Super-resolution Lens Research Articles

Water-immersion supercritical metalens

Far-field super-resolution lenses are attractive due to their great potential in the application of label-free far-field optical super-resolution. In past decades, there has been a fast development in superoscillatory optical lenses, which allows engineering of optical point-spread functions in the far-field beyond the traditional Abbe diffraction limit. With the decrease of focal spot size, the sidebands will inevitably increase, especially when the spot size is close to 0.358λ/NA, where NA is the numerical aperture. However, it is of critical importance to reduce the spot size while maintaining comparatively small sidelobes for many practical applications. Here, we demonstrate a water-immersion supercritical metalens with a high-numerical aperture of 1.15. Experimental results show the generation of a super-resolution hot spot as small as 0.33λ, which is very close to the superoscillation criterion, at a distance of 60λ from the lens. More importantly, there is no significant sideband on the focal plane, and the strength of the sidelobes near the hot spot is lower than 13.3 % of the central lobe intensity. The deep compression of hot spot and the absence of large sidelobes offer a promising way to further improve the resolution of far-field label-free super-resolution microscopy.

Constructing a Frequency-Dependent Phase Profile of Linear Dispersion for Achromatic Superresolution Focusing

Achromatic lenses are crucial to light focusing and imaging. However, conventional achromatic lenses are restricted by the Abbe diffraction limit. Although superresolution optical lenses have been demonstrated to overcome the limit, the correction of chromatic aberration in continuous broadband for superresolution lenses still remains challenging. To address this issue, we propose a generalized strategy of constructing a frequency-dependent phase profile of linear dispersion for achromatic superresolution focusing in a continuous broad bandwidth. Specifically, based on an arbitrary wavelength-independent discrete phase profile of a monochromatic superresolution lens optimized at a given single optical frequency, a frequency-dependent phase profile of an achromatic superresolution lens can be constructed as the sum of the given discrete phase profile and a linear dispersion phase term. Based on the proposed approach, broadband achromatic superresolution metalenses are designed and demonstrated in the terahertz regime. The proposed method can be applied to visible and infrared optical spectra, which could have promising potential in various superresolution-related applications.

Multiple-Wavelength Achromatic Superresolution Focusing with Optimized Constructive Interference

Recently, there has been growing interest in developing superresolution lenses to focus light beyond the conventional diffraction limit in the far field. Achromatic superresolution is particularly attractive for many practical applications. However, it remains a great challenge to realize an achromatic superresolution focusing lens with both a high numerical aperture and a small depth of focus, which is critical for superresolution imaging with high longitudinal resolution. Here, a method for preparing a multiwavelength achromatic superresolution lens with a high numerical aperture is proposed to control the wave front through a binary-phase zone plate for generating a transverse superresolution focal spot with a small depth of focus. The approach is experimentally verified with an achromatic superresolution lens with a high numerical aperture of 0.95 at six wavelengths in the visible range between 405 and 684 nm. The proposed method is practical for superresolution-related applications, including imaging, microscopy, and data storage.

Super-Resolution Imaging by Dielectric Superlenses: TiO2 Metamaterial Superlens versus BaTiO3 Superlens

All-dielectric superlens made from micro and nano particles has emerged as a simple yet effective solution to label-free, super-resolution imaging. High-index BaTiO3 Glass (BTG) microspheres are among the most widely used dielectric superlenses today but could potentially be replaced by a new class of TiO2 metamaterial (meta-TiO2) superlens made of TiO2 nanoparticles. In this work, we designed and fabricated TiO2 metamaterial superlens in full-sphere shape for the first time, which resembles BTG microsphere in terms of the physical shape, size, and effective refractive index. Super-resolution imaging performances were compared using the same sample, lighting, and imaging settings. The results show that TiO2 meta-superlens performs consistently better over BTG superlens in terms of imaging contrast, clarity, field of view, and resolution, which was further supported by theoretical simulation. This opens new possibilities in developing more powerful, robust, and reliable super-resolution lens and imaging systems.

New mechanism for optical super-resolution via anisotropic near-zero index metamaterials

In this paper, we propose a new mechanism for obtaining optical super-resolution based on anisotropic near-zero index metamaterials (AZIMs). It is found that AZIMs can not only achieve perfect transmission of electromagnetic energy but also realize a super-resolution lens. Moreover, we find the performance of super-resolution imaging is not sensitive to the loss and impedance mismatching, as analytically and numerically demonstrated. Our findings provide a new way to explore high-resolution optical imaging.

Mathematical method for designing superresolution lenses using superoscillations

We use a new mathematical method to design a superresolution lens using a superoscillation technique based on polynomial roots. We walk through an example of the method using simulations. Our method allows for ease of design by being mathematically and conceptually simpler than other methods.

