A lens performs an approximately one-to-one mapping from the object to the image plane. This mapping in the image plane is maintained within a depth of field (or referred to as depth of focus, if the object is at infinity). This necessitates refocusing of the lens when the images are separated by distances larger than the depth of field. Such refocusing mechanisms can increase the cost, complexity, and weight of imaging systems. Here we show that by judicious design of a multi-level diffractive lens (MDL) it is possible to drastically enhance the depth of focus by over 4 orders of magnitude. Using such a lens, we are able to maintain focus for objects that are separated by as large a distance as $\sim {6}\;{\rm m}$ in our experiments. Specifically, when illuminated by collimated light at $\lambda = {0.85}\;{\unicode{x00B5}{\rm m}}$, the MDL produced a beam, which remained in focus from 5 to 1200 mm. The measured full width at half-maximum of the focused beam varied from 6.6 µm (5 mm away from the MDL) to 524 µm (1200 mm away from the MDL). Since the side lobes were well suppressed and the main lobe was close to the diffraction limit, imaging with a horizontal × vertical field of view of ${40}^\circ \times {30}^\circ $ over the entire focal range was possible. This demonstration opens up a new direction for lens design, where by treating the phase in the focal plane as a free parameter, extreme-depth-of-focus imaging becomes possible.

中文翻译：

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平板镜头可实现超深度对焦成像

镜头执行从物体到像平面的大约一对一的映射。图像平面中的此映射保持在景深之内（如果对象位于无限远处，则称为聚焦深度）。当图像分开的距离大于景深时，这就需要重新聚焦镜头。这种重新聚焦机制会增加成像系统的成本，复杂性和重量。在这里，我们表明，通过明智地设计多级衍射透镜（MDL），可以将聚焦深度大幅提高4个数量级以上。使用这样的镜头，我们能够在我们的实验中为距离\\ sim {6} \ ;; {\ rm m} $之类的大距离物体保持聚焦。具体来说，当被准直光照射时$ \ lambda = {0.85} \; {\ unicode {x00B5} {\ rm m}} $，MDL产生一束光束，焦点保持在5到1200 mm之间。在聚焦光束的一半最大处测得的全宽从6.6 µm（距MDL 5毫米）到524 µm（距MDL 1200毫米）不等。由于旁瓣得到了很好的抑制，并且主瓣接近衍射极限，因此在整个焦距范围内，水平×垂直视场为$ {40} ^ \ circ \乘以{30} ^ \ circ $的成像方式为可能。该演示为透镜设计开辟了新的方向，通过将焦平面中的相位作为自由参数，可以实现超深度聚焦成像。