A light wave undulates in different ways – known as its polarisation. This polarisation of light is changed by the material it passes through and can be used to better understand nano-scale worlds in terms of drug chemistry and quantum electronics.
Switching polarisation can also be used to transfer digital information along fibre optic cables.
The electronic methods used to control the light polarisation in such applications is reaching its physical speed limit but the research team at King’s have said that they have managed to overcome this problem, allowing polarisation to be switched at timescales of less than a millionth of a millionth of a second - hundreds of times faster than current electronic methods.
According to the team this will allow us to ‘see’ very fast nano-scale processes such as chemical reactions for the first time, by illuminating them with rapidly changing light and better understand the difference in formation of nasty chemicals and life-saving drugs, and as such allowing new materials to be studied.
This could also represent a major advance in data transfer speeds. By rapidly changing the polarisation of light - to represent a one or a zero - data can be passed along fibre optic cables and help meet growing data sharing demands driven by streaming and cloud services.
The team designed nano-structured materials that can control light polarisation using light itself – a technique known as ‘all-optical polarisation control’.
These nano-structures are known as metamaterials: materials with optical properties not available in nature. These thin, lightweight materials are constructed from elements smaller than a thousandth of a millimetre in order to create exotic optical effects.
In this case, the metamaterial is constructed of gold nano-particles. A high intensity light pulse is fired into the metamaterial, injecting energy into electrons in gold particles, which in turn changes the refractive index of the material.
A second pulse is fired at the metamaterial at the same time. As this pulse passes through the material, the change in refractive index changes its polarisation. This all happens instantaneously, allowing polarisation to be changed trillions of times per second.
By simply shining two beams of light through the material, one beam is able to control the polarisation of the other at ultrafast speed.
The effect can also be observed even with one beam, whereby the polarisation of the light beam transmitted through the metamaterial changes with the intensity. This process is similar to Polaroid sunglasses which adjust themselves to remove glare whenever it is too much sunlight.
According to Luke Nicholls, the PhD student who carried out these experiments, “With everybody using more and more data, streaming videos, music and sharing pictures, we are fast approaching a point where the current internet infrastructure will not be able to cope. All-optical control provides an answer to this looming problem and hopefully sees an end to staring at the infuriating buffer wheel.”
Control of light at such short time scales could also feed into quantum information processing, where controlling the polarisation of light is integral for building successful quantum computing devices.
Professor Anatoly Zayats of King’s College concludes: “This effect opens up many opportunities for new applications. The faster you can control light polarisation, the faster you can use light to transmit data and make measurements.”
The paper, Ultrafast synthesis and switching of light polarization in nonlinear anisotropic metamaterials, is published in Nature Photonics.
