Speed Limit for Optomechanical Metamaterials

There is a speed limit on how fast the properties of light can be changed with the help of specially designed materials. This new understanding can point the way forward for the next generation of consumer electronics, such as smart watches, screens and glasses.​ ​(Source: S. Viaene & V. Ginis)

Speed limits apply not only to traffic. There are limi­tations on the control of light as well, in optical switches for internet traffic, for example. Physicists at Chalmers Univer­sity of Technology now under­stand why it is not possible to increase the speed beyond a certain limit and know the circum­stances in which it is best to opt for a different route.

Light and other electro­magnetic waves play a crucial role in almost all modern elec­tronics. In recent years researchers have developed opto­mechanical meta­materials which overcome the limi­tations inherent in natural materials, in order to control the proper­ties of light with a high degree of precision. For example, what are termed optical switches are used to change the colour or inten­sity of light. In internet traffic these switches can be switched on and off up to 100 billion times in a single second. But beyond that the speed cannot be increased any further. These unique specia­lity materials are also subject to this limit.

“Researchers had high hopes of achieving higher and higher speeds in optical switches by further deve­loping opto­mechanical meta­materials. We now know why these materials failed to out­compete existing tech­nology in internet traffic and mobile communi­cation networks,” says Sophie Viaene, a nano­photonics researcher at the Depart­ment of Physics at Chalmers.

To find out why there are speed limits and what they mean, Viaene went outside the field of optics and analysed the non-linear dynamics in her doctoral thesis. The con­clusion she reached is that it is neces­sary to choose a different route to circum­vent the speed limits: instead of controlling an entire surface at once, the inter­action with light can be controlled more effi­ciently by mani­pulating one particle at a time. Another way of solving the problem is to allow the specia­lity material to remain in constant motion at a constant speed and to measure the varia­tions from this movement.

But Viaene and her super­visor Philippe Tassin say that the speed limit does not pose a problem for all appli­cations. It is not necessary to change the proper­ties of light at such high speeds for screens and various types of displays. So there is great potential for the use of these specia­lity materials here, since they are thin and can be flexible. Their results have deter­mined the direc­tion researchers should take in this area of research. The pathway is now open for the ever smarter watches, screens and glasses of the future.

“The switching speed limit is not a problem in appli­cations where we see the light, because our eyes do not react all that rapidly. We see a great potential for opto­mechanical meta­materials in the develop­ment of thin, flexible gadgets for inter­active visuali­sation tech­nology,” says Tassin. (Source: Chalmers U.)

Reference: S. Viaene et al.: Do Optomechanical Metasurfaces Run Out of Time?, Phys. Rev. Lett. 120, 197402 (2018); DOI: 10.1103/PhysRevLett.120.197402

Link: Condensed Matter Theory, Dept. of Physics, Chalmers University of Technology, Göteborg, Sweden

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