Turning light into sound can store fibre optic data

时间:2019-03-01 10:20:02166网络整理admin

By Jason Palmer A new way to store information inside a fibre optic cable by turning it into a high-frequency sound wave has been demonstrated by researchers in the US. While the technique can store information for just a tiny fraction of a second, the result could be good news for future optical computers and high-speed optical networks, both of which will need to tuck some data away for short periods while shuttling other information around. Currently, when information needs to be stored briefly in a fibre optic network, the optical signal is converted into an electronic one and then back again later. But this conversion process is prone to errors and dissipates energy as heat. And, as data rates increase in future, that heat produced may become more than cooling technology can handle. So engineers have been searching for alternative ways to store optical information. One approach involves temporarily trapping the information encoded in an optical signal within a soup of chilled atoms. However, this requires extremely low temperatures as well as a laboratory full of equipment. What’s more, it is limited by the wavelengths that can be used. Instead, Daniel Gauthier of Duke University in North Carolina, US, and his colleagues developed a method that uses the optical fibre itself as the storage medium. It exploits the fact that an optical fibre can be made to change density when exposed to an electric field, a phenomenon known as electrostriction. The electric field generated by an intense beam of light alters the density of a piece of optical fibre in a way that corresponds to the peaks and valleys of its waveform. Since this waveform is used to encode information, that information then becomes encoded in the density variation of the material too. In order to turn that density variation into a wave, Gauthier and colleagues sent two laser beams of slightly different wavelength through a fibre – one containing the original information and a second beam carrying no information. The two beams interfere, like the ripples on a pond, resulting in a relatively slow-moving pattern of density variations – essentially a high-frequency sound wave with the data encoded on it. This way, even after the light pulses pass through the fibre, it retains the slowly moving sound wave. To “read” this information, another light pulse is sent down the fibre, reversing the process. The high and low density regions in the sound wave are transferred back onto the pulse, which contains the original data. “It is an interesting idea,” says Robert Killey, and optical networking researcher at University College London, in the UK. “It works at any wavelength, at room temperature, and can use commercially available, low-cost materials.” So far the method requires high-power pulses, and storage times are on the order of 10 nanoseconds, just enough to buffer small amounts of information. But Gauthier is convinced that new fibre materials could be used to store information for longer and that require less power. Journal reference: Science (DOI: