Depth of focus enhancement of the linear fractal zone plates

Linear zone plates leverage their unique focusing properties to serve as critical components for line-illumination microscopy and precise measurement. However, the inherent single-focus characteristic of conventional linear zone plates demands stringent focusing precision and positional stability during operation. In this paper, a novel diffraction optical element with an extended depth of focus, named linear fractal zone plates (LFZPs), is proposed, which combines the Cantor fractal structure with linear zone plates. Numerical simulations and experiments demonstrate that the designed LFZPs can generate a series of coaxial linear light-spots along the propagation direction within the focusing region, exhibiting excellent long focus-depth characteristics that are almost consistent with theoretical predictions. In addition, the focusing characteristics of the LFZPs under different parameters are investigated, and it is demonstrated that the LFZPs can significantly reduce imaging aberrations. This element with a unique property will have widespread applications in imaging and microscopy.