A magnetically controlled tunable acoustic super-resolution lens

Acoustic artificial structures have attracted much attention in recent decades due to their unique acoustic handling characteristics. The lightweight, easy-to-design feature and low cost of the thin-film acoustic artificial structure make it a great advantage in achieving super-resolution imaging and device miniaturization. However, since the film-type lens achieves super-resolution only at the resonance frequency, the frequency band in which it operates is greatly limited. In this work, considering the complexity of the vibration problem of the additional mass film, we propose a simple zero-mass method to design the operating frequency of the film-type prism. After that, a magnetic-field-controlled thin-film acoustic super-prism with a size of only six percent of the wavelength at working frequency is designed. Subsequently, based on the mechanism of magnetically induced stress, it achieves the super-resolution imaging within a frequency range from 350 Hz to 700 Hz. It provides a new idea for the design of an acoustic super-prism, and potential applications can be expected in acoustic imaging.

Coherent Magnetic Response at Optical Frequencies Using Atomic Transitions

Developing exotic optical devices such as super-resolution lenses and cloaks requires atoms that interact strongly with the magnetic field of light. Such an interaction between a laser and an ensemble of europium atoms is shown for the first time.

Engineering near-field focusing of a microsphere lens with pupil masks

Recent researches have shown small dielectric microspheres can perform as super-resolution lens to break optical diffraction limit for super-resolution applications. In this paper, we show for the first time that by combining a microsphere lens with a pupil mask, it is possible to precisely control the focusing properties of the lens, including the focusing spot size and focal length. Generally, the pupil mask can significantly reduce the spot size which means an improved resolution. The work is important for advancing microsphere-based super-resolution technologies, including fabrication and imaging.

Enhanced and tunable resolution from an imperfect negative refractive index lens

Material loss diminishes the ability of a negative refractive index material to function as a superresolution lens. We find that the transmittance of a negative index slab can be greatly enhanced at a certain evanescent field spatial frequency if the imaginary parts of the permittivity and permeability in the slab can be tuned, even when the object, lens, and image domains have overall loss. This leads to a proposed method to image the far-subwavelength features of an object by reconstructing the evanescent part of its spectrum.

Ultrabroadband superoscillatory lens composed by plasmonic metasurfaces for subdiffraction light focusing

AbstractConventional optics is diffraction limited due to the cutoff of spatial frequency components, and evanescent waves allow subdiffraction optics at the cost of complex near‐field manipulation. Recently, optical superoscillatory phenomena were employed to realize superresolution lenses in the far field, but suffering from very narrow working wavelength band due to the fragility of the superoscillatory light field. Here, an ultrabroadband superoscillatory lens (UBSOL) is proposed and realized by utilizing the metasurface‐assisted law of refraction and reflection in arrayed nanorectangular apertures with variant orientations. The ultrabroadband feature mainly arises from the nearly dispersionless phase profile of transmitted light through the UBSOL for opposite circulation polarization with respect to the incident light. It is demonstrated in experiments that subdiffraction light focusing behavior holds well with nearly unchanged focal patterns for wavelengths spanning across visible and near‐infrared light. This method is believed to find promising applications in superresolution microscopes or telescopes, high‐density optical data storage, etc.image

Ultraviolet dielectric hyperlens with layered graphene and boron nitride

The concept of hyperlens, as a novel transformation optics device, is a promising real-time super-resolution lens that can effectively transform evanescent waves into propagating waves and thus break the diffraction limit. However, previous hyperlens implementations usually adopted metal which would absorb most energy during light transmission and thus deteriorate imaging efficiency. Here we propose a novel hyperlens design based on dielectric layered graphene and h-boron nitride (h-BN) whose performance can surpass the counterpart design with metal. Our first-principle and Kramers-Kronig relation calculation shows that both layered graphene and layered h-BN exhibit strong anisotropic properties in ultraviolet spectrum regions, where their permittivity components perpendicular to the optic axis can be negative while the components parallel to the optic axis can be positive. Based on the anisotropic properties, flat and cylindrical hyperlenses are designed and numerically verified with layered graphene at 1200 THz and layered h-BN at 1400 THz, respectively. Our work provides a dielectric hyperlens approach to overcome the diffraction limit at ultraviolet frequencies, which may find applications where dynamic imaging of subwavelength features at the molecular and cellular scales is desired.

Perfect lenses in focus

Materials that refract light backwards are thought to be required for making super-resolution lenses. An alternative proposal — that conventional, positively refracting media can do the job — has met with controversy. Two experts from either side of the debate lay out their views on the matter.

Theories for the design of a hybrid refractive-diffractive superresolution lens with high numerical aperture.

By geometrical optics and the Rayleigh-Sommerfeld diffraction formula, theories for the design of a hybrid refractive-diffractive superresolution lens (HRDSL) with high numerical aperture are constructed. Differences between the profile of the diffractive superresolution element (DSE) with high numerical aperture and that with low numerical aperture are indicated. Optimization theory can obtain a globally optimal solution through a linear programming much more simplified than the corresponding one in Liu et al. [J. Opt. Soc. Am. A 19, 2185 (2002)]. The rules of the structure of the designed DSE are both theoretically proved and numerically verified. Comparison of this optimization theory with the other design theories and examples of designing the HRDSL with high numerical aperture are provided. Last, some limits of optical superresolution with high numerical aperture are set and compared with those for low numerical aperture.