湖南大学的范凡及其同事开发了一种双焦距透镜，该透镜可以通过施加电场来调节其两个焦点的相对强度。该透镜采用由液晶材料制成的双层结构。每层对施加的电场有不同的响应，将入射光分成相反极化的光束。 双焦距透镜通过将两个不同的透镜部分组合成一个来工作，每个部分具有不同的焦距 - 从透镜到其焦点的距离。这使得透镜具有两个不同的焦距。 虽然双焦距透镜最出名的是用于视力矫正，但光学材料的最新进展正在将其应用扩展到新的方向。在他们的研究中，范的团队认识到全息术的最新进展如何为该领域的进一步创新提供了潜力。 受全息术的启发 “研究人员设计了许多方法来改进基于多层结构的全息设备的信息容量，”范描述道。“我们认为这种类型的结构除了全息显示领域之外，还有可能在其他领域发挥作用。” 为此，湖南团队研究了这些结构内的层如何以不同的方式操纵光束的偏振态。为了实现这一点，他们用液晶材料制造了他们的双焦距透镜。 液晶包含可以像液体一样流动但可以保持特定取向的分子 - 就像晶体中的分子一样。这些特性使液晶成为调制光的理想选择。 双层优势 “大多数基于液晶的器件由单层结构制成，但这将光场调制限制在有限的区域，”范解释道。“为了实现更复杂和功能更强大的入射光调制，我们使用了由液晶盒和液晶聚合物组成的双层结构。” 在盒中，液晶层夹在两个透明基板之间，形成一个二维材料。当在盒子上施加电压时，分子沿电场方向排列。相比之下，液晶聚合物中的分子要大得多，它们的排列不受施加电压的影响。 范的团队利用这些差异，发现每层以不同的方式调制圆偏振光。结果，透镜可以将光分成左旋和右旋圆偏振分量。至关重要的是，这些分量中的每一个都聚焦在不同的点。通过调整透镜上的电压，研究人员可以轻松地控制两个焦点处的强度差。 在过去，要实现这种控制，只能通过机械旋转透镜层来实现。新的设计要简单得多，并且可以更轻松、更高效地调整两个焦点处的强度。 大的分离距离 为了证明这种优势，范的团队在两种类型的成像实验中使用了他们的双焦距透镜。一种是偏振成像，它分析左旋和右旋圆偏振光与样品相互作用方式的差异。这种方法通常需要焦点之间有很大的分离距离。 他们还在边缘成像中测试了透镜，边缘成像可以增强图像中边界清晰度。这需要焦点之间有更小的分离距离。 通过调整双层结构内的几何配置，范的团队实现了对焦点之间分离的严格控制。在偏振和边缘成像实验中，他们的双焦距透镜都表现得非常好，与他们的模拟预测的理论性能非常吻合。这些有希望的结果表明，该透镜在光学系统中可能具有广泛的应用。 基于他们最初的成功，范及其同事现在正在努力降低其多层双焦距透镜的制造成本。如果成功，这将使透镜能够用于广泛的研究应用。 “我们相信，我们使用多层结构创建的光控制机制也可以用于设计其他光学器件，包括全息器件和光束发生器，或用于光学图像处理，”范说。 该透镜在《光学快报》杂志上发表。 这篇文章最初发表在 Physics World 上。

😁 该透镜采用由液晶材料制成的双层结构，每层对施加的电场有不同的响应，将入射光分成相反极化的光束。

🤩 该透镜利用了液晶材料的特性，其分子可以像液体一样流动，但可以保持特定取向，从而可以轻松地控制两个焦点处的强度差。

🤔 该透镜在偏振和边缘成像实验中表现出色，与他们的模拟预测的理论性能非常吻合，这表明该透镜在光学系统中可能具有广泛的应用。

🥳 范及其同事现在正在努力降低其多层双焦距透镜的制造成本，如果成功，这将使透镜能够用于广泛的研究应用。

💯 研究人员相信，他们使用多层结构创建的光控制机制也可以用于设计其他光学器件，包括全息器件和光束发生器，或用于光学图像处理。

A bifocal lens that can adjust the relative intensity of its two focal points using an applied electric field has been developed by Fan Fan and colleagues at China’s Hunan University. The lens features a bilayer structure made of liquid crystal materials. Each layer responds differently to the applied electric field, splitting incoming light into oppositely polarized beams.

Bifocal lenses work by combining two distinct lens segments into one, each with a different focal length – the distance from the lens to its focal point. This gives the lens two distinct focal lengths.

While bifocals are best known for their use in vision correction, recent advances in optical materials are expanding their application in new directions. In their research, Fan’s team recognized how recent progress in holography held the potential for further innovations in the field.

Inspired by hologaphy

“Researchers have devised many methods to improve the information capacity of holographic devices based on multi-layer structures,” Fan describes. “We thought this type of structure could be useful beyond the field of holographic displays.”

To this end, the Hunan team investigated how layers within these structures could manipulate the polarization states of light beams in different ways. To achieve this, they fabricated their bifocal lens from liquid crystal materials.

Liquid crystals comprise molecules that can flow like in a liquid, but can maintain specific orientations – like molecules in a crystal. These properties make liquid crystals ideal for modulating light.

Bilayer benefits

“Most liquid-crystal-based devices are made from single-layer structures, but this limits light-field modulation to a confined area,” Fan explains. “To realize more complex and functional modulation of incident light, we used bilayer structures composed of a liquid crystal cell and a liquid crystal polymer.”

In the cell, the liquid crystal layer is sandwiched between two transparent substrates, creating a 2D material. When a voltage is applied across the cell, the molecules align along the electric field. In contrast, the molecules in the liquid-crystal polymer are much larger, and their alignment is not affected by the applied voltage.

Fan’s team took advantage of these differences, finding that each layer modulates circularly polarized light in different ways. As a result, the lens could split the light into left-handed and right-handed circularly polarized components. Crucially, each of these components is focused at a different point. By adjusting the voltage across the lens, the researchers could easily control the difference in intensity at the two focal points.

In the past, achieving this kind of control would have only been possible by the mechanical rotation of the lens layers with respect to each other. The new design is much simpler and makes it easier and more efficient to adjust the intensities at the two focal points.

Large separation distance

To demonstrate this advantage, Fan’s team used their bifocal lens in two types of imaging experiments. One was polarization imaging, which analyses differences in how left-handed and right-handed circularly polarized light interact with a sample. This method typically requires a large separation distance between focal points.

They also tested the lens in edge imaging, which enhances the clarity of boundaries in images. This requires a much smaller separation distance between focal points.

By adjusting the geometric configurations within the bilayer structure, Fan’s team achieved the tight control over the separation between the focal points. In both polarization and edge imaging experiments, their bifocal lens did very well, closely matching the theoretical performance predicted by their simulations. These promising results suggest that the lens could have a wide range of applications in optical systems.

Based on their initial success, Fan and colleagues are now working to reduce the manufacturing costs of their multi-layer bifocal lenses. If successful, this would allow the lens to be used in a wide range of research applications.

“We believe that the light control mechanism we created using the multilayer structure could also be used to design other optical devices, including holographic devices and beam generators, or for optical image processing,” Fan says.

The lens is described in Optics Letters.

The post Liquid-crystal bifocal lens excels at polarization and edge imaging appeared first on Physics World.