Introducing the metamaterial roadmap

The XXI century is the century of nano-materials. Nearly 60 years ago Richard Feynman, in his famous lecture 'There's Plenty of Room at the Bottom' [1], wrote that 'Up to now, we have been content to dig in the ground to find minerals... what would happen if we could arrange the atoms one by one the way we want them?'. In essence he profesied the field of metamaterials by observing that '... when we have some control of the arrangement of things on a small scale we will get an enormously greater range of possible properties that substances can have, and of different things that we can do'. Remarkably he also predicted two main nanofabrication technologies used for constructing metamaterials today. 'A source of ions, sent through the [electron] microscope lenses in reverse, could be focused to a very small spot. We could write with that spot ...'. Indeed, this is an accurate description of the focused ion beam milling technology that we use today to create nanophotonic and metamaterial devices. He also talked—far ahead of its time—about nanoimprint technology; 'We would press the metal into a plastic material and make a mold of it, then ... [evaporate] gold ... and then look through it with an electron microscope!'. Furthermore, it is rarely noticed that Richard Feynman even envisaged one of most exciting application of metamaterials in what we now call the 'Lasing Spaser' [2], a coherent array of metamaterial emitters, a metamaterial laser; 'Consider ... a piece of material in which we make little coils and condensers 1000 or 10 000 A in a circuit ... over a large area, with little antennas sticking out at the other end ... to emit light from a whole set of antennas ... ?'. About 15 years ago the metamaterials approach to changing and engineering unique electromagnetic properties became a dominant influence in photonics. Metamaterials were first developed as artificial media structured on a size scale smaller than the wavelength of external stimuli. They showed novel, now well-understood electromagnetic properties, such as negative index of refraction or optical magnetism, allowing devices such as optical cloaks and super-resolution lenses to be realized. Tuneable, nonlinear, switchable, gain-assisted, sensor and quantum metamaterials appeared and dramatically increased the potential for device integration of metamaterial technology, which is now widely researched. The next grand challenge is to develop metamaterials with on-demand optical properties that may be independently controlled at any given point in space and at any moment of time [3]. This will allow not only modulation of light's intensity or phase, but will offer control of the wavefront and the nearfield of electromagnetic radiation, thus enabling reconfigurable electromagnetic space and multi-channel data processing in meta-systems. The 'Roadmap on optical metamaterials' [4] that Journal of Optics presents in this issue is written by recognized movers and shakers in the field and aims to expose views of the leading groups on the development of metamaterial technologies in years to come. You will be impressed by the variety and depth of the ideas that this field is generating. Enjoy the reading.