Tiny lens on a chip promises bigger bandwidth

Lundberg lens could speed up fiber optics

British scientists have developed a microscopic lens attached to a silicon chip. Known as a Luneburg lens, the device can evenly focus light from all directions, which opens the potential for greatly increasing bandwidth and reducing signal noise in fiber optics and chip-based Fourier optics.

Developing Luneburg lenses has proven difficult. Physics World notes that while the concept was proposed more than 60 years ago, they require such a high refractive index (the lens is supposed to focus light equally well no matter what direction the light comes from) that they were impractical to make with current technologies. One of the challenges in making a practical Luneburg lens was that it is currently not possible to achieve the level of refractive index contrast by doping a material.

The lens created by a team of scientists at the University of Saint Andrews is a microscopic piece of silicon. Physics World describes it as being shaped like a contact lens sandwiched between two larger polymer and silica layers on a substrate. When a beam of light at specific wavelength shines on the device, it follows the interface between the polymer and silica. When the light reaches the lens, it becomes highly focused. According to Physics World, the geometry of the waveguide focuses the beam onto a spot 3770 nanometers in diameter.

But while the technique has great potential, researchers caution that the work is still highly experimental. Indeed, scientists still have more work ahead of them. Physics World notes that in an ideal Luneburg lens, the focused spot would be much smaller, on the order of 800 nanometers in diameter.

In a related note, a research team at the University of California at Berkeley have developed a Luneburg lens capable of focusing plasmons — waves of electrons — in metals.

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