Optical Circuits Up To 100 Times Faster Than Electronic Circuits

Optical circuits are set to revolutionize the performance of many devices. Not only are they 10 to 100 times faster than electronic circuits, but they also consume a lot less power. Within these circuits, light waves are controlled by extremely thin surfaces called metasurfaces that concentrate the waves and guide them as needed. The metasurfaces contain regularly spaced nanoparticles that can modulate electromagnetic waves over sub-micrometer wavelength scales.

Metasurfaces could enable engineers to make flexible and ultra-thin optics for a host of applications, ranging from flexible tablet computers to solar panels with enhanced light-absorption characteristics. They could also be used to create flexible sensors for direct placement on a patient’s skin, for example, in order to measure things like pulse and blood pressure or to detect specific chemical compounds.

The catch is that creating metasurfaces using the conventional method, lithography, is a fastidious process that takes several hours and must be done in a cleanroom. But EPFL engineers from the Laboratory of Photonic Materials and Fiber Devices (FIMAP) in Switzerland have now developed a simple method for making them in just a few minutes at low temperatures—or sometimes even at room temperature—with no need for a cleanroom. The EPFL‘s School of Engineering method produces dielectric glass metasurfaces that can be either rigid or flexible. The results of their research appear in Nature Nanotechnology.

The new method employs a natural process already used in : dewetting. This occurs when a thin film of material is deposited on a substrate and then heated. The heat causes the film to retract and break apart into tiny nanoparticles.

Dewetting is seen as a problem in manufacturing—but we decided to use it to our advantage,” says Fabien Sorin, the study’s lead author and the head of FIMAP.

With their method, the engineers were able to create dielectric glass metasurfaces, rather than metallic metasurfaces, for the first time. The advantage of dielectric metasurfaces is that they absorb very little light and have a high refractive index, making it possible to modulate the light that propagates through them.

Source: https://phys.org/

How Solar Cells Absorb 20 % More Sunlight

Trapping light with an optical version of a whispering gallery, researchers at the National Institute of Standards and Technology (NIST) have developed a nanoscale coating for solar cells that enables them to absorb about 20 percent more sunlight than uncoated devices. The coating, applied with a technique that could be incorporated into manufacturing, opens a new path for developing low-cost, high-efficiency solar cells with abundant, renewable and environmentally friendly materials.

Illustration shows the nanoresonator coating, consisting of thousands of tiny glass beads, deposited on solar cells. The coating enhances both the absorption of sunlight and the amount of current produced by the solar cells

The coating consists of thousands of tiny glass beads, only about one-hundredth the width of a human hair. When sunlight hits the coating, the light waves are steered around the nanoscale bead, similar to the way sound waves travel around a curved wall such as the dome in St. Paul’s Cathedral in London. At such curved structures, known as acoustic whispering galleries, a person standing near one part of the wall easily hears a faint sound originating at any other part of the wall.

Using a laser as a light source to excite individual nanoresonators in the coating, the team found that the coated solar cells absorbed, on average, 20 percent more visible light than bare cells. The measurements also revealed that the coated cells produced about 20 percent more current.

Source: https://www.nist.gov/