Data transfer via laser
October 20, 2015
Why are lasers not used more widely? The answer lies largely in atmospheric interference - and the technology is also prohibitively expensive. So a group of scientists at the Brno University of Technology in the Czech Republic have been working on a project to make laser communication cheaper and more reliable.
The last mile
"What we're talking about is 'the last mile' - this is last-mile technology," Professor Otakar Wilfert told DW. He is head of the Optical Communication team at the Department of Radio Electronics at Brno's University of Technology.
To transmit data over the last mile, fiber optic links are usually used. But in some situations it's not possible to use a fiber optic network, for example in the center of a town," he explained. "In this case, fiberless optical communication - like laser communication - can be used," said Professor Wilfert. He is leading the research into a field called free-space optical communication (FSO) - with a view towards making it more attractive to the telecommunications market.
In fact, beaming data via laser has a number of advantages. Unlike Wi-Fi or cable communication, it's virtually impossible to hack in to, making it extremely secure for government or military use.
Safe for humans…and birds
It also offers similar bit rates to fiber-optic cables - up to 1Tb/s. And remarkably, unlike Wi-Fi, it's not subject to special licensing. The lasers used here are in the infra-red spectrum, so they don't risk blinding people or birds and animals.
But there are obstacles. "When there is some obstruction in the way of the laser beam, you can see that we lose the signal. The signal is renewed after the obstruction is taken away," said Lucie Hudcova, assistant professor at the Department of Radio Electronics, as she demonstrated how a full color video image could be transmitted in real-time using a laser. Until you pass your hand in front of it.
Atmospheric attenuation
"We can observe effects like atmospheric turbulence or attenuation in the atmosphere. Strong turbulence or strong attenuation caused for instance by fog or snow can interrupt the signal," she explained to DW.
Professor Wilfert's research in Brno is aimed at finding exactly the right strength and wavelength of laser – and developing new technology – to make sending data via laser economically viable. "These links are not very cheap," Peter Barcik, a PhD student working on the project, told DW.
"So we would like to make them simpler, but at the same time the technology has to be robust enough," Barcik said.
Further than Wi-Fi
Distance is one limitation - the laser transceivers can beam data at each other over a maximum distance of about 3.5 kilometers. However that's still considerably better than radio signals such as Wi-Fi, and the transceivers are both portable and fully optical with no electrical circuits. So they could, for example, be placed on two buildings in the aftermath of an earthquake to quickly restore digital communication where data cables have been severed.
Indeed, laser communications' proponents say the real potential of the technology could be realized when it is used in concert with other means of communication. "I think it will exist together with the existing technologies. It will complement them," said Martin Slanina, deputy director of the University's Six Research Center - a research group focused on wireless communication.
Backbone connections
"Laser communication as a point-to-point solution is perfect for some backbone connections. It's perfect for covering some more distant areas. And it's also perfect for connecting two buildings in the city when you cannot easily dig under the ground because it's also very expensive," he told DW.
In fact the whole field of using light to transmit information is underdeveloped. "You can imagine: street lamps, lighting in a room, traffic lights - they're all LEDs and you can - in theory - use these devices for communication," said Ales Dobes, a researcher specializing in a related field called Visible Light Communication.
Old-new technology
The idea of using light to transmit data isn't new. But some might be surprised to hear just how old it really is. The first such device was something called a photophone, which transmitted an audio recording on a beam of light over a distance of 213 meters. Its inventor? Alexander Graham Bell in 1880. The technology is there. It just needs to be perfected.