Polished glass has been at the center of imaging systems for centuries. Their precise curvature enables lenses to focus light and produce sharp images, whether the object in view is a single cell, the page of a book, or a far-off galaxy.
Changing focus to see clearly at all these scales typically requires physically moving a lens, by tilting, sliding, or otherwise shifting the lens, usually with the help of mechanical parts that add to the bulk of microscopes and telescopes.
Now MIT engineers have fabricated a tunable “metalens” that can focus on objects at multiple depths, without changes to its physical position or shape. The lens is made not of solid glass but of a transparent “phase-changing” material that, after heating, can rearrange its atomic structure and thereby change the way the material interacts with light.
The researchers etched the material’s surface with tiny, precisely patterned structures that work together as a “metasurface” to refract or reflect light in unique ways. As the material’s property changes, the optical function of the metasurface varies accordingly. In this case, when the material is at room temperature, the metasurface focuses light to generate a sharp image of an object at a certain distance away. After the material is heated, its atomic structure changes, and in response, the metasurface redirects light to focus on a more distant object.
Source: “New “metalens” shifts focus without tilting or moving”, Jennifer Chu, MIT News Office