Becoming invisible is something that more than one of us has dreamt about. It’s been a long time since scientists started looking for a way to make matter invisible, but this time they’re working more on the manipulation of light and its interaction with objects. Today, a team of researchers from the National Institute for Scientific Research (INRS) in Montreal seems to have taken a promising step in this very field.
In this study published in the journal Optica, specialists explain that they have developed a new approach to make objects invisible. This technology is one of the first to manipulate the frequency of light waves which interact with an object. The purpose of this manoeuvre is to shape the light before and after the object moves, so that we can’t see any change. To understand this, we need to look at how our vision works normally.
What is the link between frequency and colour?
When you see an object, the information that goes to your retina is actually a light wave, which has been reflected to reach the eye. This wave has a certain frequency that our brain interprets and then shows us a colour. If an object appears blue to us, it is because it has absorbed all the visible components of the light, and it has reflected the only frequency we associate with that colour.
To make an object invisible, researchers at INRS in Montreal took advantage of this mechanism. They framed the object to hide with two filters, which modified the light frequency. The first filter shapes the wave so that its frequency range is not one of the colours that the object will reflect. The modified beam will then cross the object without being altered. The second output filter has the role of reconstructing the original light.
Therefore, from the viewpoint of the observer, the light hasn’t undergone any change between the light source and their eye and they can’t see the object. This method is easily applicable to two-dimensional materials that don’t absorb light that they can’t reflect. This study has certain limitations but is still a real advance compared to other camouflage technologies.
What is the advantage of this approach over the other attempts?
Other methods have worked well, only under much more specific conditions. They often involved circumventing the object by optical methods, where the gaze must then be directed in a specific way for the effect to happen. The object is therefore only invisible in one direction, amongst other issues.
'Conventional cloaking solutions rely on altering the propagation path of the illumination around the object to be concealed; this way, different colours take different amounts of time to traverse the cloak, resulting in easily detectable distortion that gives away the presence of the cloak,' explains Luis Romero Cortes, researcher for INRS, whilst speaking to The Optical Society of America.
'Our proposed solution avoids this problem by allowing the wave to propagate through the target object, rather than around it , while still avoiding any interaction between the wave and the object,' he adds. The other advantage of this new method is its theoretical validity for an object illuminated by the sun in all directions. It could also eventually be used to make three dimensional objects invisible, which could bring us ever so slightly closer to the dream of many Harry Potter readers: having a cloak of invisibility.
Applying it to the field of telecommunications
Nevertheless, other more realistic applications are already being considered. The researchers claim that his approach could be used to secure data that is transmitted by fibre optics, for example. By hiding some of the changes made to the wave in the fibres, the information it contains would be out of reach to potential third parties hoping to steal it.
The general concept of frequency redistribution in a wave could also have a huge impact. It would increase the density of information carried by each wave, which is pretty pragmatic, but not half as exciting as the idea of an invisibility cloak.