这种透镜的主要优点：可以通过电控来变换焦距的远近的透镜。也许在将来的某一天，它会成为传统双焦透镜之外的选择。
人眼睛里面的天然透镜使光线弯曲，在位于眼睛后部的视网膜上聚焦。如果眼睛有畸形或者不能正常完成这一生理功能，玻璃体就会帮着让光线经过一个称为折射的过程---这和一头淹在水里的棍子看起来弯曲是一个道理。透镜的折光度取决于透镜本身的精细形状和曲率。双焦透镜的主要原理是两个透镜被磨成一块，或者玻璃，或者塑料。 与此相反,这种新的电子透镜是平面的。它依照衍射原理聚光。衍射时，光波的波峰和波谷叠加时相互抵销，而波峰和波峰或者波谷和波谷叠加时相互加强。
据位于图森的亚利桑那大学光学科学家李国强（音）和Nasser Peyghambarian 以及他们的同事报道,这种新的透镜里面有一层液晶，夹在两层玻璃之间。玻璃的内层有一个电极安装在环形的透明电极，固定在一个榫头模型里面。施加电压在这两些电极中的任何一个都会起到加速的作用，这样光就可以通过透镜的那个部分。 这样,通过不同的环的光可以同步出来。
这听起来可能是不怎么好，但是，通过调节环上面的电压，使得对光线的削弱和加强作用使得它这样的平板能够对光进行聚集。所以通过简单地施加电压，他们可以让这种装置从一个透明的平板变为一个透镜。这就是本周他们在《美国科学院院报》上的报道。他们让这种透镜适合于老花镜，又能够通过电来实现开关控制，就像这些研究人员提供的一个原型那样。对于双焦透镜来说，这种新的电镜可以和一个标准透镜联合起来做成一个透镜，它的聚集能力在电路接通时会得以增强，李国强说。
与双焦镜头相比，“它的优点是，你可以获得整个视野更正的一个全面的区域”，哥伦比亚俄亥俄州立大学的视觉科学家Mark Bullimore这样说。这种镜头不仅可以和传统眼镜竞争，而且可以和隐形眼镜竞争。这种镜片可以通过外科手术植入眼睛。而且，Bullimore还说，“如果这项技术成熟了的话，我可以预见这将对某些病人具有强烈的吸引力。”
英文原文
'Letric Specs.
Carefully tuned voltages can change the focusing power of these prototype glasses (above) and bring a blurry image into focus.
Credit: PNAS
Bye Bye Bifocals
By Adrian Cho
ScienceNOW Daily News
3 April 2006
Here's the long and short of it: A lens that electronically switches its focus from far to near may someday provide an alternative to traditional bifocal lenses.
The natural lens in your eye is supposed to bend light rays and focus them on the retina at the back of the eye. If the eye is misshapen or not strong enough to do the job itself, glasses help bend the light rays through a process called refraction--the same one that makes a stick appear to kink when one end is submerged in water. Just how much a given lens bends light depends on its precise shape and curvature. Bifocals are essentially two lenses ground into a single piece of glass or plastic. In contrast, the new electronic lens is flat and focuses light through a phenomenon known as diffraction, in which light waves overlap either peak-to-trough to cancel one another out, or peak-to-peak to reinforce one another.
The new lens consists of a layer of material known as a liquid crystal, which is sandwiched between two thin sheets of glass, report optical scientists Guoqiang Li and Nasser Peyghambarian of the University of Arizona in Tucson and colleagues. The inner surfaces of the glass sheets are covered with circular transparent electrodes arranged in a bulls eye pattern. Applying a voltage to one of these electrodes affects the speed with which light can pass through that part of device. So light waves passing through different rings get out of synch with one another.
That may sound like a bad thing, but by adjusting the voltages on the rings, the researchers exploited the canceling and reinforcing effects to make the flat plates focus the light. So simply by applying the voltages, they could switch the device from a transparent plate to a lens, they report online this week in Proceedings of the National Academy of Sciences. That makes the lenses suitable for reading glasses that can switch on and off electronically, as the researchers demonstrated with a prototype. As for bifocals, the new technology could be combined with a standard lens to make one whose focusing power increases when the electricity is switched on, Li says.
Compared to bifocals, "the advantage to this is that you get a full field of view correction," says vision scientist Mark Bullimore of Ohio State University in Columbus. Such electronic lenses would have to compete against not only traditional glasses but also bifocal contact lenses and lenses surgically implanted in the eye. Still, Bullimore says, "if the technology were to mature, I can see where this might be an attractive option for some patients."
