Can researchers make a perfect optical lens?

Abstract

Perfect lens can break the diffraction limit by amplifying evanescent wave components emitted from objects and enable subwavelength imaging, which may potentially lead to the revolution of modern imaging technologies. This ground breaking feature has challenged the well-accepted wisdom on the role of evanescent waves in imaging, which has generated significant research interest from the scientific communities across different disciplines. However, it was also being strongly disputed at the beginning. The implementation of this lens would be technically rather difficult and challenging due to the absolute requirement of negative refractive indexed materials that are not available in nature. Artificial electromagnetic materials, widely known as metamaterials, with both electric and magnetic responses have been then proposed to simultaneously generate negative permittivity and permeability constants. Because of the issues of fabrication and loss, the perfect-lens effect was first demonstrated only in microwaves by a two-dimensional transmission line experiment using lumped circuit design with left-handed properties. For optics, which is more anticipated for applications, alternative lens designs have been developed to manipulate evanescent waves in different ways and also create subwavelength imaging. Design and experimental techniques and methodology have been intensively discussed in the literature to improve the fabrication efficiency and device performance. Significant progress has been achieved on subwavelength imaging inspired by the employment of metamaterials. However, there are still critically important technical or physical issues unsolved for all of the subwavelength lens scenarios proposed so far, which demand innovative ideas. In particular, it is still an unknown question that whether a perfect lens with negative refractive index could be made in optics. The promising future is indicated by the recent progress on the experiment for the fabrication of high-quality negative refractive index metamaterials. In this paper, from the historical and progressive aspects of perfect lens, we describe the perspective and outlook based on a survey of the available analysis of parametric and technological challenges imposed by this special lens.