Alessandro Tuniz and colleagues at the University of Sydney have designed a fibre that would be invisible over a range of colours. And because of recent developments in ways to draw hybrid materials into fibres, their proposal may be relatively straightforward to put into practice.
Such fibres could lead to interesting effects in art, architecture and fashion. They are also being studied in the broader context of building cheap, next-generation devices with special optical properties, such as fibre-based super-lensing which improves the resolution limit of microscopes. And the fibres could also provide support for optical elements but without optical distortion.
In recent years, several researchers have developed ways to cloak objects with metamaterials. They are designed to interact with particular wavelengths of light, bending them around the objects which then cannot be seen.
The new approach, however, creates a fibre that would actually be invisible, rather than hidden.
Design of an Optically Invisible Metamaterial Fibre
Alessandro Tuniz, Boris T. Kuhlmey, Parry Chen and Simon C. Fleming
Institute of Photonics and Optical Science (IPOS)
School of Physics, University of Sydney, NSW 2006, Australia
We present a simple design of an invisible metamaterial fibre operating at optical frequencies, which could be potentially fabricated using existing fibre drawing techniques.
Abstract (introduction and conclusion):
In recent years a number of approaches have been investigated to achieve electromagnetic invisibility, including cloaking through transform optics or plasmonic resonances . Here we discuss metamaterials that are themselves invisible, as opposed to possessing cloaking properties. Recent proposals of achieving optical transparency are based on alternating layers of natural materials and doublenegative metamaterials [2, 3] and transformation optics . Here we propose a much simpler approach in which optical transparency is achieved by designing a metamaterial with effective refractive index that matches the surroundings. Our structure is inspired by recent progress in using fibre drawing techniques to fabricate metal/dielectric structures, either via direct co-drawing, in which a macroscopically sized metaldielectric preform is heated and reduced in size by several orders of magnitude [5, 6], or via pumping liquid metal into existing micro- and nano- structured holey photonic crystal fibres (PCFs) . Using such techniques arrays of subwavelength metallic cylinders surrounded by a dielectric can be achieved, and as holey fibres containing feature sizes down to 30nm have been reported , there is hope that that the cost effective, large scale production of optical metamaterials (requiring metal features with sub 100nm size) is within reach of such fibre drawing techniques. Indeed drawing has significant advantages over other fabrication approaches such as lithographic techniques which are restricted to near two dimensional samples and cannot produce more than a few cm2 of metamaterial at a time . In contrast, a single inexpensive fibre perform of a few cm3 can be drawn into kilometres of nanostructured fibre, which can then be in principle be assembled into three dimensional metamaterials.
Fibre geometries impose the constraint of longitudinal uniformity. It has been recently shown, however, that important functionality can be realised with fibre-based metamaterials, such as low-loss mid-IR waveguiding , sub-wavelength waveguiding  and hyperlensing . Here we propose another interesting structure that can be fabricated via drawing of metal cylinders in a dielectric – the optically invisible fibre.
In conclusion, we have designed and characterised a metamaterial fibre which exhibits a strong reduction in scattering cross section compared to metal and dielectric cylinders of equivalent size. By changing the constituents or their filling, the design procedure can be extended to create invisible fibres at any optical wavelength, or create fibres with other arbitrary permittivity between that of the background and of the metal. By design, our device operates optimally at a given wavelength under TE polarization and normal incidence, yet excellent performance is maintained for ~10nm of bandwidth and a significant reduction in visibility over 100nm bandwidth. Optical parameters obtained from extraction procedures give a good estimate of the total scattering cross section. We believe such a structure can be fabricated within the foreseeable future by extending existing fibre drawing techniques. While being harder to fabricate, our design approach could be extended to produce 3-dimensional optically invisible structures, such as spheres, which would have a much wider tolerance on incident angle and polarization.
This material is based on research sponsored by the Air Force Research Laboratory, under Agreement No. FA2386-09-1- 4084. B.T.K. acknowledges support from an Australian Research Council Future Fellowship.
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Alessandro Tuniz, email@example.com