Image fidelity for single-layer and multi-layer silver superlenses

Abstract

In response to increasing interest in the area of subdiffraction-limited near-field imaging, the performance of several different realizable and theoretical superresolving silver-based lenses is simulated for a variety of different input object profiles. A computationally-efficient T-matrix technique is used to model the lenses, which consist of layers of silver with total width of 40 nm sandwiched between layers of polymethyl methacrylate and silicon dioxide. The lenses are exposed to nonperiodic bright- and dark-slit input patterns, with feature size varied between 1 nm and 2.5 microm. The performance of the lenses is characterized in terms of transfer function, contrast profile, error profile, and input-to-output correlation. It is shown that increasing the number of layers in a lens increases the lens' transmission coefficients at high spatial frequencies; however, this does not always lead to better imaging performance. The main reasons for this are lens-specific resonances that distort features at certain spatial frequencies, and the increased attenuation of the DC component of transmitted images, which reduces image fidelity, particularly for dark-line features. This suggests that, to achieve optimum results, the design of the superresolving lens system should take into account the characteristics of the images that it is expected to transmit.

Two-Dimensional Sub-diffraction-limited Imaging by an Optimized Multilayer Superlens

“…In this regime, incorporation of additional layers improves transmission characteristics. However, these structures show large impedance mismatch, and compared to a single-layer superlens they do not always offer better resolving power [9]. Using these structures, subwavelength resolution can also be achieved at frequencies different from the plasmon resonances of the individual layers.…”

“…While this analysis reveals a lens's transmission coefficients over a range of spatial frequencies, it does not provide a measure of image-reconstruction capability, which is required for practical imaging [9]. Due to near-field operation, superlens performance is sensitive to the coupling between object and lens, but these interactions have not attracted considerable attention in the literature [14].…”

“…Subsequently, a simulated annealing (SA) algorithm [20] is applied as a robust global-optimization algorithm, to achieve a superlens structure with optimized parameters at a wavelength of 633 nm. In the optimization procedure, the correlation coefficient is used as a quantitative measure of the imaging performance of the lens [9,21].…”

Covered Image of Superlens

“…Pendry found that if the refractive index of a layer is exactly minus one, it can act as a perfect lens which has the ability to recover, in principle, all the subwavelength information of an object in the image domain [9]. This pioneering work has encouraged immense amounts of research to theoretically design [10][11][12][13][14][15][16][17][18][19][20][21][22][23] or experimentally fabricate [24][25][26][27][28][29][30] a super resolution imaging system. Although many well known experiments have made progress in trying to realize a superlens and some encouraging results have been reported, the main obstacle for the superlens to be applied to real application is that fabrication issues remain a challenge.…”

Reflectivity and Phase Control Research for Superresolution Enhancement via the Thin Films Mismatch

“…So far, many approaches of imaging beyond the diffraction limit with superlens have been reported [13][14][15][16][17][18]. The performance limit of the metallic superlens was associated with the intrinsic losses of metal.…”