双棱镜改变写入Bragg波长的相位掩模技术

将一种可旋转的双棱镜引入到相位掩模技术中以改变光栅的写入Bragg波长.在该系统中,光纤光栅是由来自可旋转双棱镜所形成的波长为248 nm的紫外干涉条纹写入的,其中,相位掩模被用作 1级衍射光的分束器,通过双棱镜的旋转可改变两写入光束的交叉角.为了初始化Bragg波长的参考值,双光栅的顶角由相位掩模的 1级衍射角和双棱镜的折射率确定.因为在～100 nm范围内两光束的非对称旋转对光栅周期的改变是5×10~(-4) nm,双棱镜引入的光栅的闪耀可忽略.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 min.与Talbot干涉仪中平面镜的旋转角～23 s/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.

Changing Inscribed Bragg Wavelengths with Biprism in Phase Mask Technique

A rotatable biprism is introduced in phase mask technique to change the inscribed Bragg of grating.In this system,the gratings are inscribed by the UV interference fringes of 248 nm derived from a rotatable biprism,where the phase mask is used as a beam splitter,and the biprism is rotated to change the intersection angle of two beams.For initializing the reference quantity of Bragg wavelength,the vertex angles of the biprism are determined by the ±1 diffraction angle of phase mask and the refract index of the biprism.Because the change of grating period caused by the asymmetrical rotation of two beams is limited to 5×10~(-4) nm at a tunability of the Bragg wavelength of ～100 nm,the tilt of grating caused by the rotation of the biprism can be ignorable.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 ～3 min.By contrasting with the rotation angle ～23 s/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.