Loss-free and active optical negative-index metamaterials

Abstract

The recently emerged fields of metamaterials and transformation optics promise a family of exciting applications such as invisibility, optical imaging with deeply subwavelength resolution and nanophotonics with the potential for much faster information processing. The possibility of creating optical negative-index metamaterials (NIMs) using nanostructured metal-dielectric composites has triggered intense basic and applied research over the past several years. However, the performance of all NIM applications is significantly limited by the inherent and strong energy dissipation in metals, especially in the near-infrared and visible wavelength ranges. Generally the losses are orders of magnitude too large for the proposed applications, and the reduction of losses with optimized designs seems to be out of reach. One way of addressing this issue is to incorporate gain media into NIM designs. However, whether NIMs with low loss can be achieved has been the subject of theoretical debate. Here we experimentally demonstrate that the incorporation of gain material in the high-local-field areas of a metamaterial makes it possible to fabricate an extremely low-loss and active optical NIM. The original loss-limited negative refractive index and the figure of merit (FOM) of the device have been drastically improved with loss compensation in the visible wavelength range between 722 and 738 nm. In this range, the NIM becomes active such that the sum of the light intensities in transmission and reflection exceeds the intensity of the incident beam. At a wavelength of 737 nm, the negative refractive index improves from -0.66 to -1.017 and the FOM increases from 1 to 26. At 738 nm, the FOM is expected to become macroscopically large, of the order of 10(6). This study demonstrates the possibility of fabricating an optical negative-index metamaterial that is not limited by the inherent loss in its metal constituent.

Hyperlenses and metalenses for far-field super-resolution imaging

“…First, material loss is an intrinsic property of metamaterials at optical wavelengths, limiting the ultimate resolution of the lens, as well as the signal transmission efficiency, especially when resonant elements are involved. To mitigate the loss problem, several approaches may provide solutions, such as compensating for loss in the metal by addition of a gain medium in dielectrics 96 , searching for better plasmonic materials among existing elements, band structure engineering or materials doping or alloying 97,98 . Second, the object has to be placed in the near field of the lens to make use of the evanescent waves that normally decay away from the object, although the image can be projected and detected in the far field.…”

Spectrum of Cherenkov Radiation in Dispersive Metamaterials With Negative Refraction Index

“…The typical value ω pe ≈ 2 · 10 16 s −1 ([24], p.44). In a metamaterial with fishnet structure [12] we consider the bunch of electrons (charge q) moving with a velocity parallel to x direction: v 0 e x and the density of the bunch is defined by the anisotropic Gaussian as f (r, t) = W −3 exp{−[(x−v 0 t) 2 …”

“…We consider a general 3D case in Cartesian coordinates since such a geometry normally is used on the optical investigations [12]. We examine a spatially averaged metamaterial composition: nanostructured metal-dielectric composites (fishnet), similarly that was used in the experiment [12].…”

“…The investigations of optical negativeindex [1] metamaterials (NIM) using the nanostructured metaldielectric composites already have led to both fundamental and applied achievements that have been realized in various structures [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21].…”

“…The negative real part of the refractive index is typically observed together with strong dispersion, so that in general the absorption cannot be disregarded. Recently, authors of [12] have demonstrated that the incorporation of gain material in a metamaterial allows fabricating very low-loss NIM. Thus, the original loss-limited negative refractive index can be drastically improved with loss compensation in the visible wavelength range [4].…”