Over 30 years ago a simple laboratory tool for optical-vortex beams generation was reported as a synthesized ‘forked’ diffraction grating. We renew the issue, addressing specific properties of such a grating in the sense of geometrical transformation of the grating shape. Stretching or compressing the grating scale results in the astigmatic optical vortex appearance in the first diffraction order. In the case of the induced vortex topological charge higher than unity, the astigmatism forces the optical vortex to separate into a line of unity-charged vortices. The initial splitting occurs along an azimuth angle, depending on the topological charge of the vortex. We show the rotation of the pattern in the free space propagation in simulations and analytical consideration.

中文翻译：

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非对称叉形光栅产生的光学涡旋

30年前，据报道，一种简单的用于产生光学涡旋光束的实验室工具是合成的“叉状”衍射光栅。我们更新了这个问题，从光栅形状的几何变换的角度解决了这种光栅的特定属性。拉伸或压缩光栅尺会导致以第一衍射级出现像散光学涡旋。在诱导的涡旋拓扑电荷高于单位的情况下，散光迫使光学涡旋分离成一条带单位电荷的涡旋线。初始分裂沿方位角发生，具体取决于涡旋的拓扑电荷。我们在模拟和分析考虑中显示了模式在自由空间传播中的旋转。