The science of optics has revealed the scale and detail of the universe for centuries. With the right piece of glass, you can look at a distant galaxy or the wiggling flagella on a single bacteria. But lenses need to focus — they need to move. Engineers at MIT have developed a new type of “metalens” that can shift focus without any moving parts. This could change the way we build devices such as cameras and telescopes.
Currently, focusing a lens on objects requires the glass to move in some capacity, and that adds complication and bulk. That’s why, for example, high-zoom camera lenses have been so slow to come to smartphones — there’s just no room to add movable lens elements. It’s also why smartphones that do have optical zoom use multiple fixed lenses. For example, the new Samsung Galaxy S21 Ultra has 13, 26, 70, and 240mm lens equivalents in its giant camera array.
The metalens developed at MIT can focus on objects at multiple distances thanks to its tunable “phase-changing” material. When heated, the atomic structure of the material rearranges, allowing the lens to change the way in which it interacts with light. The design currently operates in infrared, but this is just a first step.
Readers of a certain age might have interacted with a similar phase-changing material on rewritable CDs and DVDs. This technology, now all but extinct, relies on a material called GST that contains germanium, antimony, and tellurium. When heated with laser pulses, GST can switch between transparent and opaque, allowing optical drives to write and delete data.
The metalens has a similar material called GSST — it’s the same stuff with the addition of selenium. This new material has a more ordered, crystalline structure that is just 1 micrometer thick. It’s etched onto various microscopic structures (see above), all of which refract light differently. The researchers call this a “metasurface.” At room temperature, the lens focuses on a nearby target. When heated, the optical properties of the metasurface change, and it focuses on a more distant target.
So, that’s a dynamic lens without any moving parts. It’s just a proof of concept right now, but it’s a very cool concept. The team believes that tunable metalens technology could eventually lead to more compact and reliable telescopes, microscopes, and yes, better smartphone cameras.
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