Remember the invisibility cloak of Harry Potter? What if you get one? Sounds bizarre? Well, this may soon become a reality! No, not by going to Hogwarts School of Witchcraft and Wizardry, and conjuring up such a cloak… But by conjuring up the unimaginable powers of transformation optics!
Transformation optics is manipulating or controlling the behaviour and properties of light and its interaction with matter at all distances – from macro- to the nano-scale. But, how do you manipulate light?
Light is an electromagnetic radiation. As all materials interact with light and other electromagnetic fields, we can control light in various ways by using these materials. This forms the basis of optical devices. For example, a lens is a device, which causes rays of light to either converge or diverge, that is, changes the refractive index.
Refraction is the bending of electromagnetic waves, including light, when passing from one material into another (Remember the experiment when a stick placed in a glass of water appears bent when seen from outside?). Every material, including air, has a refractive index – how much light will bend and the speed of light while passing through the material. Natural materials have refractive indices greater than one, or positive indices.
Transformation optics goes beyond this limitation by using a new class of materials, which are able to guide and control light on all scales, including the scale of nanometres (billionths of a metre). These are called metamaterials.
Meta in Greek means beyond. So, the term ‘metamaterial’ means something that is beyond what already exists in nature. Metamaterials are artificial structures with properties beyond those available in naturally occurring materials. They are engineered out of meta-atoms (artificial atoms), which are smaller than even the wavelengths of light! This means, that unlike natural materials, metamaterials can reduce the refractive index to less than zero – negative refractive index.
Thus, we can control light even at the nanoscale level by using these metamaterials. What can we do with this ‘power’?
Read the box below.
The possibilities are endless. Here are some of them.
Invisibility cloak may become a reality with transformation optics. It would be an electromagnetic cloak, which would bend light around itself and not absorb any. This is similar to the flow of water around a stone. It would make both the cloak and the object hidden inside it invisible!
In addition to curving light around an object, light can also be concentrated in an area. This might be used for collecting sunlight in solar energy applications.
Super-fast computers, which would use light instead of electronic signals to process information, can curb all limitations of present-day computing. Such ‘photonic’ computers would contain special transistor-size optical elements made from metamaterials.
Planar magnifying hyperlens can be designed. These would drastically improve the power and resolution of light microscopes. The focus can be made down to the nanoscale level to actually see molecules like DNA and viruses that are now simply too small to be seen! Hyperlens would also restore evanescent light, the loss of a portion of the light transmitting fine details of an image as it passes through a lens. This would quadruple the powers of lenses and imaging systems.
Exciting, isn’t it? With the advent of metamaterials and advancements in the field of transformation optics, we can envision entirely new classes of optical devices, invisibility cloaks being just one example. The possibilities are unimaginable. And science fiction may soon become science fact!