变光纤光栅的写入Bragg波长

一种相位掩模干涉仪被用于写入不同的Bragg波长的。在该系统中，光纤光栅是由来自两可旋转棱镜所形成的紫外干涉条纹写入的，其中，相位掩模被用作&;#61617;1级衍射光的分束器。并且，当两块顶角由相位掩模的&;#61617;1级衍射角和棱镜折射率确定的棱镜的底部相互平行放置时，该相位掩模给出了Bragg波长的参考值。当Bragg波长的移位为1 nm时，棱镜最大的旋转角为1 degree，最小的旋转角是~2.4 minute。与Talbot干涉仪中平面镜的旋转角~23 second/nm相比，该相位干涉仪中棱镜的旋转精度降低了2~3个数量级。替代了许多具有不同光栅周期的相位掩模，该可调谐相位掩模干涉仪仅用一块相位掩模和两块旋转棱镜就实现了写入具有不同Bragg波长的光栅。

Changing Inscribed Bragg Wavelengths of Fiber Gratings via One Phase Mask and Two Prisms

A phase mask interferometer is developed to photo-write gratings with arbitrary Bragg wavelength. In this system, the gratings are inscribed by the UV interference fringes derived from two rotatable prisms, where the phase mask is used as a beam splitter. Furthermore, when the undersides of two prisms with the vertex angle defined by the &;#61617;1 diffraction angle of phase mask and the refract index of the prism are parapllel each other, the phase mask initializes the reference quantity of Bragg wavelength. As the shift of Bragg wavelength is 1 nm, the maximum rotation angle of the prism is ~1 degree, and the minimum rotation angle is ~2.4 minute. By contrasting with the rotation angle ~23 second/nm of the mirror in Talbot interferometer, the rotation precision of the prisms is decreased by two or three orders of magnitude in this phase mask interferometer. Instead of many phase masks with different grating periods, the phase mask interferometer writes grating with the inscribed wavelength of 1450~1600 nm via a phase mask and two rotatable prisms.