Far-field imaging beyond diffraction limit using single sensor in combination with a resonant aperture

Cascaded DBR plasmonic cavity lens for far-field subwavelength imaging at a visible wavelength

We experimentally demonstrate a novel cascaded plasmonic superlens, which can directly image subwavelength objects with magnification in the far field at a wavelength of 640nm. The lens consists of two plasmonic slabs. One is a plasmonic cavity lens used for near-field coupling, and the other one is a planar plasmonic lens for phase compensation and thus, image magnification. To tune the performance wavelength to visible and to enhance the near-field transmission, distributed Bragg reflectors are integrated to the plasmonic cavity lens around the lens center, forming additional lateral cavities for surface waves. In this article, we first show numerical results about the working principle and the performance of the lens. Then, we demonstrate the imaging performance of a fabricated superlens experimentally. The fabricated superlens exhibits a lateral resolution down to 200 nm at the wavelength of 640 nm observed in the far field. Compared to our earlier design, shift invariance is achieved with the current approach. Our results could open a way for designing and fabricating novel miniaturized plasmonic superlenses in the future.

Freeform engineered disordered metalenses for super-resolution imaging and communication

Effective transmission of information through scattering media has been of great importance in imaging systems and beneficial to high capacity wireless communication. Despite numerous attempts to achieve high-resolution sub-diffraction-limited imaging through employing the engineered structures such as the so-called metamaterials or utilizing techniques like time reversal methods, the proposed ideas suffer from the fundamental limitations for design and practical realization. In this paper, we investigate disorder-based engineered scattering structures and introduce a novel technique for achieving super-resolution based on designing and employing engineered all-dielectric medium. We show that disorder in the proposed design can be exploited to significantly modify the information content of scattered fields in the far-field region. Under the presence of the designed structures, using computational methods, signals associated with ultra sub-wavelength features of the illuminating sources can be enhanced and extracted from the far-field image. Not only can the presented approach lead to remarkable enhancement of resolution in such systems, but also orthogonal transmission channels are attainable when the closely-packed sources are excited properly. The latter provides a new scheme for encoding and multiplexing signals leading to the enhancement of information capacity in emerging information processing systems. The design procedure and physical constraints are studied and discussed.

Single-shot and single-sensor high/super-resolution microwave imaging based on metasurface

Real-time high-resolution (including super-resolution) imaging with low-cost hardware is a long sought-after goal in various imaging applications. Here, we propose broadband single-shot and single-sensor high-/super-resolution imaging by using a spatio-temporal dispersive metasurface and an imaging reconstruction algorithm. The metasurface with spatio-temporal dispersive property ensures the feasibility of the single-shot and single-sensor imager for super- and high-resolution imaging, since it can convert efficiently the detailed spatial information of the probed object into one-dimensional time- or frequency-dependent signal acquired by a single sensor fixed in the far-field region. The imaging quality can be improved by applying a feature-enhanced reconstruction algorithm in post-processing, and the desired imaging resolution is related to the distance between the object and metasurface. When the object is placed in the vicinity of the metasurface, the super-resolution imaging can be realized. The proposed imaging methodology provides a unique means to perform real-time data acquisition, high-/super-resolution images without employing expensive hardware (e.g. mechanical scanner, antenna array, etc.). We expect that this methodology could make potential breakthroughs in the areas of microwave, terahertz, optical, and even ultrasound imaging.

Nanofocusing beyond the near-field diffraction limit via plasmonic Fano resonance

The past decade has witnessed a great deal of optical systems designed for exceeding the Abbe's diffraction limit. Unfortunately, a deep subwavelength spot is obtained at the price of extremely short focal length, which is indeed a near-field diffraction limit that could rarely go beyond in the nanofocusing device. One method to mitigate such a problem is to set up a rapid oscillatory electromagnetic field that converges at the prescribed focus. However, abrupt modulation of phase and amplitude within a small fraction of a wavelength seems to be the main obstacle in the visible regime, aggravated by loss and plasmonic features that come into function. In this paper, we propose a periodically repeated ring-disk complementary structure to break the near-field diffraction limit via plasmonic Fano resonance, originating from the interference between the complex hybrid plasmon resonance and the continuum of propagating waves through the silver film. This plasmonic Fano resonance introduces a π phase jump in the adjacent channels and amplitude modulation to achieve radiationless electromagnetic interference. As a result, deep subwavelength spots as small as 0.0045λ(2) at 36 nm above the silver film have been numerically demonstrated. This plate holds promise for nanolithography, subdiffraction imaging and microscopy.