Major Advance in Flat Lenses From Harvard

Hat Tip: ePhotozine  (Original story at Digital Trends.)

Harvard has created a prototype flat lens capable of successfully focusing multiple wavelengths of light at the same point.  Harvard refers to the planar lens design as an Achromatic metasurface lens.

Planar is just fancy language for flat.  Achromatic when applied to lenses means the light is not separated into its constituent colors.  Metasurface refers to the surface of a metamaterial, which is a material that has a structure that produces results that can't be produced by natural materials.  It's geek speak to describe how the lens works.

Ordinary lenses work by utilizing a curved surface to bend light.  The drawback with this method is that different wavelengths of light (perceived as different colors) bend different amounts when passing through these lenses.  This forces camera lens manufacturers to utilize multiple components to correct for this splitting of the different colors. 

(The Harvard news page has an illustration if you want a visual representation.)

Having to use multiple lenses increases the complexity of lens design and increases the amount of glass needed when manufacturing camera lenses.  This increases the cost and weight of quality lenses.

Instead of utilizing curved glass to bend light, the Harvard design utilizes a flat lens with "antennas" on its surface.  These antennas are what make the lens a metamaterial.  Light bends as a result of hitting the antenna.

The initial prototype introduced in 2012 was only capable of bending a single wavelength of light.  The research team addressed this limitation by utilizing antennas of different sizes/shapes.  Each shape or size targets a specific wavelengths of light.  The lens is capable of producing a photographic image by targeting the wavelengths corresponding to red, green and blue as these are the colors recorded by digital sensors.  (The other wavelengths are ignored by the sensor and don't need to be effected by the lens.)

The result is a single lens capable of replacing the set of three lenses used in current lens design.

At the very least, this would result in much lighter lenses.  It might also result in less expensive lenses as less material needs to be used.


Judging from the images on the Harvard site, the antennas appear to run parallel across the face of the lens.  This would result in light being bent in a single direction only.  This would not necessarily prevent the technology from being used for camera lenses.  The easiest fix would simply be using a second lens set perpendicular to the first.

The lenses would need to be set so the antennas parallel to the edges of the sensor to ensure light hit the sensor correctly.  This is a consideration not required by traditional round lenses.